Just some proof of how bad a nylon timing gear can end.
Caught this one just in time!

 

cool , how many miles?

 

Yup, nylon gears can mess stuff up in a hurry. Pontiac also loved using them for a while. I find chunks of nylon in the bottom of the pan pretty often when rebuilding one.

 

It held together for a Loooong time, right ? ... probably far longer than its designers ever dreamed. But, no matter; entropy always wins.

yup, its bits are in the pan & pickup; along w/ bits of the OE intermediate distributor-oil pump drive shaft's collar.

* Dusky
cannot view Most of pics in your hotrodders build thread ... tinypics are gone.

 

Start to worry after 80,000 miles. The test is to remove the distributor cap and see how far the rotor turns in either direction. The more it turns the looser the chain.
There were buba tricks used at the dealer that let you take the front cover off and leave the pan on. Some engines needed to be lifted to remove the pan and the trick actually worked.

Dom

 

Rotor 'slop' is due to end play in the distributor and dist drive gear and cam gear play. Are you thinking that you can actually turn the cam with the dist rotor??? I don't think the valve springs will let that happen.

 

Yes, you can turn the cam... I have done it many times as a mechanic at a dealership. Not a easy turn, but worked for all of us. Wont work if the chain is stuck on the gear, just before it jumps. Most, when jumped just changed the idle to ZIP or real high. Neglected then it happens. Valves and pistons MATE.

Dom

 

Well, not quite. The oil pump locks the dizzy. Be tough to turn the rotor.
What you are referring to is removing the dizzy cap, rotate the crankshaft clockwise while watching the rotor. Then rotate the crank CCW while watching the rotor looking for excessive delay & play.
I knew what you meant.

 

Yes, that will work, but this is not just a idea I had, you CAN grab the diistributor cap and rotate the cam. The crank will stay stationary and the oil pump is there just for the ride! the rotation( by hand) of the rotor will turn the cam in either direction. A good gear will not allow it to turn where a worn with all the plastic gone will allow the distributor to turn the cam either way and denote slop in the gear. Was something done at tune up by mechanics that wanted to sell timing gears. And yes we removed the timing cover , did a mod, and HAD to use the same rubber gasket with silicone. Had to loosen pan gasket screws half way back and wedge front of pan down to remove timing cover. EASY with 2 1/4" phillips screw drivers forcing cover down enough to remove it. Then, you clipped the edges of the cover so you could replace the cover. Was standard practice at the Chevy dealer on cars that needed engine lifted to remove pan.
Why can you turn the cam with the distributor? Well because not all the springs are against the turn. Some are actually helping the cam turn as the spring is going down the cam ramp almost a even action as the springs worked together, one pushing and the other pulling.
Then you sprayed the area and sealed it with silicone and that was it. Yes, you wiped the squeezed silicone off.

Dom

 

I would have to call you out on that. That seems far-fetched.
At least 4 if not 8 valve springs will fight the cam from turning. Yes, some lifters will be on the downward push, but even then . . . . . .
And each valvespring, pushrod and lifter has around 300 lbs of pressure on the cam lobe.

I would be willing to bet a chilidog, fries and a root beer float, that with the timing chain completely off of the cam gear, that you still can not budge that cam sprocket with all the valvetrain still connected by turning the plastic rotor.
Maybe with a ratchet / socket / breaker bar on the cam sprocket bolt, but not with the rotor.
As said earlier, the oil pump will fight you too. It takes a hefty electric drill to prime an oil pump.

I think what you are experiencing by turning a plastic distributor rotor is not actually the cam moving, but rather the advance timing plate. It moves quite a bit.

 

Heads , Drop it!! I thank you for telling me I did the impossible. You can call me a liar. But you can't take my experiance of what I did and can do. Old mech VS new. WONT join that. I know what I did and you can't take that away. I treat it as a complement that I was able to do what you say can't be done. Stay friends and drop it.

Dom

 

hmmm.... I'm gonna go look up my part number and see what I have..... dammit.
UPDATE: Looks like I'm ok non-plastic/nylon/garbage..

14088784

Crankshaft Sprocket

• Single-roller-type for ZZ-design 350 HO engine

12552129

Camshaft Sprocket

• Single-roller-type for ZZ-design 350 HO engine

 

I used a Cloyes double roller gear and sprocket back then and now and they seem to do the trick.

Dom

 

If anyone thinks they have one of these pieces of crap in their engine, it needs to be replaced before bad stuff happens. I did the turn the crank by hand thing and the distributor had a long pause before it started moving. I rebuilt the engine and sure enough I found all the little plastic pieces in the pan and oil pump suction and a ton of slop in the timing chain due to the missing plastic. Replaced it with a Cloyes all metal gear and chain set and won't need to worry about that anymore.

 

Actually, the nylon coated cam sprocket looked like a good idea on paper. Looked even better on the drawing board.
The nylon removed half of the metal-on-metal wear from the chain. The nylon reduced vibrations & harmonics. And the nylon softened valvetrain noise somewhat.
What the engineers did not know back then was, the nylon would still be around four decades later. Either intact, or at the bottom of the pan.

Us older posters remember, when a vehicle was nearing 90,000 miles, it had one foot in the boneyard.

 

Even if you could (even though you can't) rotate the cam with the distributor cap, how could you clearly tell how much the rotor is moving the cam vs the advance mechanism and distributor slop allowing the rotor to move without moving the cam?

 

Now a days the engineers just make the chain tensioners out of nylon, so we can all suffer the same BS in the future.

 

What year C3s came with nylon timing chain gears?

 

Pretty much every GM product from mid 60's through the 70's

 

SORRY, but try it!! I did it a hundred times! AND you can turn the cam gear by HAND.....
You never tried to rotor by hand!!.
I made a living supporting my 4 kids doing this.

Dom