Cam chain tensioners: Why do some go bad?

[cuong-nutz]

Why is it that some just go bad? @spooph I think I recall you taking the new ones apart so maybe you can offer some insight?

[spooph]

what do you mean by "some just go bad"?

I wouldn't say they go bad. I think Kawi didn't write instructions, or include in the maintenance schedule that they should be maintained, and therefor nobody maintains them.

The new-gen design was definitely over-engineered, and I think was meant to be maintenance free, which is why it's such a pain and therefor not on the maintenance schedule but I think that's Kawi being over-confident.

All of the ones I've looked at tended to start getting less than optimal results after 30K, some higher than that. I'm not sure if mileage though, as time seems to play a large factor here too... Moisture, heat/cold (being run in adverse and cold conditions) don't seem to help them either.

So, I don't mean to scare anybody, but if you're camchain isn't quiet your could probably use a rebuild.

If "going bad" means failure, I saw a pre-gen properly "fail" when the spring actually broke inside, but that's the only one I've ever seen properly "fail".

If anybody wants their's rebuild, I'm sure we can figure something out. Otherwise I'll have some time here in the next few weeks to do a write-up on how to do it yourself.

Mind you, it is not easy. If you guys want that write-up, please remind me as I tend to forget things - it's a huge flaw and I know, please help me out.

Hope this helps.

[Ghostt]

@spooph does the NewGen one work on the PreGen?

There's a similar issue with the EX500, but it's an easy fix just bolt on one from a 2nd Gen(94&up) and your all set, the 2nd Gen is a better design than 1st Gen.

[cuong-nutz]

When I said bad, I was referring to the intermittent ticking. It's a whole lot more prominent now on startup. I might change the oil and see if it helps.
Then proceed with a valve adjustment, then swap in my 300 tensioner if the tick is still there.

[choneofakind]

Subbed for write-ups. I'm about to go order a manual one, but I'm researching proper technique for adjusting those first.

[Ghostt]

Originally Posted by choneofakind

Subbed for write-ups. I'm about to go order a manual one, but I'm researching proper technique for adjusting those first.

Word of warning, I've seen too many adjusted improperly, and blown engines.

[choneofakind]

Yeah. Hence looking for proper adjustment method before buying one. Considering manual bs rebuilding the automatic or using a newer model that bolts up.

[spooph]

Originally Posted by Ghostt

@spooph does the NewGen one work on the PreGen?

There's a similar issue with the EX500, but it's an easy fix just bolt on one from a 2nd Gen(94&up) and your all set, the 2nd Gen is a better design than 1st Gen.

I don't know as I've never tried. If I can get my buddy to bring his 250 down I will try it...

Originally Posted by cuong-nutz

When I said bad, I was referring to the intermittent ticking. It's a whole lot more prominent now on startup. I might change the oil and see if it helps.
Then proceed with a valve adjustment, then swap in my 300 tensioner if the tick is still there.

How many miles? And yes, that's how mine started... I would look into a replacement or rebuild of some kind for sure. It's easy to get out and cheap insurance... Mine had gotten so bad that I had to replace the cam chain...
I'd do the tensioner first though, to isolate the clicking...

[Ghostt]

@spooph,does rebuilding the old just mean a new spring? Part #92081? Or is there more parts? Or should I just get the whole part #12048?

[cuong-nutz]

Originally Posted by spooph

How many miles? And yes, that's how mine started... I would look into a replacement or rebuild of some kind for sure. It's easy to get out and cheap insurance... Mine had gotten so bad that I had to replace the cam chain...
I'd do the tensioner first though, to isolate the clicking...

I have no idea how many miles are on this motor as it was used and I can't remember if I swapped the tensioner with my original motor. If I did, than it has at least 30k miles. The bike is due for small overhaul so that's why I'm going through that process. I would love to slap Shawn's turbo set-up on.

[Ghostt]

http://faq.ninja250.org/wiki/Cam_cha...sioner_removal

[Motofool]

Originally Posted by cuong-nutz

Why is it that some just go bad? ........

The automatic tensioner is a one-way ratcheting mechanism.

The theoretical advantage over a traditional manual adjuster is that it should adjust itself, as the cam chain wears and becomes longer.

The disadvantages are:
- The spring puts tension on the chain and chain sliders, which accelerates their wear.
- The ratcheting mechanism is marginal, once it develops certain wear, it allows excessive chain slack; hence, the noise.

About the spring:
Its only function is to push the ratcheting mechanism forward as the chain stretches.
It is not strong enough to prevent the chain from working loosely.
It takes tremendous force to keep the loose (unloaded) side of the chain from moving back and forth (rattling).

Only when the rotation of the valve's cams produces the minimum tension on the leg of the chain against which the tensioner works, the spring is able to push and move the plunge to eliminate any chain slack.
When the cams produces the maximum tension on that leg of the chain, only the ratcheting effect can keep the plunge in the new position.

About the ratcheting mechanism:
It is basically a cylindrical plunge surrounded by a ring of balls that get jammed against a conical surface.
I said it is marginal, because it is designed for eventual failure: some backing (and consequent loosening of the chain) develops sooner or later.

Steel balls have infinitesimally small points of contact and huge contact pressures (Pressure = Force / Area of contact).
Those few points of contact feel the previously mentioned high force with which the chain pushes back, multiplied several times by the wedge effect of plunge-conical surface.
That high force induces pitting and microscopic deformation of the surfaces of the balls, plunge and cone.

The factory neither applies nor recommends lubrication of those parts, which in my opinion accelerates the pitting of the surfaces in contact.
Little relative movement and high pressures are the worst conditions for effective lubrication.

Once developed, the damage of the points of contact grows, which allows more and more backing up of the plunge.
In severe cases, the balls are not round anymore and cannot roll to firmly jam the mechanism in reverse, as originally designed.

The case of the pre-gen Ninjas is worst because, rather than directly as with the new-gen tensioner, the plunge pushes via a L-shaped pivot that soon hits the crankcase, stopping any further forward movement before the chain develops its maximum tolerable wear (stretch).

About the solution:
- Periodic inspection of the contact surfaces and application of high pressure grease. Replace any part that shows any sign of wear, pitting or deformation.
- Install a manual tensioner and adjust it during each valve adjustment (bonus: the lack of spring pressure over the chain extends its useful life). There should be a minimum slack left, like for the transmission chain, rather than pressure over the chain, which could break it (a little force exerted by the bolt of the tensioner multiplies the tension in the chain several times).

For more information, read this:
http://www.dansmc.com/camchain_adjust.htm

[spooph]

@Ghost - I would pull the tensioner and pull it apart, grease it up and see how long it keeps the rattle at bay...
@Motofool - I'm not sure where the ball bearings you are speaking of are, although I can easily see the same principles apply...

[Motofool]

Originally Posted by spooph

....
@Motofool - I'm not sure where the ball bearings you are speaking of are, although I can easily see the same principles apply...

That is part 14020 in the schematic for the pre-gen posted by Ghost above.

I have not pulled apart the new-gen tensioner, but the principle is the same.

[csmith12]

Originally Posted by choneofakind

Yeah. Hence looking for proper adjustment method before buying one. Considering manual bs rebuilding the automatic or using a newer model that bolts up.

1. remove old one
2. install manual one
3. Adjust finger tight + 1 full turn of the new to "ball park" it
4. start bike and hear it chatter (if no chatter sound loosen it until chatter is heard)
5. adjust SLOWLY (tighten) until chatter goes away
6. back off (loosen) 1/2 or 3/4 turn (very mild chatter will come back)

The chain will stretch somewhat over a period of time depending on your riding habits and may need adjusted again. LOCTITE the nut after the 2nd adjustment.

It's a chain, better too loose than too tight and don't expect 100% silent operation.

[Motofool]

This is what one of the manufacturers of manual tensioner has learned about noise and failure of timing chains:

http://www.clems-garage.com/CCT/about_tensioners.htm

Here is the problem and solution for the pivot of the pre-gen Ninjas that I mentioned before:

http://www.clems-garage.com/CCT/elim...50_1st_gen.htm

[CZroe]

I don't trust myself and my bad hearing with a manual tensioner and I can't keep buying OEM automatic tensioners, so I'd love to see a J/K/L/300 tensioner teardown/rebuild guide.

[corksil]

I might be in trouble on this one. 27k, 2009. Started hearing clattering from what I thought to be valve noise.

Disassembled and adjusted valves. They are not perfect, as my shim kit only had 0.05mm increments. Two exhaust valves were too tight.

Now everything is reassembled. Valves not perfect but all are within specified range.

When I got the bike started, minimal clatter noise. After 5 minute idle, slight clatter returned on cam chain/right side of bike.

Rode 500 feet, clatter increased. Turned off bike. 5 mins later turned it back on and terrible terrible noise started while idling. Not as terrible as piston/valve contact, but sounds like cam timing chain jumped a tooth.

Going to go put it back up on stand, put in neutral and turn over by hand w/spark plugs out to feel for piston/valve interference.