Stuck valve

[njskiatomic]

My 1986 xr250 had no compression. I could push the kick starter with my hand. My friend had the same bike and his was a timing problem due to a stretched timing chain. I assumed I had the same problem. When I was taking the valve cover off I started to loosen the springs on the valves and one of them made a loud cracking noise like the valve was slamming shut. Out of curiosity I pushed the kick starter with my hand and the engine seemed to have compression. Is it possible that something was stuck on the valve or spring preventing the valve from closing? Has anyone ever experienced something like this? Befor I disassemble the engine any further I think I'll put the valve cover back on and see if the thing will start.

 

[uts]

If something was stuck on the valve or spring it probably would have caused some considerable damage. My guess is that this valve is well on the way to it's end. It may not stick again straight away but soon enough it will die. Might be time for a head reco.

 

[reelrazor]

".... I started to loosen the springs.."

How exactly were you loosening the springs?

Valves will stick due to a)a foreign object between the valve and seat. b) carbon(which is also a foreign object but is dislodged from the valve itself or the combustion chamber) and c)lack of lube between the valve and guide.

'a)' will happen while running and will cause the bike to backfire and die

'b)' same as above but can also happen cold/on startup

'c)' will happen after the bike has sat-i.e. runs fine, a week(month/year) later you try and start it and no compression

All conditions are a crapshoot to continue running the bike. If it was 'c' you can probably continue to run it until winter and then think about a valve job at least. In the old days guys would make sure they parked four stroke singles with the engine at TDC so the valves were closed when they sat.

 

[njskiatomic]

uts, I thought of that also, but I figured I would try to run it now and see what happens. I live in New Jersey and the riding season will be over soon. A rebuild will make a good winter project. Thanks.

reelrazor, Let me correct myself. An auto mechanic friend of mine was lossening the valves, not me. He was doing it through the adjustment plugs. In his opinion he seems to think that the springs have good tension. You may be right about a valve job in the near future, but like I told "uts", the season will be over here pretty soon. I think I'm in the 'c' category. The bike had sat for over a year. That's a great tip about leaving it at TDC. Thanks.