Re: 1975 02tii unleaded fuel conversion (archive)

What needs to be done,if anything,to convert my 1975 2002tii to unleaded fuel? It has a '121' cylinder head with higher compression and it's been suggested that I lower it with a different head gasket, is this needed? Some articles recommend changing the valve seats and stem guides, others say nothing has to be changed. What did BMW do when unleaded came in?

The lead in the gas acts as a lubricant. The valve seats in unleaded cars were changed to hardened valve seats. I'm not sure what BMW uses in stock heads whether they are cast iron or hardened. Maybe some one out there knows. Also, unleaded gas has a tendency to cause the engine to ping or knock so retarding of the timing may be required. As far as I know, these are the two major things that are affected.
As long as the seats are of the hardened type you should be good to go. Guides are lubricated by oil and slightly by the lead. Just use a good quality replacement guide and postive seals and the valves should work out good for you. Do not change compression, all this would do is decrease performance potential. It may help decrease the tendency to ping but this can be corrected by retarding the timing.
Be sure you use the tii head gasket, different from the stock gasket (and more expensive). It has a special metal ring to help seal in high compression engines.

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