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I just finished rebuilding my 1985 CR 500 engine I have in a 1997 frame. I checked everything in the bottom end, put new starter gear, clutch kit, all new OEM seals and gaskets, new water pump shaft and seals and a new kicker. I also got a freshly rebored cylinder, new 90 mm vertex piston and rings, a new OEM wrist pin bearing, resurfaced head and three layer OEM metal head gasket and OEM base gasket. I did a compression test with no carb and no pipe and it read about 130 to 135 PSI. Should I expect this to increase to the normal 150 to 160 after break in? Does 130 to 135 sound right before the rings are "seated"? I have replaced everything so I really do not know what I could do if this is on the low side.

Who did the machinework?

AlisoBob wrote:Who did the machinework?

I bought a rebored cylinder off Roosty so I l know its a good bore job. I re-surfaced the head on different grades of sand paper on a sheet of glass to be sure it was flat and true. I checked with straight edge afterwards.

Then the bore is round, and its sealed. There is no "break in" on good machine work.

If you want more compression, kick it harder...




Seriously, push the kicker over on the compression stroke by hand. Push it in little "bumps" and when you release it.. it will push back.

Its all good.

AlisoBob wrote:Then the bore is round, and its sealed. There is no "break in" on good machine work.

If you want more compression, kick it harder...




Seriously, push the kicker over on the compression stroke by hand. Push it in little "bumps" and when you release it.. it will push back.

Its all good.

I remembered reading something you said about this before and it does "bounce" so to speak with your hand. I will re-assembly and see how she runs - then again since we are having a snow storm here tonight there is no rush I guess.

CR500PHIL wrote: I remembered reading something you said about this before and it does "bounce" so to speak with your hand.

Then dont worry about it.

Different compression gauges, kicking speed, barometric pressure, port timing..all kinds of shit = measured kicking compression.

If its bouncing, its good.

Run it.

Mate
I just checked my wr250 smoker compression 170psi after lots of kicking.
Pulled the top end off to check everything and do a little power valve work.
Rings still in spec,bore good etc

Reassembled, Kicked away and 55psi??? wtf?
I swapped the schrader valves in the tester around and Bam 215psi.

I also suspect that vehicle compression testers may not be all that sutiable for small capacity or slowly cranked engines.

There are a lot of variables involved for sure. I am going to ride it - if it hauls my arms out of their sockets I will be happy - if not I will look into it.

Mine with new top end on a 2000 motor with stock head turned 165 before it was ever started. I kick it hard a few times untill the pressure gauge stops going up.

If you have a buddy that has a tester it will prolly read a different # than the 135 you got.

The kicker bounces like a ball when you push on it and it certainly feels as much or more than the rebuilt 89 engine I had in my AF. That engine ran great once I got it jetted properly. I have it ready to start now so if if it ever warms up here I will try it.

seanmx57 wrote:Mine with new top end on a 2000 motor with stock head turned 165 before it was ever started. I kick it hard a few times untill the pressure gauge stops going up.

If you have a buddy that has a tester it will prolly read a different # than the 135 you got.

Just for fun I tried the same tester on my 670 skidoo engine using electric start and it read the same - around 130 to 135. That is either an awful coincidence or a crappy tester. I vote for the later.

Haaaa!! When I tested the wr250 and got 170 psi.
Then I tested my mates wr250 same year etc
170 psi too ,that got me thinking a bit ...dodgy tester for sure.

I rebuilt my 2000 CR250 2 years ago after the tab on the plug fell off on a 10 hour motor. bad day. Luckily it just trashed the head and a light hone cleaned the jug right up. New piston/rings/head, 210 PSI before I started it. 63 semi hard hours later I'm at 218 PSI same tester.

Well I have no worries about the compression - I just got off the bike and it starts perfectly, idles and pulls like a jet. She pulled the front wheel in every gear I tried so far with ease and in most cases I had to slack off on the gas since the front was still rising. I have a slight surge on idle so I have to adjust the pilot screw or possibly switch to a larger pilot jet - very minor stuff. This will be a fun summer for sure. A bunch of young guys were staring perhaps wondering what the hell I was on that was pulling like that. I love CR500s!

You gotta' get that Zip Ty airscrew.... its my most used mod...

AlisoBob wrote:You gotta' get that Zip Ty airscrew.... its my most used mod...

I will definitely be ordering one of those.