10 replies to this topic

[James]

Ive just reshimmed the valve clearances on my 04 900. Im at the stage where Ive put the cams and front cam chain guide back in and Ive hooked up the cam chain.

THE RAW FACTS
1. The crank is on the T Mark.
2. The marks on the exhaust cam sprocket align perfectly with head (punch mark up) and the camchain is nice and tight up from the crank to the exhaust cam. But...
3. When the marks on the inlet camshaft align with the head (again, punch mark up) there is a little slack in the camchain between the sprockets. When you tension the chain, the marks slip a few degrees backward.
4. When the marks on the camshafts are correctly aligned, you would have to move the inlet cam a lot more forward (i.e. the other way) for the sprocket to pick up on the next tooth. The way its set now, the cam moves the least degrees to achieve a taught chain run.

THE QUESTIONS
Does that sound like its set right? Its difficult to get clear photos, but Ill try if itd help.
Does anyone have a chain link or pin count from the obvious reference points on the cam sprockets?

SUPPLEMENTARY PHILOSOPHICAL QUESTION
Why-oh-why didnt I read the excellent top end strip thread in Knowledge Base BEFORE I whipped the cams out? Cable tie the camchain to the sprockets. Simple. Genius!

Edited by Jim, 21 October 2017 - 11:14 pm.

[Studley Ramrod]

You could try turning the crank and chain around to the next line up with T mark and no1 at TDC to see if it lines up better.  You might have hit a part of the chain that's stretched.

[fixitsan]

Sounds like chain wear. The cam sprockets and threaded holes in the cam ends where the bolts hold the sprockets on are not extremely high precision parts, and if they're anything like most cars there's usually a degree or two of variation from sample to sample.

[James]

You could try turning the crank and chain around to the next line up with T mark and no1 at TDC to see if it lines up better.  You might have hit a part of the chain that's stretched.

  

I’ll give it a go. I want to be 100% happy with what I’ve done to it before I put it back together again
 

Sounds like chain wear. The cam sprockets and threaded holes in the cam ends where the bolts hold the sprockets on are not extremely high precision parts, and if they're anything like most cars there's usually a degree or two of variation from sample to sample.

Good point. I’ve had the same with other bikes I’ve rebuilt, if it’s ‘out’, it’ll only be one tooth out. I’ll be able to do something about it

In the meantime, can anyone help out with a pin count on the cam chain? That’s the number of pins between the ex-mark (on the inlet) and the in-mark (on the exhaust)?

In the PDF Yamaha manual (from JBX’s site), the diagram of the cams (page 5-17) is unclear. There appear to be 13 pins, but the chain isn’t meshed on the exhaust cam properly. Mine probably looks almost exactly like that.

 

 

 

Turn a cam which way to mesh the camchain? (possibly a new party game )

 

Edited by Jim, 23 October 2017 - 05:53 pm.

[steve27bha]

Does this help? Before my valve check Feb '15.

 

 DSC08357 - Crop.JPG   112.89KB   7 downloads

 

This also shows the trick to prevent the problem - zip-tie the chain to the sprockets before dismantling.

[James]

Steve, that might well do, thanks for taking the time to post.

Cheers,

Jim

[James]

UPDATE:

For reference, its 14 pins from the I mark (on the inlet cam sprocket) to the E mark (on the exhaust sprocket).

When the exhaust cam was set right the inlet was just a tad retarded which I put down to a 27k miles of wear. Anyway, its all back together and running sweet No big difference from before, but at least I know the valve clearances are correct

Edited by James, 07 March 2024 - 07:54 pm.

[steve27bha]

UPDATE:

For reference, its 14 pins from mark to mark......

 

Errr - not according to my picture.

 

I can see more pins than that just in the open top run of the chain, before counting round the sprockets.

[James]

Errr - not according to my picture.
 
I can see more pins than that just in the open top run of the chain, before counting round the sprockets.

As per the diagram in post #4 (above) Steve, it is 14 pins from mark to mark... that’s the ‘inlet’ mark (on the exhaust cam sprocket) and the ‘exhaust’ mark (on the inlet sprocket).

[steve27bha]

Ah. I misunderstood what was being counted, assuming it to be from the E to the I marks at deck level.

[James]

Ah. I misunderstood what was being counted, assuming it to be from the E to the I marks at deck level.

Good point Steve and easily done. I’ll put the correct detail in my ‘UPDATE’ post, save anyone misinterpreting it.