Thread: Big Problems with my 540

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OK, not technically a hot rod, but I have a 540 BBC in my airboat. We were out yesterday and when my buddy started the boat to pull up to shore to pick us up there was a terrible knocking noise. We deduced that the nut came off the top of the carburetor stud and then the stud broke and fell through the throttle body and into the #5 cylinder.
Fast forward to this morning, took the spark plug out and fished the broken pieces of the stud out with a flex magnet and put it all back together. Started the motor and there is a knocking noise. Doesn't sound like a constant rod knock (not sure why the bearing would go anyway? Anyone care to diagnose my bad luck?

Welcome to CHR! My guess is that the stud got tangled in a valve and you've bent a valve. The knock is the rocker slapping the valve stem, which is not returning to the relaxed position. Just a WAG,,,,

Originally Posted by rspears

Welcome to CHR! My guess is that the stud got tangled in a valve and you've bent a valve. The knock is the rocker slapping the valve stem, which is not returning to the relaxed position. Just a WAG,,,,

or the bent valve hanging down touching the piston

Or some more pieces stuck in the top of the piston hitting the head-do yu have alum or iron heads-what type intake manifold? If a 180* type pices will go back and forth into all 4 clyinders of the 180deal
2 end cyl on one side, 2 center cyl on other side-------3,5 and 2,8

was throttle linkage or return spring bracket fastened to carb with that stud?

Aluminum heads, fuel injected. I believe the nut came loose up top and it snapped at the base of the MAF sensor and fell right in. I ran the magnet down all four cylinders of that side.
I'm assuming everyone would agree I need to pull the head off of that side? I've never dug into bent valves. Repairable or are the heads junk?

if it didn't run very long or at too high an rpm, could only need a touch up on the seat and some new valves-it it broke and pieces got hammered between the pistin and combustion chamber-could get nasty----------180 manifold - pieces could cross over to other side probably to the end cylinders on that side-lucky you didn't have stainless nut/stud as magnet wouldn't work plus iron heads would be probalem also
good luck, I'd pull both sides to check every thing out-after all an air boat the engine is pretty open????????

Originally Posted by walteman

Aluminum heads, fuel injected. I believe the nut came loose up top and it snapped at the base of the MAF sensor and fell right in. I ran the magnet down all four cylinders of that side.
I'm assuming everyone would agree I need to pull the head off of that side? I've never dug into bent valves. Repairable or are the heads junk?

Uhhh, yeaaah, pull the heads; as to repairable, depends on how much damage has been done.

.

Originally Posted by walteman

Repairable or are the heads junk?

There's no way to know until you pull the heads. You could be looking at anything from an easy fix to one cylinder/chamber, replacement of one head, or a full rebuild if it wedged into a cylinder wall and gouged the bore. Once you have it down to be able to pull one head, it'd be silly not to pull the other one too, to eliminate any questions. Like Jerry said, on an air boat it should be easy access? Just don't drop stuff into the lake!