>Fitting hardened seats and tipped valves certainly will, but may be largely
>unnecessary depending on the specific engine, it is the higher revving OHV
>domestic engine of the 60's and 70's that are at grave risk, the A series
>suffers VSR with unleaded fuel at 1 thou per 5 mins run at 60 mph equivalent
>apparently.
>
>
>Now, our American chums haven't seen any leaded pump fuel for many years, yet
>the list, whilst understandably heavily biased with US subscribers as you'd
>imagine, is quite free of VSR hassles, questions and tales of woe it
seems. Can
>we deduce therefore they are all just pumping the standard stuff into their
>trucks and the VSR bogey has been a non-event for MV engines ?
>
>One pace forwards all those US MV owners who have _definitely_ wrecked their
>motor on unleaded, lets be hearing from you.
I'll submit my experience, studies and conclusions:
Early 1951 M38 w/ original L-Head. No hardened components.
1968 M715 original 230 OHC Comes with hard exhaust seats and
valves with positive rotators.
1944 GMC DUKW original 270 came with harden seats and valves.
I got mine with "soft" exhaust valves, which I changed
to hard ones with rotators.
Where I live, NY state, the lead was dropped from 1-2 grams per gallon
to .1-.2 grams around 1980. I only had the M38 at that point and all was well.
Soon after, (10,000 miles or so), engine started to skip.
Burned valves. Replaced and reseated the exhaust valves, used a lead
replacement
additive, engine lasted 12,000 miles. Exhaust valves again.
I have always kept the speed to 45 mph the first time, and the second
time 55mph. I had added the Warn Overdrive at this point. These
road speeds kept the revs to about 2600 rpms.
Have since rebuilt with hard seats and valves and added passive valve
rotators to the exhaust setup. By the way, that became stock with the M38
in later production.
The GMC had soft valves when I got it, and these didn't last long. I went
to harden valves with rotators here again. The original seats were fine.
The M715 has all the hard stuff, and has been fine. However, it does like
higher octane fuel, contrary to its 1968 85 octane rating. It will rattle
with todays 87 grade. Retarding the spark and higher octane fuel is the
deal here. Has to do with what 85 octane in 1968 was and what (85) 87 grade
is today. They are not close. One more note about the 230 OHC, it is a
hemi-head design. Good power but fuel sensitive. Anyone remember
the old Chrysler Hemis???
Conclusion:
If your engine is "worked regularly", do the valves and seats
with hardened material. In our case, all these vehicles are under-powered
so the motors are worked.
My M38 and M715 are and have. GMC does also, tough pulling heads, or
anything for that matter, in a DUKW. Its engine is worked regardless.
Low compression engines are a bit harder on exhaust valves. Less
heat is converted to mechanical power and is exhausted. I've
seen many manifolds swapped out due to heat warppage on low compression
motors then on higher compression ones. Imagine what the exhaust valves
are seeing.
During all this, I managed to obtain valve applications notes from TRW.
Same conclusion. Wish I had this hard info back in 1980.
These are my experiences and what I have done to correct my problems.
When put in perspective to an engine rebuild, the better valves and seats
with the added labor to install these seats is cheap.
Besides, there are more important things in life. Like....are
the parts in my fuel pump and carbeurator "New Gas" compatible.
Joy To All......Happy Thanksgiving !!!!!
Ted Hintopoulos
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