I was just curious, my xj650j supposedly has an auto adjusting cam chain tensioner. Are these prone to give any trouble? Do I need to replace it at any certain interval or mileage? Or maybe replace it when I need a chain?
Thanks for any info
Richard B.

They're a coil spring loaded unit that is non-adjustable, so you shouldn't need to touch them until it's time to replace the camchain.

Having said that, as the camchain wears it will stretch and release the tension on the adjuster spring - and sometimes the spring will simply not expand due to age or fatigue. This can loosen the chain enough to make some noise even though the chain may not need replacing.

Yamaha uses conventional camchains (unlike 80's Kawasakis which use the HyVo type) which can be quite harsh on the camchain guides - so you will need to make sure you inspect / replace these as well when it's time to do the camchain.

I've heard that too Hillsy. I think you are right. I think that perhaps on the older models G and H that they didn't have the auto-tensioner. In my manual it says that you should adjust it manually every 3000 miles...

In my 1981 H manual it says:

( Woot Note: I have found removing the plugs makes this easier!!!)

The Yamaha auto adjuster was the most reliable one for the time. I worked in a bike workshop for a few years and we had GSX's GPZ's and XJ's come through regularly - and the Yamaha seemed to have the most durable and best designed valvetrain, with the only possible weak link being the adjuster spring issue that I said earlier. Mind you, that was pretty rare.

The first thing we used to change on GSX / GSXR / GPZ motors that we tweaked for performance was the auto camchain adjusters. We ended up having a bucket full of old stock ones that we couldn't even give away. They were universally considered to be crap. Here's a link to the APE adjusters that we used:

http://www.sudco.com/apeCamchain.html

Strange enough, they don't list one for the XJ (however, the Yamahas are all the same except for the R1). This probably says one of 2 things:

1) people generally don't hot up XJ's or

2) the stock adjuster is an OK design

I'd probably lean towards the latter - and just make sure to replace the spring as a first port of call if the camchain starts to make any noise.

Is that a simple unscrew and put in new one procedure??? I might have to invest in that!

Sure is - the spring bolt is on the very back of the tensioner (facing the back of the bike). Make sure your timing is lined up (as per the specs you posted for the adjustable tensioner), undo the bolt and the spring should pop out.
At this stage you can insert a screwdriver in the hole and give the tensioner a gentle push to ensure it is fully adjusted against the camchain guide (it has a ratchet mechanism so it wont spring back out).
Best to replace the spring rather than try to stretch it if it is loose - over extending the spring can put excessive pressure on the guide which can wear it down prematurely (remember, it rubs against the camchain). Also, you don't want the possibility of the spring breaking later on down the track.

Thanks for the info guys.
Richard B.