Ideal cylinder compression?

amstel78 · Post by **amstel78** » 08:45 pm Jul 25 2012

Manual states 119-185 psi as the usable compression range on an E series 200. My reading tonight on a cold engine is around 141-142 psi. Is this in your opinion acceptable or indicative of good rings? I haven't had the top end off yet, so I do not know if the PO had done any work to it.

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rbates9 · Post by **rbates9** » 09:16 pm Jul 25 2012

It is getting low but should be fine for a while. The H 200 is something like 91?Psi to 151 Psi.

Post by **SS109** » 09:24 pm Jul 25 2012

Sounds fine to me!

amstel78 · Post by **amstel78** » 09:30 pm Jul 25 2012

rbates9 wrote:It is getting low but should be fine for a while. The H 200 is something like 91?Psi to 151 Psi.

So if I understand you correctly, an optimal compression reading should be at the higher end of the spectrum; i.e. 170-180 psi?

I was under the assumption that if it was too high, that's indicative of carbon buildup, or something else wrong, etc.

Out of curiosity, what's a nominal compression reading after a top-end rebuild?

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amstel78 · Post by **amstel78** » 05:46 am Jul 26 2012

I rechecked compression again this morning just for the heck of it and I got 150 psi on the gauge. Seems to be right around the middle of the usable range so I think it's fine.

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amstel78 · Post by **amstel78** » 06:05 pm Jul 26 2012

Still wondering out of curiosity what a typical compression gauge would read after a typical top-end rebuild. By rebuild, I mean new piston and rings. Anyone care to chime in?

Oh, and do most folks here just replace the piston and rings, or also replate the cylinder walls? Is replating even necessary?

rbates9 · Post by **rbates9** » 06:07 pm Jul 26 2012

I rebuilt the top end of my 2000 200 and before I tore it down I checked the 12 year old top end for compression and had a 150 Psi reading. I put in a new piston and rings and checked after about 4-5 hours of riding and it had 145.

So a new top end should be toward the high end of spec. The reason I said it will be fine for awhile is as things wear they tend to wear quicker the closer they get to the end of their life. If it was my bike I would look thru the exhaust port and check the cylinder and the front of the piston to see the general condition. If it looks fine then go with it. If you find that it is starting to have power issues or start hard then check it again.

Also it looks like you are checking the compression with the carb off. When you do a compression test the carb is usually on and you need to hold the throttle wide open as you kick it. With the carb still on you are going to have some fuel and oil getting into the cylinder to help with sealing the rings so that could bring up your reading a bit as well. If you felt like doing another check you could spray in some WD-40 or something of the sort and see what you get then.

amstel78 · Post by **amstel78** » 06:21 pm Jul 26 2012

Thanks rbates. Will put the carb back on later and test compression then. I actually took the carb out earlier to check the reeds, and they seem to be fine. Not sure if they're stock or if they're aftermarket but their general condition looked good, so I think I'll leave them as is.

As for a proper compression test, the manual actually suggested taking a reading while the motor was warm, but I'm finding it hard to thread the adapter into the cylinder head with the fuel tank on.

Anyway, appreciate all the help you guys have been giving me. This site is great!

Post by **SS109** » 06:53 pm Jul 26 2012

Man, you are thinking about it too much. It has good compression. Run it!

kawagumby · Post by **kawagumby** » 07:03 pm Jul 26 2012

My compression tester is my right foot. I don't need no stink'n gauge. Seriously.

Zillions of smokers since the sixties and never used a compression gauge once.

amstel78 · Post by **amstel78** » 09:55 pm Jul 26 2012

You might feel I'm thinking too much about it, but I'm learning. Before this bike, I had no experience with 2 strokes. This is my way of understanding concepts and setting a baseline for future reference. We all have to start somewhere.

Post by **SS109** » 02:35 am Jul 27 2012

Just log what compression you have now and check it in a year. That's about all you need to do!

amstel78 · Post by **amstel78** » 05:25 am Jul 27 2012

Fair enough. Btw, I like your screen name. Have about 2k rounds of the stuff in my basement.

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Post by **SS109** » 01:58 pm Jul 27 2012

amstel78 wrote:Fair enough. Btw, I like your screen name. Have about 2k rounds of the stuff in my basement.

Thanks! Yeah, I only have about a case and a half left.

amstel78 · Post by **amstel78** » 02:14 pm Jul 27 2012

SS109 wrote:
amstel78 wrote:Fair enough. Btw, I like your screen name. Have about 2k rounds of the stuff in my basement.
Thanks! Yeah, I only have about a case and a half left.

Stock up now before prices go back up!

I remember back in the late 90's, early 2k's, I could pick up a crate of 7.62 Nato for about 200 dollars. That's 1,000 rounds of quality brass. Now, it's 400-800 depending on brand. Ridiculous. A crate of 5.56 is about $275-300 in my neck of the woods. I'm thinking of converting one of my ARs to 5.45x39 since it's dirt cheap.

There's been a few sales of M855A green tip lately.. fairly decent round. Personally, I like the older M193 and the Korean PMC boat tailed .223. I've also been shooting quite a bit of Russian (Silver Bear) 308 which is really a very good and inexpensive round. Fairly accurate; about 2-3MOA @ 100. As long as it's minute of man, I don't complain too much. No problems with Silver Bear extraction in my AR-10 or M1A.

Sorry for the OT. Back to your regularly scheduled KDX programming...

Post by **SS109** » 03:49 pm Jul 27 2012

Yep. I should have started buying about a year ago! The election is coming up and there is always a run on guns/ammo if a democrat wins.

I have been shooting some cheap PMC Bronze and Wolf (both 62g) in it for now in an effort to save the good stuff. However, I do think I'm going to start buying the M193 instead of the M855/SS109 as the rifle seems to shoot more accurate with it.

amstel78 · Post by **amstel78** » 05:14 pm Jul 27 2012

I believe the 55gr M193 utilizes a boat tail projectile whereas the SS109 62gr has a standard slug. Same for the PMC Bronze which I've gotten great results with at 100-300 meters.

The 193 is a nasty round though. I've seen photos of a guy who was shot through the leg with M193 that left a 5" exit wound. The round was still supersonic when it penetrated and the resulting shockwave snapped the thigh bone and obliterated the knee joint.

The 109 penetrator otoh doesn't yaw and cavitate a well usually resulting in a through and through.

What is your barrel's length and twist rate?

P.s. Try the Silver Bear. It's cleaner and more consistent than Wolf. You can also get it in 62gr hpbt.

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diymirage · Post by **diymirage** » 05:52 pm Jul 27 2012

is that like the tunderbolt .22LR?

Post by **SS109** » 08:01 pm Jul 27 2012

amstel78 wrote:The 193 is a nasty round though. I've seen photos of a guy who was shot through the leg with M193 that left a 5" exit wound. The round was still supersonic when it penetrated and the resulting shockwave snapped the thigh bone and obliterated the knee joint.

The 109 penetrator otoh doesn't yaw and cavitate a well usually resulting in a through and through.

What is your barrel's length and twist rate?

That is another reason I was thinking of switching back. The M193 just has better threat stopping ability compared to the M855 which is not doing very well in A-stan and Iraq stopping threats quickly.

The rifle has a 16" pencil barrel, chrome lined, and a 1/9" twist. I built it for the wife to be as light weight as possible. Built it on a Sun Devil billet lower and a J&T upper kit with chromed bolt and carrier. Otherwise it is really just a basic AR. Put a Tac-Latch on it, M4 butt stock, CAR hand guards, A2 grip, P-mags, A1 birdcage FH, and a fakepoint.

diymirage · Post by **diymirage** » 08:24 pm Jul 27 2012

SS109 wrote: That is another reason I was thinking of switching back. The M193 just has better threat stopping ability compared to the M855 which is not doing very well in A-stan and Iraq stopping threats quickly.

The rifle has a 16" pencil barrel, chrome lined, and a 1/9" twist. I built it for the wife to be as light weight as possible. Built it on a Sun Devil billet lower and a J&T upper kit with chromed bolt and carrier. Otherwise it is really just a basic AR. Put a Tac-Latch on it, M4 butt stock, CAR hand guards, A2 grip, P-mags, A1 birdcage FH, and a fakepoint.

AND it sits on the couch and watches melrose place with you ?

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