Top Cam Idler

the sprockets that zed1015 makes work great, use them myself

LarryC wrote:

RonKZ650 wrote: It's the rubber center that goes bad, the rest of it never causes trouble. Heat and time eat up the rubber. I doubt $0.02 worth of difference i you're running stock or 1075 kit. Miles is kind of hard to say. Engines run hotter in city riding even though less miles, rubber is gettin older every day. Time and heat combine. I have 80,000 miles on my KZ1000 and never touched the idlers. The KZ650 centers went bad at about 150,000 miles. All 3 of the idlers will go bad with enough heat and miles.

Not so. I've seen many with failed bearings.

That could be. Bearings go bad, but always running in oil I never had problems with them.

LarryC, with respect, as I know you are a bit of an expert when it comes to heads. However, I have to agree with Ron650, I have never seen these little needle rollers wear out (lose their hardening or collapse). My observation is the shock rubber mount they are in, always becomes brittle or just disintegrates, leaving the the sprocket teeth to be free and loose from its bearing.

I have seen relatively new looking sprockets wobble about, due to the rubber bonding just shearing or falling away.

For Zed1015.... Do you have to turn out or scrape the remanence of the rubber? Also regarding concentricity... Do you have to turn away (back to metal) the rubber beside the sprocket teeth for griping in the lathe chuck, or do you make a mandrel?
RegardZ.

Garn wrote:
For Zed1015.... Do you have to turn out or scrape the remanence of the rubber? Also regarding concentricity... Do you have to turn away (back to metal) the rubber beside the sprocket teeth for griping in the lathe chuck, or do you make a mandrel?
RegardZ.

Hi. Tho outer steel sprocket ring just presses off but the center steel core needs the bonded rubber removing.
I prefer to use the center core rather than just boring the alloy to take the bearing as i feel it would be less prone to wear during future bearing changes.
Maybe a bit overkill but i prefer to do things only once.

A quick rundown.

1. Alloy bar firmly in chuck.
2. Mike the removed steel insert and turn alloy bar to same dimension.
3. Use manual tailstock feed screw to press sprocket ring on to bar( It is a not a heavy fit)
4. Clock the top of the sprocket teeth to ensure concentricity then turn off the rubber either side of teeth and lightly touch on to the steel to square it up for the chuck.
5. Bore the center but not to finished size.
6. Part off.
7. The steel center core once cleaned of rubber is set up on a mandrel and clocked for truth, if there's any runout it gets squared up in the lathe.
8. Set the sprocket in the chuck, clock the teeth again then bore the center to the size of the center bush. The center can then be pressed in, it is slightly wider than the sprocket ring and alloy insert so ensure there is equal amounts protruding either side.
9. Fit the bearing.

Garn wrote: LarryC, with respect, as I know you are a bit of an expert when it comes to heads. However, I have to agree with Ron650, I have never seen these little needle rollers wear out (lose their hardening or collapse). My observation is the shock rubber mount they are in, always becomes brittle or just disintegrates, leaving the the sprocket teeth to be free and loose from its bearing.

I have seen relatively new looking sprockets wobble about, due to the rubber bonding just shearing or falling away.

And your point would be what? The sprocket doesn't wabble on the shaft because of anything other than the bearing or shaft being worn out. The rubber is an entirely different matter altogether. That and the condition of the cam chain have absolutely nothing to do with the sprocket wabbling on the shaft. :whistle:

LarryC, my point is, the wobbling has nothing to do with the needle rollers being worn or damaged (90% of the time), it is to do with the sprocket outer being detached from the bearing housing. Meaning, when viewed from the side there are two separate parts..... (1) sprocket outer and (2) bearing housing! The needle roller bearing is in tact.
Regardz.

I have no doubts that the bearings can fail and make the sprocket wobble. But the rubber damper between the bearing and sprocket can also fail and cause wobble. That was the case with mine. The bearing still feels as smooth as a new one, but the rubber gave out so badly that the sprocket became loose and wobbly on the bearing. In the pics I marked a tooth on the sprocket with white paint as a reference. Comparing the first 2 pics you can see how much play there is between the bearing and the sprocket. The third pic shows how worn the rubber inside of the sprocket became from spinning on the outside of the bearing and the fourth shows the rubber coating on the bearing. Even though the bearing spins freely on its shaft the sprocket also actually spins around the outside of the bearing with no resistance. Ed

650ed wrote:

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Yep! that's definately buggered and must not be used.
Teeth appear ok though so a prime candidate for an alloy center.
Feel free to send me all your suspect idlers :laugh:

650Ed, your photo's illustrated exactly the main form of breakdown of these cam idler sprockets.
RegardZ.

on a short sample size.....nothing like Larry has seen....all failures have been the rubber center.

Could the bearing have failed....heated up and facilatated the rubber center to fail...quite possible on one of them.....the other bearings looked and felt fine.

Garn wrote: LarryC, my point is, the wobbling has nothing to do with the needle rollers being worn or damaged (90% of the time), it is to do with the sprocket outer being detached from the bearing housing. Meaning, when viewed from the side there are two separate parts..... (1) sprocket outer and (2) bearing housing! The needle roller bearing is in tact.
Regardz.

Really....were you in my shop, at my work bench for the last half a dozen motors I rebuilt?

4TheKZ1000 wrote: on a short sample size.....nothing like Larry has seen....all failures have been the rubber center.

Could the bearing have failed....heated up and facilatated the rubber center to fail...quite possible on one of them.....the other bearings looked and felt fine.

It's just age,contaminents in the oil and many heat cycles etc that ruins the rubber.
All the rubber components go the same way, bottom roller, top idler dampening blocks, those little rubber oblongs that sit on the idler shafts etc.
The rubber idler centers become un bonded as a result of this and the fact, that like a vehicle tyre running on the road they are subject to constant deflection away from the point of force ( in this case the camchain) as they rotate.
Under normal circumstances this deflection allows the rubber to take up any small fluctuation in the camchain length to maintain a constant tension and allows for any slight mass production inaccuracies during their manufacture.
Once the rubber becomes brittle this deflection force eventually breaks it up.

I have seen failed bearings where the needles have started to eat through the sides of the drawn cup. This is usually acompanied by the failed rubber and collapsed idler so wether the rubber went first or the bearing is debatable. Chicken and egg.

All i will say is that if, in an ideal world, you are re-building a motor of unknown history/mileage i would replace the bearings with new for what little they cost whatever condition they appear.
Why risk the cost of another top end strip/build or ruining a big money motor for the sake of a few pence/cents item.

That said! those needle bearings are tough little buggers.