Nylon Timing Gear & chain replacement

[Joe L.]

Re: Nylon Timing Gear & chain replacement

As I have said before those timing gears were crap. My brother & I both had new 1970 ones that failed a GTO & a Grand Prix . My brother in law was service manager for Packer Pontiac in Pontiac Mi. & said they were breaking all the time on new cars. I replace all of mine. I think it is the main reason so many Corvettes have CE blocks.

Kenneth------

Just so everyone understands this. ALL 1966-91 Corvette PRODUCTION small blocks used an aluminum camshaft sprocket with nylon teeth, a powder metal crankshaft sprocket, and a Morse-type chain. ALL, every one ever made. GM ceased selling the nylon tooth camshaft sprocket in SERVICE more than 40 years ago in favor of the cast iron sprocket. But PRODUCTION applications used the nylon tooth. If one finds a 1966-91 small block that doesn't have one, then that engine has a replaced sprocket.

ALL 1965-74 Corvette big blocks used an aluminum, nylon toothed camshaft sprocket, a powder metal crankshaft sprocket, and a Morse-type chain. This includes L-88, ZL-1 and LS-6. GM NEVER offered a cast iron camshaft sprocket or steel crankshaft sprocket for big blocks in OEM SERVICE. The only sprockets ever available were nylon camshaft and powder metal crankshaft. If one finds anything but the foregoing in a 1965-74 big block, then it's been replaced with non-GM parts. For the better, of course.

[King M.]

Re: Nylon Timing Gear & chain replacement

I fit everything and measured several times ( I prefer to do my own homework to verify) and surprisingly the clearance between the timing cover and the front of the new chain is nearly identical to the original. No problem with the timing cover. The extra width is oriented towards the block side which creates the narrow spot at 12 O'clock. That was too close for my liking even though it did not appear to actually touch. I felt it was better to grind it down a bit to allow some extra space for heat and wear expansion with a nice safety margin.

This is where I had block to chain interference with my cloyes true roller was at the 12 o'clock position on the block and had to clearance it a bit.

[Duke W.]

Re: Nylon Timing Gear & chain replacement

Duke------



After carefully examining it, I can absolutely confirm that the individual roller links on this chain definitely rotate. Absolutely no doubt about it, at all. Of course, the photos I am posting cannot show that.

That's what I expected, so as the chain moves around the sprockets, the relative motion is between the roller and the bushing that is held tightly to the chain links with the pin. The roller has enough radial an side clearace to easily rotate. That's how any roller chain operates, which is why I consider the "True roller" moniker to be marketing bunk.

Your analysis does show that the 9-3100 is made up from some stronger materials, which will aid durability in abusive applications such as drag racing with 5000 rev clutch drops and power shifting. But this is not typical of vintage Corvette operation, which is why I recommend the OE replacement truck roller chain at one-third the cost or less and putting the saved funds into durability and/or performance enhancing mods such as better conn. rods and head massaging.

Duke

[Kenneth B.]

Re: Nylon Timing Gear & chain replacement

Kenneth------

Just so everyone understands this. ALL 1966-91 Corvette PRODUCTION small blocks used an aluminum camshaft sprocket with nylon teeth, a powder metal crankshaft sprocket, and a Morse-type chain. ALL, every one ever made. GM ceased selling the nylon tooth camshaft sprocket in SERVICE more than 40 years ago in favor of the cast iron sprocket. But PRODUCTION applications used the nylon tooth. If one finds a 1966-91 small block that doesn't have one, then that engine has a replaced sprocket.

ALL 1965-74 Corvette big blocks used an aluminum, nylon toothed camshaft sprocket, a powder metal crankshaft sprocket, and a Morse-type chain. This includes L-88, ZL-1 and LS-6. GM NEVER offered a cast iron camshaft sprocket or steel crankshaft sprocket for big blocks in OEM SERVICE. The only sprockets ever available were nylon camshaft and powder metal crankshaft. If one finds anything but the foregoing in a 1965-74 big block, then it's been replaced with non-GM parts. For the better, of course.

Yes I understand that. Maybe 1970 ones had a issue. all I know is what happened to our 70 cars. The GTO put a piston through the side of the block. I got lucky & it striped when I started it up. The original nylon ones in my 70 LT-1 & 454 Are in the back of the Corvette & CI ones are installed. Why did GM not sell the nylon ones over the counter?

[Mark E.]

Re: Nylon Timing Gear & chain replacement

I love the Duke-Joe point, counter-point banter. Very entertaining- and educational too.

Some dumb questions after reading this:

- Is a Morse-type chain different than a roller chain? A Google search suggests Morse is a brand of chain.

- Was noise the only reason GM used nylon teeth? Maybe cost as well? Is it possible the engineers wanted a known weak point in the valve train in case of catastrophic failure, and they chose the timing gear?

- Should I worry about the timing set in my 1970 LS5? It was rebuilt by the PO in the late 1980s, and runs fine with 10k miles on it. Assuming the timing gear set was replaced, how likely is it a nylon gear set was used? Were any available as service replacements at that time? The engine was definitely built on a budget in anticipation of selling the car, so I suspect a low cost set was selected.

- Do nylon gears degrade with time as well as mileage? Maybe they get more brittle over time?

Thanks guys.

[Duke W.]

Re: Nylon Timing Gear & chain replacement

A Morse chain otherwise known as a silent chain was invented and probably patented by the Morse Chain Company decades ago, so the patents are long expired, but the name is still used, and I think the company is still around. A Web search should yield photos of each, which clearly show the design differences.

Like any other organic material, nylon tends to become brittle and weak with age, and the rate of degradation increases exponentially with temperature.

Do you seriously think engineers would intentionally design a weak part whose failure causes major consequential damage like the valves hitting the pistons? Whatever their reasons and reducing noise is a reasonable assumption, it was a poor choice because they failed to see the unintended consequences, which cost their customers a lot and took a toll on GM's reputation.

Roller chains, usually with steel crank sprockets and cast iron cam sprockets were used on truck engines where durability took presidence over noise.

Duke

[Joe L.]

Re: Nylon Timing Gear & chain replacement

Yes I understand that. Maybe 1970 ones had a issue. all I know is what happened to our 70 cars. The GTO put a piston through the side of the block. I got lucky & it striped when I started it up. The original nylon ones in my 70 LT-1 & 454 Are in the back of the Corvette & CI ones are installed. Why did GM not sell the nylon ones over the counter?

Kenneth-------


I have no information that there was a particular problem with the nylon-toothed cam sprockets during 1970. I think they were always somewhat of a problem. I can tell you that as evidenced by the "jumping around-timing mark" and "clattering" sound, my late 1969 350 had a nylon toothed cam sprocket that started to fail at no more than 10,000 miles. It never actually catastrophically failed but when I removed it at 100,000 miles about 1/3 of the teeth had already fallen off. How it kept running, I do not know.

So, why did GM not supply the nylon toothed sprockets over the counter? Well, first of all, in the case of small blocks they did supply them for awhile. The 1966-only wide version (also SERVICE for 1955-65) was sold until the the late 1980's. The narrow 1967+ MAY have been sold from 1967 to 1975. I'm not sure that it was but it MAY have been. However, if it was ever sold in SERVICE, it was discontinued in early 1975 and replaced by the cast iron sprocket. However as I previously mentioned, the nylon-toothed sprocket continued to be used in PRODUCTION right through at least 1991. So, why the nylon tooth in PRODUCTION and the cast iron for SERVICE for 40+ years? Well, here's my THEORY of why this was done: when selling a new car, quietness of engine operation might be a factor in someone making a decision to purchase (or NOT purchase) a vehicle. So, the auto manufacturers want to make the engine operate as quietly as possible. In their minds, the nylon-toothed aluminum cam sprocket, the Morse-type chain, and the powder metal crankshaft sprocket are all the best choices for maximizing quiet operation. They want to "squeeze out every last drop" of quiet operation. Quiet operation will NEVER lose a sale. In SERVICE, quiet operation is not so important. At that point, they've already sold the vehicle, it's probably got quite a few miles under its belt, and when someone sees the condition of the nylon-toothed sprocket, they won't want to use another one, anyway.

In fairness, though, GM did sell the nylon-toothed sprockets for big blocks. They used them in PRODUCTION and they sold them in SERVICE. In fact, they never sold anything else. They still have available the nylon-toothed sprocket for the narrow 1967-74 L-36, L-68, LS-5, and LS-4 applications.

[Joe L.]

Re: Nylon Timing Gear & chain replacement

I love the Duke-Joe point, counter-point banter. Very entertaining- and educational too.

Some dumb questions after reading this:

- Is a Morse-type chain different than a roller chain? A Google search suggests Morse is a brand of chain.

- Was noise the only reason GM used nylon teeth? Maybe cost as well? Is it possible the engineers wanted a known weak point in the valve train in case of catastrophic failure, and they chose the timing gear?

- Should I worry about the timing set in my 1970 LS5? It was rebuilt by the PO in the late 1980s, and runs fine with 10k miles on it. Assuming the timing gear set was replaced, how likely is it a nylon gear set was used? Were any available as service replacements at that time? The engine was definitely built on a budget in anticipation of selling the car, so I suspect a low cost set was selected.

- Do nylon gears degrade with time as well as mileage? Maybe they get more brittle over time?

Thanks guys.

Mark------

Duke has answered most of your questions.

As far as what was used in the rebuild of your engine, IF the timing set components were purchased from GM, the ONLY camshaft sprocket cataloged by GM and available from GM for your application now or ever is a nylon-toothed aluminum. So, if stock GM components were used, which is quite frankly very unlikely, that's what was used. Otherwise, you most likely have an aftermarket cast iron sprocket, either double roller or original Morse style.

By the way, the Morse-style chain is also referred to as an "early link" type chain.

[Pat H.]

Re: Nylon Timing Gear & chain replacement

Kurt,
I believe GM still sells the Truck Timing gears and chain. When I replaced my soft cam in my 77, that what the GM parts guys told me to use.

[Duke W.]

Re: Nylon Timing Gear & chain replacement

If GM sells them it's probably the OE-replacement manufactured by Cloyes, sold under their name and also the NAPA Timing Products brand... just like "Delco" ignition system parts are made by Standard Motor Products and dropped into "Delco" boxes.

Duke

[Joe L.]

Re: Nylon Timing Gear & chain replacement

That's what I expected, so as the chain moves around the sprockets, the relative motion is between the roller and the bushing that is held tightly to the chain links with the pin. The roller has enough radial an side clearace to easily rotate. That's how any roller chain operates, which is why I consider the "True roller" moniker to be marketing bunk.

Your analysis does show that the 9-3100 is made up from some stronger materials, which will aid durability in abusive applications such as drag racing with 5000 rev clutch drops and power shifting. But this is not typical of vintage Corvette operation, which is why I recommend the OE replacement truck roller chain at one-third the cost or less and putting the saved funds into durability and/or performance enhancing mods such as better conn. rods and head massaging.

Duke

Duke-------


With all due respect, I think you should get your facts straight before you say something like this.

I can't speak to the configuration of roller chains used on bicycles or motorcycles. I haven't touched a bicycle chain in about 50+ years and I wouldn't touch a motorcycle chain for love nor money. However, it's always been my understanding that the rollers on the truck-type double roller chains and those on the lower cost aftermarket double roller timing chains do not actually rotate. Of course, I really haven't had much personal experience with them since I've never actually used one.

So, I contacted Cloyes Technical Service about this issue. The Cloyes 3023X double roller timing set uses a chain in which the rollers do not rotate. I'm quite certain that the other brands like NAPA which you mentioned are exactly the same set in a different box and part number. I also feel quite sure now that my original understanding of all these lower cost double roller timing sets, including the GM truck double roller sets, also have rollers which do not rotate.

Cloyes advises that their 9-1100-series Street True Roller timing sets use a US manufactured roller chain with 0.250" rollers in which the rollers actually rotate. The Cloyes 9-3100 True Roller-series uses an ultra premium chain manufactured in Germany by Iwis with 0.250" rollers which actually rotate. (Note: apparently, the Iwis German-manufactured chain has replaced the British-manufactured Renold).

I continue to use and highly recommend the Cloyes 9-3100 for small blocks and the Cloyes 9-3110 for big blocks. Are the lower cost timing sets with rollers that do not rotate adequate? Absolutely YES, as I've said all along. They're not for me, though, and they're not what I recommend. To me, among other reasons, the extra cost of the 9-3100/9-3110 is like an insurance policy that you only pay once for. Plus, as I've also said before, they're tried-and-true having been around and widely popular for 45 years.

[Duke W.]

Re: Nylon Timing Gear & chain replacement

I've never heard of a roller chain where the rollers don't rotate - bicycle chain, motorcycle chain, engine timing chain, whatever. It think your guy at Cloyes is misinformed. Most "techincal service people" are just hired off the street and don't know much about the products they sell other than the script they get to answer questions.

Perhaps if the OP has not installed his timing cover he can check. If you have any GM or OE-replacement roller chains you can verify.

Wikipedia has a good write-up on roller chains - variations of the basic design principle and how they work.

https://en.wikipedia.org/wiki/Roller_chain

Duke

[Joe L.]

Re: Nylon Timing Gear & chain replacement

Kurt,
I believe GM still sells the Truck Timing gears and chain. When I replaced my soft cam in my 77, that what the GM parts guys told me to use.

Pat-------


It's no longer available. The timing set was last available under GM #12341093 but it was discontinued without supercession about 8 years ago. The components of the set, once available individually, are all discontinued, too.

[Mark E.]

Re: Nylon Timing Gear & chain replacement

Do you seriously think engineers would intentionally design a weak part whose failure causes major consequential damage like the valves hitting the pistons? Duke

Isn't it possible, even likely, that the valve train was designed with a designed failure path? It's a common engineering practice to design a "weak link" that predictably breaks first during system failure in a way that minimizes damage.

For example, what if the cam bearings fail, and the camshaft seizes? With an all steel timing set, isn't there a good chance the cam will grenade in the block causing a big mess? But what if the timing set was the designed failure path? The gear breaks instead of the cam.

I don't know if this is why the timing gear was designed with nylon. But it seems curious Chevrolet would under design a critical part of its engine just so it would run a bit quieter. Is it possible the engineers specified nylon teeth for another reason?

[Joe L.]

Re: Nylon Timing Gear & chain replacement

I've never heard of a roller chain where the rollers don't rotate - bicycle chain, motorcycle chain, engine timing chain, whatever. It think your guy at Cloyes is misinformed. Most "techincal service people" are just hired off the street and don't know much about the products they sell other than the script they get to answer questions.

Perhaps if the OP has not installed his timing cover he can check. If you have any GM or OE-replacement roller chains you can verify.

Wikipedia has a good write-up on roller chains - variations of the basic design principle and how they work.

https://en.wikipedia.org/wiki/Roller_chain

Duke

Duke------


I do not have an OEM GM double roller timing set and I do not have any aftermarket equivalents. I never acquired any mostly because they are parts I would never use. I could now acquire some but I think it would be a waste of time and money. I am quite confident that the information I received from Cloyes is accurate. One of the primary reasons is that it's completely consistent with what I've known for years.

Regardless of what Wikipedia might say, they are not referring to a particular chain. Attached is an except relative to timing sets which came out of "How To Hot Rod Small Block Chevrolets" by HP books. Incidentally, the part numbers they show for the Chevrolet Truck double roller timing set components are the correct part numbers of the now-discontinued parts. So, my long-time understanding of the rollers used in these double roller chains, the information I received from Cloyes, and what's written in the attached excerpt are all 100% in sync.


timingchainexcerpt 002.jpg