Engine noise
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Welder User
Joined: Feb 2009
Posts: 5,269
Likes: 50
From: northwest MT
Engine noise
Got a knocking noise at 2500 plus rpm in my '77 300. Wondering if it could be a broken piston skirt. What would that sound like?
Noise occurs more under load or if I get on the throttle. No noise on deceleration.
Engine runs great with good power and has good oil pressure.
Noise occurs more under load or if I get on the throttle. No noise on deceleration.
Engine runs great with good power and has good oil pressure.
Fleet Mechanic
Joined: Nov 2002
Posts: 1,643
Likes: 69
I can almost guarantee a 1977 engine has cracked or broken piston skirts. These pistons have a steel strut cast into them to help control heat expansion. Unfortunately the struts introduce stress points which eventually lead to cracked skirts. The good news is that the engine can survive many thousands of miles with broken skirts.
Modern hypereutectic replacement pistons are much stronger and need no steel struts.
It could be another cause, like a timing gear getting ready to go, or even carbon build-up in the combustion chamber.
Modern hypereutectic replacement pistons are much stronger and need no steel struts.
It could be another cause, like a timing gear getting ready to go, or even carbon build-up in the combustion chamber.
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Welder User
Joined: Feb 2009
Posts: 5,269
Likes: 50
From: northwest MT
FTF, thanks for the reply (X 2). I think I''ll run it for a while and see if it get's worse. It will need a rebuild sooner or later anyway.
The carbon build up is a possibility, any way to help that?
The carbon build up is a possibility, any way to help that?
Lead Driver
Joined: Dec 2000
Posts: 6,298
Likes: 47
From: South central, Minnesota
If it was me I'd throw some additives in the oil and fuel. Then search for and pick up a good rebuildable engine core. And just drive the one you've got in there until it craps out or you get the other engine finished. That way your truck isn't down anymore then it has to be.
Fleet Mechanic
Joined: Nov 2002
Posts: 1,643
Likes: 69
Yup. Here's a little trick my boss taught me.
Fill a gallon jug with water. Hook up a 3/8 hose to your intake manifold and run the hose into the passenger compartment. With a warmed up engine sit behind the wheel with the jug o' water between your legs and the end of the hose in your hand.
FLOOR IT - yes WOT.
Before the engine reaches redline plunge the end of the hose in the gallon of water. The engine will start to bog down as the water enters the hot combustion chambers and instantly steam cleans everything in there. Modulate the engine speed by withdrawing the hose and plungeing it back in as the revs increase until the gallon of water is gone - passed out the exhaust pipe.
Change oil.
Clean the carbon soot off your driveway or garage floor.
Fill a gallon jug with water. Hook up a 3/8 hose to your intake manifold and run the hose into the passenger compartment. With a warmed up engine sit behind the wheel with the jug o' water between your legs and the end of the hose in your hand.
FLOOR IT - yes WOT.
Before the engine reaches redline plunge the end of the hose in the gallon of water. The engine will start to bog down as the water enters the hot combustion chambers and instantly steam cleans everything in there. Modulate the engine speed by withdrawing the hose and plungeing it back in as the revs increase until the gallon of water is gone - passed out the exhaust pipe.
Change oil.
Clean the carbon soot off your driveway or garage floor.
Moderator
Joined: Dec 2007
Posts: 7,987
Likes: 104
From: Boise, Idaho
FTF, I've done this too just by holding the throttle open in the engine bay and pouring the water down the throat of the carb. It works quite well, and yes, there was quite a pile of soot on the driveway. 
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