1977 425 timming chain

[Koa]

Hi Caddy doctors, I feel I will have to change my timing chain. The reason, what makes me feel so: engine is noisy, not enough power, not possible to adjust the timing point. It just goes up and down on the scale while adjusting. Please consider these items - is it really time for the new timing chain?

And if so, please give me some advise, how to procede, where are maybe some critical points to take care  during the procedure.
I just like to do some favour for my beauty before next season       

[The Tassie Devil(le)]

G'day Karol,

The first thing you need to do is to do a simple test to see if the Timing Chain is stretched, or the Nylon Teeth coverings have gone from the Cam Gear.

With the Distributor cap removed, note where the Rotor is, and place a chalk mark on the Harmonic Balancer at the Timing Pointer.   Then wind the engine backwards and see how many degrees the Crankshaft turns before the Rotor begins to turn the other way.

If there is a large movement of the Crank, before the Rotor turns, around a couple of degrees, then you can be pretty certain that the Timing gear and chain require replacement.

Remember that if there is no nylon pieces on the Cam Gear, the Sump will have to come off to enable cleaning out, plus, the Oil Pump Pickup screes will probably be full of bits, so will need removing and cleaning out.

If you are going to do the task yourself, you need a Shop Manual to guide you through it.

Bruce.

[Koa]

Hi Bruce, thanx for Your reply.

.... how many degrees of crankshaft would be still acceptable?

[The Tassie Devil(le)]

Not sure, as I have never done this with a new engine, but after allowing for the take-up of play at the Distributer Drive (Cam) and Driven gear, plus the gap in the Crank Gear to Timing Chain and Cam Gear, it shouldn't be much.   

With a worn-out Cam Gear and stretched Timing Chain, there would be a very noticeable gap before the Rotor began to move.

Another method is to remove the Distributor and carefully view down the hole to see if you can see the condition of the teeth.

Here are pictures of a badly worn gear, but the engine still ran beautifully.

The difference between the good, unbroken one and the stripped one is huge.

Bruce.

[Koa]

Veeeerrrrrrry surprising pictures.
What is actually the purpose of the Nylon here?

[bcroe]

Veeeerrrrrrry surprising pictures.
What is actually the purpose of the Nylon here?

The mfr will tell you it is quieter.  I have never
been able to hear an all metal set, likely the real
purposes are to use a cheap molding process instead
of an expensive machining process, and to assure you
will need to buy a new car eventually.  Bruce Roe

[Koa]

purposes are to use a cheap molding process instead
of an expensive machining process, and to assure you
will need to buy a new car eventually.  Bruce Roe

------- I would believe this in case of any other car, but HERE ??

[bcroe]

------- I would believe this in case of any other car, but HERE ?? 

Do not be deceived.  The parts in a 70s Cad are very
much the same interchangeable parts used on lessor
brands.  Just that some things optional are standard
on the Cad (12 inch rotors, etc) and there are a lot
more gimmicks (not related to propeling the car)
like auto leveling, AM/FM/CB radio, trunk pull down,
illuminated lock, on and on. 
Bruce (has taken apart and assembled a lot of stuff) Roe

[J. Skelly]

------- I would believe this in case of any other car, but HERE ??
[/quote]
Just like the cheap plastic hinge assemblies used on the '67-'70 Eldorado front seat center armrest.

[Koa]

Well, I can believe, the plastic teeth can reduce the noice. But our parts suplyer (Rockauto) offers only the "only steel" option.
Is there a chance to get the "plastic version" also?

[TJ Hopland]

As far as I know the aftermarket never made a plastic option.  I would imagine back in the day if you went to the dealer you could have bought a plastic one. 

The options you get now is a link belt chain or a roller chain.  Link belt is the original style made up of many small thin plates.  Roller chain is like a bicycle.  For a stockish build and the way most of these engines and cars get used either will be fine.   I have not paying attention lately but back when I was Cloyes was still a good brand.  Many others had issues with the crank sprocket shattering hopefully when you installed it vs when the engine was running.       

[35-709]

Certain you won't notice any noise difference between the plastic coated gears and the steel gears available today. I wouldn't want to put back a known problem/weakness in any case.

[Koa]

1.Does anyone know, what years had this plastic gears?

2.Is it still possible to get an engine with the original plastic gear? Is something like this still to find or is nowadays the aftermrket version everywhere? I mean a car with really low mileage, is there still a chance, that the plastic gear will still be OK?

[bcroe]

If you find a NOS plastic tooth sprocket, it will
about as old as the one you have now.  Since years
can kill them, it would still be a time bomb to
destroy your engine at an unpredictable time. 
Bruce Roe

[Chopper1942]

Don't waste your time installing a plastic gear set.  Back in the day, we only installed steel gears, usually with a link chain because it was cheaper. Chevy used roller sets in the MD truck engines, so we would install the OE sets.  Also, on some sets the timing in the gear is changed for emission reasons.  If you get a good Cloyes set with steel gears, like for a performance engine, the timing won't be modified and the crank gear won't crack when you install it.  The crank gear on the OE plastic sets and the cheap aftermarket set crack is because they are sintered powder metal.  When I had to use them for warranty repairs I would boil a can of H2O and submerge the crank gear in it and quickly drive it on with a piece of pipe that would go over the crankshaft.  If you search, there is a lengthy discussion about installing a timing gear set and tip on fixing the cover to prevent thread stripping.

Here is the link:  1970 472 timing chain

[Bob Hoffmann CLC#96]

Hi,
 I have a NOS plastic gear set. Please contact me directly at bobscads@comcast.net.
 Do NOT send me a  PM.
 Thanks, Bob

[Eric DeVirgilis CLC# 8621]

I was told the timing gear with the coated teeth was more expensive to manufacture and was done to reduce noise. Detachment of the coatings resulting in catastrophic failure seems to be relatively rare in the 425. I'm sure there are far worse things in modern cars.     

[Chopper1942]

I've worked on various engines and it was a given that if was equipped with an aluminum cam gear with nylon/plastic coated teeth, it would fail.  If you are lucky, the pieces don't plug the oil pump pickup and take out the rods or main bearings.  You need to remove the oil pan and clean out all the pieces. 

I can only recall a couple of timing failures with steel gears.  The link or roller chain will stretch and if bad enough, can jump time.  Plastic gear failure guarantees jumped timing and if it is an interference engine, you will have bent valves and possible piston damage.

Don't waste your time and money installing a plastic cam gear.