Reducing cam bore ID in an aluminum cam pulley?

[Nut124]

I had to remove a DOCH Fiat ex cam pulley because it was not running "true". The pulley OD, and the timing belt, was wobbling by about 20-30 thou causing a pulsating belt whining noise.

The problem seems to be that the cam boss bore in the aluminum pulley is about 20 thou larger than the cam boss, permitting off-center installation.

Could I "dimple" the pulley to reduce clearance? The cam is in the engine, but I have another cam box I could use to true up the pulley before bolting on the engine.

This is the best available aftermarket stuff for my application.

Thoughts?

[Kevin Johnson]

https://www.mcmaster.com/foil-shim-stoc ... m-stock-6/

Perhaps this type of material could be used on the end of the cam to incrementally increase the OD?

[englertracing]

Machinist solution...
Bore cam pulley and sleeve


Mechanic solution
Like Kevin said shim stock.

[Sparksalot]

What englertracing said. They both will "work" but one will be repeatable, and the other is a kludge.

[travis]

Option #3 (the aerospace solution)...nickel or hard chrome plate the ID undersize, then hone to the desired size.

[Kevin Johnson]

The next Captain Obvious move to check both cams and sprockets ("pulley").

If the sprockets are consistent in ID then...

Perhaps closer examination of the camshaft is called for, particularly the journals.

~~~~~~~~~~~~~~~

Twenty thousandths of an inch is close to .5mm (FIAT is metric). A novice machinist could easily mistake graduations and this calls into question the other measurements on the cam.

[Nut124]

Thanks for the suggestions. Yes, bore and sleeve would be the correct solution but would likely cost me $150 or so.

I think I will try the shim wrap on the cam. It is needed there to keep the pulley centered while I torque the cam bolt. Once tight I do not think it would move.

[Nut124]

The next Captain Obvious move to check both cams and sprockets ("pulley").

If the sprockets are consistent in ID then...

Perhaps closer examination of the camshaft is called for, particularly the journals.

~~~~~~~~~~~~~~~

Twenty thousandths of an inch is close to .5mm (FIAT is metric). A novice machinist could easily mistake graduations and this calls into question the other measurements on the cam.

I have multiple cams and they all measure the same 29.95mm. The pulley is likely made in china for a US aftermarket company. Not sure why the ID is so big. The intake pulley from the same source runs absolutely true. Different batches? When you get stuff made in china, you never will know who/where it was actually made, unless you deal directly with the mfg.

[rebelyell]

good suggestions
also, how about tig the pulley ID and mill it to fit cam snout ?

[PRH]

What does the manufacturer say the hole size is supposed to be?
If it doesn’t match what you have(and is correct for proper fitment on to the cam) , will they replace it?

[Nut124]

The US vendor is sending me a new pulley. It is likely be just like the one I already have.

I got some aluminum foil tape ready to put on the cam. This is a 2-piece adjustable pulley. I find that there is about 0.015 radial play between the inner and the outer piece as well. This would affect concentricity of the outer wheel any time the cam timing is adjusted with belt tension on. I will need to shim this gap as well.

[Nefario]

I got some aluminum foil tape ready to put on the cam.

There's these guys for allowing bearings to be mounted in oversized, loose-tolerance housings. Take a look at their "AN" series. I don't know how you get just one, maybe ask for a sample or find a distributor?

http://www.usatolerancerings.com/index. ... g-download

PS "tape" seems like a really bad idea. You have the squishiness and sliding layers of the adhesive. I might look at K&S Brass shim stock from Ace Hardware.

[Nut124]

I got some aluminum foil tape ready to put on the cam.

There's these guys for allowing bearings to be mounted in oversized, loose-tolerance housings. Take a look at their "AN" series. I don't know how you get just one, maybe ask for a sample or find a distributor?

http://www.usatolerancerings.com/index. ... g-download

PS "tape" seems like a really bad idea. You have the squishiness and sliding layers of the adhesive. I might look at K&S Brass shim stock from Ace Hardware.

Very interesting. Thanks.

I have the pulley back in the engine, all adjusted. Running true now. The shim is only needed until the cam bolt is tightened. After that, the bolt holds the pulley tight. I had to find a way to tighten the bolt w/o using leverage on the pulley to keep the cam from turning as that would have forced the pulley off center as far as allowed by the remaining gap. I locked the cam with two large wisegrips in the cambox and used an impact wrench to tighten the bolt w/o any force on the pulley.

Running good now and no more whining belt noise.

[Dan Timberlake]

Can the shim migrate backwards into the lip seal ?

10:47 here -
https://www.youtube.com/watch?v=cZbyHf0dwak

[Nut124]

Can the shim migrate backwards into the lip seal ?

10:47 here -
https://www.youtube.com/watch?v=cZbyHf0dwak

A good question. I hope not. I do not think there is any movement there that would work the shim tape around.

In the linked video, I do not like it that he has paint on the pulley where it mounts at the end of the cam and under the bolt washer. I would worry about the paint thinning and resulting in the bolt coming loose.