sat up...low compression

This might help others not to panic if it happens to you. My '00 426 sat unstarted in my garage for about 5 weeks due to many reasons. Tonight, I wanted to do some maintenance and began my engine starting routine. First, I pull in the compression release lever and kick the engine through about 20 times without touching the throttle and leaving the petcock valve closed. This is to pump oil to the head before lighting the engine. Once I released the compression release lever, and tried to bring the engine to TDC, I noticed that the compression was very low. I could feel that I had SOME compression, but not nearly what I should have. I began to kick steadily on the kickstarter to try and bring the compression up. Slowly, it began to build compression. Suddenly, it fired, without me trying to start the engine. I let it run for a bout 3 minutes and shut it down. Now, it had normal compression. I could even stand with all my weight on the kickstarter at TDC and it would hold me there for about 3 seconds before it would slowly move beyond TDC. What comes to mind to me about why this happened is that the cylinder wall needs some oil splashed on it to seal the rings and make compression. By having sat idle for over a month may have let the rings and cylinder wall get a bit "dry". I think that from now on, I will kick the engine through about 30 times at least every 2 days. Having very little compression gave me a terrible anxiety attack. That was not fun.

I had the same experience. Sounds pretty normal.

Glad you raionalized this out before devided to tear the top end apart :)

5 weeks!!!

Perhaps there was a bird's nest or two in there.

What's up with that??!!


I just finished a fresh ring install due to the same problem. Bike sat for a few weeks with no riding. Went to start and much less compression than normal. I figured a valve problem so I tore the top end down and eventially found that the top two ring gaps (wiseco piston) were perfectly aligned. I figured this would contribute to low compression. Odds seem small that you would stop the engine with the rings in this position very often. New rings (with gaps staggered) seem to have taken care of it for me. Hadn't thought of the oil though... good idea.


Boit, same thing happened to me right after having rebuilt the top end. I installed the 420 kit very carefuly staggering the rings per manual / Wiseco method. Valves and head cleaned to perfection and so forth. Then with young neighbor anticipating our loading the pick-up for moto school I kicked over and over as if a valve was open. Decided to park the bike for about an hour and got back to it. Tried again and my neighbor noticed that it was firing. ( I was too frustrated to hear anything after having stayed up all night to get my ride ready for the school ! )

Well it fired up after a few more tries and has been running like a champ eversince. No smoking, can't budge the kikstarter when not using the release.

BTW I woul play with the comp. release and it worked fine through the whole ordeal. Never figured it out.

It's just one of things that I can't accurately explain. Whatever caused it has not apparently damaged anything. It still runs great and has excellent compression now. Thanks for the comments.

Just a curious question, but when you guys are done for the day, do you kick it around until you feel compression (all valves are closed)?

Same thing here guys......wanted to get oil to the top end and kicked about 30 times with compression release held in.....Won't start now and there is little compression. I just hope it comes back.........I'll keep you posted.

Yeah, I pickup up on that here in TT that it's best to leave the bike at TDC when parked for a while or right after post wash warm-up / dry-off. Something about valve seat crystalization on the mating surfaces due to possible moisture getting in there. Possibly this is also a neutral position for the valve train / springs etc. Sounds logical enough to me. Always a good idea to leave any sort of equipement / machinery in a neutral non load / stress position.

SirThumpalot: I leave my engine at TDC any and every time I shut the engine down. I'm so anal about it, I even do it when I roll up to the starting line and shut it down waiting for my moto to start.

Motostyle: If you can't get the compression to come back by kicking it through several times, you might consider adding a little 2-stroke oil in through the spark plug hole and trying it again.


You know that anxiety attack thing that went through your head? Mine is full on right now. I just re-ringed this thing, so I had the whole top end apart. I had compression when it all went back together and now it's not "magically" coming back as it did for you guys. I pulled the comp release and went through about 30 strokes to get some oil up top. Then, no compression. Could a valve stick open for some reason? I put some oil in the cylinder when it went back together. Wouldn't no compression be related to valves instead of the ring seat? I am bummed if I have to take this thing back apart. The thing that I'm worrying most about is somehow I had the timing off and bent a valve. My split personality is starting to wail on me right now. Let me know what you think before I tear back into the motor. :)

I feel for you...I really do. You might want to go back and check your valve/cam timing and valve lash. It certainly COULD be valve related since it appears that your rings should be fine. Hopefully, your compression release is operating correctly and not holding an exhaust valve open slightly. If you still can't locate the source of the problem, you might consider having a leak-down test performed.

Ok, here's the latest. I checked the valve timing and it's spot on according to the marks on the cams and the flywheel. That's good news. One thing I noticed as I kicked it over. Air is coming out of the oil breather tube when I do this. Meaning, a valve is sticking open I'm assuming. I'm going to check my valve clearance since an exhaust valve could be way out of adjustment or the compression release stuck the exhaust valve open like your saying. Any other ideas?

When you checked your cams. did you make sure the lobes were pointing away from each other as illustrated in the manual? There are only limiteda avenues of compression loss in a 4-stroke...either the piston rings to cylinder clearance is too great allowing compression to blow by the rings....or there is a loss of sealing at one or more valves. The cylinder head could be leaking. The spark plug could be loose or missing the gasket. In my case, since the bike was fine before it sat for a few weeks, I had no reason to suspect anything major. However, since you've had the top-end apart recently, there are implications. Keep looking hard at the valve reliability issue before moving to the next logical step. I'd like to know what you eventually find.

It's normal to have pulses from that breather tube as the engine is turned over. The piston pressurizes the crankcase on its downward stroke and that pulse is vented through this tube. It does the same thing as a PCV valve on your car.

Yup, the cam lobes are pointing away from each other at about a 45 deg or so and all the marks line up properly. Here is what I did find though when checking valve lash. The far right intake valve is stuck open. (When standing over the bike) I can't get a .002 feeler in between it (let alone a .010), which is about as thin as they go. All other valves check out OK. I'm going to remove the cam on that side and check the shim. Maybe it is slightly out of alignment? I'll keep you posted. Thanks Boit.

Deleted my post, didn't reload the screen and my reply looked way out of context. :)

[This message has been edited by sirthumpalot (edited 06-30-2001).]

Way cool! And thanks for letting us know what you discovered. When a member has a problem and post what the solution is, it helps us if we ever run into the same problem.

Success!!!! Just so happens that the right Intake valve shim was not seated down correctly. I never took it out in the first place, but it must have been knocked loose in taking the top end off. She has full compression and all of the valves are in spec for Ti 01's. It fired up this morning like a champ. I think I'll go and reward her with a couple of hours of MX today. Thanks for all of your advice Boit and other TT members. It's good to be Thumpin' again.


Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now