Nylon cam gear years

[bucket]

It failed in my '78 at around 140k.

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^Iirc, that happened not long after I had the stock sprocket out of my '91 454 and I PUT IT BACK IN. Lol. So far, that sprocket is still sprocketting. Probably close to 100k on it.

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I even put the stock peanut cam back in that thing, after I already had it out.

 

[edgephoto]

This was my timing set. I have owned this truck since 1988. Not sure how many miles but somewhere close to 200K

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[Ricko1966]

It failed in my '78 at around 140k.

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^Iirc, that happened not long after I had the stock sprocket out of my '91 454 and I PUT IT BACK IN. Lol. So far, that sprocket is still sprocketting. Probably close to 100k on it.

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I even put the stock peanut cam back in that thing, after I already had it out.

I think it failed about 130k and you kept driving. LOL

 

[CorvairGeek]

Pontiac V8s did seem to have a higher failure rate than other GM products. Interestingly, the Trophy 4 (1/2 of a 389 V8, '61-'63) supposedly had a really good timing chain setup that was good in the V8s too. The 1/2 a V8 was entirely too rough to get acceptable service out of the V8 set.

 

[bucket]

I think it failed about 130k and you kept driving. LOL

Lol, you are sort of correct about that. I made it down to Knoxville TN when I got slowed down in heavy traffic. While creeping along in traffic with the window down, there was a noticeable lope at idle and throttle response was still fantastic. I wondered what might be going on, but it sounded great and even got a compliment from a fellow motorist. I made it to about 1 mile from my exit to Adel in south GA, then the sh¡t hit the fan. My in-laws had to come tow me the couple miles to their house.

 

[1977banana]

The nylon gear is fine as long as you don't leave it too long without changing, because they do wear and fail eventually. The real culprit is a loose stretched chain on a nylon gear as that destroys them pretty quick.
As I remember, Smokey liked them because they dampened harmonics carried from the cam through the distributor which reduced spark scatter at high rpm, and were lighter. but I am old too and that's from memory. Later on belts provided the same advantage. Trucks used to have steel gears (3 ton, 5 ton h.d. apps) because the nylon didn't last as long perhaps because of heat etc. not really sure other than that.
Over the years we always swapped out the nylon for steel because it just looked stronger, not really sure if it mattered.
With a performance cam and headers you don't hear any noise difference, but in a stock set up that's quiet you might, but who's listening for that I don't know.

 

[Mike_82_Shortbox]

Yup, the 1974 shows the same photo...


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.

I'm probably late to the game here, but the Chevy 396/454 is not an interference engine. The nylon sprocket can blow itself to pieces at 80 miles an hour on the freeway, and you can just replace the timing gear and chain set and be on your way.

 

[edgephoto]

I would bet with today's plastics they would last way longer then the plastics from the 60s, 70s or 80s.

 

[Ricko1966]

Everyone who is curious look at an original Morse chain like would have gone on a nylon sprocket. The chain has tapered cogs that engage with the sides of the gear teeth, like gear teeth for a very positive engagement,kinda like a budget gear drive,and if things start to wear they engage deeper to still maintain a more positive engagement. Same style chain as in transfer cases. Rollers are like motorcycle sprockets and chains,sloppier when new and even more so as they wear.

 

[bucket]

I'm probably late to the game here, but the Chevy 396/454 is not an interference engine. The nylon sprocket can blow itself to pieces at 80 miles an hour on the freeway, and you can just replace the timing gear and chain set and be on your way.

100% false. I lost mine doing 70mph. It bent every single exhaust valve pushrod. I was very lucky that the valves seemed to have survived.

 

[ASPEC]

I'm probably late to the game here, but the Chevy 396/454 is not an interference engine. The nylon sprocket can blow itself to pieces at 80 miles an hour on the freeway, and you can just replace the timing gear and chain set and be on your way.

Even if that is the case you still end up with an oil pan full of chunks.

100% false. I lost mine doing 70mph. It bent every single exhaust valve pushrod. I was very lucky that the valves seemed to have survived.

My fear exactly.

 

[CorvairGeek]

Even if that is the case you still end up with an oil pan full of chunks.


My fear exactly.

and jammed in the oil pump pickup.

 

[bucket]

Even if that is the case you still end up with an oil pan full of chunks.


My fear exactly.

Yes, I forgot about that part. I changed the oil before driving it again and there was definitely a lot of chunky stuff that came out the drain hole.

and jammed in the oil pump pickup.

I ended up putting about another 10k on mine and no issues with oil pressure. I've got an engine swap planned soon, so I'll eventually get to pull the pan and see what still lurks.

 

[Turbo4whl]

and jammed in the oil pump pickup.

I bought a 1971 402 BB to put in my '82. The car it came out of had just over 100K. When tearing it down for overhaul, I dumped all the original timing gear teeth out of the oil pick up screen. So that running engine got a timing set sometime before that.

 

[Matt69olds]

I’m pretty sure all the classic GM engines are interference engines.

I know for a fact the Pontiac and Oldsmobile engines will bend every exhaust valve if enough nylon flakes off. And if you just replace the chain without cleaning out the oil pump pickup, you can almost certainly plan on serious engine noise soon after. You cram enough nylon in the pickup, it starves the engine of oil.

I have replaced lots of timing sets over the years, I have NEVER heard a difference in engine noise. I have always heard the nylon quiets chain noise, but I bet there is more to it than just noise.