Nylon cam gear years

[ASPEC]

Good Morning,
Does anybody know in what years and in what GVW that GM used the nylon cam gear in the mark IV 454? Searching yielded no definate answer.
Thanks in advance for your help.

 

[edgephoto]

I just replaced the timing set on my 1987 GMC. I have owned it since 1988. It had nylon teeth on the cam gear.

 

[bucket]

My '91 454 has the original nylon cam sprocket still.

 

[legopnuematic]

Not definitive, but this is from the 1973 truck service manual, depicting a big block with nylon cam gear:

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[Goldie Driver]

My '91 454 has the original nylon cam sprocket still.

I thought that was a 70s only dumb idea.

I was obviously overestimating their ability to correct previous errors...

 

[Ricko1966]

I thought that was a 70s only dumb idea.

I was obviously overestimating their ability to correct previous errors...

It wasn't a dumb idea,and most of the cars went thier whole life without a failure,the transmissions gave up,the bodies rusted away,and the rings gave up way more often than timing gear failures. But the dealers weren't getting noise complaints. Smokey Yunick and Cliff Ruggles prefer them for racing applications. Now we don't say Honda,Toyota,Mazda,VW everyone is stupid when timing belt fails at 10 years 120,000 but was supposed to be changed at 5 years 80,000 we look at that as owner neglect. A timing set is a wear item also. Supposedly the O.G. Gm Morse chain and nylon sprocket is more efficient and controls timing better than a double roller. Just change it at 100,000.

 

[ASPEC]

Not definitive, but this is from the 1973 truck service manual, depicting a big block with nylon cam gear:

Yup, the 1974 shows the same photo...

It wasn't a dumb idea,and most of the cars went thier whole life without a failure,the transmissions gave up,the bodies rusted away,and the rings gave up way more often than timing gear failures. But the dealers weren't getting noise complaints. Smokey Yunick and Cliff Ruggles prefer them for racing applications. Now we don't say Honda,Toyota,Mazda,VW everyone is stupid when timing belt fails at 10 years 120,000 but was supposed to be changed at 5 years 80,000 we look at that as owner neglect. A timing set is a wear item also. Supposedly the O.G. Gm Morse chain and nylon sprocket is more efficient and controls timing better than a double roller. Just change it at 100,000.

Agreed. Was just hoping I wouldn't have to go in there. Truck has a numbers matching engine, frame, trans, dif, and it doesn't look like the heads or front tin have ever been off. Heck the water pump looks original with gm cast part numbers and all...
Can't risk damaging a 50 year old survivor big block so in we go.

Thanks everone.

 

[Goldie Driver]

It wasn't a dumb idea,and most of the cars went thier whole life without a failure,the transmissions gave up,the bodies rusted away,and the rings gave up way more often than timing gear failures. But the dealers weren't getting noise complaints. Smokey Yunick and Cliff Ruggles prefer them for racing applications. Now we don't say Honda,Toyota,Mazda,VW everyone is stupid when timing belt fails at 10 years 120,000 but was supposed to be changed at 5 years 80,000 we look at that as owner neglect. A timing set is a wear item also. Supposedly the O.G. Gm Morse chain and nylon sprocket is more efficient and controls timing better than a double roller. Just change it at 100,000.

To each, their own. I am not a fan of timing belts either as I see that as a planned obsolescence. Timing chains are typically a life of the engine item if the engine is maintained and the gear & chain are metal in my experience. Most of the nylon coated ones I saw failed around 70K.

 

[fast 99]

It wasn't a dumb idea,and most of the cars went thier whole life without a failure,the transmissions gave up,the bodies rusted away,and the rings gave up way more often than timing gear failures. But the dealers weren't getting noise complaints. Smokey Yunick and Cliff Ruggles prefer them for racing applications. Now we don't say Honda,Toyota,Mazda,VW everyone is stupid when timing belt fails at 10 years 120,000 but was supposed to be changed at 5 years 80,000 we look at that as owner neglect. A timing set is a wear item also. Supposedly the O.G. Gm Morse chain and nylon sprocket is more efficient and controls timing better than a double roller. Just change it at 100,000.

Some of the 90's and up GM V-8's came with a single roller chain. Replaced several high millage motors and frankly the chain was tight enough to reinstall. Wonder if this was a replacement for plastic?

Back in the late 70'S and early 80's I replaced a ton of failed Pontiac plastic timing chains. Most vehicles were likely near the end of their life. Unsure why we saw more failed Pontiacs than other brands but we did.

 

[Ricko1966]

Some of the 90's and up GM V-8's came with a single roller chain. Replaced several high millage motors and frankly the chain was tight enough to reinstall. Wonder if this was a replacement for plastic?

Back in the late 70'S and early 80's I replaced a ton of failed Pontiac plastic timing chains. Most vehicles were likely near the end of their life. Unsure why we saw more failed Pontiacs than other brands but we did.

That's kinda strange with the Pontiac failures,maybe a run of bad gears certain years. Everyone started running nylon gears on Damm near everything early 60s . Ford,AMC,Chrysler,all the GM lines, they were still running them in the Grand Nationals and Corvettes through 91. Sorry @fast99 now I've gotten off track,and wish I hadn't quoted you. Anyway as many millions and millions of cars had these gears sure some are going to fail. I've heard of way more spun bearings,rods through blocks,Damm near every kind of failure other than cam gears. Sure I've seen a couple,but back too the original point,kinda strange that you saw such a high incidence on Pontiacs,wonder if they had a run of bad gears at some point. I still think 90 percent or more of cars with nylon gears were junked or got engine rebuilds with the original timing gears still in them and functioning. Remember life span of a car back then was 10 years 100,000 miles

 

[77Dmax]

I believe the primary reason for the nylon teeth was a production issue. Was easier and cheaper to make the nylon teeth vs. machining the metal gear.

People love to hate on them, but they did usually last just as long as the rest of the car.

 

[Ricko1966]

I believe the primary reason for the nylon teeth was a production issue. Was easier and cheaper to make the nylon teeth vs. machining the metal gear.

People love to hate on them, but they did usually last just as long as the rest of the car.

It cost more to make the nylon gears they still machined teeth on the gears they just coated them with nylon,the issue was noise.And the ability to run tighter tolerance. The given reason for the nylon failure was chain stretch so the chain no longer meshed correctly with the nylon. I don't really believe that but that's what manufacturers state. You'll find nylon coated gears with the nylon chipped off and the chain still loosely on the sprockets,and still on time. If people would check timing gear stretch when doing cap and rotor,most of these woukd be caught. It's easy. Cap off roll the engine clockwise with a breaker bar, line up TDC on the timing tab. Put a finger on the rotor,pull the breaker backwards until the rotor moves. Look at the timing tab. More than 8 degrees,change timing set,it's stretched or the nylon is coming off.
These were off running engines,definitely would have failed a rotor test,a long time before this.People had probably bumped the ignition timing several times in the past never questioning,why is so far off? Why is it running bad? It's like the guys that add brake fluid when the light comes on,not looking for the real problem,or the it was just a blown fuse,without looking for why it blew.

 

[fast 99]

More than 8 degrees,change timing set,it's stretched or the nylon is coming off.

That's one of the diagnostic procedures I use for a non running engine.

Can't explain seeing more Pontiacs either. I think most of them were 389 grocery getters. Just remember doing a lot more Pontiacs than other brand. Could be as simple as more sold in the area, who knows. Was a money maker, could beat flat by a lot.

 

[77Dmax]

It cost more to make the nylon gears they still machined teeth on the gears they just coated them with nylon,the issue was noise.And the ability to run tighter tolerance. The given reason for the nylon failure was chain stretch so the chain no longer meshed correctly with the nylon. I don't really believe that but that's what manufacturers state. You'll find nylon coated gears with the nylon chipped off and the chain still loosely on the sprockets,and still on time. If people would check timing gear stretch when doing cap and rotor,most of these woukd be caught. It's easy. Cap off roll the engine clockwise with a breaker bar, line up TDC on the timing tab. Put a finger on the rotor,pull the breaker backwards until the rotor moves. Look at the timing tab. More than 8 degrees,change timing set,it's stretched or the nylon is coming off.
These were off running engines,definitely would have failed a rotor test,a long time before this.People had probably bumped the ignition timing several times in the past never questioning,why is so far off? Why is it running bad? It's like the guys that add brake fluid when the light comes on,not looking for the real problem,or the it was just a blown fuse,without looking for why it blew.

It was my understanding that the gear was cast with the teeth and set in a mold for the nylon. This eliminated any machine work. I'm not saying this is gospel.

Coincidentally I've also heard people talk about noise reduction with nylon gears. I've swapped dozens, seems like you as well, and never heard any difference. Is that an old wive's tale?