Spark Plug Questions

[Danillac]

Hello all, I have a 1976 500 in a 1986 dually. My problem is this, spark knock, detenation. I have richened the carb, adjusted the timing up and down. I have re-curved the distributor, but I cannot get the spark knock out. The spark knock is mainly when the engine gets to operating temperature. I wonder if the plugs could be the problem. The plugs are Bosch Platinum. Could it be that these plugs are of the wrong heat range? I drive this truck daily, and pull a decent sized camper. I need to get this taken care of. Please help!!!!!

[STDog]

Anecdotal, but my '70, 10:1 copmression 472 was knocking under a load, especially in the summer. I had to mix gas to 96-97 octane to make it inaudible. I'd tried all those tricks to now avail.

Oil pump quit, and forced a rebuild. Heads and pistons cleaned. found 4 bent valves (3 intake 1 exhaust). Put it all back together, and now knock on 93 octane. Everything stock and set to the book.Even in 100 degree ambient temps.

My guess is deposits in the combustion chanmber were the problem. Your engine is lowere compression, but it could be similar. What octane fuel do you run? Do a leak test on the cylinders to check the valves and rings. Clean the combustion chamber.

Might work, couldn't hurt :)

[Danillac]

Okay, I did not give enough information about my application. My engine again is a 1976 500. This is what I was told by the fellow I bought the truck from. The engine has a 270 Comp cam in it. The carb is a stock 1974 piece off a 500. I have rebuilt the carb, but that is it. Again, I have moved my timing up and down and it changes nothing. I do know that this does not happen when the engine is cool. I was thinking it could be the plugs. I also thought maybe the distributor is sick. Thanks again.

[k10caddy]

what're the plugs gapped at? have you checked the resistance of the plug wires?
also, just to make sure... are you completely certain it's not it's not an exhaust ping?

[Danillac]

The plug wires are new and are the 8mm variety. I know they can go to crap just like an older set. I have not checked the plug gap myself. The guy I bought it from said he gapped them at .045. What do you mean by exhaust ping? I am sorry for the dumb question, but I have never heard that term before. I don't think it is exhaust, it is only when the engine is warm. Only on take-off and under load on the highway. Thanks again.

[DOC]

Danillac,
I agree with k10. A small exhaust leak will get bigger as the engine warms up. If it is a small leak, most of the time you can only hear it under load, and the engine warmed up. It sounds just like engine pinging, or spark knock. One way to tell is to power brake the car with the hood up and some one listening under the hood. Your will most likely hear the noise at one of the exhaust manifolds.

DOC

[Danillac]

Hey fellas, I just put a new set of manifold gasket on my beast. I believe I have most of the problem taken car of. I bought a re-curve kit awhile back. I was running the lightest springs in the kit. I changed them over to the heaviest and I have not heard any detenation. I don't have a good hard take off, but it seems to have good pull. Thanks for the input. I will take any other that anyone is willing to give. If you would like, you could e-mail it to me directly my address is [email protected]. I believe I will take the time in the near future to change out the cam as well. It currently has a "270 Comp" cam in it. I believe I will put in one I have that is not so "wild." The one I am going to use is a .255 intake lift and .305 exhaust lift. I know it is not big, but for pulling, I believe this will work out quite nice. Danillac in Missouri