Posted: Sat Aug 31, 2019 8:07 pm Post subject: RMC Engine
I have a like new RMC engine that while covered in dust runs great and has great power. Oil pressure is normal at 40lbs.
I would like to drive my M38 often. But, it has not been regularly driven probably for decades.
I can get ethanol free gas from a Pure Gas station but beyond that it there anything else I should do to keep the engine in good shape in 2019 for a 1951 vehicle?
I hate to take it apart as it runs great as is with just a tune up. I would prefer not installing hardened valve seats etc. or replace gaskets etc. as it seems to be OK. Is there anything I'm missing in assessing the engine for regular use again?
She'll do ok on ethanol free gas but addition of lead should be done without hardened seats. The easiest way to do this is buy a few gallons of 100LL aviation gas at any small airport and mix it about 1 gallon per tank of unleaded non-ethanol. Yes the AVGAS is a bit more expensive by about $2 a gallon but you're only using one per tank of unleaded. You could try lead substitutes also. I am old fashion and we always say "If it ain't broke , don't fix it!" _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
I'll give you a slightly different take, and you can do what you want, lol.
If your rubber/plastic in the fuel system is NOS or similar then ethanol free is the way to go. Most modern fuel line/pump diaphragms/filter housings/rebuilt kits etc. are better prepared for alcohol exposure. If your jeep sits for any period of time, regular ethanol fuel has a lifespan of two to three months. You can extend that with "Stabil" or similar. AVGAS is awesome, but I don’t think required. It’s also typically higher octane, and may require timing and carb adjustments. Even just running 86 octane typically requires advancing timing to 7-8*btc instead of the 5* noted in the manuals.
These engines are 1940’s technology. They weren’t designed around leaded fuels so much as in spite of it. They’ll run on octanes in the 60’s. The weak valve spring pressures, generous valve guide clearances and relatively low RPMs pretty much make hardened seats and lead additives a waste of time (my opinion). You can do either to no harm, but I don’t believe either is required.
Of more importance, and again only an opinion, is to use a zinc rich oil or an zinc oil additive (like ZDDP) to take care of cam lobes and tappets (lifters)…
Don't do or not do anything without making up your own mind-
The engine runs perfect which is so unusual for a jeep this old from my experience. There are lots of aviation, off road and farm tractor fuel sellers around here so fortunately getting gas of some kind should not be a problem. Finding specific oils will take some work but is doable too.
I have rebuilt the fuel system once before and will do it again with a new repo M38 gas tank, lines, etc.
My goal is to get it as close to new again and make it as reliable as possible!
Got a price today of $2.95 a gallon for 100% gasoline @ 87 octane. Fuel source is probably Exxon as the station is Exxon although the Pure Gas pumps are separate from the regular gas pumps and include off-road diesel.
For reference $2.95 is about 60 cents more than the lowest priced 87 octane 10% ethanol gasoline price local to that area. So that is a pretty steep price increase.
Still worth it for the problems avoided hopefully.
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