Cam chain top idler and side gear wear?

[sprint]

How do you determine if the top idler and the two side gears need replacing?

What up and down play should you have or what is considered acceptable?

With all replacements fairly expensive not something to be done unnecessarily.

With respect to the top idler, am I right in believing that gear runs on a separate collar and not directly on the the pin that is staked alone?

[zed1015]

Top idler runs a needle roller bearing on a hollow hardened centre which the retaining pin runs through.
There should be minimal radial play, side to side play is normal but if the gear can be twisted out of the vertical plane then the damper rubbers may have perished separating the outer sprocket from the centre.
The bonded rubber dampers can be replaced with solid ally if you have a lathe.
The needle bearing rarely gives trouble but can be replaced easily if needed and they are available cheaply from bearing stockists.

[sprint]

Top idler runs a needle roller bearing on a hollow hardened centre which the retaining pin runs through.
There should be minimal radial play, side to side play is normal but if the gear can be twisted out of the vertical plane then the damper rubbers may have perished separating the outer sprocket from the centre.
The bonded rubber dampers can be replaced with solid ally if you have a lathe.
The needle bearing rarely gives trouble but can be replaced easily if needed and they are available cheaply from bearing stockists.

Thanks for the reply.

In the case of the top idler it can be seen and felt that it is the center that is moving up and down on the retaining pin.

Is the center normally held against the side plates and not able to move?

What is the position with the two side gears? There is some up and down movement on the shafts, what is acceptable?

[zed1015]

There is always some slight movement within the needle roller bearings but too much should be obvious to an experienced mechanic.
You really need the idlers out of the head for inspection of the rubber dampeners and needle rollers.
They should rotate smoothly with no graunching or excessive looseness.
Can't really help much more without actually having the parts in my hand.

[sprint]

Thanks for the reply.

I have all the parts out of the head and barrel. I think the side gear tension wheels are OK. The top one has definitely had it.

The engine does not look like it has ever been apart with the o-rings at the base of the barrels totally hardened and simply breaking into pieces. Will replace the plastic rollers and the front guide as well as the top idler.