Fritz55ChevyTruck

Hi Guys and Gals.
I'm the proud owner of a 1955 Chevy 2nd series Truck. Al tough she is rebuild onto the chassis of a Chevrolet Commador 1980 with the 3 speed auto and the 250 6 cylinder engine. As in most cases the previous owner did not give all the information on the Truck so now its is a case of elimination.

The engine keeps on pre-igniting and is giving me a hard time. I have had the distributor, carburetor, (colder) plugs changed.Timing has been set advanced retarded and no sweet spot has been found. She does not get hot and runs at about 90 deg C. The mechanic also removed the intake and out let manifolds to check for carbon on the pistons - none. The compression ratio on all cylinders are in 10.5:1. This is higher than the stated factory specs of 8.5:1. The cam is not standard, according to the mechanic it is a "rough"cam. I'm more of a body person and my knowledge of the motor is limited. Any advise will be greatly appreciated.

-Chevy
-1955 2nd Series
-Rear wheel drive 2W RHD
-250 CUBE INCH / 4.1 L
-Sidestep
-Customized

oldchevy

Did you try a higher octane gas?

Fritz55ChevyTruck

Hi OldChevy
Yes I have, but has no effect?

kevinkpk

Heat range on spark plugs? What I've read with distributor, Id' recommend 10 deg BTDC. as a start, gap on a plug .30" and a heat range around 4.