compression question

[rmxtgh]

i had a leakdown test and it showed 98%.....about 6 hours of riding later some dufus crashed into me.......the impact bent my bars and knocked the spark plug cap off my bike......now when i go to start it....i dont need to use the decompression release cuz the kickstarter kicks almost as easily as a two stroke...i know if you dont clean the air filter etc you'll lose compression but seems very strange to me to lose it pretty much instantly due to one crash.........any ideas???

[BlackSheep]

I assume its a 400 or 426 because it still has a manual decompressor, is the lever bent or cable hung up, is the decompressor arm bent holding the exhaust valve open?

[rmxtgh]

my bad...its an '01 426 with very low hours on it.

[rmxtgh]

hte lever/cable seems to work fine....doesn't look like its bent but.....i dont have another yz to compare it to in order to see if its returning all the when i release the lever....it seems to be....with my finger i can't push down the arm down any furthur on the top of the cylinder.

[rmxtgh]

any body????

[YZ426F Rider]

Damn...I can barely pull the spark plug cap off my bike by hand!

Does the bike run? You could have a kink or bend in your compression release where it enters the head...but if you were losing compression (sounds like you are for sure) I'd think the bike would not be running very well. How is your right radiator? Is it bent back into the compression release lever?

Probably should pull the valve cover and take a look to see if the compression release is sitting flat on the lifter. Check your valve clearances also...if the release is engaged at all your right exhaust valve clearance will be WAY off.

[David37]

I would try disconnecting your compression release cable from the compression release arm on your engine. If your compression comes back you have a problem with your compression release cable. If you still have no compression, check your compression release arm on your engine and see if you can manually disengage the compression release. If the compression release arm does not move you found your problem. IMO from your description sounds like your compression release mechanism on your engine may have been damaged/bent during your accident.

[rmxtgh]

it does run.....took me about 20-25 minutes of kicking to get her to fire....thats not a surprise though since this happened way back in april and i just parked her and rode my trail bike in the woods since then.....she seems to run decently....had a little popping on startup but again with the time down and without stabilizer its not surpriseing....i just went up and down the street once so not like i tested her out real well but seemed to run just fine .....yes hte right radiatior is bashed in a bit too..

[rmxtgh]

how much is a tool to test the compression and what is the right psi?