Worn Timing Chain

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nm9stheham

nm9stheham

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For those of you with older /6's, here is an example what happens to the timing chain as it wears. The first pix is of the old one and you can see all the slack hanging below. The 2nd pix is of the new replacement chain set and the slack is minimal.

The chain slack/wear can be judge by turning the crank pulley back and forth by hand and seeing how far it moves against the timing tab with just modest effort. (The crank will turn but the cam will not if you don't turn too hard.) This old chain allowed the crank to loosely turn 6 degrees. The new chain allows it to turn only 1 degree. That eliminates 5 crank degrees of slack.

This difference in old versus new chain slack is a measure of how many crank degrees by which the cam is retarded with the old chain versus how it came originally from the factory. 4-5 degrees is a significant change in engine operation. Test drives after this chain replacement showed very notable improvements in:
- Idle stability.. no more 'hunting' in the idle speed
- 'Off the line' torque and perkiness (typical with advancing cam timing)
- Smaller throttle openings for the same acceleration and cruise
- Better throttle response at highway speeds

So if you can turn your crank easily back and forth by 3-4 degrees, you ought to be considering a new chain. More slack than that, and you should definitely do so. A new stock style Cloyes chain does not cost much (and there are better chains out there), and the installation is easy for a modestly experienced mechanic.
 

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Sink to soak the new chain in heavy weight oil before installing. Yes the oil will drip and make sealing the cover more difficult. Better than waiting for the engine to properly oil it.
 
I always just slob Vasoline all over them.
 
I have noticed the same improvements after changing the worn chain and gears on my 318.
Timingchains are a wear item and idealy should be replaced after so many miles.

In addition to the above text, I would like to add;
- Reset your ignition timing!

Only after I re-set the timing I felt the best performance gain again, especially at low rpm torque and mid-range.
 
You can actually get more HP from a worn timing chain. Racers often install a cam at the "4 deg retarded" marks for this reason. I speak of costlier timing sets w/ several keyways that allows selection of valve timing. A worn chain can cause the spark timing to jump around. For those who add a crank trigger for spark (few slanters have), that wouldn't occur. Worst-case is when a loose chain causes the cam to jump a tooth, but that is more common w/ the Mopars that had a nylon timing gear (some BB's).

Just stating some info. I agree w/ installing a new timing set. Indeed, I set my small block timing set at the "4 deg advanced" keyway for better low-end torque and mileage, and to compensate for future wear.
 
I just load it up with engine assy lube (lubriplate). It basically liquifies and becomes part of the oil. I use it for all the bearings too. The only exception is using heavier "cam lube" on flat tappet cams initially.
 
The stock slants and 318's had cheap timing chain and gears that wear fast.

I don't run anything less than equivalent to a stock 340 double roller or better. Usually better.

I once replaced the timing chain and lifters on my 68 Cuda with 84 k miles and gained a little over 2 mpg from the efficiency improvement, not to mention it ran much better.
 
The JP which is the old Rollmaster is the best you can get for a slant. They ain't real cheap, but they are very high quality.
 
krazykuda said:
The stock slants and 318's had cheap timing chain and gears that wear fast.

I don't run anything less than equivalent to a stock 340 double roller or better. Usually better.

I once replaced the timing chain and lifters on my 68 Cuda with 84 k miles and gained a little over 2 mpg from the efficiency improvement, not to mention it ran much better.
Click to expand...
I hope to see a mileage improvement in this case; seems possible since the throttle openings are now smaller. How much is TBD....

My main point of posting this was for the newer car guys lurking here to be aware of something that seems mundane but is really pretty important in engine operation. Regardelss of how you fix it, it is something that is pretty easy to rectify on these cars.
 
anyone just replace the chain? I heard the gears wear, not so much the chain...fact or friction? I think it would be more pronounced in the double roller as it has much less gear area than the multilink.
 
I guess I would not even consider not changing the chain, as the chains are also subject to wear in the internal links and will 'stretch' due to that, regardless of what is going on at the contact areas with the gears. In the case in the photos above the gears showed minimal wear on the contact faces, so the chain stretch was likely the main contributor to the 5 degrees or so of cam timing slippage.

In this situation, I first put on the new chain and cam gear with the original crank gear and checked the slack. I then put in the new crank gear and re-checked and the overall slack decreased noticeably with the new crank gear, so the original crank gear either had worn some more than I could detect or was not compatible with the new chain. The shape of both gears' teeth on the Cloyes replacement was different from the original unit, so that might explain it, and it seemed to be inviting more problems to run the new chain with the old crank gear.
 
These are actually sprockets instead of gears. Anyway... they do wear. Look for the flat on top of each tooth to be smaller in width. That's the easiest place to see the wear. The radius between the teeth has worn to elliptical shape.
I've seen the tooth tops worn razor sharp, shorter, and to one side before the chain jumped. Just for the sake of saying, Dancing on the throttle is what stretches to chains quicker. If the engine rpm never changed the chain and sprockets might last 3 or 4 times as long. The major wear event would be start like every other engine part.
We could drive them like that only if the world was all downhill. :)
There is one guy who attends local cruise-ins and such who takes every opportunity to fire up his and jack the throttle half dozen times. Happens once per hour average. Premature tow Homer. DOH !
 
Chain set is usually about 8 more than the chain itself. I can see the wear in the first pic. look at the cog teeth.
 
Sprockets..... I should indeed be using the right terms. Thanks. All good comments above. Yeah, we all have a local guy like you referred to! Vrooom vroom....#-o
 
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