360 Compression - Valve work needed?
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From: Miami FL
360 Compression - Valve work needed?
'72 F250 360cid
Chasing a misfire on the driver side bank and wondering what everyone thinks.
Pulled the plugs and #5 was black with soot & wet with gas, #7 has dirty oil deposits. Compression test confirmed low #5 & #7 & re-did test with teaspoon of oil in the lowest reading cylinders and it didn't jump up significantly. I think I'm looking at valve work here, what does everyone think?
Thanks for any opinions.
#1 = 115 (125 Wet)
#2 = 135
#3 = 128
#4 = 130
#5 = 55 (55 Wet)
#6 = 130
#7 = 20 (45 Wet)
#8 = 130
Chasing a misfire on the driver side bank and wondering what everyone thinks.
Pulled the plugs and #5 was black with soot & wet with gas, #7 has dirty oil deposits. Compression test confirmed low #5 & #7 & re-did test with teaspoon of oil in the lowest reading cylinders and it didn't jump up significantly. I think I'm looking at valve work here, what does everyone think?
Thanks for any opinions.
#1 = 115 (125 Wet)
#2 = 135
#3 = 128
#4 = 130
#5 = 55 (55 Wet)
#6 = 130
#7 = 20 (45 Wet)
#8 = 130
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Pulling the heads is the next step. You should know more after giving #7 the closeup eyeball.
You can certainly throw a valve job in it and try to run it.
Was it burning oil? Pumping oil out the PCV breather?
You can certainly throw a valve job in it and try to run it.
Was it burning oil? Pumping oil out the PCV breather?
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From: Miami FL
It was idling pig rich when I picked it up, ended up backing off the idle mixture to get max idle vacuum. But at idle vacuum gauge bounces erratically and RPM fluctuates. Everything smooths out when driving, but lifting off causes backfiring through carb.
More Turbo
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From: Lacey
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From: Long Island USA
Sounds like valves. You never know, though, if someone had the top end apart already, there could be a pushrod that's too long and the valve isn't seating. One way to tell would be to take the rocker shafts off, and put compressed air into each cylinder and listen for where the air is going.
Lead Driver
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Get a bad cylinder on it's tdc, screw in a air chuck adapter in place of the spark plug. Regulate your air down to around fifty pounds. Have someone hold the front of the crank with a breaker bar (the air might push the piston down). Listen to where the air is escaping. Even if you can only hear it escaping out the exhaust and or carb, I would rebuild the whole motor. Putting fresh heads on old rings and worn cylinders never works out. You end up with a oil burner.
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From: Miami FL
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New User
Joined: Mar 2019
Posts: 4
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From: Miami FL
Get a bad cylinder on it's tdc, screw in a air chuck adapter in place of the spark plug. Regulate your air down to around fifty pounds. Have someone hold the front of the crank with a breaker bar (the air might push the piston down). Listen to where the air is escaping. Even if you can only hear it escaping out the exhaust and or carb, I would rebuild the whole motor. Putting fresh heads on old rings and worn cylinders never works out. You end up with a oil burner.
I will go ahead a pick up an air chuck adapter and pull the rocker cover. I'm guessing I should be able to tell then which valve is is off, then pull the head and inspect the guides.
But it definitely sounds like I am at the beginning of a rebuild here....
Totally agree with doing the bottom end at the same time; my cousin just had the heads redone on his '82 F100 and two weeks later the rings gave out
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More Turbo
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From: Lacey
Valve guides are absolutely necessary for valve seats to seal in order to make compression. The angle of pressure from the rocker arms will push the valve stem off it's intended straight line of movement without guides.
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