Where is it written

[spstan]

where is it written that one has to replace a timing chain at between 80,000 and 120,000 miles? Finally got my 1975 NY'er running smooth (MSD distributor makes the car run like it is fuel injected - naturally this happens with only 2 months to go before winter).

Any way the car has around 78,000 miles and with smooth running accomplished the next thing I'm thinking is replacing timing chain. So I'm thinking if I drive gentle and change the oil every 2500 miles will this help preserve the timing chain? I mean is it written in stone that the timing chain will fail? Does any one have a story of a high mileage NY'er with the original timing chain? Paul

 

[Toolmanmike]

A timing set will fail sooner or later. Frequent oil changes may prolong the life of the set but it won't help the inevitable. The original timing set has nylon teeth on the cam gear to cut down on noise. As the gear wears, the chain will wear and stretch. If you have a round 80,000 rounds on you engine it would be a good idea to change the set. install a quality double roller set and it will be the last time you will have to do that job. Done right - done once. You may find this:

 

[Darter6]

The silent chains with the fiber cam gear are known to wear and teeth break off.
So is it written in stone,no but most of us are maintenance anal and it will keep us up at night thinking about it.

 

[3C's & a D?]

It's not written in stone, more like nylon. Glad to hear your new distributor is working well. It may work a bit better with a new chain and gears. Gears wear with use and there's a good chance you're missing a few nylon teeth. Both of these will allow for slack.

Personal story - 1971 Newport 383-2, 727, 2:76. 113,000 miles, engine never apart. After about 5-6 hours at 70-90 MPH I brought it up to 110 but it wouldn't go higher as it had in the past. Stupid me, kept pushing it, then BANG! Skipped a tooth and had to drag it home. Given that it took sustained high RPMs to make it fail, I would think that if you were to drive gently, as you say, you should be good. Sometimes the broken off teeth will clog the oil pickup, you know it's time then.

 

[spstan]

It's not written in stone, more like nylon. Glad to hear your new distributor is working well. It may work a bit better with a new chain and gears. Gears wear with use and there's a good chance you're missing a few nylon teeth. Both of these will allow for slack.

Personal story - 1971 Newport 383-2, 727, 2:76. 113,000 miles, engine never apart. After about 5-6 hours at 70-90 MPH I brought it up to 110 but it wouldn't go higher as it had in the past. Stupid me, kept pushing it, then BANG! Skipped a tooth and had to drag it home. Given that it took sustained high RPMs to make it fail, I would think that if you were to drive gently, as you say, you should be good. Sometimes the broken off teeth will clog the oil pickup, you know it's time then.

Yeah 3c I think the car has been above 110mph once in its lifetime (if cars live). Thing is I read somewhere that you can take off the fuel pump and feel inside to see if the chain is loose ( thus avoiding taking off the timing chain cover or taking off the distributor cap and turning the crank). Is this true? Which is the easiest path to take? Paul

 

[3C's & a D?]

Yeah 3c I think the car has been above 110mph once in its lifetime (if cars live). Thing is I read somewhere that you can take off the fuel pump and feel inside to see if the chain is loose ( thus avoiding taking off the timing chain cover or taking off the distributor cap and turning the crank). Is this true? Which is the easiest path to take? Paul

I'm not sure you can access it from the fuel pump port, possibly from the distributor. I've always checked for play by twisting the distributor. Perhaps someone has a better method?

 

[Toolmanmike]

Put a socket on the crank bolt and turn the engine over back and forth until the distributor rotor moved. With a sloppy chain and gears it will take a lot of movement to move the rotor.

 

[CBODY67]

It might not be "written in stone", but anecdotal evidence from times past indicates that 80K is a good, general figure to work with. For some brands, 80K is nearing the max mileage, by observation. Usually, the nylon will crack with age, rather fissure, than progress from there like a tire that is old and getting ready to separate. Then, one day, something happens and you THEN wish you'd done it sooner.

As painful at it might be (cost and time) to do a timing chain replacement, it CAN be less expensive than a wrecker bill (which always seem to be going up). So, consider replacing the OEM chain with a quality roller chain as "Cheap Insurance" for a long life for your engine . . . period.

When you do the replacement, be sure to douse the new parts in assembly lube, front and back, after installing them. They only get "splash" oiling.

110mph in that Newport was not even 4000rpm, so not quite so "high rpms" as suspected. More like "just loafing along" . . . just past the torque curve peak a bit.

Enjoy!
CBODY67

 

[CBODY67]

Thing is I read somewhere that you can take off the fuel pump and feel inside to see if the chain is loose ( thus avoiding taking off the timing chain cover or taking off the distributor cap and turning the crank).

Just like a prostate exam, the "feeler" has to know what is being felt. AND how "out of whack" it might be.

 

[413]

You have been on this timing chain kick for 5 months Now.

please answer these questions for us:

1) what were all of the problems you have fixed since then?
2) how many miles have you driven?
3) is the same timing chain and gears in the engine?
4) did the chain cause any of your problems?

 

[spstan]

413: questions in order 1) Ebay vendor sent me rebuild kit with wrong seats for Holley 4175. had gas dripping from EVAP cannister and gushing out of rear bowl vent tube. Suspected high fuel pressure but eventually replaced seats with correct ones from Mike's Carb. No leaks, no flooding, no gas smell - saved an $800 carb I was about to trash.

2) due to carb problems had to take car off road for about a month. I only drive the car about 1500 miles every summer and I baby it. No jack rabbit starts , no 90 mph - maybe it hits 2500 rpm tops (don't know - don't have tach)

3) engine has original timing chain and gears

4) I don't think so. Car runs very smooth now. Almost like fuel injection.

Do you get a warning (heads up ) before the chain fails or is it just like massive heart attack - Bam and you're done? Paul

 

[CBODY67]

Not always "BAM and done", can be a sudden extended crank time when starting and a few backfires, sometimes. Different from the hot heat soak re-start in that the cranking speed does not change, tries to start, backfires, cycle repeat. In one case on a running engine, as I saw one time in about 1976, you can advance the distributor one spark plug wire notch and the running engine suddenly ran better. So, "one tooth off", jumped, was the diagnosis.

Glad you got the other issues taken care of. Now you can plan for a minor weekend project.

CBODY67

 

[3C's & a D?]

So, consider replacing the OEM chain with a quality roller chain as "Cheap Insurance" for a long life for your engine . . . period.

This is the best way to look at it. Another term that comes to mind is "preventative maintenance". You have an 800 dollar carburetor, what's a good timing set go for, 150$? Cheap insurance.

 

[Just Carbs]

If the car has been run with 10,000-mile oil changes most of its life, it needs a new chain.
If it's the original nylon tooth 1970s chain, it needs a new chain regardless of oil schedule.

 

[Big_John]

3) engine has original timing chain and gears

How do you know this?

Here's my thoughts.. The nylon gear teeth do tend to self destruct with mileage and AGE. The cam gear is a cast aluminum piece with nylon teeth that gets brittle as time goes on and falls apart. It's at 48 years and counting. The chain wears and stretches with mileage but it's not the failure point.

IMHO, you should change the timing chain and gears. Those pieces sometimes gather in the oil pickup and shut off flow to the oil pump, even though the chain hasn't jumped. Not a good scenario either way.

But will it happen? Who knows? I don't have a crystal ball... What happens if it does? Depends... Possibly you jump a tooth... With the low compression engine, there's a good chance you won't bend any valves, but worst case is you bend a bunch of valves and have to take care of that. When it happens is anyone's guess. It could (and often does) happen when you're starting the car for example.

So. it's up to you... If you know the consequences, and you are willing to take a chance, then leave it. I'm sure there's a lot of guys running around with old chains. Just understand it is something that can fail and may cost you more to fix the collateral damage than change it before it goes. It might strand you somewhere too.

Your car, your money, your call.

 

[57fury440]

If the nylon teeth on the sprocket let go at highway speeds you can do some damage to the engine.

 

[413]

Engine damage is very rare, especially with 75K miles. And especially since you drive it normally.

the chain tends to get looser as mileage goes up. This retards the cam timing so power goes down and it can make it heat up easier.

if your car is running smooth like EFI right now then the chain is in good/decent shape.

 

[Triple Pickle]

Timing chain failure cometh as a thief in the night. Believe that.

 

[Toolmanmike]

Timing chain failure cometh as a thief in the night. Believe that.

I lost a timing chain in my RoadRunner just idling. It just quit and wouldn't restart. As soon as I hit the key I knew what it was. Sounded like I was doing a compression test with all the plugs out. LOL It had around 80,000 miles of hard use.

 

[volaredon]

I had to replace the water pump (yeah I know this is a 318 but aged nylon doesn't care) on my car around 46k, as the bearings went out and screeched like a scalded cat-again due age not miles-
In a SB there's like 4 more bolts to do the chain once water pump is off. So I did. And even at that low of miles that chain was sloppy as hell. One backfire plus slop in chain running on 40 yr old nylon teeth and it wouldn't have been good.
I still have the car, now with 56k miles.

As for which chain to buy I like the Edelbrock
I think they call it their "tru roller" line.