I wanted to revive this thread to address the issue of using lower cost 975-46 engines as a parts source for tank engines. I have had the good luck to aquire a couple of these high horsepower helicopter engines and will share what I have learned about them. Please include your comments and experiences with these engines. There are still very nice -46 engines available for reasonable prices. These are helicopter engines, some of which can produce up to 550 hp ( take off) using high octane aviation fuel (100/130 or 115/145). These are the ultimate refinement of the R975 engine and were designed and built by Continental after WW2.
r975-46-.JPG r975-46--.jpg
The initial impression you get is that this is a much more heavily built engine. The crankcase is heavier, the rear crankcase is simpler and heavier than a C1 or C4 and the magnetoes are larger, the carb huge! In front a larger oil sump, a longer crankshaft (as per all aircraft engines and cylinders that are bigger than C1 but smaller than C4s. The thin web of a C1 or C4 crankcase is easily damaged either by rod damage (piston fails striking sides) or when bearing ejecta is smashed between the case and rotating crankshaft counterweights. The -46 case is solid where cylinders mount and much sturdier.
Inside there are several other differences. Pistons in C1 & C4 engines are 5.7 comp ratio (early ones cast later forged) while aircraft and the -46 are 6.3 comp ratio ( though higher ratios were used in prewar aircraft engines). All tank engines use "square" comp rings. The -46 and some aircraft variants use tapered keystone compression rings. The tapered rings are widely used on diesel engines and are currently used on the standard Continental 1790 diesel tank engine. A variety of oil scraper rings can be used. Note that all the forged pistons have reinforced ridges in the back, only the 202050 cast has none.
23-09-18, 03:43
R975-46 engines
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