valve shims and cam wear

You may have been following my recent threads on engine removal. the purpose of this was to find out the cause of the cam wear noticed in a routine service as described above. The following slides show may analysis. There is no obvious wear cause. Looks like either the inlet valves were too long, or more likely the inlet valve seats were machined too deep. the exhust valve need replacing due to pitting.
Kevin
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addtional slides
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last slides. Comments and suggestions very welcome. I may have drawn the wrong conclusions.
Kevin
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John, thanks for the feedback

yes I had decided to re-use the cams, as there is nothing wrong other than the very small chips on the edges. The chips do not feel as if they will scar the valve shims. They havn't so far.
Not sure how to test the valve guides for wear. I measured the valve stem diameters and they are just in tolerance. More wear to valve stem near head than top, which is not surprising. The valves do rock side to side very slightly when near closed. Difficult to measure, but less than 0.1mm. I will put in a complete set of new valves and then re-test the movement. If there is a better way to test the guides, please let me know.

I am just glad the valve seats are in good condition, one suggestion was that the valves may have hammered into their seats. The seats look bronze. Is that standard? I have run on 98 Octane unleaded for 6000miles, the seats look very good, exhaust valves rough, so may be they were not unleaded rated.

Kevin

 

The start of this thread was 19th November 2008 when I was carrying out a routine 6000mile service and checking the valve clearances. There were clear wear marks on the inlet cam lobes. After some checking, the cause was due to the cam lobe colliding with the cam follower bucket edge before touching the valve shim. I could not get adequate valve shim to lobe clearance without using too thin shims. In order to solve the problem the heads had to be removed. To do that, the engine had to come out. So after just over two months I have a reasonable explanation of the cause and a simple solution. New standard inlet valves. At least i can clean the engine and engine bay at the same time, so there will be some visual difference to go along with the peace of mind.
Kevin
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As per previous post today. A throttle cable break resulted in need to remove the air box, which exposed the cam covers and reminder to do the valve shim service. Attached are some photos and analysis.

I find it easier to remove the inlet manifold complete with carbs. After disconnecting the fuel pipes, its just 4 bolts to lift the complete unit out. take care of the exposed inlet ports in the heads, would be easy to for something to fall in.

Removal of the cam covers is straight forward, if not frustratingly tight access to the end caps and fillers at distributor end.

I initially forgot to remove the header tank for better access when lifting the rear cam cover. No need to remove, just undo the two header tank mounting bolts and tie back out the way. Easier to get to the mounting nuts by first removing the inspection panel in the boot (trunk!).

Kevin
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And now to the shimming.

Its not the most pleasant of jobs. Both measuring and removal of the shims is a right pain. There is no easy process/tool for the job. Some years ago I purchased the upper photo tool set, which I failed to get the hang of. Decided to purchase the set in the lower photo. Certainly better and good enough for the job.
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Not enough hands available to photo the full process. Hopefully this one helps which shows the latter stage of flipping the shim out. Use in conjunction with some of the previous post in this and other threads.
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Measuring shim clearances is tricky (at least for me). Measuring once, rotating the cam and re-measuring does not always appear to give the exact same result. Of coarse it should, however, it is down to technique and judging the fit or slide of feeler gauge.

Below is a summary of what is measured and how the gaps have changed over 5634 miles. Now, a caution here. My records of the last shim measuring shows that I achieved exactly an average tolerance on all 12 valves. While I recall spending quite a bit of time shimming, I suspect that although all were in tolerances, there was some variation. None the less, the summary here shows apparent wear relative to previous recorded measurement.

Light, medium, dark gray bars in the charts are gaps per cylinder at 0-miles, 5634-miles and after this re-shim respectively. Black line at the top represents the heel of the cam, and the two red lines the lower and upper tolerance per manual. Red circles shows those gaps that were out of tolerance.

Both charts are plotted at same relative scales.

Note a total of 5 valve clearances were out of tolerance and requiring replacement shims. 4 of the 5 from the exhaust side. Perhaps not surprising as these run the hottest and in a more wearing environment.

New shims purchased from Superformance
All gaps now back in tolerance.
Cams look good with no additional anomalous marks to that reported in the previous posts in this thread.
Engine running nice and smoothly.

Kevin
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