Cam chain tensioner and the big decisions ...

Hi all,

I've done a search but cannot find a post that fits. I was given my 1983 XJ750R, all original with just 17,000 miles on the clock, but it hasn't run for at least fifteen years, and was just sitting in a shed.

I've already done the carbs and won't ride it without doing the brakes, tyres, etc. so that side of it is all good. Now I'm into the engine, valve clearances etc. and was chatting with a mate who has an XS1100. His cam chain tensioner disintegrated, the chain broke and a couple of valves crashed into the pistons, which also broke. It made a hell of a mess.

He advised changing this before I do anything else. Given the engine is 28 years old and that part is some kind of plastic, what's the chances mine is going to do the same thing? I'm thinking of doing a ground up resto on the whole bike anyway but I'd love to get it going and take it for a cog. That's a bit of a dilemma, where do you stop once you split the cases?

Now seems like the ideal time to bite the bullet, pull and strip the engine, freshen it up with a hone, a set of rings and bearings and a valve lap, repaint the frame and coloured bits, service the forks, brakes, clutch etc. and just generally go the whole hog.

Any first hand experience on broken cam tensioners welcome, cheers, Ian

 

There is no way of telling for sure. The auto tensioner is not plastic its metal. It pushes on a plastic guide I believe you have to pull the head to change the guide. More then likely was adjusted to tight thats what caused the problem . It should be good for adleast 40k if its been adjusted properly

 

Iandmac your mate really has no way of knowing what went first could have been one of the plastic guides broke then the chain jumped time valve crashed into piston, piston ate valve, locked up motor chain broke and then wiped out the tensioner who knows what happened but I understand your concern I have a 650 with 40000 miles on it and just adjusted the chain the other day mines a 1980 so its the manual tensioner and to tell you the truth I have never heard of anyone having problems with the automatic tensioner or timing chain I have heard of people have problems with the manual tensioners self induced problem though. Where do you stop when tearing down the engine? Why tear into it if it has good compression, runs and shifts good? Ride it and collect parts as you find them then wait for the weather to turn and make it an off season project. If you just want to freshen it up hone it ring it lap it like you said but no need to split the cases.

 

The cam chain tensioner on the XS1100 is different form the one on the 83 XJ750. The XJ is an automatic tensioner so it keeps the correct amount of tensioning on the chain. The XS tensioner did slip if not maintained/torqued correctly.

You may have a hard time finding new rings, there are some out there but are hard to find and when you do find them they are expensive. There is a chain guide for the starter clutch chain that does disintegrate but unless you need to crack the case for some reason I would not worry about it too much.

Check the compression. If it’s good I wouldn't take the engine apart (unless you really want to) good luck.