Cam chain tensioner

Right, now that the 9R is sporting a shiny new set of sparking plug type
items (no threads stripped thankfully), the next job is to replace the cam
chain tensioner on the R6. I have a glistening new one sitting next to me,
beside the HBoL.

(Just went for the standard one btw, Loz)

HBoL instructions say I have to remove the tank and carbs, is that usual?
Seems like an awful lot of work for an easy replacement. Does the FOAK
reckon I'll have to go down the stripping route or might I be able to just
get enough access without that palaver?

The simple solution would be that I'd nip outside and have a look at the
bike to see, but it's not over here atm.

Btw, I phoned Yamaha UK about whether the chain should be changed and bloke
was a little non-committal. Said that technically speaking probably right,
however camchains built to last a long time - also no set period of
checking/replacing. His recommendation was change tensioner and if still
got a rattle, then chain. The garage who suggested I get chain done reckon
they replace cam chains all the time.

 

Beelzebub says...

I guess they will do, if people believe what the dealer tells them every
time. It's a very rare thing to have to replace though and not at all
commonplace in any of the dealers I visit. My bigges dealership said
they replace about 3 a year, and that's out of all the bikes their 6
mechanics service and maintain. Say each mechanic does 2 services a day,
5 days a week for 46 weeks a year taking into account holiday and
sickness......come on, I'm shit at maths, someone help me....please....

 

You can tell if a chain is knackered my measuring the distance between a
set mumber of links, I think the HBoL should list the maximum that
measurment should be somewhere. Any larger, and the chain is knackered.

Mt HBoL lists measurments for the cam chain and the final drive chain.

 

He's generally right. Provided the rider hasn't shagged it and the
design of chain/tensioner is decent.

More than likely a lot are replaced unnecessarily; a simple tensioner
replacement would probably have done in a lot of cases.

A camchain is running in a near perfect environment as far as chains go,
being fed with oil all the time. Wear isn't great under normal
circumstances, but what wrecks them is a combination of harsh
acceleration, crap oil, old oil, slack tensioners.

 

How does that work then?

 

Inertial loading.

 

Like a fucked tensioner or bouncing off the rev limiter?

 

Using the patented Mavis Beacon "Hunt&Peck" Technique, Beelzebub

Yes. Get on with it.

And take pictures.

--
Wicked Uncle Nigel - Manufacturer of the "Champion-105" range of rearsets
and Ducati Race Engineer.

WS* GHPOTHUF#24 APOSTLE#14 DLC#1 COFF#20 BOTAFOT#150 HYPO#0(KoTL) IbW#41
SBS#39 Enfield 500 Curry House Racer "The Basmati Rice Burner",
Honda GL1000K2 (On its hols) Kawasaki ZN1300 Voyager "Oh, Oh, It's so big"
Suzuki TS250 "The Africa Single" Yamaha GTS1000

 

Both, and neither, depending on the state of the engine and rider.

If you accelerate anything mechanical, it's going to put a loading on
the drive. Even though camchains aren't pulling anything like as much
load as a final drive chain, the principle still holds. Let's face it,
lots of riders aren't all that mechanically sympathetic and thrash the
**** out of their engines quite a lot. All the internal bits suffer
accordingly. Continual harsh acceleration will stress the camchain links
and promote wear; in an engine with a badly designed or sticky tensioner
the process will be exacerbated and the camchain will need replaced much
sooner than would otherwise be the case.

 

An unmaintained and thrashed engine is going to go pop sooner, that's a
fair thing to say.

I'd guess that this is why race engines tend to have things like good
quality chains and manual tensioners.

 

Can you put some numbers to your theory?
How does the component of the camchain tension due to engine acceleration
compare to that due to engine speed?

I doubt that it is significant even at WFO in first.
Maybe if you give it full throttle in neutral?

 

Nope, can't be arsed.

At steady speed, there'll be minimal wear; it's my contention that
sudden changes in speed will lead to chain stretch. Obviously, some
chain wear and stretch is to be expected, else a tensioner wouldn't be
needed at all; but continual hamfisted use of the throttle will
accelerate this wear.

By that time, something else is likely to go bang if you do it long
enough and often enough. It's amazing that more camchains don't snap,
considering what they put up with. The dynamic load on the chain won't
change much at any engine speed, since the valvetrain is a constant
load, irrespective of what the bike's doing at that engine speed.

See above point.

Mostly what I'm saying, is that camchains put up with a lot of stick and
are likely to have their lives shortened by unsympathetic use of the
throttle (both up and down). If there's a slack tensioner, that'll add
to the problem.

 

So you are talking through your hat.

There is not a constant load on a camchain at a constant speed, as you
would know
if you tried turning a cam by hand; it probably gets smoother at high speed.

You have no evidence that the load on a camchain due to acceleration
is the same order of magnitude as the load at a constant speed (due to
friction, valve mass, spring forces, etc.)

What's the moment of inertia of a typical camshaft and pulley?

 

Yes, it probably gets smoother as it gets faster, true.

Yes, yes, yes, but what about sudden changes in load, eh?

Why don't you tell me?

 

Another big factor I'd think, is resonance. Every cam chain will have
its resonant frequency, and it's when those resonant conditions are met
that I'd expect forces to be high. All completely theoretical though..

 

It's be interesting to find out, but I'm sure the engine makers have
done it. IMO, when a relatively lightweight component like a camchain is
allowed to whip about because of a faulty automatic or slack manual
tensioner any wear that's already there will greatly increase because of
shock loadings.

To add to my other thought on the matter, it wouldn't just be harsh
acceleration, it'd be sudden changes in load direction (rapidly on and
off the throttle, like a dancing monkey) that wouldn't be doing it any
favours in the longer term. That, combined with the above whip might
lead to breakages.

Fortunately camchain breakages are quite rare; just as well really.

 

Just what do you think the camchain drives?
"rapidly on and off the throttle" might do things to your transmission
but they won't have any effect on the valve gear.

And to recap, a back of an envelope calculation suggests that if you
took the engine from tickover to the redline in 1 second the strain on
the chain due to acceleration would be of the order of 2Kg, which is
peanuts compared to that due to other forces at a constant engine speed.

 

Chains jumping teeth are more usual though, but the only ways I can see
this happening is through FOD or a knackered tensioner, or a really
knackered chain.

 

Not really - this was more or less the reason for the early CX500
camchain tensioner breakages.

 

What did Honda do to fix the problem? Beef up the tensioner?