Timing chain on early C4

[Walter F.]

My 84 has the orginal timing chain at 151,000 miles. The car runs fine, but should the chain be replaced with this kind of mileage ? How long does a timing chain last in a Chevy small block ?

[Joe L.]

Re: Timing chain on early C4

My 84 has the orginal timing chain at 151,000 miles. The car runs fine, but should the chain be replaced with this kind of mileage ? How long does a timing chain last in a Chevy small block ?

Walter------


I believe that nylon cam sprockets were still being used in PRODUCTION for 1984 although GM SERVICE sprockets were cast iron well before that time. 151,000 miles is a LONG time for a nylon toothed cam sprocket. My original 1969 sprocket was long gone by 100,000 miles and the timing set was pretty much the same as your 1984 set.

Generally, when a timing set has excessive wear you will note an irregular "clatter" made by the chain as it strikes the timing cover. When a chain gets this bad, it needs to be attended to right away.

Something else you can do to assess the condition of the timing set: put a timing light on and observe the timing mark on the balancer. If the mark is steady at a particular point with no "jumping around", your timing set is probably OK. However, if it "jumps around", your timing set is on the way out.

[Patrick H.]

Re: Timing chain on early C4

And if you get to this point, where you lose oil pressure because something is clogging your oil pump intake, you waited too long...

[Duke W.]

Re: Timing chain on early C4

I recall the nylon cam sprocket timing set was replaced with a steel sprocket by the mid-seventies. My late seventies P & A catalogs show three different sets - the "wide" silent chain set from the sixties, the truck roller chain, and the later "narrow" silent chain, but I think by this time was back to a steel cam sprocket.

Spark scatter is common with the sloppily built distributors of the era that had way to much end play, so I don't consider spark scatter a good indication of timing chain wear unless distributor end play is shimmed up to the two to five thou spec in the '63 shop manual.

Duke

[Joe L.]

Re: Timing chain on early C4

I recall the nylon cam sprocket timing set was replaced with a steel sprocket by the mid-seventies. My late seventies P & A catalogs show three different sets - the "wide" silent chain set from the sixties, the truck roller chain, and the later "narrow" silent chain, but I think by this time was back to a steel cam sprocket.

Spark scatter is common with the sloppily built distributors of the era that had way to much end play, so I don't consider spark scatter a good indication of timing chain wear unless distributor end play is shimmed up to the two to five thou spec in the '63 shop manual.

Duke

Duke------


The nylon toothed cam sprocket was replaced with a cast iron sprocket by the mid-70's but only for SERVICE. As far as I know, the nylon toothed sprocket was used for PRODUCTION engines right through the end of Gen I small block manufacture. (SERVICE engines may have used the cast iron sprocket).

My distributors have always had end play at factory spec (i.e. 0.060"). With a worn timing set my balancer timing mark was "all over the place". With a Cloyes 9-3100 it was rock steady; no perceptible variation, at all.

[Duke W.]

Re: Timing chain on early C4

The last distributor I overhauled a few years ago showed about two degrees total spark scatter prior to removal and measured .043" end play prior to disassembly.

I shimmed up end play to .003" on assembly, and the timing mark was dead on from idle all the way up to 5000, which was the maximum test RPM after re-installing, and the L-79 was perceptibly smoother with the blueprinted distributor.

Duke