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| compression test on engine that hasn't run since assembly http://www.kawi2strokes.com/forum/viewtopic.php?f=14&t=14542 |
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| Author: | 2stroke [ Mon Aug 23, 2021 3:22 pm ] |
| Post subject: | compression test on engine that hasn't run since assembly |
Despite 35 plus years of wrenching on bikes, I confess to not having owned a compression tester until this year, bought one when I was going through some issues with my XT500. I would get a fresh bore on some of my bikes at times. My S2 that I've been working on for the last couple years is getting close. Im doing the body work now. Mechanically, it could run now. I was on standard bore when I tore it down and since money is always an issue, I opted for a new set of standard pistons and rings. I am only seeing 65 pounds on two of the jugs. So says my harbor freight tester. Ive been too lazy to test the center cylinder. Im sure I put some sort of oil on when assembling the top end but it may be dry by now. In normal operation, the cylinder is wet with gas/oil residue. I know if I dump some oil down the jugs, compression will go up and of course that is a quick and dirty test to see if you need a top end. Im just wondering if I should run the engine, get it through a couple heat cycles and then see where it lies. I never did think the bike was as peppy as it should have been, but it ran out well. I am tempted to just buy the oversize slugs now and bore the cylinders. I'll have to price out the boring, but I have been BURNED badly by people I have paid to bore my cylinders recently. I do a fair amount of machine work at my new (4 years now) job, and I have access to equipment. The whole time I have been thinking, gee...if I could only do my own bore and crank work....I could bore my own stuff at this point, but I have some other spares I want to practice on first. It was such bad timing when I was working on the engine of this bike. Money is a bit easier these days, and I bought some measuring tools in the meantime that I could have used to measure clearances etc. Ughhh....as I write this, Im thinking I should just do the top end the right way. Its not like it would be hard to pull the jugs. |
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| Author: | Jim [ Mon Aug 23, 2021 4:18 pm ] |
| Post subject: | Re: compression test on engine that hasn't run since assemb |
What's the history of those pistons and cylinders? The S2 has very small cylinders. If your tester doesn't have the check valve right at the spark plug threads it might read that low with perfect cylinders. This can be the case if the check valve is at the engine end of the hose and there's an adapter between it and the spark plug hole. Where is the check valve? |
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| Author: | 2stroke [ Tue Aug 24, 2021 11:00 am ] |
| Post subject: | Re: compression test on engine that hasn't run since assemb |
Check valve is on the gauge end, at the end of a 20 inch hose. I put all 3 plugs in and kicked it over, it feels crisper than I remember. I do have a weird stubby kick lever on it. The cylinders are the ones that were on there years ago when I got it. Pistons looked good back then. I didn't put many miles on them myself but who knows whether they are the originals or not. I think Im just going to see what I get with these. |
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| Author: | Jim [ Tue Aug 24, 2021 11:09 am ] |
| Post subject: | Re: compression test on engine that hasn't run since assemb |
Were you holding the throttle wide open when you kicked, and then kicked until the gauge quit rising? |
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| Author: | ALTERED IMAGE [ Tue Aug 24, 2021 4:14 pm ] |
| Post subject: | Re: compression test on engine that hasn't run since assemb |
No. Valve must be as close as possible to spark plug hole. Junk the junk HF gage. And... When you get a real gage, check "schrader" valve spring. It must-must be loose to about 1 gram spring opening. Use the same sized valve holder assy. as the spark plug threads and ceramic. As stated above, small chambers/bores are super sensitive to test gage volumes. 20" wow. p.s. comp checks are usually a relative gage measure from multi-cyl. engines. cliff |
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| Author: | Jim [ Tue Aug 24, 2021 4:51 pm ] |
| Post subject: | Re: compression test on engine that hasn't run since assemb |
I took what 2-stroke said to mean the valve is at the engine end of the 20" hose, but this answer was ambiguous. |
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