Farmall 2-71 Repower
During the 1940’s or 50’s (I have never found references to the exact dates) Detroit Diesel offered diesel conversion kits to allow their 2-71 diesel engine (a 2 cylinder uniflow 2-stroke diesel) to be retrofitted to Farmall M series tractors. Sales Engineering Bulletin No 9 from Detroit diesel describes the conversion kit . Today, such conversions are very unique collectors items for antique tractor buffs – however the original conversions are quite rare and in recent years a few people have created their own conversion. Some documentation of their conversions can be found with a little searching on the internet.
Having spent the early years of my career at Detroit Diesel, I have always had a special fondness for the Series 71 engines and their history and a desire to own one I could use. Living a rural area with 29 acres of meadow and woods to maintain and over a half mile of driveway to keep clear of snow, the idea of having a Detroit Diesel powered tractor was appealing. There were several tractors that had factory original Detroit Diesel power, Massey Ferguson 98, John Deere 435 , and Oliver Super 99 and 1950. However, growing up on a the farm in Wisconsin with all “Red” power the idea of a Detroit powered Farmall was appealing to me.
While the Farmall M was the original target for the conversion, the Farmall Super M, Super MTA and 400 and 450 models all used variations of the same basic engine and tractor structure. I chose the Farmall 400 for my conversion project, this model having later features of independent PTO, Torque Amplifier and live hydraulics with multiple valves.
The attached pages (found under “Hobbies” in the menu) cover historic documents of the conversion kit, pictures documenting my conversion process (still in progress), and upgrades to the engine and it’s fuel system.
Update: I made upgrades to the engine build due to some issues and will be updating the “Step by Step Story” in the future. Basically I ended up with coolant in the oil and head gasket compression seal leakage into the coolant.
Head gasket upgrades were made to Series 71 engines, in the early 1950’s. The exception was the 2-71 which retained the “low block” design until it went out of production in 1987 with the original “low block” 1938 design. The new high block design used individual compression gaskets and “o-ring” seals for oil and coolant versus the original 2 piece body gasket. The result is nearly all the head bolt loading going to the compression gaskets.
My failure analysis shows the J-B weld fix of the erosion around the water holes in the block did not hold up well. It is likely the higher cylinder pressures from the 18.7 compression ratio pistons and the added boost (2 inches Hg) due to the coated blower, in combination with larger output injectors caused higher cylinder pressure resulting in the compression gasket leakage (bubbles in the radiator).
The fix I pursued was machining steel inserts for the block to fix the erosion at the water holes. I experimented with and changing to 17:1 turbo pistons to decrease cylinder pressure. however I did not like the poorer cold starting and increased white smoke so went back to 18.7’s. I also shimmed the liners to near .006 inch protrusion to increase the load on the compression seal. I have also retarded injection timing about 3 degrees with the injectors to lower peak cylinder pressures – more on injector combinations of P&Bs and tips to be published in the future.
I saw some suspicious wear near the top of the liners, this may have been due to the coolant in the oil and or in combination with the higher cylinder pressures and or insufficient lubrication. Detroit diesel used different oil ring packages, typically high tension oil rings for injectors below 60 mm3, reduced tension oil rings for non turbo engines above 60 mm3 and a single lower oil scraper in the lower groove for turbo engines with larger injectors. To be most robust relative to lubrication, I have decided to go use the turbo rings with the larger injectors I’m running with the increased boost.
A final update is the engine had relatively low oil pressure. This was solved and is covered by a separate page on the site.