Reusing the rear cam chain tensioner and cam chain (1981 XS650)

[MadeThatMyself]

Hey guys! I'm new to the forum and rebuilding a 1981 XS650 Heritage Special. I've been a forum reader for a few months now and finally decided to become an active member.

My engine has 29k miles, ran when I bought it, but has super low compression, so I decided to tear the whole top end down and do some investigative diagnostic work. I am trying to determine whether or not I can reuse my cam chain and the rear tensioner. When I took it apart the tensioner was properly adjusted and the chain seemed to be in decent shape. After I removed the jugs, I noticed that there are some small grooves in the rear tensioner face where the chain rides, but nothing I would describe as excessive.

I am planning to replace the front cam chain guide either way, but how do you determine if there is too much wear on the rear tensioner guide? Is there a method to evaluating the chain as well? I most likely need over sized pistons/rings and a bore/hone based on the look of the jugs, so I am trying to keep my costs down in other areas that may not need new parts. At the same time, I would prefer not to open the engine back up in 3 months.

Thanks for reading!

 

[gggGary]

The rear guide is seldom replaced, usually ready to go on giving years of service.

 

[MadeThatMyself]

Thanks gggGary. Is that true for the cam chain too?

 

[lakeview]

Contributors with a better grasp of the technicalities than I have shown that minor chain wear may result in borderline timing issues that are hard to compensate for.
In my view it's a peace of mind thing to replace it and money well spent.

 

[gggGary]

Thanks gggGary. Is that true for the cam chain too?

Not so much? IMHO it depends on prior maintenance, unfortunately I think a lot of cam chain adjustments are done wrong. (not by anyone here LOL) resulting in excessive tension, creating problems with the front guide and chain stretch. On points bikes a frequent WTF moment, is when the points can no longer be adjusted to correct timing, chain stretch has changed the cam/crank relationship.

 

[MaxPete]

Yup - I'm with Lakeview and Gary on the chain.

As stated, the rear timing chain guide and tensioner assembly has virtually no history of failure, but opening an engine and not replacing both the front guide and the timing chain is likely false economy. The front guide is definitely the weak point in the XS650 engine and the timing chain, while very unlikely to actually break, can "stretch" to the point where valve and ignition timing cannot be adjusted properly.

NOTE: chains do not actually stretch. What actually happens is that the little pins wear within the bushings in which they ride in each link and a few thousandths of an inch at each pin combines to be a measurable amount of added chain length over the hundred or more links (see below). If you leave it long enough, the chain will not mesh properly with the sprockets on the crank and camshafts.

Exactly the same thing happens with drive chains - the pins and bushings wear due to dirt and lack of lubrication and the chain appears to "stretch" while at the same time, the sprockets wear and that leads to all sorts of unhappiness.

Just be certain to buy the correct chain for your year of engine. From what I recall, the timing chains for the earlier engines (1970-'73) had 102 links and the later bikes (1974-'84) had 106 links. Don't forget to buy a couple of joining links at the same time (one to practice on...)

Also note: you cannot and must not try to mix an early cam and a later crank or vice-versa.

 

[Superjet]

You should check to see how much adjustment is left after it being properly adjusted. If you only have a few threads left on it (adjuster), you may as well change out the chain.

 

[MadeThatMyself]

Thanks for the input guys. I think I'll be replacing the front guide and chain for peace of mind.

Not to stir up conversations that have already been beat to death, but should I really be concerned in buying the guide and/or chain from MikesXS? There seems to be a lot of concern for the part quality. I cant seem to find any other options though.

Also, are there any tips for breaking/riveting the cam chain? Should I just invest in a tool- any suggestions? Do all 106 link chains come "endless" like the ones on MikesXS? I was not planning to crack the case open, so I would need to break the endless chain before I even start trying to reassemble.

 

[XSLeo]

There is a way to check for excessive cam chain wear when engine is together.
Under the round cover on the right side of the engine, where the advancer unit is on points engines. Nothing on a TCI, The cam has a hole for an alignment pin.
Turn engine to TDC then check what direction this hole points. It should point straight up or down. As the chain wears the section from the crank up past the front guide gets longer. This lets the cam timing retard. You can tell this by how much the pin points away from straight. A few degrees probably won't hurt much. If it is 10 or more degrees it can effect cam timing enough to effect the way it runs.
This is why the points plate runs out of adjustment slot.
You can't do that now with engine apart.
Leo

 

[XSLeo]

I never had a chain breaker to use for the job.
To break the old chain I used a grinding wheel on a Dremel tool to grind the pins to a bit less than flush with the side plates. Then use a pin punch to drive the pins out of chain.
On the master links I have used the pins had a shoulder that the side plates set against. They can't be gotten too tight.
I install the link in the chain, slip on the side plate then use a large pair of vise grips to start the peening process. The vise grips crimp the ends of the pins enough so the side plate won't fall off. I then back up the back side of the link with a heavy hammer, I have a three pound hammer. I then use a smaller ball peen hammer, around 16 ounces to finish peening the pins.
It does take much, just get the edges of the pin peened over all the way around. Tight enough so the side plate won't wiggle. Make the pin head swell out like the rest of the chain.
If you look at the way a lot of the pins on the factory master links they look like they just laid the chain on it's side and hit with a cold chisel.
Leo

 

[gggGary]

Will toss in that a heavily worn or missing front guide rubber will also make, show up as cam rotating rearward in relation to crank.
Diagram from the slightly different XS1
Credit TwoManyXS1Bs

 

[MaxPete]

Now THAT is a very useful figure - and one that I will shamelessly swipe.

Thanks Gary!

Pete

 

[XSLeo]

That's a good diagram of the chain and the other parts. Looking at that you can imagine what can happen as the chain gets longer. The cam will be behind where it should be and the tensioner will be adjusted farther in to compensate.
On the chain I would recommend a brand name chain, Such as DID, Tsubaki, not sure on spelling. Mike's more expensive chain is a DID, You may shop around and find one on Ebay or other parts places maybe cheaper.
They often are a better chain than an off brand. I might try an off brand drive chain, being on the outside it will be easy to change out than the cam chain.
Leo

 

[MaxPete]

Yup - again, I concur with Leo. The timing chain is not a huge deal to replace - BUT - it isn't a 20 minute job either and there would also be a lot of gaskets to be replaced so you don't really want to cheap out on it. Get a good one and it will stand up for many years/miles.

Pete

 

[Superjet]

To remove the old one I used a 1 time tool called a cam chain link remover...broke with the tool pin stuck in the link!!! returned to amazon for a refund. Next time will use the dremel for sure now that I got one on sale a few weeks back.

Did the same as Leo for the install of the chain quite easy once you get the head tightened down enough to slip the link in and wrap the chain over the cam. Took a whole day to remove the old gaskets, seals and O-rings to button things back up without leaks!

 

[5twins]

Many consider the Tsubaki chain a bit better (stronger) than the D.I.D. one. Best place to get one is directly from Yamaha, it's cheaper than Mike's. It comes split and includes a master link .....

https://www.partzilla.com/product/yamaha/94500-02106-00?ref=62d1e0c2d701e33ae846d25fa478f585d31cc7fc

If you wanted an extra master link, they are actually about a dollar cheaper from Mike's.

https://www.partzilla.com/product/yamaha/94600-02001-00?ref=54683d3c3d82bf99cc93da75326c95168d51e012

https://www.mikesxs.net/master-link-rivet-cam-chain-bf05m-xs650-sr500-xt500.html

 

[xjwmx]

Rear adjuster have the same rep as the bottom end. But -- they do go bad! Rear adjuster can wear out quickly if it spent much time overtightened. Getting it off is probably worse than separating the carbs. Same impossible screw kind of idea...

 

[MadeThatMyself]

Thanks for the feedback everyone. I really appreciate it.

 

[MadeThatMyself]

I wanted to add some rear cam guide pictures to see if this changes anyone's opinion about running it or not. Let me know what you think

 

[gggGary]

looks good to me.....