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As a slight aside - hardness values have been quoted for the cam and followers/lifters (I think 50 - 60 Rockwell C). And there has been mention of hardening, case hardening, Nitriding etc.

 

If you are presented with a certificate stating the hardness value (very unlikely) or the bloke says it is to whatever Rockwell 'C' don't sit back smiling - it could mean absolutely nothing.

 

Rockwell 'C' is a measurement taken using a bench mounted device that applies a load of 150KG at a point and gives so much deformation.

This is all well and good if the whole of the parent material is homogenous.

If you have a case hardened cam and use true Rockwell 'C' you will get an average reading of the parent material and the hardened surface. (biased towards the parent material) Thus the hardened surface may be 55 Rockwell 'C' but giving a parent + case of eg 40.

 

To measure the case hardening you need a hand held device that works using a 2KG (or less) load so that it only see the case hardening.

 

The problem is that you haven't a clue what is what.

The only thing you can do is use a reliable manufacturers product who works to controlled standards.

After the intial design/prototype the hardness testing can be done away with or used on a sample basis as the standard process takes care of the rest.

 

 

Use quality products from known sources - listen to the grapevine for problems etc.

 

Roger

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I have the original cam and cam bushings in the engine in my 1958 TR3A. The cam followers (tappets) are also the original ones. I used Castrol 10W30 for the first 80,000 miles from new - then when I restored my TR from 1987 to 1990, everyone was using 20W50, so I did the same. Now 105,000 more miles of touring type driving (total = 185,000 miles), the only issues I have had in this area is that I found rectagular surface wear on some of the flat bottom surfaces of the tappets which run on the cam. This square or rectangular appearance tells me that these tappets were not rotating as the should be. Other tappets had the familiar (desirable) circular pattern indicating that these tappets had been rotating as they should. In three engine re-builds, I have lapped the flat bottoms of these same original tappets all three times to get the wear patterns off and so they would be flat again. I never had them re-hardened and as I stated above have never had issues in this area. I have to assume that the hardness depth must have been quite deep when they were made originally.

 

Four years ago, right after the third engine rebuld, I started to use Castrol 10W30 again with 4 oz of ZDDP Plus additive every oil change because of the "flat tappet engine" we all have. I have not needed to add any oil between oil changes during these last four years whilst driving 10,000 miles.

 

Don Elliott, Original Owner, TS 27489 LO

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