Cam/Crank timing

This is on a TRX450. When the dot on the crank gear and mark on the side cover are lined up, should the piston be at the top or somewhere in the stroke?

I know this in the wrong forum, ThumperTalk takes me to ATVtalk when I go to Honda ATV's.

I got this job from 3 other people who couldn't get the bike to run. I'm suspecting that the cam/crank is out of time. I have zero compression with new piston, rings ant correct valve adjustment. It will pop through the exhaust but thats it. I'm thinking the gear on the end of the crank is out of time which is throwing me off on the rest of it. The jack legs before me had the clutch in wrong, so, I'm thinking this gear is out of time.

Thanks for your help,

Scott.

I'm no expert but I have re-shimmed a couple times and just finished installing a new crank/piston/cam into my '05 CRF 450R. Here's what I do.

I put a long screwdriver down through the spark plug hole so I can physically see when the piston is at top dead center, I use that as my base to line everything else (other marks) up. With the cam lobes pointing to the back of the bike I'll then line up the marks on the cam holder with the marks on the cam sprocket.

The last time I re-assembled the engine I had the piston and TDC and lined up the marks on the cam holder/sprocket. Depending on how you looked at the marks, it appeared that they were either right on or off just a little bit. I moved the chain 1 tooth on the cam sprocket to get the right timing. When I thought I had it lined up I put the piston right at TDC again and it was off considerably. My point is that those marks can look like they line up, but if you're not at TDC it's not going to run (or it'll run poorly). I put my timing back to the way I had it and the bike runs like a champ.

To answer your question, yes the piston should be at top dead center when the marks line up. There are three marks to line up, the one on the right hand side of the crank/inspection hole, the one on the left hand side of the engine (flywheel) and cover and the last is the cam sprocket/holder. But like I said, I start with the engine at TDC and go from there.

Here's a link to a really good post about timing with pictures (thanks to crf-f crf-r trx cbr) :

http://www.thumpertalk.com/forum/showthread.php?t=586690

Good luck.

Use the timing mark on the flywheel (there is where it is at):

JT001.jpg

then the cam gear hash will line up with the tower arrow:

JT015.jpg

you can check the right side gears to be sure you are not 180* out, but not needed. These are more like the 02-06 motors. The pics previous are of the newer 07-08 cam with the lever weighted decompression.

I was looking at the fiche for the TRX and saw that the gear on the end of the crank has splines. If the gear and crank aren't timed together, it throws everything else off. I'm gonna look at this then I get home. The dummies had the clutch off, so, the might have taken this gear off.

This pile of junk is about to drive me nuts.

Thanks for the help,

Scott.

Scott, the cam gears are pressed on and, in a few instances, can rotate and really cause a lot of problems with diagnosis. Just one more thing to be lookin for..

yeah the clutch side is the balancer gear. It would give you a hell of a motor vibration, but would not effect the cam timing.

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