Top Dead Center?

[Barry Eller]

I replaced the steel distributor gear with a bronze gear. I had been told to do that as I have a roller cam in my 502. I lost my mark as to where to reinstall the distributor. I removed the left valve cover, removed spark plugs, and hand rotated the engine until the valves on # 1 cylinder are both closed and the timing pointer aligns with the mark on the harmonic balancer. My question is, the exhaust valve closed just as the marks aligned up and the intake valve on #3 cylinder just started to open. Am I at TDC on # 1?

Any tricks to getting the oil pump slot to align to the slot key? And does the position of the distributor matter as long as the rotor points to #1?

[Carl C]

Sounds like you may be at TDC of the exhaust stroke. I like to find TDC of the compression stroke by disabling the ignition, pulling #1 plug and putting a finger over the plug hole. Have someone bump the starter repeatedly until you feel the compression and then line up the marks. Then go to about 8 degrees before TDC and line up the rotor with the #1 cap terminal.

[BillG]

Barry,
Why would you replace the proper steel gear with a brass gear? The correct gear for long life is the steel one.

BillG

[Barry Eller]

Barry,
Why would you replace the proper steel gear with a brass gear? The correct gear for long life is the steel one.
BillG
My understanding is the steel in the roller cams is softer than flat tappet cams. Wear out the distributor gear instead of the cam.

[MOP]

The whole idea of a bronze gear is to save the gear on the cam. Barry "do not" worry about the oil slot yet!!! Put the cap on and mark the distributor housing where #1 wire is on the cap, tap the engine over with your finger on the spark plug hole for #1 when you will feel the the compression and you will see the corresponding mark on the balancer will be quite close, put the distributor in lined up with the mark. Put a little downward pressure on the distributor housing and tap it over again the distributor will drop into the oil slot, at this point you will be pretty close on timing.

Phil

[BillG]

Barry,
I think you will find that a roller cam is harder than a cast cam. That is why stock roller engines have steel gears. If you used a cast gear on a roller steel cam it will wear out quickly, the same as a bronze gear. Maybe in a boat because of the limited use as compared to a car that would not be a problem.
I don't think the manufactures would use steel gears if they thought cast ones or bronze would last.
Just my .02 cents

Bill G

[Rootsy]

a billet steel camshaft core is all that requires the bronze gear... flat tappets and most hydraulic rollers these days are a cast core and can use the steel gear... hydraulic rollers, etc that can use the steel gear have an austempered gear on the bumpstick.

both valves closed = tdc of the compression stroke... exhaust closing, intake opening = TDC at the beginning of the intake stroke... you want the compression stroke. from there it is irrelevent where the distributor goes as long as the housing is phased to the rotor correctly and the plug wires in the correct spot on the cap... but if you want to keep the plug wire location you are gonna have to get it in place CLOSE to where the #1 plug wire is... you ahve some leway from there in housing rotation to get things timed...

[Barry Eller]

Thanks for the great information. I think the old gear on my OMC distributor is cast. It looks worn as well. I'll go ahead with the bronze gear for now, its not that big a deal to change out, now that I know how to find TDC. Thanks again.:yes: