R975 Radial engines

[BCA]

Hi Des,
Your R975 Base Shop Data Manual went out to you by airmail yesterday. Perhaps there is another person by my name you'd like to contact!?!
.......... Brian

[Bob Phillips]

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.

[Bob Phillips]

All early aircraft engines and C1 tank engines use a 6 7/8 inch impeller with 12 vanes. I do not have a C4 impeller but the manual shows what appears to be a larger diameter impeller with 16 vanes. Can anyone provide outside dimensions? The -46 impeller is 8 1/8 inches diameter and has 16 vanes. It also has holes through to the back.
Valves in the -46 and C4 have larger diameter stems than C1, and are not interchangable. I believe the -46 exh valve has an even larger diam stem than a C4.
Crankshafts, of course much longer in aircraft applications than tank engines but the C4 and -46 use a single nut and sleeve to hold the two front bearings in versus the earlier two nut method of the C1. Could you cut down a -46 to work in a C4?? Not sure.

pistonstop.jpg pistonsrear.jpg superchargers.jpg -46superchargerrear.jpg

[Bob Phillips]

Cylinders- I was prompted to provide this information by an internet photo of a C4 engine that appears to have been rebuilt using -46 cylinders. This seems like a great idea given the scarcity and high prices of C4 cylinders. Hopefully one of the forum readers will recognize the picture and provide details on this rebuild. I assume it will require custom baffles around the cylinders.

C4-46cyls.jpg r975-46cyl.jpg

[Hanno Spoelstra]

Hello Bob,

Over a year ago I came across pictures of a Continental R-975-46A radial engine for sale for not too silly money. I too wondered about the interchangeability of parts, or even a complete engine swap into a M4 Medium tank or related AFV.

Thanks for offering some insight into the detail differences.

Hanno

PS: Here's what I found about about it:

Continental R-975-46A radial: from aero, to tank, to aero engine

Aircraft variant of the Continental R-975. This is the -46A version as used post-WW2 in the Piasecki PV-18 (Navy HUP-3 Retriever, Army H-25A Army Mule) helicopter. It was offered for sale on the Antique Aircraft Parts Exchange FB group, and shared here as it may be of interest to Sherman tank restorers. While originally a Wright design, during WW2 Continental built more R-975's under licence for tanks than Wright did for aircraft (> 53,000 vs. >7,000). After the war, Wright showed no interest in continuing to manufacture the R-975. Continental then introduced its own R-975 version for aircraft, the R9-A. It was basically similar to other R-975 engines, and its compression ratio and supercharger gear ratio were unchanged from the R-975E-3, other improvements in the R9-A allowed it to achieve 525 hp (391 kW) for takeoff, surpassing any Wright version. A military version, the R-975-46, could reach 550 hp (410 kW), and was used in Piasecki's HUP Retriever and H-25 Army Mule helicopters. Continental's production of R-975 engines continued into the 1950s.

16143329_1229046150507700_8307036516151579028_n.jpg 16299003_1229046143841034_5686256705943836334_n.jpg 16174946_1229046147174367_2074506135361185057_n.jpg

Power to the HUP-1, HUP-2 and HUP-3 helicopters is supplied by Continental R-975-42, R-975-46 or R-975-46A air-cooled, nine cylinder radial engines. These were based on the Wright-designed tank engine.

The engine is located within the fuselage aft of the fuel cell and firewall. It simultaneously drives two three-bladed rotors through drive shafts and reduction transmissions. The rotor blades of the HUP-2 are of either wood or metal (later versions) construction.
16300067_1229070160505299_1017659345989160425_o.jpg

Continental R-975-42 as used in the Piasecki PV-18 (Navy HUP-2, later UH-25 Retriever)
16299903_1229079077171074_1047669078119215567_o.jpg

[David Herbert]

There were a number of prototype and very low volume vehicles built with R975 engines. The most obvious being the original M8 High speed tractor (R975D4) and some of the very high mobility 8 x 8 trucks by Corbitt (T33 and T33E1)(R975C4). The fan in Bob's post #12 is a design that I have not seen before, with the blades braced to each other and the exhaust looks as if it has the outlets very low down compared to WW2 applications that had them right at the top or half way down each side.

One of the significant improvements with C4 cylinders was that the cooling fins were made much bigger with bigger gaps between them as the very fine fins on the EC2/C1 and presumably the -46 engines clog up with dust in tank applications.

David