Shimming the Camshafts

[4129R]

I have just spent a frustrating weekend trying to grind in valves, and then re-shim the tappets to give the correct cold clearance between the cam follower buckets, and the cam lobes.

First. one of the exhaust valves was a bit "battle damaged" around the stem, so I decided to replace it with a new exhaust valve I had in my collection, rather that wait for the valve head to fall off and the whole engine go bang.

The new exhaust valve had a shorter stem above the collect, which seems to use a different type of disc shim, rather than the "top hat" shim.

Eventually, I managed to work out the correct disc shim to get, and surprisingly QED list it as costing £3.00 + VAT + P&P.

Then I decided to check all the other 7 clearances. 5 were within tolerance but two had no gap at all.

Now comes the hard part. My feeler gauge is in "thou", the workshop manual is in "thou" but my micrometer is in mm, so measuring the thickness of the shims needs to be converted back into "thou".

I worked out the required shim thicknesses, but they were nowhere near those listed for top hat shims.

Does anyone know where you measure the shim thickness. I measured the thickness of the bit that goes on the valve tip to give the tip to shim thickness, but this appears wrong from what is available.

Before I have a long chat with QED, has anyone out there shimmed up the cams using top hat shims, which go on the longer valves, and have a different style of cam followers from the disc variety on the shorter valves? . 

[EuropaTC]

Sorry, I can't help on that one other than to say your measurement logic seems right to me, that's how I'd do it. By any chance do the top hat shims have anything engraved on them ?  Both my engines are standard disc shims and that's all I've got experience of, and of course they are very easy to measure.  I think a phone call to someone who knows what they're doing is in order !

Brian

[jbcollier]

Shim thickness is measured between the two contact surfaces.

Sounds like you "ground" things a fair bit.  The valves should all protrude into the combustion chamber similar amounts.  Valves that are "low" or "recessed" may require new seats.  You can trim the stems to gain more clearance.  Shims are easily trimmed (albeit oft times bloodily) with fine paper on a surface plate (or smooth concrete).

If there is any doubt about one exhaust valve, change them all.

TC heads do not last long at the best of times.  If you don't know what you are doing, get someone who does to do the work.

[4129R]

It seems QED don't list top hat shims as thin as I require, as they would be too thin to last.

So QED supply thinner cam followers.

I have ordered two, as a place to start. With negative clearance, you need to get positive clearance before you can start measuring things.

I have ordered an Imperial caliper on eBay, which measures up to 1", so I can compare like with like, rather than having to convert 1mm to 39.37 thou.

[EuropaTC]

I'm curious, why does your engine have top hat shims on it ?  I'd started off by assuming it wasn't the usual TC, but has it had something done in the past to require a move away from standard disc shims ?

On the Ebay purchase, I've got 2 digital vernier calipers from sellers in China which go from metric to imperial on a button.  They were silly-cheap and I was so surprised the first one actually worked and compared with my olde-worlde manual one that I bought another to leave on the bench for day to day instead of using a ruler ! 

Brian

[4129R]

The engine I am working on came in the bits in the 40ft container, ex Louisiana, ex Houston, ex Chicago, and full of mud in all the vital holes c/o mud dawbers.

The 8 valves on the Weber head have 7 top hat valves, and one with a strange shim. I am using followers and shims from a spare head I had. I am using new valves where necessary, which are a different length.

All very Heinz 57, but if shimmed correctly, it will work properly.