Cam chain tensioner fail

One thing I forgot to mention in my update on my work bike is that the cam chain tensioner slips periodically, mainly when the motor is cold. Once they start to slip, it's only a short step away from serious failure which can cause disaster.

I went through several new (read expensive) genuine TTR250 tensioners  on my old bike before I bought a manual one for it from the US. Problem solved for ever; just got to be careful not to overtighten the chain.

With that in mind, I ordered a Krieger manual tensioner for the WR-R. It's yet to be fitted, but going on experience I will never have to buy another bloody tensioner.

The problem for us is that our engines are subjected to so much slow running in hot weather, combined with occasional bursts of full throttle up to the limiter, and sudden deceleration to a dead stop, sometimes stalling   from high revs. Anyway, the WR-R one has only lasted 7500km, which is greatly less than the TTR managed. I think that because the WR engine is more responsive and has less flywheel effect, the revs rise and fall quicker and the tensioner can't handle it.

I know a lot of you are going to respond by saying how hard you flog your bike etc etc, but that isn't what roots tensioners imo. It's the conditions described above, which is a different scenario. Some bikes, notably Kawasaki's Stockman, are blessed with extremely tough engines including good tensioners, which rarely fail. Others... Pity the Kawasakis are very nasty to ride imo, something which neither of my Yamahas can be accused of, particularly the WR.

I never heard anyone having problems with the WR250r timing chain tensioner.  I wonder where these stories come from?

Kawasaki KLX250 yes but not a Yamaha WR250R/X

wankle wrote:

...I wonder where these stories come from? Kawasaki KLX250 yes but not a Yamaha WR250R/X

2010 - Chain Tensioner, new Yamaha issued part number
2012 - Chain Tensioner, new Yamaha issued part number (redesigned for reliability)

my wrx has a bad engine rattle sometimes, im thinking the tensioner is on its way out. i was goin replace it with the updated design, but a manual tensioner sounds much better.

I am not trying to be a dick, this is an honest question. How do you know why a part number changes? Is there a tsb associated with the new number?

wankle wrote:

I never heard anyone having problems with the WR250r timing chain tensioner.  I wonder where these stories come from?

Kawasaki KLX250 yes but not a Yamaha WR250R/X

I apologise for rattling your cage - that is not the intention of my posts at all. I'm just reporting what happens to my bike, especially because it's often used outside its design paremeters.

As you've probably guessed from the other posts (very interesting, I didn't know the tensioners were upgraded. R1s had an upgrade due to tensioners backing out at high rpm too), it isn't a story. It's a fact. So I have elected to bypass the argument and have bought the Krieger manual tensioner. End of problem. Easy.

beee wrote:

I am not trying to be a dick, this is an honest question.  How do you know why a part number changes?  Is there a tsb associated with the new number?

Sometimes there is a recall to solve a problem - some R1s were, I think, recalled to have new tensioners fitted. I haven't heard of this with our bikes. Failed auto tensioners are very common, though. I had an XR600 which had three new tensioners in 63,000km. As I said, the TTR250 ones fail often (and not only mine), and so do DRZ400s (I think the original aftermarket manual parts were to cure their issue).

Factories don't change parts for fun. Unless a design is altered to cut costs, it actually costs them money to upgrade a part. They often do it in the middle of production runs, which creates a headache for spares people. Logic dictates that they will only upgrade a part if they think it will cost them more if it fails than if they leave it alone. A fully failed tensioner in a single is bad enough, but really expensive to fix in a multi if the valve timing goes wrong!  

Resurrecting an old thread...

At 15,000 miles my 2012 WR250R Cam chain tensioner appears to be slipping after it sits for a bit.

Occasionally on a cold startup there is a rattle for about 3 or 4 seconds and then everything quiets down. Order a manual CCT and since I am going to go in there I probably will check my valve clearances as well.

rsteiger wrote:

Resurrecting an old thread...

At 15,000 miles my 2012 WR250R Cam chain tensioner appears to be slipping after it sits for a bit.

Occasionally on a cold startup there is a rattle for about 3 or 4 seconds and then everything quiets down.  Order a manual CCT and since I am going to go in there I probably will check my valve clearances as well.

I had the cold start rattle for almost a year on my '12 around 8k (mostly dirt) miles though those were largely with 13/51 gearing so really less. I install a Krieger which has worked well since. I still have a rattle at cold start which makes sense to me but once things warm up the motor sounds and runs normally.

-morgan

rsteiger wrote:

At 15,000 miles my 2012 WR250R Cam chain tensioner appears to be slipping after it sits for a bit.

What do you mean by "slipping"? Obviously the chain is not jumping teeth otherwise you would have had serious problems, so in what way is the chain "slipping"?

johnkol wrote:

rsteiger wrote:

At 15,000 miles my 2012 WR250R Cam chain tensioner appears to be slipping after it sits for a bit.

What do you mean by "slipping"? Obviously the chain is not jumping teeth otherwise you would have had serious problems, so in what way is the chain "slipping"?

The chain is not slipping the tensioner is slipping.

Once the bike fires up and oil pressurizes the tensioner it not applies the correct tension to the cam chain and the rattle goes away.

Usually don't have this issue if I ride the bike every day but when it sits for a week and I go to start it about 50% of the time I get the cam chain rattling when starting.

Ordered a Krieger manual cam chain tensioner a bit ago and will replace the stock one once I have some time to work on the bike.

rsteiger wrote:

The chain is not slipping the tensioner is slipping.  

Once the bike fires up and oil pressurizes the tensioner it not applies the correct tension to the cam chain and the rattle goes away.

I still can't follow.

I thought that automatic tensioners employ a simple spring-and-ratchet mechanism that pushes the chain slider against the cam chain; had no idea they were connecting to the engine oil system. Is the tensioner on the WRR not using a spring and ratcheting mechanism? You're saying the spring action is being provided by engine oil pressure?

johnkol wrote:

rsteiger wrote:

The chain is not slipping the tensioner is slipping.  

Once the bike fires up and oil pressurizes the tensioner it not applies the correct tension to the cam chain and the rattle goes away.

I still can't follow.

I thought that automatic tensioners employ a simple spring-and-ratchet mechanism that pushes the chain slider against the cam chain; had no idea they were connecting to the engine oil system. Is the tensioner on the WRR not using a spring and ratcheting mechanism? You're saying the spring action is being provided by engine oil pressure?

Not completely sure on the WRR.

My 2010 Beta 520 RR used oil pressure to help actuate the CCT. In the first gen Beta motor (mine) there was an issue with the CCT not holding position when you started it after a prolonged shutdown - would rattle like crazy until the oil pressure stabilized. In 2012 they released a kit too replace the tensioner and after that it was quiet on start up.

Mine makes noise for the first 3 or 4 seconds after starting it following a prolong shutdown (see the original posters comment at the top) and then it is quiet. Too quick for everything to come up to temp so I am thinking it is either oil pressure hitting the system or the slop in the cam chain allows the tensioner to extend back out.

Once I replace it I will have a better idea.

The tensioners are oil pressure assisted i.e. oil pressure doesn't supply all the force applied to the plunger. There is a spring in there too, and the plunger is stopped from backing out by a friction system in this case. Tiny movements polish the plunger, the grip slips on the polished area, which eventually increases the size of that polished area, and so on until the tensioner is fully failed.

Being rolling-element bearings throughout (apart from camshaft bearing surfaces in the head), there isn't a great deal of oil pressure in our engines compared with plain-bearing ones. So any assistance given to the tensioner isn't massive, I'd suggest, though I might be wrong.

I think automatic cam chain tensioners suffer from flawed theory in the long term, particularly when used in engines subjected to hard revving and sudden variations in those revs e.g. when suddenly backing off from peak revs in the lower gears. Also, if correct tension is applied to the cam chain when the engine is cold, there is extra tension applied to it when the engine has reached correct operating (or even higher) temperature because the auto tensioner won't back out to cater for block expansion.

I've been bagged out for saying this, but there is obvious truth in it. A correctly adjusted manual tensioner will have the chain rattling until operating temp is achieved, then it will be quiet. Clearly the aluminium engine has expanded more than the steel chain, thus pulling the slack out. The slack when cold isn't a hell of a lot, but it's there. (Care is needed - it doesn't take much to over-tighten the chain!).

Erm, end of book...

66T wrote:

I think automatic cam chain tensioners suffer from flawed theory in the long term

Let's take a step back here and realise what we're saying. Cars have been using automatic chain tensioners for decades without any problems, and without needing any adjustment or replacement for the entire life of the vehicle. Even cars that are regularly raced never have any tensioner issues.

So clearly automatic tensioners do not have any fundamental flaws; it must be the execution that sometimes fail.

Hmm. Well, I fully realise what I'm saying, from first-hand experience.

When used under difficult conditions on an extended basis, my experience is that lots of motorcycle automatic tensioners do fail (repeatedly), especially on single-cylinder engines, but they aren't alone. XR600 and TTR250: Multiple fails. WR250R: 7000km. I rode the XR for 63,000km, the TTR250 for about 75,000km, all offroad. My WR250R is only half that at 36,000, with a manual tensioner after the fail.

Not only that, just look at the efforts gone to by Yamaha to provide the R1 with a tensioner that wouldn't back out at high rpm. Just check the part number if you don't believe me.

And the early model of my Tracer 900/FJ900 suffered from an unreliable tensioner (currently on version #8 according to the part number).

The list goes on and on. Not everybody has an auto tensioner fail by any means, but everyone I know who uses DRZ-400s for stock work and has a few km on board has had their tensioners fail. Strangely, though, no one I know has ever had an XR400 one go wrong. Another good tensioner I know of is the design used in the TT600/XT600/XTZ660/XT660 series. So it certainly can be done.

But you only have to sniff around in Google to see that tensioner issues in WR250Rs aren't isolated. The current one is on version #11 according to the part number.

Basically whatever happens in cars bears absolutely no relevance to motorcycle equipment in the main, in my opinion.

I've seen signs of a Xtz660 (same as xt600) tensioner starting to fail, the locking tab that prevents the tensioner from backup uot, has scrubbed a few teeth, and was backup out a xtra notch. Mine os however good at 180.000km

Xt350 had a weird leif/snail-spring, wery prone to braking.


I think most bikes can/will rattle a bit,after many days of standstill. Usually just until oilpressure builds up, and reaches the head.

Some info from the man I bought the manual tensioner from and the reason why he started to make manual cam chain tensioners for motorcycles:

http://ns53.webmasters.com/*clems-garage.com/httpdocs/CCT/A_Bit_of_History.htm

My WRR tensioner is from that man. The only thing to watch for it that the chain isn't overtightened, as he says. Otherwise, hop on, ride as hard, or as slow, as you like, and the tensioner won't fail. Mine does weep a bit of oil past the O-ring, but I guess if I was that worried about it, I'd fit a new one!

And I shouldn't have said anything about Tracer 900 tensioners, as today I noticed mine is failing at <4,000 km! When warranty runs out, a manual one goes in - regardless. I hate those auto things! Well, except the ones on the 600/660 Yamahas I've owned over the years.