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Compression test finally!

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So i did my compression test today. It was about 60 degrees and at 1500ft elavation. So the thing said about 180 so is that in big time need of rebuild or what? Thanks for any help guys :worthy::thumbsup:

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180 sounds good. But the only way to know if it is truly a good number is to know what it was after break in of a new top end. Then take that compression and compare it to what you have now. After comp. drops 10% to 15% Or after a set period of hours of use, it is time for a new top end. I have a 2000 CR250 that puts out 175 psi at 75 degrees at 3000 ft.

Also each compression tester is going to give you a different number. So my compression compared to yours does not neccesarily mean that yours is good or bad just different.

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Umm... he may give you a number but that is not going to help you any. The compression for YOUR bike is going to be with YOUR compression tester after you put in a new top end, break it in, and then take the compression.

Then you have base number to work with.

Each time you do a top end you will need to do this as the number will not always be the same for each top end, it will be pretty close to the same, but cylinders wear and this can change things. Also cross hatching on the cylinder walls wears down then the rings will not seat as well on that top end and you will end up with less compression. There are several variables at work and the compression for YOUR bike is specific to YOUR bike only for THAT top end.

Take the pipe off and look into the cylinder. That may give you an idea as to the condition of the top end.

The only sure way to know is to put in a new top end yourself. Otherwise it's condition is anybodys guess.

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Do you have an adapter on the end of you tester? they usually come with one. I'm saying this because it will add to the size of the chamber and make the reading lower. there is a check valve located in the first fitting at the end of the hose. if you add the adapter, the reading goes down.

If not, I'd say do the top end. I had an experienced honda mechanic tell me a cr won't run right if it does't have 200. and at 1500ft. it should be at least 190.

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Do you have an adapter on the end of you tester? they usually come with one. I'm saying this because it will add to the size of the chamber and make the reading lower. there is a check valve located in the first fitting at the end of the hose. if you add the adapter, the reading goes down.

If not, I'd say do the top end. I had an experienced honda mechanic tell me a cr won't run right if it does't have 200. and at 1500ft. it should be at least 190.

When I asked at the Honda dealer here, what the compression for a cr 250 should be? they told me the CR will run on anything over 110, go figure? Here at +5,000' on my gauge I've never seen more than 165 on any of the 250's I've owned, (CR, YZ, KTM). I think it's odd that none of the factory service manuals for these, mention anything about compression readings! Recently I did the top end on the CR, prior to dissasembly I got 160, everything looked good and was within spec. Still I installed a new piston and rings, had the head milled and the squish distance reduced, held a pressure test of 10psi for 15 minutes, thought for sure I'd finally get a reading closer to 200. But after break in, all I got was 165!! :thumbsup:

Just my 02, but from my experience thus far, I tend to agree with AV8R.

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All I can say is, I have a 00 and two testers, 1 says 230 and the other says 235 at sea level. I had a 96 cr250 that read within 5lbs of the 00. Both stock motors. (except the 00 has wiseco pro-lit piston).

make sure the check valve on the tester in the threads of the head. (no adapter), hold throttle open and kick hard till it peaks.

When I do a top end, I replace all, measure bore, hone if needed, check ring gap.

You may already know this and more, just trying to help.:thumbsup:

There's no doupt, you can probably buy 5 guages and get 5 different readings.

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