modifying heads for proper squish height, squish area / velocity, and dome cc, (& a little porting info)

[Chuck78]

Does anyone here have any experience or knowledge on modifying 2-stroke heads?
Now that Ron Black has fully retired, this leaves a bit of a void in the KDX world, especially for the 220 which has a head that leaves a lot to be desired as far as squish clearance.

I'd talked to Ron in March and he said he was still doing 220 heads, but not really any other work. I didn't get a chance to pull the head off my old 220 due to my Mom's battle with cancer, and 2 months later, no replies whatsoever from Ron and Bobby Black... I hope Ron is doing okay, but I took that as him being fully retired.

I've got an old 1959 South Bend Heavy 10L metal lathe that I've been learning to use as needed, and have been curious about the science behind optimizing 2-stroke head squish band widths and dome profiles, as well as how to fixture the KDX heads up in a lathe to perform these operations.
I've been reading up a lot on my lunch breaks and late evenings on this advanced 2-stroke tuning topic, trying to bring more knowledge to the KDX community as our legendary gurus age and retire... Feel free to correct any information which I've misinterpreted or missed, I'm here to learn as much as the rest of you or more. If Ron were responding to emails and still cranking out his work, I would not be posting one bit if this publicly, as you can't ethically take a man's knowledge earned through decades of hard work, and just use it for yourself when the guy is still making a living off of it. But instead now, I'm trying to invoke some of the more active generations to consider learning more about this work so at least they'll know what their 2-stroke engine builder machinist is talking about, and can spot of the builder doesn't really give any concern to optimizing the squish band height and overall head volume/compression ratio... and in rare cases, someone might actually be ambitious enough to learn the finer details and attempt these mods on a metal lathe if they have one at their disposal!


Here's three KDX220R heads that I've got.

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Left is a head that someone milled/faced down 0.40mm for significantly tighter squish band clearance and higher compression, but did not touch the squish band or dome, resulting in tight squish height (I'm guessing near the bare minimum of 0.80mm or maybe closer to 1.0mm, I have not confirmed standard KDX deck height or head gasket compressed thicknesses yet). As you can see, although the tightened squish band height surely improved squish velocity and combustion, this head suffered a slight bit of pre-ignition detonation, the pitting marks of melted missing metal scarring the squish band and chamber, which is also very power robbing as well as hard on crank and rod bearings. Too much compression as well as too rapid of squish band air/fuel velocity (from the outer portions of the cylinder and being forced towards the dome/spark plug/flame front and creating mixture turbulence to improve combustion spread as well) can both cause detonation.

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Reducing the squish band width while maintaining same squish height / clearance will reduce the squish velocity slightly, and is an important tuning/design tool, but higher octane on the tighter clearances is best advice. You'll get a lot better bottom end power for tight woods riding with the tightest clearance (but top end power suffers on a 2-stroke when you have too high of compression), but high octane is best for the heating of the air/fuel mixture due to the tight clearance as well as if you don't machine the dome for more reasonable compression ratio. Higher octane is also a good thing for slow hot summer tight woods riding with less air moving through the radiators... As is a slightly richer mixture for better piston cooling.

Center in the picture is my Ron Black 220 head... The great KDX tuning master's work

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This head has had 0.80mm milled off the head gasket surface, squish band cut and reshaped slightly to around 8mm width from machining the dome wider to cut off the radiused transition to the squish band, and from what I can roughly tell, cutting the chamber about .38mm deeper (material removal, not a measurement off of the new head gasket deck surface height). This head has a taller squish height than the shaved head on the left, despite a lot more height taken off the deck surface of the head, with a squish of about .68mm from the head gasket deck surface (+compressed gasket thickness +/- piston protrusion @ TDC + total squish height). I'm speculating Ron's heads were on the safer side of adequate squish height of closer to 1.20mm total (.048" or so), but still at the wider ranges of the sweet spot to where the squish velocity effect really starts taking place and making a difference.

*note - these are all late night rough measurements with a micrometer, I haven't made a plexiglass blank yet to bolt to the head to seal the chamber off and use a graduated syringe to fill and measure chamber volume with water. YET...




On the right in the first photo is a totally stock and fairly clean 69mm 220 head... much taller squish height, 1.11mm gasket surface to edge of squish band. I'm guessing these heads stock are running maybe 1.7mm or 1.8mm squish height. I need to measure some KDX head gaskets, Wiseco, Athena, and OEM, to get some better data here.

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Around 1.25mm is the point where the squish height and squish band start really losing effectiveness, and the engine starts operating less efficiently. Optimizing the squish band height and keeping the compression ratio in check, will make jetting more consistent throughout varied conditions, as well as require a smaller main jet size, as a stock 220 head will use more fuel to get the same combustion, since the combustion is less efficient due to not having the squish velocity causing turbulence to mix up the mixture amongst the flame front, as well as a significant amount of the air fuel mixture lingering on the outskirts of the cylinder and not fully combusting in the effective portions of the power stroke before the exhaust port is exposed as the piston travels downward...

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There's a lot of science and math behind 2 stroke squish bands, porting, crankcase volume and crankcase compression etc... I'm just starting to grasp this, but the head work is the most critical part, and also the most advanced knowledge that an amateur home hobbyist (rookie) machinist and novice bike builder/tuner will likely get into if even touching the head themselves.
To reiterate, the squish band, the more flat outside portion of the combustion chamber area, is there to promote more efficiently mixed and properly timed combustion, but this doesn't really have much of an effect unless the squish clearance is 1.20mm or less (some say 0.050" which is about 0.48mm). Running this tighter around 0.80mm works very well, but the actual squish band width may need to be narrower in order not to exceed the maximum recommended squish velocity. Too high of velocity will compress the air too quickly in this area as opposed to out in the dome of the combustion chamber area, and can cause pre-ignition detonation which is always to be avoided... 1.0mm is a safer bet with that in mind, and also allows for a bit more wear and tear on the crank and rod bearings, which will change the clearances slightly, as well as piston rock in the worn cylinder bores with a worn piston, and also figuring in rod stretch at high temperatures and high RPM... this is a real thing, the rods actually do stretch a very miniscule amount. Everything adds up.

The squish band width and height both have to be calculated to figure squish band total area, in order to achieve the targeted optimum squish velocity without exceeding it. The minimum desired squish velocity would basically force the mixture out from the edges of the cylinder towards the flame front (as well as causing turbulence to scatter the flame front amongst this newly introduced air/fuel mix from the outskirts for even better combustion) at a rate that most of it has combusted before the piston has been pushed down to the point where the exhaust port is exposed or "opened." One thing to consider here, if running higher compression for added low end power and response, higher octane fuel is required, and high octane fuel actually burns SLOWER than lower octane fuel... so the squish velocity for high octane has slightly different optimum requirements than for standard 87 pump gas... running race gas in a 2-stroke really doesn't help you much, unless somehow it also contains more BTU (any non-ethanol gas contains more BTU's of potential energy than 93 octane 10% ethanol gas blends, FYI...
Basically the biggest factory here is to make sure the squish velocity is timed such that the squish velocity event is completed by the time the exhaust port is exposed by the piston. And again, squish velocity is dependent on adequately slim squish band height as well as squish band area (height vs width of the squish profile in the head).

As you can imagine, a ported cylinder with raised port heights will also come into play, and will require pushing the squish velocity up to the maximum allowable in order to get the same complete burn to take place before the exhaust port is exposed.



The squish band angle generally needs to roughly match the angle at the edge of the piston crown, but say if the piston were at a 10 degree angle at the edge, it's commonplace to make the squish band at an 11 degree angle just to make sure there are no variances due to cast piston irregularities or piston rock which would cause the squish to be taller at the edge of the piston vs shorter at the inner edge of the squish band. This is a bad thing, as it will heat up the mixture even more and risk detonation, since the mixture would be ever so slightly compressed further when funneling it down.
Another thing to note is that due to larger bores increasing the compression ratio due to more available volume of air to compress, often times the piston manufacturers will give the oversized pistons a slightly more mellow dome than the standard bore. This would work on the safer direction as far as squish band angle, but also will make it less optimal if going say +1.00mm oversized piston and only just machining 0.50mm of material off the perimeter to get the extra 1.00mm of bore diameter. So when going oversized piston, both the angle and the width of the squish band need to be re-evaluated vs standard bore. Most people don't even consider this. The 223cc "225 kits" are somewhat popular due to Eric Gorr's well known big bore work, so boring and re-plating a 200 or 220 to 223cc is a common and popular mod. No sleeving required of the plated cylinder, cast iron or steel sleeves are generally a huge downgrade, and should always be avoided even if a cylinder requires welding repair work.

Lastly for now, reiterating that too high of compression ratio on a 2-stroke actually hampers high RPM power, and takes more away from that than the gains that higher compression gives the low/mid power and throttle response. There is a fine line. optimized squish band height promotes a lot better combustion, but when shaving just the deck surface of the head, you'll also be increasing the compression ratio quite a bit, which then in turn needs to be taken back out by enlarging the dome portion of the combustion chamber. As we see here by the work of the wizard himself, it looks like widening the dome to cut away the radiused transition between the dome and the squish band is the ticket... Ron has more decades of experience building and tuning and machining engines, and his work speaks for itself, he really has all of these variables completely dialed in as he's done up the perfect head for stock 220 port heights and stock bore size.

My big quest here is also an even greater quest, as I have a ported 223cc cylinder that I have no matching head for, and I need to do more than just copy my RB head here, I actually need to recalculate everything slightly with any altered port timing (I think the port heights are still stock at the higher end) and the larger area/volume of the overbore. The squish band widths are said to be a loose guideline of somewhere around 50% of the entire bore area's square centimeters etc... But this figure is just a rough starting point, and is dependent on all the factors I've outlined above.

[Chuck78]

This also brings up some other nice info... I was chatting with a veteran 2-stroke tuner and KDX enthusiast, who always insists on leaving the 220 port heights alone, not increasing them to the higher heights of the 200 cylinders, but instead porting the 220 cylinder to widen the intake ports only, out to the width of the 200 intake ports, not touching anything else except for knife edging the back sides of some of the ports and cleaning up all the casting flaws and rough areas and polishing the exhaust port only.
He was telling me that the port timing and lower port height of the 220 really contributes to better combustion efficiency which translates to a directly relatable improved fuel range over a similar KDX200 with it's higher port heights...
This is all basic porting work that can be done if someone has a 200 cylinder to compare, or a rubbing of a 200 cylinder to copy the intake port mapping... my ported 220 cylinder I believe has had a little bit of work done to the exhaust ports, but the heights look to be near stock thankfully, after learning of this guy's professional opinions and experiences. Very good knowledge to be armed with in the quest for building the ultimate KDX in this day and age of modern 300 and 150 2-strokes and their technological advancements. With some major suspension work and some lesser engine / carb work and a modded head, the water cooled KDX200's and 220's really can stand up fairly well to a more modern bike up to a certain extent (where they are out gunned by 300cc worth of power in the wide open areas only). The 220 with mods will go anywhere in the tight gnarly woods that a modern 300 will go, as I've learned this firsthand... it's biggest drawback is the pilot usually, in my case! I've surprised myself making it through a lot of sections far above my pay grade, but also these aren't always the most graceful passes

I'll see if I can link the two places with port timing and port mapping info on our 220 and 200 H cylinders for reference, as that was GREAT info to dredge up on here and someone's personal site.

[Chuck78]

Here's another very highly knowledgable source of KDX and general 2-stroke information, Jaguar (Michael Forrest) who occasionally frequents this forum and makes custom CDI boxes for higher performance KDX ignition curves:

https://dragonfly75.com/moto/sqVelocity.html



same info here but posted into a forum (posting as an alternate/backup of this wealth of knowledge):

https://www.everything2stroke.com/threa ... ost-548582


Jaguar's (Michael Forrest's) "All About Squish Bands" YouTube video:





And here's a quick video of an easier head's machining operations on a lathe. It's easier because it's an older head with a perfectly centered spark plug hole, so all one needs is a mandrel attachment with spark plug thread side on one end, and you can chuck up the head in a lathe.
Our KDX's are not so luck, but have an offset spark plug for more proper combustion efficiency, and therefore a special fixture has to be made up to mount a KDX water cooled head in a lathe's 4-jaw chuck or onto a face plate instead of a 4-jaw.



This guy skips a lot of setup and measuring, but the video shows re-facing the head gasket surface, re-cutting the angled squish band, and using a radius cutter on the lathe toolpost to make concave profile cuts to clean up and/or enlarge the combustion chamber dome.



Lastly, for a total DIY method with no actual squish band width / & squished mixture velocity calculations vs port timing etc, this guy does it DIY (cutting down to 1.00mm squish and correcting the chamber dome volume) without any special machinist equipment and tells you about compression ratios and actual compression pressure. Interesting methods he has... I also use a perfectly flat milled slab(s) of stone as surface plates in conjunction with floor sander sheets and a fresh can of 3M aerosol contact adhesive... works awesome for my 1977-1980 Suzuki GS400/550/750/1000 twins and 4-cylinder 4-stroke heads and cylinders!

Part 1:

Part 2:



And here's another one. The concave radius cutting on the lathe is using different tooling that's less obvious as to how it works, but the result is the same. This guy has a really nice graduated cylinder with a valve he uses instead of a big liquids syringe with graduations / measurements, and I like this better... He measures with the head upside down, with a greased plexiglass piece just set down and sealed onto the head, no fasteners, but it'd be more difficult to get all the air pockets out this way, but the volume isn't THAT critical... The other guy fills through the spark plug hole, so his is more likely to leak from the bolted on plexiglass piece, but he can get all the air out pretty well that way due to the combustion chamber being a dome or upside down funnel to move the air directly to the only exit...


Michael Forrest has a free Microsoft Excel Spreadsheet advanced program to calculate squish band width, volume, velocity, compression, etc linked above and discussed in his videos, and I've also found an app for Android 4 through 9 to calculate squish info...I've installed it on my old phone (I'm beyond Android 9 now), but haven't opened it yet.

[Chuck78]

For those not fortunate enough to have gotten a Ron Black head mod especially on the 220's, Eric Gorr Racing is still doing full service work up until the end of the year when he will scale back as he moves a bit closer to retirement. Tom Morgan Racing is also a highly reputable engine builder capable of this work. I've also heard that Ken O'Connor Racing is another good source, although I don't have any knowledge of his work yet other than reading people referring others to him. These skilled tuners/builders all seem highly competent to calculate proper squish area, velocity, and head volume etc in relation to port timing, in order to get you the most ideal head profile if you aren't ready to try and DIY it...

I wish Ron Black were still around! Heck, I would've flown out to the west coast if he'd be willing to teach me his ways of 2-stroke head work and some basics of 2-stroke porting and other tuning! No such luck so far though.

Wish me luck here on figuring out how to make the most optimized 223cc KDX220 head for my spare cylinder!

[Chuck78]

Here's the topic about the 200 vs 220 port maps, some measurements, port heights and port timings mostly for the 220. This can be beneficial by using the 200 port map that I more directly linked at the latest post, and widening the 220's intake ports to these specs, as well as knife edging, and polishing the exhaust port and doing some casting cleanup work.

viewtopic.php?f=86&t=15852


The guy who digitally scanned the ports said:
The KDX200 exhaust port opens at 86 deg ATDC, and the transfers at 117 deg ATDC

KDX200
Exhaust duration - 188 deg
Transfer duration - 126 deg
Blowdown - 32 deg

KDX220
Exhaust duration - 178 deg
Transfer duration - 117 deg
Blowdown - 30.5 deg

KDX220_PortLayout_zps520d8397.jpg (249.54 KiB) Viewed 12841 times

KDX200_PortLayout1.jpg (1.49 MiB) Viewed 12841 times

[SS109]

All great info and thanks for sharing what you have learned.

I honestly think setting squish on our heads isn't too big of deal as long as you aren't trying to wring every last bit of power out of the engine. A 1 to 1.2mm squish should get you 90% of the way of potential max benefit from doing the work without the risks and the associated squish speed calculations and such. The K.I.S.S. principle applies here so don't overthink it too hard. I think RB learned this over all the years he worked on KDX cylinder heads hence why he didn't need us to test the existing squish before he did work to them.

On porting the KDX220, I'm not a fan. Having ridden two 220's that have been ported back-to-back (I believe both were done by Fredette) with my stock cylinder they feel complete weak on the bottom and only seem to build some power from the mid to upper range feeling more like a 200. Only thing I do to my cylinder ports is remove any casting flash/bumps and put a polish on the exhaust ports taking great care not to touch port height or width at the cylinder bore at all.

Thanks again for all the info. It has made for good reading.

[kdxdazz]

great write up chuck,i'll be sure to read this through a couple of times when i put my 220 engine back together which has an rb head but has been decked and milled to the point of being unusable unless using thick copper gaskets which i had custom made. standard head gasket is 0.25mm from memory

[kdxdazz]

another thing which i think is missing and would be good to add in to the equation is the milling of head or cylinder will advance ignition timing which again is not great for high rpm power

[Chuck78]

great write up chuck,i'll be sure to read this through a couple of times when i put my 220 engine back together which has an rb head but has been decked and milled to the point of being unusable unless using thick copper gaskets which i had custom made. standard head gasket is 0.25mm from memory

Thanks!

How did your custom copper head gaskets end up sealing for the long term vs a stock type embossed MLS (Multi-Layer Steel) gasket?

another thing which i think is missing and would be good to add in to the equation is the milling of head or cylinder will advance ignition timing which again is not great for high rpm power

Milling the head gasket surface on either won't advance any timing, whether it's ignition timing or port timing. The only milling that would affect timing would be turning the cylinder base down on a lathe, to bring the ports closer to the crank centerline, requiring a head that's closer to stock "squish depth," since the piston will come up into the head area tighter otherwise, but this only alters port timing.

Milling any off the top wouldn't change spark timing in relation to crankshaft rotation whatsoever.

However, adding more compression ratio will definitely hurt the top end power on a 2-stroke so I've learned from reading a lot online. That's why Ron Black re-does the chamber volume a fair amount to get the compression ratio back down to a good number, as to still boost low end power a but but not affecting high RPM power any, and not require race gas either.

[kdxdazz]

great write up chuck,i'll be sure to read this through a couple of times when i put my 220 engine back together which has an rb head but has been decked and milled to the point of being unusable unless using thick copper gaskets which i had custom made. standard head gasket is 0.25mm from memory

Thanks!

How did your custom copper head gaskets end up sealing for the long term vs a stock type embossed MLS (Multi-Layer Steel) gasket?

another thing which i think is missing and would be good to add in to the equation is the milling of head or cylinder will advance ignition timing which again is not great for high rpm power

Milling the head gasket surface on either will advance ignition timing??? I thought that the oy milling that would affect timing would be turning the cylinder base thickness down on a lathe, which only alters port timing?
I don't see how taking any off the top would change spark timing in relation to crankshaft rotation?

However, adding more compression ratio will definitely hurt the top end power on a 2-stroke as I've learned. That's why Ron Black re-does the chamber volume a fair amount to get the compression ratio back down to a good number, as to still boost low end power a but but not affecting high RPM power any.

unless i have misunderstood the timing mechanism but if you are bringing the spark plug closer to the crown of the piston wouldn't that advance the timing?
i didn't use the copper head gaskets for any length of time due to the chronic over heating issue,pin holes in the cylinder was the issue but should be fixed now i have a sleeve but each time i pulled off the head i couldn't see any evidence of leakage past the copper head gasket

[Chuck78]

Good to know, I was curious about how well a copper head gasket on a water cooled engine would seal for the long-term.

I don't believe the measurement of ignition timing has anything to do with the distance between the piston at TDC and the spark plug, only has to do with crankshaft rotation position.
A contained intentional explosion's forces will begin upon ignition, not substantially relative to the volume of the chamber or the depth vs width of the dome or of the piston installed height.
Squish height and chamber volume are the #1 most critical measurements in this topic. Squish width is pretty darn close to ideal as stock, but if you raise compression ratio slightly, the squish width should be recalculated as well to keep things fine tuned for those that are concerned with making plenty of power.
Now on a ported cylinder, squish width becomes much more critical to recalculate and alter when machining the head.
There's actually an app for Android 4 through Android 9 phones to do all the squish calculations. I installed this on an older phone of mine, but have yet to open it up to browse the app's functionality.

Also, I've talked to a few people about porting recently, and also read a lot of people saying that their ported cylinder and squished head didn't perform as they'd hoped.
I believe that this is because of the amount of intensive engineering that really needs to go into the porting, port timing, squish velocity and squish band width, as well as crankcase compression/ volume etc, or at least the amount of trial and error making the ports bigger and raising them up higher and just milling the head for squish taking into account physics behind the squish velocity versus port height.
There's a lot that can go wrong when just making ports bigger or higher without doing the engineering work to make everything work together efficiently as an engineered system that works effectively.
Some people excellent bike builders and carb tuners etc, but perhaps the porting and head work is best left to the best of the best technical wizards two-stroke tuning.

[Chuck78]

I honestly think setting squish on our heads isn't too big of deal as long as you aren't trying to wring every last bit of power out of the engine. A 1 to 1.2mm squish should get you 90% of the way of potential max benefit from doing the work without the risks and the associated squish speed calculations and such. The K.I.S.S. principle applies here so don't overthink it too hard. I think RB learned this over all the years he worked on KDX cylinder heads hence why he didn't need us to test the existing squish before he did work to them.

I believe RB never needed customers' squish height measurements because the KDX engines all measure fairly consistently tight on factory tolerance variances, and RB would just set them to an effective but safe height.
RB re-machines all surfaces/profiles on the underside of the heads, although on a stock porting cylinder, he doesn't appear to have changed the squish band width much. It's just cut deeper, and then the deck surface machined even further down.

On porting the KDX220, I'm not a fan. Having ridden two 220's that have been ported back-to-back (I believe both were done by Fredette) with my stock cylinder they feel complete weak on the bottom and only seem to build some power from the mid to upper range feeling more like a 200. Only thing I do to my cylinder ports is remove any casting flash/bumps and put a polish on the exhaust ports taking great care not to touch port height or width at the cylinder bore at all.

I talked with a well versed KDX tuner who advised me that if one wants to keep the best characteristics of the 220, one should not touch the height of the ports at all, especially the exhaust ports, and only widen the intake ports, knife edge the back sides of the transfers, clean up casting irregularities, and polish the exhaust side.

The port timing on the 220 also increases the fuel efficiency of the 220 over the 200.

I don't understand why people want to take a 220 and make it more like a 200. All of my casual trail riding buddies on KDX200's get on my 220 are are in awe of how easily and gently the front wheel can be lofted over logs / rock ledges / mud holes versus the 200, which needs to be up in the RPM's a significant bit higher to loft the wheel to a lesser extent. The 220 has proven itself so well to me as being an incredibly potent weapon and highly useful tool gnarly woods trail settings. I think I may take my 2 stock porting 220 cylinders and clean up the ports a bit and also do some minor porting alterations myself based on this really useful conversation I had with this fellow KDX220 rider and well experienced 2-stroke engine builder.

I may send off one head to Eric Gorr right now so I can have it matched to my ported 223.2cc cylinder to run ASAP, but I hope by winter I will have had the time to make a fixture to bolt these up to and hold in my lathe so that I can start doing these heads on my own.
Maybe finally I could start getting some money back from my KDX obsessions instead of just dumping money into motorcycles non-stop modding them & maintaining them while also crashing and smashing & 'em up!

[Chuck78]

Just milling the head to get the squish to 1.2 mm is going to require race gas or high octane pump gas + potentially octane booster on really hot days at least. While boosting the low end power a lot, the higher compression is also going to detract from the high RPM power due to the way two strokes operate.
The head above that I have that was just milled and not cc'd for a corrected volume definitely should shows detonation marks, which could be caused from being too lean, I would bet were caused by running a fine line of air fuel ratio to make the most power, and encountering detonation on a hot day or on some slow going technical trails, working the engine hard. I would like to avoid having an engine that requires high octane plus octane booster in order to avoid permanent engine damage...

[SS109]

Just milling the head to get the squish to 1.2 mm is going to require race gas or high octane pump gas...

If that was in reference to what I said earlier then you misunderstood me. My point was all things being equal, which would mean the head's volume was the same as stock, 1.2mm of squish would be fine for most.

Anyway, I love how you deep dive this stuff and hope you keep doing it as I'm learning from it as well!

[Chuck78]

Anyway, I love how you deep dive this stuff and hope you keep doing it as I'm learning from it as well!

I love how you took a deep dive on the CDI boxes ! I'm hoping for the day that you might get back on those and make a new revised version with less initial advance to eliminate the kick back

[kdxdazz]

any updates chuck on what you have learnt about squish band,working on my engine right now, stock head with stock gasket is 0.9mm squish but my cylinder has been decked a few times before while trying to get the head gasket to seal then again when it has been sleeved, my RB head with a 1mm copper gasket has 1.10mm squish clearance, although i want my engine to run well even more important is it runs cool in these thailand jungles, i didn't have any detonation issues with the rb head and 1mm copper gasket,
i guess i should CC both heads so i can work out compression ratios or i could put the heads on with piston at TDC and fill up the combustion chamber with oil but to be honest don't want to go to all that trouble
i have a few different thicknesses of head gaskets now,i think from memory stock head with a thick head gasket ran the most smooth but had less response than the rb head

[Chuck78]

With your cylinder decked several times, I'd be very concerned with knowing how much height has been taken off of it. I haven't mocked up a KDX engine to measure stock deck height (piston protrusion or piston depth down the hole at the wrist pin axis), but that's going to be helpful to know in terms if how Ron Black's machining work was intended to perform.
Generally a squish if 1.0mm or 1.2mm is the sweet spot however. But... This can't just be achieved by decking the head or cylinder, as the dome needs more volume added if taking away volume from decking.
That's where cc'ing the head really helps.

I put my head mods on hold for now (until winter) as I've been busy doing repairs and maintenance trying to make the most out of the last 2 months (now 5 to 6 weeks) of nice weather riding season, and my wife's KTM 200 has unexpectedly needed some substantial work just to make it to these rides...

I was looking at some lab equipment measuring devices commonly used in cylinder head work, ptfe/acrylic burettes with stop cocks. A tall skinny graduated cylinder with measurement makings and a valve on the bottom. Using this in conjunction with a piece of plexiglass will do what we need. I will pick one of these up at the end of riding season so that I can measure the von black head to get a better idea of the volume needed to run 90; octane non-ethanol Sheetz gas. I've got lot of calculations to do in order to learn the dimensions needed for this ported 70mm 223cc overbored cylinder though. I also need to go in and add some epoxy as I have learned a bit about cylinder porting, & the knife edging was not done properly, it needs to be shaped like an airplane wing, not the reverse of that. Teardrop shaped with the rounded edge being the leading edge. This cylinder was done the opposite as old schoolers used to think was best.

[Chuck78]

great write up chuck,i'll be sure to read this through a couple of times when i put my 220 engine back together which has an rb head but has been decked and milled to the point of being unusable unless using thick copper gaskets which i had custom made. standard head gasket is 0.25mm from memory

Thanks!

How did your custom copper head gaskets end up sealing for the long term vs a stock type embossed MLS (Multi-Layer Steel) gasket?

another thing which i think is missing and would be good to add in to the equation is the milling of head or cylinder will advance ignition timing which again is not great for high rpm power

Milling the head gasket surface on either will advance ignition timing??? I thought that the oy milling that would affect timing would be turning the cylinder base thickness down on a lathe, which only alters port timing?
I don't see how taking any off the top would change spark timing in relation to crankshaft rotation?

However, adding more compression ratio will definitely hurt the top end power on a 2-stroke as I've learned. That's why Ron Black re-does the chamber volume a fair amount to get the compression ratio back down to a good number, as to still boost low end power a but but not affecting high RPM power any.

unless i have misunderstood the timing mechanism but if you are bringing the spark plug closer to the crown of the piston wouldn't that advance the timing?
i didn't use the copper head gaskets for any length of time due to the chronic over heating issue,pin holes in the cylinder was the issue but should be fixed now i have a sleeve but each time i pulled off the head i couldn't see any evidence of leakage past the copper head gasket

@kdxdazz where did you get your custom copper head gaskets made?

That's good info to know if I ever need anything thicker, but also, I was considering building a KX144 "KDX150R" woods bike potentially.

I'd be milling a lot off of the cylinder base to tailor the port timing more towards torque, as well as a head with a wider squish more towards low end torque, running 93 octane or higher (Sheetz 90 octane non-ethanol + toluene as octane booster), in attempts to get an even lighter Kawasaki 2-stroke woods bike, but the Motocross CDI's aggressive ignition timing advance curve is the only big thing that gets in the way (of roll-on power for traction vs light switch rocketship acceleration on roll-on), although a heavier flywheel might help out with that.

[kdxdazz]

Thanks!

How did your custom copper head gaskets end up sealing for the long term vs a stock type embossed MLS (Multi-Layer Steel) gasket?





Milling the head gasket surface on either will advance ignition timing??? I thought that the oy milling that would affect timing would be turning the cylinder base thickness down on a lathe, which only alters port timing?
I don't see how taking any off the top would change spark timing in relation to crankshaft rotation?

However, adding more compression ratio will definitely hurt the top end power on a 2-stroke as I've learned. That's why Ron Black re-does the chamber volume a fair amount to get the compression ratio back down to a good number, as to still boost low end power a but but not affecting high RPM power any.

unless i have misunderstood the timing mechanism but if you are bringing the spark plug closer to the crown of the piston wouldn't that advance the timing?
i didn't use the copper head gaskets for any length of time due to the chronic over heating issue,pin holes in the cylinder was the issue but should be fixed now i have a sleeve but each time i pulled off the head i couldn't see any evidence of leakage past the copper head gasket

@kdxazz where did you get your custom copper head gaskets made?

That's good info to know if I ever need anything thicker, but also, I was considering building a KX144 "KDX150R" woods bike potentially.

I'd be milling a lot off of the cylinder base to tailor the port timing more towards torque, as well as a head with a wider squish more towards low end torque, running 93 octane or higher (Sheetz 90 octane non-ethanol + toluene as octane booster), in attempts to get an even lighter Kawasaki 2-stroke woods bike, but the Motocross CDI's aggressive ignition timing advance curve is the only big thing that gets in the way (of roll-on power for traction vs light switch rocketship acceleration on roll-on), although a heavier flywheel might help out with that.

i got my copper head gaskets laser cut in thailand,quite cheap too,about 15 US dollars, another option is to have them water jet cut
i spoke to the well known keng kawasaki who is famous for his klx250 big bore kits, he said getting copper head gaskets over 0.9mm thick is very hard to get them to seal on motorcycle engines, there is just not enough clamping pressure, he gets his gaskets made old school of graphite and steel fire ring,swears buy them but they do require a couple of retorques

your kx125 idea sounds quite challenging, with my limited knowledge on motorcross bikes i would say the close ratio gearbox is awful in technical trails and the lack of an airbox lid makes a lack of torque and a snappy throttle, i only know this as i owned a yz426 and a wr450 at the same time and did many comparisons. i bought 2 nsr150 engines that i will eventually put in to a woods bike but surprisingly the engine weighs the same as the kdx200 engine,about 25kg, nsr150 engine comes with autolube,big flywheel,high output stator,28mm carb, wide ratio gearbox,smaller ports, you probably wouldn't want to go any bigger than a 30mm carb on a kx125 woods bike so again i can see some strong challenges a head of you

[Chuck78]

I'm not a fan of the steel fire ring type head gaskets on aluminum, as they deform the aluminum during their compression, whereas a multi-layer steel gasket with embossing does not do this much at all.

What was the thickness of the copper head gasket you were running?

I figured with a close ratio motocross gearbox on a KX144 woods bike KX125 build, I would simply just gear the bike down so that first gear is where I want it, as the amount of time that I spend over 40 miles per hour in the woods is very limited.
I've never given any thought to lacking an airbox lid, & I have no airbox lid on either of my KDX's....