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Mark,
I have just removed the cylinders and found the valve seats, valves and guides to be in excellent condition. Somewhere along the line, I am pretty sure these were replaced and not much mileage was put on them. If this is the case then is there any way that I can determine if these components are made for lead free petrol? I cannot make out all the markings on the valves. The clearest one is an inlet valve SLW 5U and EIN. On the exhaust valve all I can make out is AUS. (EIN and AUS are probably German for Inlet and exhaust)
As for the pistons the markings that appear on both are identical (71.92, H, and a triangle with the inscription 12 and NURAL) except for 3/69 and 9/66. Hopefully these last numbers are not manufacturing dates! I take it that these pistons are standard 72 mm nominal.

Mark,

I just removed the pistons from the connecting rod and found that although they appear to be the same on the outside, the castings on the inside are quite different. They bear the number 7237C and NORAL and the other 7237 followed with what looks like a / (definetly not a C) and Noral on the inside and the same number 3210 with the corresponding 8-66 or 3-69 also imprinted.The piston marked 8-66 does look older! So from what I can make out, I have a pair of unbalanced pistons. Should I be concerned? After checking clearances I found that I could get away from purchasing oversize pistons by simply honing the cylinder walls to remove the superficial scratches. However, if my suspicions are correct, do you think that going to the first oversize is really necessary?

Hi Pierre

The numbers are the mould numbers from Nüral. The name cast inside is also Nüral but with wear to the form, the "ü" starts looking like an "o". As long as the play of piston to cylinder is within factory tolerance which is well described in the factory manual, you can still use the original pistons if their ring grooves are ok. Check the end gap of the old rings as well. You might be better off just replacing the rings. If all of the above applies, then a light honing is all that you would need. Pistons should be balanced anyway, even when purchasing a new pair. This is an easy job which you can do yourself using a letter scale. The easiest way is to remove weight from inside the gudgeon pins than grinding away masses of aluminium.

Hope I've answered your questions.

Best regards,

Mark
Mark Huggett GmbH

Hi Pierre

Yes, the 3/69 and 9/66 are the manufacturing dates which would suggest that these are not the original pistons. Nüral actually hold about 60% of the OEM piston market in Europe. and where also the main suppliers of BMW. Their pistons were also generally lighter than the Mahle and KS. The triangle is the company logo of Nüral. While Nüral are Europes largest piston manufacturers, the are almost unheard of in the replacement market as this does'nt seem to interest them at all. They were devoured by the Federal Mogul group a couple of years back which did'nt help matters either. Here, KS and Mahle are by far the better known names within the replacement market.

Regards,

Mark
Mark Huggett GmbH

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I think the seats are the only parts that can be made for "lead-free" duty. And I don't think there is any way of telling this by their appearance in the engine.