compression help

[travis_mandeville]

Hey you guys, one cylinder on my vision, test real, low, almost nonexisent,  after adding oil, compression built up to so much the engine couldn't turn over.  After releasing pressure, and repeating a few times, compression gradually went back down to less than 25 or so, after maybe 6 times.  I know oil should build up compression when it's the rings or cylinders, but is there any way it could do it to a head gasket leak? And why would compression build up so high?  Man, I could use some help here, wanto get this bike running for summer.

[JaBey]

I ran some compression tests a few weeks ago on my buddies bike Travis. His averaged at 120psi per cylinder. However, we built his bike out of a parts bike that hadn't run since 1986. :P So to be sure we had good wet walls when we first started it I put a little oil in the cylinders and put my finger over the hole and turned it over to blow out any excess. When I put the plugs back in however, it really struggled to turn over from the high compression. I believe this was much more due to the fact the the starters are so poorly geared and powered on these bikes. Most of my other bikes turn over at 2 to 4 times the speed on my Visions. I would not read to much in to it not turning over.

With your problem, it can only be 3 things. Rings, Headseal (gasket or surface), or the valves. If it drops off so suddenly, I would rule out the rings. Since it has a water jacket, the only way to tell if the head is leaking on the inside is oil in your water, or water in your oil (most likely). Also check for high pressure in the gearbox. Ruling this out, take the valve cover off and see that the valves are fully closing and the valve shims are properly gapped. Either a bent valve, or carbon deposit on a valve seat can cause the effects you are experiencing. Hope this helps.

[Lucky]

Does it make any noises while cranking (or running)?
unusual results sound like it could be something like a bent/stuck valve, poss broken spring & the keepers have come out..?
so sometimes it seals, causing high compression, sometimes it sticks open giving low compression..
just a thought, I might be way off, but pull the valve cover, crank it with the plug wires off, and see if all the valves are moving properly.
--Lucky