Excessive Spark Knock Causes
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Freshman User
Joined: Jan 2005
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Excessive Spark Knock Causes
My 351w is just back on the road from a blown head gasket. The gasket blew out between the #2 and #3 cylinders. I was passing gases between the two pistons causing a huge spark knock. They were passing gases across the head gasket and firing at all the wrong times.
So thats history, new head gaskets (did both sides for the fun of it) and now I'm back up on all 8. Now I seem to have excessive spark knock under load. Its not even close to as bad as it was before the head gasket change but worse than before it blew. The problem is I drove the truck with the blown gasket for about 50 miles. I'm thinking that the blown head gasket stressed the rod bearings causing excessive rod bearing clearance on those two pistons.
Questions for those in the know. Does this theory make sense? Can I replace those two rod bearings on the 2 and 3 pistons without pulling my motor and heads? Have my wrist pins failed? Any suggestions would be helpful.
So thats history, new head gaskets (did both sides for the fun of it) and now I'm back up on all 8. Now I seem to have excessive spark knock under load. Its not even close to as bad as it was before the head gasket change but worse than before it blew. The problem is I drove the truck with the blown gasket for about 50 miles. I'm thinking that the blown head gasket stressed the rod bearings causing excessive rod bearing clearance on those two pistons.
Questions for those in the know. Does this theory make sense? Can I replace those two rod bearings on the 2 and 3 pistons without pulling my motor and heads? Have my wrist pins failed? Any suggestions would be helpful.
Elder User
Joined: Apr 2004
Posts: 544
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From: Ocala, Florida
You may have a lot of carbon build-up from incomlete ignition. Did you clean the combustion chambers when you had the heads off? If no, then you can use STP comlete fuel system cleaner. Cleans the entire fuel system, the valves and the combustion chambers. Or, your problem could be cheap gas, or timing (too advanced).
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Freshman User
Joined: Jan 2005
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Thanks for the reply. I did clean the heads when they were off. There was just a thin layer of carbon. The engine knocks a little worse when its hot. The timing is set at 8 deg BTDC. Its a carb.
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