R975 Radial engines

[Bob Phillips]

Good question about the cams, David. I had a quick run through the manuals and here is what I found. The M18 (G163) book lists 3 cams;
-G104-7006836 (CO201932) being standard for C4
-G104-0100293 (CO200742) (C66800) bolted for the C1
( this C1 being replaced/superceded by)
-G104-1531497 (CO242347) rivetted for C1
so it seems to suggest that there were both C1 and C4 cams...BUT
-my interchange book lists cam 201932 as interchangable in both C1 and C4 engines. Then check out the photos below. I just got these today and they show the damaged engine with sheared off bolts (that restarted this thread a couple of weeks ago) going back together with NOS bolts. Look closely and you can see the number on the cam of this C4 engine. It says 202347 which is supposed to be a C1 cam.(This is the cam in my early Sexton book with C1)
Finally, I reread the " Ordnance Development of the Wright-Continental R975 Radial Engine", from the Sherman Site. It makes reference to changing the aircraft cam for ground use. " To obtain the highly variable speeds required in tank operations, the engineers changed the intake and exhaust cams to decrease the valve overlap, to obtain higher torque at lower RPM and to improve idling characteristics...". But there is no mention through the rest of the report (including where changes made to upgrade C1 engines to C4s are listed) about a different cam. the report says that 85 percent of the parts between a C1 and C4 are interchangable.

So, without a 201932 C4 cam to examine, I would conclude that the cams are interchangable between the C1 and C4.

bcam1.jpeg bcam2.jpeg