911 Camshaft position and thrust washer clearance to housing

[Gary71]

OK so this might not be the easiest to answer but I'm seeking some advice!

I was fitting the second cam pulley tonight in advance of doing the timing and noticed a couple of things I could do with some guidance on.

The camshaft is not central in the hole of the alloy sealing ring within the timing case. I don't think this is an issue, and may have been there all along, but is this usual? I guess the cylinders expand when running which will move the cam outwards relative to the case as this will run cooler.



Next question is concerning the thrust washer that cam pulley tightens against. Without any pulley on you can pull the cam in and out down it's length by 1mm or so. Looking at the washer you can see it has worn a groove against the alloy flange, which is surprising for a steel washer!



My concern is that when you tighten the cam nut it might clamp this washer against the flange rather than the shoulder on the camshaft. With the cam pulled all the way out it's barely flush to the flange, hence the groove that has been worn.

It's all been running with this set of parts for many many years so I'm tempted just to bolt it all back up together, but are there any experts out there that can comment?

[fetuhoe]

Gary,

I think you need to deal with the axial float and the thrust washer wear.

The cam rotation is really a function of the cam housings and I would make a quick check of the cam run out just to be 100% confident.

This should be a maximum of 0.02mm TIR at the centre journal.

I don't think expansion will help with the position of the cam/cover as I would expect everything will grow together.

The axial float of the cam at 1mm is way too much and needs to be between 0.15 and 0.2mm. This could accelerate chain wear.

The thrust washer is fitted with the taper into the cover and the wear you are seeing would take place between the shim and the thrust face as I would expect that the taper would clamp the thrust firmly into the cover and not allow rotation between these two parts.

I would replace the thrust and the shim, make sure that the sprockets are carefully aligned.

As long as everything can rotate freely the eccentricity of the cover position shouldn't be a major issue.

[Gary71]

Many thanks for the feedback. I will check as described and order up some new parts.

[Gary71]

I've placed the order with the OPC and I'm going to strip it all out again so I can measure everything.