camshaft gears, idlers - condition check

wrote:

If you break a cam chain you'll wish you bought the Liska's.
Steve

 

Break because of what? Any part can break. I seen images of plastic disintegrating, etc. Here my question what is the must? All my parts look OK. Original parts gazz shows in his blog I wouldn't even touch/replace, but he is building new engine, so different budget

I am replacing chain with NOS chain by the way,

  All the rubber parts in the cam drive system harden & become brittle with age and, especially, heat.  The thin rubber insert in the idler sprockets are of particular concern.  While the solid rubber idler wheels might only shed copious amounts of rubber particles as a result of brittleness, the rubber inserts in the idler sprockets eventually collapse, allowing the outer sprocket ring to ride on the outside surface of the solid steel inner race.  That failure can happen suddenly & without warning.  At a minium, the camchain will flail around, making racket & eating away at any metal it touches.  If the camchain skips teeth because it's suddenly slack, all sorts of undesirable & destructive events can happen very rapidly, from crashing valves up to grenading the motor.

   We've seen 'mechanics' supposedly 'evaluate' idler sprocket condition by pressing hard sideways using both thumbs on the inner race.  If it moves & can be pressed out by hand from within the rubber insert they will replace it.  If it doesn't move it goes back into the motor.  We don't support that position.  A used idler sprocket isn't worth risking the entire motor.

   If you're so deep into the motor that the camchain is being replaced, best practice is to replace all the camchain idlers; the solid rubber rollers and idler sprockets, plus the idler shaft rubber damper blocks.

Good Ridin'
slmjim & Z1BEBE 

Ordered #1 and #5 from Liska. Other 3 gears would be too much, so going to DIY fix, machine metal inserts. Started yesterday on a lathe. I am not good machinist to make press-fit parts, but I do have micrometers now. Will make it happen.

So far made tools to disassemble old ones. And since I have extras, no big deal even if I damage one. Going to pickup some alum bar stock today.

wrote:

The idler wheel rubber centres also go hard and collapse and it's pot luck how long they are going to last if you re-use them.


 

Zed,

What material do you use for making those inserts? Aluminum or steel?

Here is copy from your old post with my comments. Do you have any corrections/suggestions?

1. Alloy bar firmly in chuck. Check
2. Mike the removed steel insert and turn alloy bar to same dimension. Check
3. Use manual tailstock feed screw to press sprocket ring on to bar( It is a not a heavy fit). Check. BUT, it's my lather or whatever - but after pressing gear on part get's distorted and I get some runout. Bad.
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.

I want to do it slightly different. Specifically, do as much as I can without removing stock. And not sure I need to reuse steel center core, what is the point? 
I can machine outer surface to size and bore for bearing at the same time. This will give exact concentricity. Then I just need to press gear and bearing in and part off.
 

When i originally made the first set i just replaced the rubber with T6 /HE30 aluminium and used the original steel center.
I don't do that now as it's not needed and make the whole center from aluminium pressed into the sprocket ring .
I set the bar in the chuck , turn to size, press on the sprocket ring, turn off the old rubber from the sprocket then bore for the bearing and then part off ready for the next one .
All without moving the stock which keeps everything as accurate as possible.
Once i've made a batch i face them off to the correct width and then drill them for lightness using a little six hole drill guide i made that locates in the center for easy repeatability without having to mark them all individually.


 

Today spent couple hours at a lathe. Bought Mitutoyo calipers, I had $20 junk. Lathe is in inches, I can't really read those dials so all by feel and I am getting hang of it. I can catch 0.02-0.03 easily now. Second was much quicker.

Will repress bearings once I receive them (on order). Not going to copy you on drilling holes. Stock sprocket 75g and new ones 57 so they lighter already.
I have some spares so will make myself set and make some for ebay to compensate for some time/materials and Liska parts.