Thu May 22 16:38:11 1997 - Message No. 886
From: Pierre DEBRAS

Subject: Re: run-in


Hi Federico,

the run-in process of an engine is vital for the rest of its life. The
engine is made of couple of parts (cylinder-piston, shaft-seat ...) that
requires a given play. When the enginer designs the engine, he gives
nominal values to each part, but when manufacturing the parts, it's not
possible to get the exact nominal values. Thus each part has a tolerance,
which is the limit acceptable around the nominal value. During run-in,
each part wears out against its "counter-part". As the process is based on
wearing out, it requires some time. That's why a good run-in will
progressively brings the engine to its maximum rpm. So, "after 1000 km no
limit" does not sounds a good idea. You should rather increase max. rpm
gradually. There should be recommendation on this topic in the manual. Bad
run-in can really ruin a mechanic: parts may overheat and destroy surface
coating.

By the way, to come back to our current oil discussion :-) I've often
heard not to use synthetic oil for the run-in because it will not allow
sufficient wearing out. Have some idea/info on the subject ?

Pierre



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dipper@normans.isd.uni-stuttgart.de