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Now I've heard that people haven't really seen a difference, even with
hardened seats. Does anyone else have an opinion on this???
John
Hi John,
I'm no authority on gasoline, but in the brit iron newsgroup, there was
an excruciatingly detailed and long thread on leaded gas and 60-70's
brit bikes specifically, and older engines in general. The final answer
was, of course, it depends....doesn't it always?
In summary, the findings were that iron headed engines probably are more
prone to valve seat recession than are aluminum headed engines as the
valve seat inserts used in aluminum headed engines typically are harder
than the iron used to cast a typical cylinder head.
That much said, a tiny bit of lead, or lead substitute, appears to go a
long way. Studies quoted indicated that one tank of leaded gas in four
fill-ups usually was enough to prevent recession even under "hard-use"
conditions (towing, extended high speed operations, etc.). Apparently it
takes a while to consume the lead/lead substitute deposited on the
seats.
Additionally, under moderate use conditions (probably the way most of
use our older "lead gas design" engines), recession from unleaded gas
does not appear to be a problem.
The basic consensus was that it made no sense to tear down an engine to
replace the seats unless they are bad. If you have an engine torn down,
there is no reason to replace the seats unless they are bad. If you can
find/use lead substitutes, it surely would not hurt to do so, but you do
not need to be religious about it unless you are driving/riding the
engine hard. Finally, if you have an aluminum headed engine, you
probably have even less to worry about.
For my TR6 (iron head and low compression) and BSA's (aluminum heads and
relatively higher compressions), I do use lead substitute mixed in the
gas, but I am not compulsive about it. If I were going to do some
serious cross country riding/driving, I probably would take some along
with me, but studies indicate you probably are not going to trash your
engine by running unleaded gas under moderate operating
conditions--racing, towing, etc., now that appears to be a different
story.
Just my two cents worth--no more of that IMHO stuff for me---hee, hee,
hee :)
doug
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