The Stovebolt Site Forums The Shop Area Engine Shop Crank/Cam Timing Issue

I'm assembling my completely rebuilt GMC 302 and discovered the following; when crank/pistons and valve train are at #1 cylinder TDC the flywheel marking is NOT on the pointer on the bell housing. The pointer is dead on the firing position for 2/4 pistons. Since the flywheel only goes on one way what needs to be corrected? I'm sure it will run in this condition I'll just have to mark the flywheel with the new TDC position if I want to use the pointer as a TDC indicator. Since the engine is out of the truck I can refit the cam chain if that corrects he problem.

Are you sure you are not 180 off?

There's no law that says you MUST use #1 as your timing reference. Why not just use #2 as your timing point? You can always set up with a dial indicator and a degree wheel to get an accurate place to re-mark the reference for 1/6, but why bother? BTW, the current mark should refer to cylinders 2 and 5, not 4. Companion cylinders on ALL inline sixes are 1/6, 2/5, and 3/4.

Firing order: 1 5 3 6 2 4

Companion cylinders:
1 5 3
6 2 4

Good luck!
Jerry

cam-crank "timing" at assembly is not "on that/its mark" at "the same time" as the same as engine/ignition timing is on "its mark"

one or the other or both may be on "TDC", depending on the engine

Thanks, your right about pairings. Would refitting the cam chain allow me to reorient the flywheel?

#1 values are in the correct position for firing, so it's not 180 degrees out.

Don't understand your response, mate?

Possibly, but it would be necessary to verify the cam timing by finding the "split overlap" position of the #6 intake and exhaust valves by degreeing the cam to be sure the correct timing of the #1 valves is present with the piston at top dead center. We do that on overhead camshaft racing engines pretty often after milling the cylinder head, which creates an error with the crank/cam timing marks. Do you have any access to a racing engine builder who might be able to explain the cam-degreeing process?

On further consideration, the position of the dowel pin in the crankshaft would have to be relocated, no matter where the timing chain is oriented. The error is between the flywheel and the pistons, not the cam. I believe some military 302's had a #1 cylinder that was not accessible, so timing was set on the #2 cylinder.
Jerry

Timing chain?!

Good catch, Carl- - - -I've never seen a 302 with a timing chain!
Jerry

Are we working on an inline 6 or a V6?

The V6 is a 305
Jerry

So, are references above (by Roverman & Jerry) about a 302 timing/cam chain questionable relative to a 302 GMC straight 6??

Assuming we're talking about an inline 6, (not a V6), a timing chain can't be involved. Let me check into the 305 V6 on firing order and cylinder numbering- - - -back soon!

305 V6 firing order is 1 6 5 4 3 2

Companion cylinders:
1 6 5
4 3 2

The 305 and 379 V6's do have a timing chain, and the timing marks are supposed to align with the cam sprocket timing mark pointing down, and the crankshaft timing mark pointing up.

Jerry

you're right I've not had the cover off--it's all gears, so that appears to complete things

How can it be "completely rebuilt" if you haven't had the timing cover off of it? I've seen a few engines like that which were pretty obviously "rebuilt" with a couple of cans of spray paint.
Jerry