timing chain replacement selection advice / what if got after opening it up

[idahovette]

Some of us don't have the luxury to wait around........we are on "borrowed" time as it is!!!!..........lol............uh what, wait

 

[SirRobyn0]

Thanks everyone for the advice on timing chain selection. I'm in the middle of the job and will post progress as I go in my build thread

here >> https://www.gmsquarebody.com/threads/1984-c-20-driver-thread.35123/ << Pretty much starting on post 55. Thanks again.

 

[85 Squarebody76]

How long did they use the nylon upper gears on small blocks?
I know my '72 Chevelle had one.
Then as I was cresting a hill on the freeway, the teeth finally let go and the chain rolled over all of them.

A new double roller went in there.
It still ran after that, but it was never right as I did have to replace a bent pushrod.

I wonder if you might have a nylon upper gear in there....

I know when I was working on them back then they most always had a aluminum nylon coated upper gear. GM did that to help quiet down the gear noise.. at least that what the factory rep told me. I always replaced them with an all steel upper gear when I did the work

 

[Octane]

I had old cars with that nylon gear that lasted 95k to about 140k,it was just a guess when failure would occur. Snatching a car around and hotdogging them, always made them wear more. I ripped out a few.... I've had the engine running at roadspeed and also at idle speed at a stop light, they just would let go and leave me sitting there.I used a breaker bar on crank bolt to judge the timing chain freeplay. One van I had with a 305,the chain was stretched to the point of falling off.

 

[SirRobyn0]

I know when I was working on them back then they most always had a aluminum nylon coated upper gear. GM did that to help quiet down the gear noise.. at least that what the factory rep told me. I always replaced them with an all steel upper gear when I did the work

Ya, some guys were speculating that I might find one in my engine, I really wasn't sure not knowing the mileage and really not knowing when they stopped with the nylon upper gear. Of course the replacement I'm installing is all metal.

 

[Ricko1966]

How long did they use the nylon upper gears on small blocks?
I know my '72 Chevelle had one.
Then as I was cresting a hill on the freeway, the teeth finally let go and the chain rolled over all of them.

A new double roller went in there.
It still ran after that, but it was never right as I did have to replace a bent pushrod.

I wonder if you might have a nylon upper gear in there....

The reason I hit like is I also had a nylon gear on a 72 chevelle 307 let go.I also bent pushrods,but I pulled the heads and had the valve jobbed. Before I put it back together,because I knew what bent the pushrods.

 

[SirRobyn0]

I should probably wrap up this thread.

So I replaced the timing chain while I had the transmission out getting rebuilt. I found that someone in the past had installed a double roller chain. It has some slack but wasn't terrible. I went ahead and installed the standard wide chain, for my peace of mind, plus that chain will probably out last the life of this engine.

However replacing the chain did not solve the timing anomaly, so I'll be putting a distributor shortly.