4 Stroke Compression - How much is Needed to Fire?

[coolpool]

I'm trying to re-life a 84 200M for a friend which was sitting for many, many years. It only had 30 lbs of compression until I adjusted the valves and put a little oil in the cylinder. I got 80lbs out of it but it went down once the oil dissipated I suspect. Now I have 65 lbs but I get not so much as a pop out of it with good spark and fresh fuel? How much compression is needed to hear this run again?

[shortline10]

100 psi to make it pop but it should be in the 165+ range to be healthy.

[threewheelin-feelin]

100 psi to make it pop but it should be in the 165+ range to be healthy.
yeah i had a 200s that would run at about 110psi but not well

[coolpool]

Oh boy this thing sounds like it's pooched for sure, thanks!

[350for350]

Maybe we now know why it was sitting for so long.

[gimmeamidget]

That compression seems really low. Is it possible the rings froze in the piston gap and new rings would bring it back to life?

[coolpool]

I sprayed inside the cylinder with Kroil and inverted the front end so the piston was in a flat position and let it sit for a week thinking the exact thing. No change. I've shelved it for now as the whole trike is basically junk. If I get bored I'll see what some of my other spare 200 engines have for compression and do some swapping. From the looks of the completely worn hand grips and foot rests this thing has seen many a hard mile.

[John Tice]

You need the cylinder measured to see if it’s round & straight? At the very least it needs an accurate hone job with a new set of rings properly gapped. 147psi cranking compression is about 10 to 1 & seldom does a stock cylinder have this high of a compression ratio. Your stock cylinder & piston has a +.0015” or a little more skirt clearance. It it’s got more a quality bore job may be in order unless all of the wear is on the piston it’s self; if so you a new std. piston set is needed.

http://i1152.photobucket.com/albums/p497/johntice1/image-134.jpg (http://s1152.photobucket.com/user/johntice1/media/image-134.jpg.html)
Measuring with dial gage

http://i1152.photobucket.com/albums/p497/johntice1/P1210342-Copy-1.jpg (http://s1152.photobucket.com/user/johntice1/media/P1210342-Copy-1.jpg.html)
Proper honing on a Sunnen set up