My brother Jack has a '71 Chevy 1/2 ton long bed with we think is the original 350 V8. It has been in his wife's family since new. As far as we know, the engine has never been opened up.
We pulled the oil pan today so we could stop oil leaks at the pan and the rear seal. After I left, Jack pulled the oil pump and found this mess in the sump screen. Plastic bits and pieces.
I know Pontiac used plastic/nylon on their cam sprockets in the late 60's/early 70's. Did Chevy do the same?
Last edited by Bill Hanlon; 11/09/202511:55 PM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
Bill - Unfortunately the answer is yes. Original 1971 Chevrolet 350 cam gears (36 tooth) for all applications is listed as GM# 3896960 according to the below extract (1st pic) from an October 1970 Chevy Master Parts Book covering the 1971 model year.
A web check came up with an NOS GM 3896960 Camshaft Timing Gear being offered on evilbay. The 2nd and 3rd pics below are screengrabs from that ad showing the overall gear and close up with the specified part number shown.
Looks like it's time to fully open up Jack's 350.
PS - I found that Chevy also used a nylon type cam gear even in similar year Big Blocks under GM# 3856356.
Last edited by Gdads51; 11/10/202512:30 AM.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
All the GM makes used the nylon gears, including Cadillac. Even Ford and Mopar used them in some engines.
When they deteriorate, the white plastic shavings clog up the oil pump.
Seemed like a good idea at the time , I guess. Nice and quiet.
1950 Chevrolet 3100 (Ol' Roy)
1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)
The truck was bought new by my brother's father-in-law in '71. My guess is that at some point before it was given to my brother's wife 25+ years ago the plastic teeth failed and someone replaced the gear (and maybe the whole timing set) without removing the pan and cleaning out the debris. The truck is still running okay, but only has an oil pressure idiot light, so no telling actual pressure.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
Original 1971 Chevrolet 350 cam gears (36 tooth) for all applications is listed as GM# 3896960 according to the below extract (1st pic) from an October 1970 Chevy Master Parts Book covering the 1971 model year. 
