I replaced head gasket and had head resurfaced on my truck about 2 years ago while I was replacing timing chain. Ever since then, there has been a popping/rattle sound when the engine is under a load pulling hills. Its always been tough to recreate because it doesnt do it all the time. Ive been under the truck several times thinking there was something loose causing the rattle, but never found anything. A couple weeks ago, I starting wondering if maybe it was a spark knock that I was hearing. My timing has been set at 5 degrees with the jumper installed after warming the engine, but if I retarded the timing to around 0 or roughly 2 degrees after TDC the noise went away. I also filled up once with 93 octane gas and set the timing back to factory setting of 5 degrees and the noise wasn't there either. I hate to keep just buying premium gas, but I was hoping I could find an answer here as to what I could do to fix the issue? Could it be something to do with the head resurfacing and loss of material there? Or is there something else I should check? Also, there are no codes when checking the CEL. Thanks

 

Forgot to add that even at 0 to +2 degrees there’s not a noticeable loss in power but the knock goes away. I have also checked the timing mark on the balancer and it’s perfectly lined up with TDC.

 

Where does the bolt sit that holds the distributer in place? Is in centered in that slot, or is it pretty far to the left/right?

 

It’s probably about between center of slot and rotated fully clockwise.

 

Might be worth checking distributer first. Make sure all the wires on the cap are going to the correct plug. Cap should be numbered.
After that, Get #1 cylinder to tdc and confirm rotor is pointing to #1 on cap(if off 180 degrees rotate crank one full revolution.)
If all that checks out than I'd pull valve cover and check timing marks. Make sure it's not off a tooth.

 

I checked the bright link on the camshaft sprocket about a week ago and it was at 12 o’clock and on the tooth with the dimple when the crankshaft pulley mark is on 0. I had originally thought that maybe the crankshaft pulley had slipped and the mark was off but I confirmed with a piston stop in the number one spark plug hole. Distributor rotor was lined up with number one marked on cap.