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Old 11-05-2016, 12:03 AM
10,875 posts, read 41,221,323 times
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TrapperL must be running a whole 'nother military engine series than I saw from those 1950's low RPM/long stroke T245 L-Head engines that Dodge supplied in their '50's 3/4 ton truck.

These originally were a workhorse low RPM engine of 230 cu in rated 78 HP at 3200 RPM. The compression ratio in military engines was 7:1, specifically to be able to utilize low octane fuel supplied to the military. 80 octane was the spec. Later versions delivered as much as 103 HP, which was still a very low compression ratio engine with very modest cam and ignition timing parameters.

You do not need 100 octane fuel per Trapper L ... "You can get the required octane that the engine was designed to use there. The "regular" octane has a 100 rating. Otherwise, performance, if you can call it that in the little flathead engine, will suffer."

Unleaded 85 or 87 octane regular fuel is more than sufficient to deliver all the performance that "the little flathead engine" can possibly deliver.

And I'd caution you to drive it very conservatively at modest speeds. This engine had a well known reputation for scattering when pushed to the higher RPM's due to the low gearing range of the transmission in the military truck. Designed for heavy loads and slogging around, not cruising at higher speeds, the long stroke engine ate rods and pistons with regularity.

Unless you are planning on driving this beast a lot of miles at high speeds, you'll not encounter valve seat erosion problems of any real consequence on today's unleaded fuel. They simply don't wear out all that fast. Generally speaking, you'll wear out the bottom end as fast or faster than the valve seats.

Even if the valve seats needed attention, these simple L-head engines are easy to replace the seats with upgraded seats in the block. I've seen it done without even removing the engine from the chassis. Lift the head, weld in an old worn out valve cut down to fit inside the seat (it's so easy that even I, a not very good welder, have done it with a wire-feed welder), allow the seat to cool and the old valve stem is your handle to pull the now shrunken seat out of the block ... they'll almost "fall out" of the block. Replacement seats drive easily into place and we used a Neway valve seat cutter set to cut the three-angle seat ... better than factory new. (Last one I assisted on a few years ago was an early 1950's Pontiac ambulance with a straight-8 engine. I'd bragged on this process to a resto shop in South Dakota and they called me up to "prove it" to them ... a paid opportunity to go visit one of my favorite hot springs. With my Neway set in hand I flew up there in a couple hours. They'd pulled the head and valves before I got there and we had the new seats in and cut by that afternoon, much to the satisfaction and delight of the shop owner. Didn't even need my Neway set, they had the pilot and cutters already ... but "forgot" they did when they'd called me).

PS: even if you can't do all this work yourself, it's simply not that "big" of a deal to work on these engines and have an automotive machine shop do the stuff you can't or don't have the tooling to do. These old lumps were designed to be easily serviceable, even out in the field.

PPS: allpar site posts that: "Plymouth-Dodge-DeSoto-Chrysler straight six and eight cylinder ... duty trucks were equipped with sodium cooled exhaust valves and stellite seats." If that's the case for the T245 engine, then you've already got the hardened valve seats that are well capable of dealing with unleaded fuel and no need at all to mess around with lead substitute fuel additives.

Last edited by sunsprit; 11-05-2016 at 12:23 AM..
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Old 11-05-2016, 09:47 AM
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Originally Posted by Fleet View Post
Unleaded fuel only? I think that started in 1975. My 1976 Cadillac requires unleaded fuel only.
Yes it was 1975. That was not the point of my post but thanks anyway.
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