Greetings. I have a 389 YE cast # 9778789 dated coded E246 so this tells me 1966. What years did Pontiac use the nylon chain gear? Any chance there may be one in there from factory, getting mixed info from searches some say 64 was last year for these. 

The Main reason OEM Timing gears are  covered in Nylon...Is for Gear/Chain Noise suppression...

The last Pontiac engine that I tore down was a 400 that was out of a 1978 Trans Am (was a stock type rebuild)....It still had the original factory nylon covered timing set...If I remember correctly (was a few years ago) the engine had jumped timing due to the Nylon coming off of the cam gear...and most of it wound up in the oil pan...That prompted the owner to just go ahead and rebuild the entire engine...

Edited March 14, 20233 yr by TWO LANE BLACK TOP

Thanks for that info. Yeah can be a mess if it’s deteriorating that’s for sure. Just got the car so I am trying to determine what I have to deal with. I read some info that the 389 used this type until end of 66 others state end of 64. 
still un sure. Is there a way to see what’s in there by taking the fuel pump off and having a close look maybe using a bore scope through the opening for the pump arm?

I don't wish to contradict my good friend Two Lane. He's been there and done that way more than I when it comes to engine tear down and rebuilds. I trust his judgement when it comes to these things.

That said the best information that I have says that Pontiac stopped using nylon timing sets after '71. That does not mean that there were not over the counter replacement nylon sets floating out there for a long time as NOS or replacement parts well after '71.

Ok that’s something to consider thanks. It’s probably best I plan for a pump and timing cover removal, a new set of gears is pretty cheap and a gasket kit as well. I am going to remove the fuel pump and have a look up there with a bore scope first and will post on what I see if anything cheers. 

On 3/12/2023 at 5:55 PM, BONNZO said:

Greetings. I have a 389 YE cast # 9778789 dated coded E246 so this tells me 1966. What years did Pontiac use the nylon chain gear? Any chance there may be one in there from factory, getting mixed info from searches some say 64 was last year for these. 

What do you have the engine in?  We like pic's.

If it was mine, I’d JustA put in a Cloyes timing set! Noise coming from the timing gear/chain would be the last thing I would hear over the rumbling exhaust!  
JustA kidding!

A chain set, particularly a double roller (twin chain) set, is cheap long term insurance.

Here in Australia, Holden followed GM's lead and also used nylon timing gears in it's 6 cylinder engines. They were notorious for failing at any time, as I found out one day about 200 miles from home - a tooth would break off and engine would stop. But then, they also thought that a nylon distributor drive gear would be a good idea. Honestly, what were they thinking? Steel replacements for both were sold for decades. The guys are right - tear it down and replace the timing gear no matter what. Cheap insurance.

Thanks for the input folks. I am gonna wait for Jack Frost to take a hike and then get busy. No heat in my shop right now. Pic for justa6. 65 Bonny. 

Well, the pic may be for Justa, but you can't stop the rest of us from enjoying it to!  Awesome Bonneville bro. 

That's hot enough to melt the snow in your driveway!  Thankz for sharing your pic.  Keep us up on what your doing with your ride and chat it up in the forum.

Ha ok glad u like, couple more pics in my intro post as well cheers. 

Nice...Got to love the full sized Pontiacs... I'm with the fellow Pontiac guys...Changing the Timing set is Sound advise..Personally I like the nice pleasing Whine of an Intentionally Noisy timing set..

Edited March 16, 20233 yr by TWO LANE BLACK TOP

I had a 1968 GTO RamAir lll auto.  While turning something over 5,000 RPM in second gear, smoke billowed from the hood scoops, I turned the key off, and coasted to the side of the road.  Not good.  I called my brother in law and he hauled the car by rope and F150 the 20 miles back to the house.  The compression test showed NADA.  I yanked the heads and found nearly all the valves were bent.  Luckily none of the pistons were broke, but a couple took some pretty good licks.  I was shocked to find the cam sprocket was made from aluminum and nylon; with most of the the nylon teeth missing.   Whose bright idea was that?   I flushed the oil system as best I could, installed an all metal timing set, and  the reworked heads.  She started right up and ran for a few thousand miles until I got the bright idea to convert my 400 to a RAM AIR lV.  By the time I got done I could have purchased a Baldwin Motion Performance 427 to drop in the GTO.  Now that would have been something to behold.

Edited December 7, 20241 yr by Deadeye

Don't recall if GM put nylon gears in, but do recall always going to all metal when working on my cars. Justa seemed like a no brainer.

Pontiac was not the only automaker to use nylon time chain/gear sets. Ford did as well. It was sometime during the 1971 model year that Pontiac stopped using the nylon timing sets and switched to metal ones.