Nylon cam gear years

[legopnuematic]

My 79 (350 small block) had the original timing set blow up at some point, guessing late 80s as it was parked in 1993 and the heads had been redone and were very clean, and a new timing set installed.

The old chain was flopping around pretty good and wearing into the cover

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And found all this down in the pickup, parts of the gear, the garter spring for the front seal.

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[Turbo4whl]

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

The 402 I spoke of had 8 bent valves, memory is bad but I think they were the intake valves. You could not see it until they were in the valve resurfacing machine.

 

[Toad455]

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.

The nylon fell apart on my 69 Delta 88 with 455 engine and jumped time at 56K miles. It was the original gear set.

 

[AuroraGirl]

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.

Noise and harshness is lowered

Misfires, knock, neglected oil, and early early nylon formulation lead to failures, but so would other parts in the engine for the same issues (first three)

The nylon gear turned out to be a VERY bad idea for the buick v6 and they used it through the 3.8l LG3 in fwd cars.
Its not uncommon to grenade the engine because of interreference valve contact because of failure at 80k or sometimes less. Sadly a lot of those old 1980s fwd car owners were burned by this , up to now. I see a person every few months come in the buick forums with the problem.

Timing gear on the ford 300 i6 being nylon makes them much quieter , but that doesnt use a chain.

 

[AuroraGirl]

Modern oil and lessons of the past help things

 

[ASPEC]

Well, parts are on hand and I will tear it down this weekend. I will post picks of what I find in there.

 

[JBswth]

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

If you didn't ever run too low on oil, and got rid of the car when it got close to 100,000 miles, and didn't try to keep the car for more than 10 years, you probably would never have a problem, but if none of those limitations apply, the nylon would start breaking up in pieces. I had to replace the timing set on my 66 Ford Galaxie with a 352 for that reason. Every Buick Nailhead that I had used metal sprockets, and every Chevy 6 used timing gears, just like a Flathead Ford, most Ford 240s and 300s, most Pontiac "Iron Dukes", or a Studebaker V8.

J.B.

 

[JBswth]

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.

That's what I always heard as well.

 

[JBswth]

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?

No, but the difference is tiny on a new or rebuilt engine. Most people wouldn't be able to tell the difference, but it could give the manufacturer bragging rights for quietness, then, buyers would convince themselves that their car really is quieter than their friends's/relative's/neighbor's car.

J.B.