Planning on Millennium Technologies 225 kit

[Chuck78]

That info you referenced of mine was a copy&paste quote from Ron Black's older posts on this forum.
One could adjust the radius cutter with the head on a lathe so that a tighter radius was cut between the inner edge of the squish band and the top of the chamber nearing the spark plug hole, to reduce compression of a milled head to increase volume, without taking as much from the spark plug thread area top of chamber... But I'd be afraid that'd make for less efficient combustion.

What octane requirements does Millennium give with their kits? That could explain it if they recommend 93 octane etc. I get away with 90 octane non-ethanol (I'm loving Pennsylvania's Sheetz gas stations moving into Ohio with cheap diesel and affordable non-ethanol 90!) just fine on my Ron Black head.

Ron Black states he keeps the head volume *almost* stock in order to avoid the need for race fuel or octane booster (I believe he recommended 91 octane still? Check that though), and to avoid shortening the service life of the engine.

Higher compression will give more torque and low end throttle response, but also higher cylinder pressures and more loading on the big end rod bearings, so the bottom end rebuild frequency may be slightly increased (a lot of our bikes are out there running on 32:1 on stock bottom ends still 20-25+ years later still though, fwiw).

[Chopperpilot]

They said '91'..... I told them I have 90 non-ethanol available up here and they said that would work. Alaska doesn't have any ethanol in the gas at all, which is nice (freezes in the winter from all the water in it).
I installed the spark plug into the head last night and it essentially bottoms out with the spark plug threads and the hole threads flush with each other and only the electrode protruding into the chamber.

[billie_morini]

Chopperpilot, thank you for your private message indicating you'll disassemble your recently Millennium-serviced cylinder.

[Chopperpilot]

Ok, got tired of waiting for a 'thermostat' gasket to show up so I made one out of fel-pro material and fired her up! Went through a couple of heat cycles and took a short ride yesterday. Power seems to be way up (shocker!). Of course I haven't done a full throttle anything yet, but 2nd gear throttle will lift the front tire. Carb tune seems like it's pretty close, I kinda copied a TT jetting based on a RB'd 220. I should probably do a re-introduction thread that covers the 2025 version of my bike with the 225 BBK, YZ250 forks, and Gold Valved shock.

[Chuck78]

Great to hear, chopper!

[Chopperpilot]

I started another thread in this section going over the mods on the bike in general. Went for a full ride on Sunday and man, it was amazing. Fuel injection like throttle response.

[Chopperpilot]

Done a few rides now. The difference is truly amazing. I know the saying about it's not the arrow and all, but this will definitely increase your riding ability. I went to my practice hillclimb (when I go check my mail, convenient!) and here is where the engine mods/BBK really shine. At the end of last summer I did a ride with a tricky climb to get back. I had a new gummy tire on so traction wasn't a problem, but the issue was the bike would either stall, or wheelie. Well, no more! The bike will climb with very little to no clutch and I can stop on the hill and get started again with the kind of throttle and power that makes it easy to start moving again without stalling or lifting the front wheel.

[billie_morini]

Chopper, this is a very cool report. Thanks!

[Chuck78]

Hey chopper, haven't heard from you much for a while, how's life in Alaska, and how's the KDX doing this year? I hope all is well with you.

This is the response from Millennium when I asked about future top ends with this kit vs going to a standard 220 bore:
"The BBK will start you off with the A-size piston, and with good maintenance and ring changes, you could get 200+ hrs before a B-size piston is needed. You also can have it replated back down to the A-size 4 or more times.



The BBK also comes with custom porting so everything works together just like an off the rack 220.



Sincerely,

Jason Duplantis

Sales Manager

Millennium Technologies

1-888-779-6885 ext 371

I emailed this same guy at Millennium over the weekend after finding some deep wear only in the location of the top piston ring on a 70mm cylinder that I have that was plated by CV Tech in Canada. The rest of the cylinder measures out nearly perfectly at 70.000mm to 70.005mm, but the plating has quite a groove where the top ring stops. I believe this 70mm cylinder and piston was also ran with the stock 69mm head, and the piston was smacking into the head as witnessed by some marks on the very edge of the piston.

Well, Jason suggested I contact Wossner for a B or C size, stating that they did not currently have any of these in stock. I believe now that he was just stating what is available for some pistons above when mentioning that after 200 hours or so, with regular maintenance, the freshly plated 70.00 mm big bore KDX cylinder could jump up to a B-size piston when worn in to 70.01mm. I don't think he actually checked to see if they offered a B-size piston for these, & I highly doubt they have had any available in recent history, unfortunately. For me, this puts a 70mm big bore as a last resort option when the cylinder is significantly gouged and would require an extreme amount of welding.

At this point I think I'm no longer going to try and use my low-end torque oriented extra wide extra tight clearance squish band Japan-market 1994 KDX220SR head for my 70mm head modification, and will just get a stock head since the cylinder is also decked 0.30mm and really should be replated fresh since I can't have it honed out for a C-size as none exist.
I also measured the ports and found that by default the 220 exhaust port is raised about 1 mm when boring it out to 70mm due to the angle of the port where the main powervalve is the intake was raised 1 mm and the transfers raised 0.50mm, with all the intake and trans ports opened up a fair bit, so this is going to rev a bit higher anyway. I'm going to make sort of a torque plate to ship it out for plating with the studs installed still, and a rubber or neoprene head gasket cut out sandwich on the deck surface so the acid stripping of the plating does not remove any head gasket surface, but will not be doing this on the base gasket surface as I wouldn't mind dropping the port timing just a hair back down as well as being able to utilize the stock height of the stock 220 head with the already reduced cylinder deck height as opposed to running a Ron Black type head mod or Fredette milled head to get the squish clearance tighter where desired.