Jump to content
Sign in to follow this  

crf250 lost compression all of a sudden

Recommended Posts

Ok so i have a 07 crf250r it had a complete rebuild when i got the bike. it had the 13:1 pistion kw ss valves and a new crank. and a stage 1 hot cam. The bike has always been kinda hard to start i guess due to the extra compression. But i went to a track to day and was riding. it started up pretty easy i rode it around easy and let it get warm then i started to ride the track. i rode maybe 15minutes and over a triple the bike just died. made the sound of a 2stroke fouling a plug. it ran like normal before this and had its normal power. once i landed i treid to kick start the bike and noticed it had very little compression. when you kick start it by hand you can hear the air being sucked in through the air filter.

I dont belive the valves are bad because i checked them maybe 2hours of bikek time. and the exhaust were at .012 and the left intake was .005 and the right was .004 they have not changed since day one of me owning the bike..

But two races ago i did notice that my hot start was what i think stuck open. Because the head pipe got glowing red real fast. so i took the carb off and fixed that and it now works fine.

So could the rings just be burnt ? i would think if the valves was bad it would be hard to start before they just went out in the air in like three seconds.

Share this post


Link to post
Share on other sites

UPDATE: So i went to check the valves and apparently the timing chan has broke..the chain as all kinds of slack in it, you can tell that it is broke for sure. so what could have this all messed up ? from turning the kick starter over the piston seems to me moving fine and has no rattleing around noise....alos how could have the timing chain just broke ?

Share this post


Link to post
Share on other sites

i guess it wouldnt hurt to pull the head. i had to remove the cam to get the old timing chain out... up from the sound of it i didnt hear as un normal noises...and from where the cam was it stopped with the lobes facing forward and not pushing down on the valves. the chain stoped the cam from spinning anymore...so hopefully the valves are still good...and btw ya the chain was way old...i have found like 4 cracks in other links that was just waiting to brake...thank god the seasson is all the way over now.

Share this post


Link to post
Share on other sites

If the timing chain broke and it's easy to kick, you took out a valve or punched a hole in the piston. If there's low compression with the timing chain off and none of the valves are open, you should barely be able to kick it over. You have to remember, this thing was spinning at 6-11k rpms or more, and when that chain broke, that cam was still turning at 1/2 the rpm's that the crank was. That cam didn't stop the instant the chain broke. Shit's going to happen when it's out of time that bad and turning at that speed. You need to remove the head and see whats damaged. I don't believe the chain stopped the cam from turning and not doing any damage. If it did, play the lottery, you're one lucky dude!

Share this post


Link to post
Share on other sites

charlie you just the one that i was hoping would chime in...i got the head removed today..the piston does not have no holes but some feint marks here is a pic...also the bike isnt like 100% dead on compression i dont think.. it still had a little but nothing like what it did when it was fresh...also if here is a pic of the bottom on the head.

IMG_0203.jpg

IMG_0205.jpg

Share this post


Link to post
Share on other sites

While you have the head off, take some rubbing alcohol or even some water and pour it into the intake and the exhaust ports. Do 1 side at a time. See if any liquid makes it past the valves. That will at least tell you where your issues are at. Unfortunately, I can't see the pictures. If you PM me, I'll give you my e-mail address and you can send me the pictures that way if you want.

Charlie

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

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

Reply with:

Sign in to follow this  

×