Cam chain tension advice - contacting cam cover at higher RPM

Hey team,

I've fairly recently started riding my XJ again after its been off the road for a number of years and have noticed an issue with the cam chain tension.

Part of the work I did while it was off the road was put a new cam chain in it, re-using the old guides, tensioning as per my Haynes manual multiple times. The issue I've noticed is that at certain RPM, particularly when coming off the throttle, I'm getting contact of the cam chain with the cam cover. I can also pull up on the cam chain and see some slack, which I suspect shouldn't be there.

Please see this video for a visual run down:

(Shameless plug: I've done a few proper videos on my channel about my journey with the XJ if you're interested )

Does anyone have any thoughts on what you'd check from here?

I'm thinking I'll:
- Triple check that I've done the chain tensioning procedure correctly.
- Look at removing cams and the guides to inspect (I don't recall issues when they were out last time)
- Maybe it's an issue with the tensioner? Can they lose their prong power over time?

Any other ideas or suggestions for things to look into?

 

Also, is it possible to remove the rear cam chain guide without taking the head off?

 

When you assembled the top end did you make sure the exhaust cam chain guide was in the pocket in the bottom of the crankcase? There is a photograph of it in the Haynes manual.

 

Great question, Franz. It was a while ago now, but from memory I spent quite a while trying to ensure it was seated properly. There is every chance that I still didn't get it right and that this could be the culprit.

I'm wondering how I would check that this is seated correctly.. Perhaps if I take out the tensioner unit, then tightened the retaining nut (highlighted below), I might expect to feel any play in the guide firm up as that nut is tightened? If it doesn't then I'd guess that the guide isn't seated?

Or I just bite the bullet and start tearing things down... (I'm trying to avoid taking the head off, since head gaskets are hard to come by here in New Zealand)

 

You tighten the bolt until it seats against the bottom of the tensioner blade guide. Then back it off a quarter of a turn then tighten the locknut.

 

Exhaust guide location.




With the camshafts removed you could use a torch and inspection mirror to check this with the engine in the frame.

 

If you take the plugs out and rotate the engine anticlockwise can you see any slack in the chain? Don't remove the head until you have checked everything you can first.

 

You nailed this one, Franz. Did as you suggested and see lots of slack in the chain. To the point that I can easily get the center guide out. No good.



I guess next steps are to get a cam out and inspect the guide. Will keep you posted. Really appreciate the help.

 

OK, I've had the cams out and poked around a bit and honestly, I can't see anything major wrong. The guide seems to be seated really well, but I'll continue checking that a bit more thoroughly from here.

It feels like with this system, there are only so many things that could be incorrect:

- Chain - Pretty sure this is fine. I replaced it last time I had the engine apart. It's done about 100km of riding since then.
- Tensioner - by all accounts, it sounds like this doesn't really fail. It's the automatic type, so what could really go wrong there?
- Guides - I'm still thinking this might be the issue. Do the rear guides fail over time?

I've tried searching through old photos to see if I can find one of my guide, but to no avail.

Is it feasible that the short squared off section of the metal backing to the guide could get rounded over time? Seems like that could be a potential wear point:

 

One other possibility was the chain a genuine Yamaha part or aftermarket? Could be wrong chain . Same with guides and the guide could be breaking up which means it is moving around and could effect tension of the chain.

 

Yep - can you count the number of links?

 

Thanks very much for all the help here, guys. Just wanted to close the loop on this one for anyone who finds this in the future. TL;DR: It was the front guide that I had wrong.

After a few weeks break from wrenching on the XJ, I dug in and pulled both cams, and really took my time with getting the rear and front chain guides in place properly. it turns out that it was actually the front guide I had wrong! I was led astray a bit by the manual, which sorta just casually suggests to "place the front guide in", not mentioning at all that it also has a recess in the bottom of the crankcase that the lower end should rest in. My front guide was not in that recess correctly.

The best thing I found for helping me figure this out was this video from Mezzmo Engineering. There is one spot that clearly shows the two recesses.



Long story short, make sure that you also place the bottom of the front guide correctly.