Very strange compression problem
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Very strange compression problem
Bought a 79 F250 Super Cab Camper Special w/400 to keep it from being parted out. It hasn't run in 2 years, but the PO said it was running well when parked. Some fresh gas and a new battery it it sprang back to life --- on half the engine. Passenger side bank (1-4) running strong (125-150 psi compression). Drivers side bank (5-8) not running at all (0 compression on all cylinders.) Leak down test shows all cylinders on the driver's side bank leaking from the exhaust valve. You don't need a listening hose, you can feel the air from the test coming out of the tail pipe!
Removal of valve covers shows all valves moving normally, although there was some moisture under the cover and some tan sludge in the cover. The engine has great oil pressure, warms up and maintains temperature fine, no steam out the tail pipe, oil looks normal,. water looks normal.
I am totally baffled. Again, PO said it "pulled like a tank" when parked. Any ideas?
Removal of valve covers shows all valves moving normally, although there was some moisture under the cover and some tan sludge in the cover. The engine has great oil pressure, warms up and maintains temperature fine, no steam out the tail pipe, oil looks normal,. water looks normal.
I am totally baffled. Again, PO said it "pulled like a tank" when parked. Any ideas?
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The valves all seem to be moving normally when cranking the motor over with the starter. I pulled a couple of rockers and tapped on the end of the valve stem with a plastic hammer. They sound like they are hitting the seat normally. This has got to be a really BIG leak. When I put the leak down tester hose in the plug hole, there isn't even enough compression to blow my finger off the other end of the hose. In fact , I can't even feel any pressure at all.
I plan on pulling the head this weekend. I'm just trying to figure out what could have caused ALL the cylinders on this bank to lose ALL compression - while the truck was sitting.
I plan on pulling the head this weekend. I'm just trying to figure out what could have caused ALL the cylinders on this bank to lose ALL compression - while the truck was sitting.
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Laughing Gas
Joined: Jan 2006
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From: New-brunswick,Canada
Only removed one spark plug at the time when doing compression test. Could be a leak from the head gasket juping from one cylinder to another ? It happend to me with a different motor but it was just with 2 cylinders...removed the head just like hollenjoe said.
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Compression test was run with all plugs out, throttle wide open, ignition disconnected, approx 5 compression strokes on each cylinder. I've seen gaskets fail and valves burn, but 4 dead cylinders? All on the same bank? I can't figure out what would only affect one bank.
Keep in mind this truck was supposedly running well when parked, now it won't even pull my driveway.
Keep in mind this truck was supposedly running well when parked, now it won't even pull my driveway.
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I'll definitely post when I pull the heads. I'm thinking right now that it is an old problem and that it was running this way when parked. Maybe caused by the carb lean on one side. It was also timed early, so maybe the combination took out the exhaust valves?
We'll see . . .
We'll see . . .
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Plan is to pull the other head tonight and get them both to the machine shop.
Lew, yes it is carburated. I haven't really checked out the intake yet.
Any ideas what I should look for? I don't want this to happen again.
Lew, yes it is carburated. I haven't really checked out the intake yet.
Any ideas what I should look for? I don't want this to happen again.