CrossedUp

I realize this is a long shot but, is there any way of telling whether or not a motor ('65 327, 250HP) has a nylon cam sprocket without removing the timing cover or having x-ray vision?

Thanks,
-Doug

Bluestripe67

X-Ray vision as far as I know. Dennis

GUSTO14

Doug, is there any reason you have to doubt that it has a nylon gear? Is there any evidence that the engine has been apart for a rebuild before? The use of the nylon gear was pretty much universal in the past, particularly so with lower horsepower engines. They were much quieter and generally lasted more than long enough if the engine was maintained.

If you drop the pan, you should be able to get a bore scope up there and see the cam gear. And actually because they used a different style chain, you should be able to tell just by viewing the chain it self. I can't offhand think of any other way to get into the timing cover to view the gear.

Once the gear starts to deteriorate...

it's not uncommon to find pieces of nylon in the pan. Check the oil carefully the next time you change it and if you find small pieces of nylon, you probably have your answer.

Good luck... GUSTO

CrossedUp

Thanks Gusto,

The car has 73k original miles and it appears that the engine's never been apart. I'm installing a new De Witts radiator in a couple weeks and, being that far into it, might as well go ahead and pull the timing cover.

GUSTO14

Hey be careful, soon we'll have you dropping a new cam in it, along with a set of heads and an intake... well you get the picture.

Actually for the price of a new timing chain and gear set and some gaskets, it certainly can't hurt.
Cloyes 9-1100 - Street True Roller Timing Chain Sets - less than $40
http://www.jegs.com/i/Cloyes/220/9-1...17#moreDetails

Good luck... GUSTO

MikeM

I think you are wasting your time and money unless you're having problems. Despite what you read, many of those nylon timing gears ran for a very long time without problems.

JMO.

Ironcross

If it was never taken apart, the nylon gear was used on every factory V 8 Chevy including the famed L`88

MikeM

The early V-8's used the iron gear. Not nylon. I don't remember exactly when the nylon gear came along. Maybe 1960 or so?

Ironcross

What I can say is my 62 was nylon and so was all the high or low performance BB`s

jim lockwood

I'd say someone changed that gear.

My FI '60 and my 300 HP '63 both came with steel gears. My (admittedly dim) memory is that nylon gears didn't come along until the '70s.... at least that's when I first became aware of them.

MikeM

From Joe Lu-Chee-Uh!


Joe Lucia (12484)

August 18th, 2004, 04:58 PM

Tony------

As far as PASSENGER CAR and LIGHTTRUCK (including Corvette) PRODUCTION engines go, all small block and big block originally used the "Morse" or "early link" type chain. This goes from 1955 through the end of the installation of Gen I small blocks in the above-referenced vehicles. Som MD and HD truck engines used a "double roller" type chain, although the rollers were not a "true" roller design.

The crankshaft sprockets for passenger car and light truck engines were mostly "sintered iron", although some may have been steel.

As far as the camshaft sprockets go, it's confusing. Prior to 1967 the PROUCTION camshaft sprockets MAY have been cast iron. The SERVICE camshaft sprockets for 1955-66 small blocks were definitely cast iron.

Beginning in 1967, if not earlier, the small block PRODUCTION sprockets were changed to aluminum with nylon teeth. Beginning with their introduction with the 1965 model year, the camshaft sprockets for big block passeneger car and light truck engines were mostly of the aluminum/nylon design, although some may have been cast iron. For big blocks, I believe that the nylon camshaft sprockets used for PRODUCTION engines were used right through the last installation of these engines in passenger cars in 1975.

For 67 and later small blocks, I believe that the aluminum/nylon gears were used for most, if not all, PRODUCTION engines for passenger cars and light trucks right through the end of their use a few years ago in PRODUCTION vehicles. This applies to Gen I small blocks only inasmuch as Gen II used a completely different design timing set. However, for SERVICE, the only gears catalogued by GM for 67+ small blocks were cast iron.

Why the difference between PRODUCTION and SERVICE? I believe that it's a function of "engine noise considerations". For a PRODUCTION engine, GM wants them to be as quiet as possible. That's what the vast majority of customers want and that's what may affect their inclination to purchase a particular vehicle. For SERVICE, this is not so important. For SERVICE, customers and mechanics want to see a "steel" gear (especially after they've removed the aluminum/nylon gear with missing teeth). So, for 67+ small block SERVICE, cast iron gears are catalogued and sold. The aluminum/nylon camshaft gear, sintered iron crankshaft gear, and Morse chain are all part of a "quiet-as-possible" engine design strategy.

For MD and HD trucks, where engine noise is not a significant issue and DURABILITY is, double roller type chains are used with cast iron camshaft gears and steel crankshaft sprockets. This is true for both big blocks and small blocks. The pieces can be used for performance applications, too. However, I prefer a Cloyes True Roller timing set to any GM pieces for either big block or small block.

Gen VI big blocks with hydraulic roller camshafts ALL use a single "roller" timing set. This includes a "powder metal" camshaft gear and a steel crankshaft sprocket. It is not possible to use a double roller timing set on a Gen VIbig block with PRODUCTION-type hydraulic roller camshaft.



FWIW, I have a 327/350 built in January of '66 that has the factory installed nylon gear still In it. I've had the engine since new so I know it hasn't been changed.

Pilot Dan

Well after reading this, I discovered there is another way to see the cam gear. While doing an intake manifold R&R, I discovered there are two holes in the front part of the engine large enough to get a good view of the gear top. It would be possible to rotate the engine and see the entire gear (with the intake removed) I found. Notice the gear through the left hole below. This engine (a 68 327) has the nylon gear and it looks perfect all the way around. It won't save you any time labor wise, but if you have another reason to have the intake off, you get a free look at what you've got.

427435

The stock cam gear in my L71 (whatever it was) wore out around 100,000 miles. Bent all the valves and dented all the pistons!!!

I never raced the car or abused it.

Pilot Dan

Wanted to update because this is worth taking a second look at. My cam gear looked fine as inspected, but I had what I considered an unacceptable amount of play in the timing chain (10*), so I tore it all down to replace the chain and gears. The cam gear broke while I was disassembling it and the chain had way too much play. Lesson learned here is the nylon/plastic does age and become brittle even though it appeared fine. I re fitted with a beefy Double roller Cloyes chain and that was the best money ever spent on avoiding a major problem down the road. Had a bit of a time getting the new chain on it was so tight, but it worked out great. If you have one of these gears, do yourself a favor and replace it. Even if the cam gear was metal, the chain stretch made the repair an upgrade IMO

MikeM

10* is a lot of play.

You can rotate the crankshaft back/forth with the engine in the car and "feel" how much slack you have in the timing chain/sprockets and read the amount on the balancer.

Kerrmudgeon

The steel gears are noticeably noisier than nylon, so put a engine stethoscope on the timing cover and you'll hear metallic noise if it's a metal gear. Find a stock chevy to compare if you can find one.

6T7L71CPE

This is the front main cap of a BBC I've got apart, a couple pistons were newer replacements and the exhaust valves had been replaced. Sure looks like it lost its nylon gear years ago.