Melted a piston?
 

Well, after getting the carb/idle problem worked out on my friends boat, I'm afraid he melted a piston.
Engine: 502, intercooler, B&M 250 blower, single dominator, 6psi boost, 30 degrees total advance.
He ran it out of gas (incorrect guage) at nearly WOT. The engine started misfiring. Compression check showe 0 psi on cylinders 1 & 2. The guage didn't even flicker while cranking. Remaining cylinders were at 135psi.
Anyone ever burned a valve or blown a head gasket wher the compression guage didn't even move while cranking?

Re: Melted a piston?
 

Might be lucky & just messed up some exhaust valves. If you inject compressed air in the cylinder you will hear where it is excaping. I bet he messed up an exhaust valve at least.

Re: Melted a piston?
 

I just did a compression test yesterday and was reading 0 lbs on a cylinder. I popped the head off and had a bent exhaust valve. The compression guage did not move at all.

Re: Melted a piston?
 

Gary,

this one showed no compression at all.

Re: Melted a piston?
 

Check The Valves ,ive Tuliped Many Exhaust Valves When A Carb Has Gone Lean Under Load,ran Like Hell Before It Stopped

Re: Melted a piston?
 

Check The Valves ,ive Tuliped Many Valves When A Carb Has Gone Lean Under Load,ran Like Hell Before It Stopped,

Re: Melted a piston?
 

I did that to a 7.4 MPI at WOT. I have one piece of what's left of the #1 piston. Exhaust valve started sticking when it appearently went lean and "POP" and that was all she wrote as soon as the piston hit it. Left a gapping whole in the cylinder where the oil and water exchanged places as she was locked tight. RIP 7.4 MPI. :)

Re: Melted a piston?
 

Good news is that it's not locked up and will still run.
Didn't have my leakdown tester, but that's the plan. Hoping for the best preparing for the worst.

Re: Melted a piston?
 

Gary- For what you're describing, you may not need a leakdown tester. If you have an old plug shell that you can weld an air hose nipple to, just pump those cylinders up when they're at TDC. Simplest thing first. Pull those valve covers and drop the tip of a mechanics stethoscope down the past the cam into the bottom of the block. The scopes with a rubber hose work best for this. If nothing abnormal, then drop the exhaust manifolds and listen through the exhaust ports.If you haven't done this before, which I doubt, you may want to calibrate yourself on a good cylinder. Relatively speaking, you'll hear a pretty good 'whoosh' sound even on a good cylinder down in the block as air rushes past the rings. Usually intakes leak nothing. Due to the environment exhausts run in, you usually will hear a little leakage from a good exhaust valve.Let us know how you make out

Re: Melted a piston?
 

Bad news. Air was whisling through the breathers when hooked to #1 cylinder. Expensive weekend.