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Car is a 1976, stock L-48/auto trans w. 142K miles (I think the miles are correct):
When I purchased the car a month ago I was told it had a gear drive in it. It has the stock timing cover.
When I checked for timing wear I get 12* of crank shaft rotation before the distributor rotor begins to move and I figured the guy misunderstood something.
Turns out, it does have a gear drive in it. I had forgotten that some will fit under the stock timing cover.
I know nothing about gear drives and am looking for a little help.
I have the intake manifold removed and got my bore scope into the timing chest for a couple of pictures:
Top back side of cam gear:
Looking down the right side of the cam gear:
I see that the cam gear and, I guess I'd call it the intermediate gear, are not lined up 100%.
I assume this is the cause of my 12* of rotation before the distributor rotor begins to move.
I will mention here, I was surprised at how stable the timing marks are when checking the timing with a timing light, this explains it.
Is this an adjustment that can be made if I remove the timing cover?
Are these things junk and I should replace it with a double roller chain set?
I don't have any personal knowledge with gear drives. We ran comp eliminator years ago and most small blocks used a high
quality double roller chain. We shifted at 9200 rpm and chain wear was never a issue.
Now most comp engines are running a belt drive
the 12 degrees is slop between the teeth, twice. 6 degrees or so each side of the intermediate gear. my suggestion for that setup is getting 10 cents a pound for it at the scrap yard and putting in a timing cgain. and i wouldn't trust that cam. nobody puts a gear drive on a mild cam.
The gear misalignment has nothing to do with your cam play. The gears are worn, you can see it on the edges of the gear where the material has “mushroomed” over the edge.
And people put gear drives on anything because they like the noise, sounds like a supercharger.
As far as I know it's the stock cam, the engine still has the stock pistons and stock heads.
I measured exhaust lift but my dial indicator wasn't square to the lifter bore, I came up with les than factory lift.
The plan is to run it for a year or two while I get everything else working better (notice I didn't say "fixed", I doubt I'll ever have everything fixed on this car) then build another engine for the car.
Right now I'm resealing the intake manifold, I suspect it had a vacuum leak, I couldn't get the car to run very well at all.
I'll install a new timing chain in a few months, along with headers and dual exhaust.
I am surprised the gears wore that much.
The idea behind gear drive is to eliminate chain stretch.
I guess the difference between cam and crank centers is too much and the gears were never right.
even a double roller will stretch.
I am curious if there are gear sets with different diameters to to tighten the gear lash?
Maybe the guy that installed the gear set used the 6 deg advance setup?
I was surprised it's bad as well but I don't know the quality of the parts that were installed.
The roller rockers I found had CQED etched in them on one end. I can't find that anywhere when I search for rocker arms.
One was damaged along with the pushrod, another one had a crack in the casting.
They all got replaced.
The good news is I'm not too worried about it jumping time while I drive it for a few months while I gather parts for the next stage.
Good point, thanks. It would be awfully easy to check it now while the manifold is off.
I almost got it installed today too, I'm glad now that I didn't.
Bullshit cheap gear drive.....
Absolutely zero reason to run one in any engine short of one that runs a cam drive fuel pump (Enderle).
Get rid of it.....
Thanks Jebby, can I ask why you recommend that one over the others?
I installed a Cloyes double roller set in a Jeep 258 years ago, there was one option for that engine.
When Cloyes makes numerous options for the same application I like to understand why some are recommended over others, for my own education.
I checked the wear in the timing gears, I get about 8-9* of crank rotation before I felt the cam gear move.
So I have 3-4* of wear on the distributor drive. I'll run that distributor for now, it's a no-name brand with a Napa module in it.
I will upgrade to the recommended Chevy Performance HEI in the near future.
Because a Cloyes double-roller just works, without issue. There are single chain and the plastic cam gear ones. It's $38 and never fails, no more questions needed.
It's called a "True" roller meaning that some knock-offs are not. This is a heavy duty set with close tolerances.
As I recall, it fits tight on the crank / cam. Zero slack.
Cloyes states that the rollers are extra strong at 0.250 thick. I believe the link pins are thicker too.
Each chain takes half the stress load placed on it.
Just before you install the chain, drown it in a bowl of oil.
03-13-2022, 03:34 PM
Camshaft Gear Drive
