Nylon timing gears

[Walter F.]

I have heard that some 350 Corvette engines use nylon timing gears instead of steel. Any truth to that ?

[Joe L.]

Re: Nylon timing gears

I have heard that some 350 Corvette engines use nylon timing gears instead of steel. Any truth to that ?

Walter-------

ALL 1966-91 Corvette small blocks and all 1965-74 Corvette big blocks used a nylon-toothed, aluminum camshaft sprocket. The crankshaft sprocket was powder metal.

[Walter F.]

Re: Nylon timing gears

I have also been told you should drop the oil pan because nylon gears can clog the oil sump pump. Have you ever heard of that happening?

[Jim D.]

Re: Nylon timing gears

To add to what Joe stated - If yours has one, get rid of it ASAP. They are prone to failure. My L-72 had one. Double roller is the way to go.

[Michael W.]

Re: Nylon timing gears

I have also been told you should drop the oil pan because nylon gears can clog the oil sump pump. Have you ever heard of that happening?

Yes, very common.

[Jim D.]

Re: Nylon timing gears

I have also been told you should drop the oil pan because nylon gears can clog the oil sump pump. Have you ever heard of that happening?

I seriously doubt that but what would actually happen is that the nylon would break off and the timing chain would jump. Seen it a few times.

[Patrick H.]

Re: Nylon timing gears

I have also been told you should drop the oil pan because nylon gears can clog the oil sump pump. Have you ever heard of that happening?

Yes. I have photos of it at home, but a year ago I swapped the timing chain on a 72 which was, over the course of the preceding year, showing decreasing oil pressure. The pump intake was packed with nylon pieces, and most of the teeth on the timing gears were missing their coating.

If your engine runs well, timing is stable, and oil pressure is good, I would not personally change the gears "just because."

[Michael W.]

Re: Nylon timing gears

I seriously doubt that but what would actually happen is that the nylon would break off and the timing chain would jump. Seen it a few times.

Where do you think the teeth end up?

[Kenneth B.]

Re: Nylon timing gears

Yes they are. My brothers 70 GTO timing gear let go at 80 MPH. Put a rod through the side of the block. This is a lot of the reason many low mile Corvettes have a CE block.

[Joe L.]

Re: Nylon timing gears

All-------


I should have mentioned that while all PRODUCTION 1966-91 small block camshaft sprockets were nylon-toothed, GM discontinued for SERVICE the 1966-only nylon sprocket 20 years ago. The 1967-91 small block nylon sprocket was discontinued from SERVICE in February, 1975 and replaced by cast iron sprocket GM #340235. Just to be clear, while the nylon sprocket was discontinued from SERVICE at this time, it continued to be used in PRODUCTION right through 1991 for Corvettes.

Corvette big blocks always used nylon camshaft sprockets in PRODUCTION and those were the only type sprockets ever cataloged by GM in SERVICE, right to this very day. However, only the 1967-74 except L-88/ZL-1/LS-6) sprocket ("narrow") remains available from GM. The 1965-66 and L-88/ZL-1/LS-6 nylon sprocket ("wide") was discontinued without supersession many years ago.

[Domenic T.]

Re: Nylon timing gears

I worked in a Chevy dealership as a mechanic in early 1971 and those nylon sprockets were failing big time. The life span was about 70 to 80 thousand miles. When we tried to get the all metal ones they were in demand and parts guys would try and sell you the nylon one, telling us they were made with nylon tips to reduce engine noise! True but the noise comfort ended up in a big bang when the chain slipped across the missing nylon tips and the open valves met with the rising pistons.
You could remove the distributor cap at about 60K and twist the rotor back & forth and listen to the chain slap. Some were lucky and the chain ate thru the timing cover before the big bang.

Dom

[Patrick H.]

Re: Nylon timing gears

Found the photos.

Note how the timing gear has almost no nylon still in place.
The pieces you see I removed from the oil pump intake just to see how much was there.

I told the owner about 2y prior that his timing chain was hitting the inside of the cover - you could hear it.
The next year I told him that it took a long time to get oil pressure when I first started the engine after storage, and he told me through the summer that it didn't happen again.
Last spring there was hardly any pressure, so I told him it was time to take a look.

After the new chain, he told me it runs better than it has in years. I'm sure that's true, even from the limited amount I drive it.

Patrick

[Joe L.]

Re: Nylon timing gears

Found the photos.

Note how the timing gear has almost no nylon still in place.
The pieces you see I removed from the oil pump intake just to see how much was there.

I told the owner about 2y prior that his timing chain was hitting the inside of the cover - you could hear it.
The next year I told him that it took a long time to get oil pressure when I first started the engine after storage, and he told me through the summer that it didn't happen again.
Last spring there was hardly any pressure, so I told him it was time to take a look.

After the new chain, he told me it runs better than it has in years. I'm sure that's true, even from the limited amount I drive it.

Patrick

Patrick------


Do you still have this sprocket? If so, is it embossed "3896960" on the other side?

[Kenneth B.]

Re: Nylon timing gears

My brothers GTO was only 3 months old in 1970 when it let loose. Brother in law was service manager for Packer Pontiac in Detroit in the day and changed out my 70 Pontiac
to a metal one under warranty. My 70 LT-1 had one in it & I changed it. Still have the nylon one I took out.

[Patrick H.]

Re: Nylon timing gears

Patrick------


Do you still have this sprocket? If so, is it embossed "3896960" on the other side?

No, I'm quite sure it's gone, but having moved twice in the last 6 months I can't tell you where anything is.
I should have harvested the pressure relief spring from the oil pump, though.

Patrick