Change those cam chains!

Recently I talked about the problems I had getting my cam chain tensioner to properly tighten the cam chain during my rebuild. http://www.thumpertalk.com/forum/showthread.php?t=244895&parentpage=4

Well, I finally determined I had a bad cam chain and the new one arrived today. While waiting for the new chain to arrive I decided to finish as much of the motor work as possible and install the engine in the frame. I guess I forgot I still had to change the cam chain and that meant pulling the head (or so I thought).

Today, I decided to try and manipulate the old cam chain off the crank gear even with the front cam chain guide in place. To my surprise I was able to move the front guide enough to get the old chain off and the new one on. I removed the two bolts on the rear guide and it easily moved enough to allow me to remove the chain there as well. Goody, Goody :naughty:

I successfully got the new chain on and got the cams timed. While I've still got a bunch of stuff to install before it runs I went ahead and tried kicking it over. It seems to work great. The new piston has all sorts of compression the the Autocomp feature works great and it kicks over like a healthy 250 two stroke.

You may not think you have to install a new cam chain but after seeing these pictures, the facts tell me I should always replace the cam chain whenever I pull the cylinder for rebuild.

Here are some pictures.

This is the new chain and the old chain side by side. Notice any difference?

http://www.bmnellis.com/images/yz426/camchain1.JPG

Here is a closeup of the difference in length.....it's almost 1/2 inch even tho the #of links is the same. It just stretched which is why my cam hit the valves in the first place.

http://www.bmnellis.com/images/yz426/camchain2.JPG

Here, I've removed the old chain without removing the head. The rear chain guide bolts have been loosened and the guide moved.

http://www.bmnellis.com/images/yz426/camchain3.JPG

Here is the new chain installed before installing the bolts for the rear guide.

http://www.bmnellis.com/images/yz426/camchain4.JPG

Here are the cams installed and properly timed.

http://www.bmnellis.com/images/yz426/camchain5.JPG

The cam chain tensioner now tightens the cam chain just like it should.

If I hadn't seen the difference myself I might not have believed it.

Hope this helps.

Excellent post guy! Helped me a lot. Thanks for the pics... :naughty:

Wow, that chain is stretched alot. Kinda makes me want to go out and check my chain.

What kind of shape are the sprockets in? You would think with the chain that badly stretched they also would be in need of replacement. Just wondering. Tdub

This is a great post - I learned to always change the cam chain for a top end

and they are cheap $20.00 compared to the damage that can occur - they are always going to stretch over time

The sprockets should be ok as they are higher tensile strength/harder metal than the chain - look at over time if you are a long term owner

Some will even say replace the cam tensioner - you can test the mechanism to see if it is properly working - but they are cheap to replace also -

Great post and great pictures :naughty:

Thanks

Could you tell that the old chain was loose durring disassembly, or did it look normal until you tried to reassemble?

Could you tell that the old chain was loose durring disassembly, or did it look normal until you tried to reassemble?

No, since the motor would not turn over prior to disassembly due to 3 bent valves. The chain itself looks normal, it wasn't until I couldn't get the tensioner to tighten things up that I looked closely at how much play there was between each pin.

What kind of shape are the sprockets in? You would think with the chain that badly stretched they also would be in need of replacement. Just wondering. Tdub

The sprockets were in pretty good shape but since the cam is a new 450 unit obviously would be. The intake looks servicable by comparison. Another indicator that the chain is highly worn is the fact that it will not sit on the sprockets properly and want to "ride up" on the sprocket teeth.

Some will even say replace the cam tensioner - you can test the mechanism to see if it is properly working - but they are cheap to replace also -

I only read ancedotal posting re: tensioner problem and my inspection of the innards of the tensioner convinced me that replacement wasn't necessary.

Replacing the cam chain is a cheap and easy job, and should be done at least every two years, even if nothing more is needed. Annually is wiser, more often than that if it's a high hour race bike. It just avoids a lot of misery.

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