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Shade Tree Mechanic
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I have a 52 3100 straight 6 back firing badly. what is the best way to check for a burnt valve? Compression test? Idles rough when you give it gas it backfires out the exhaust. Sometimes with a big cloud of smoke.
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Joined: Oct 2009
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Compression check. Check it dry and then squirt oil in cylinder. If compression does not change, the problem is in the top end. Ether valves or head gasket. If compression comes up after the oil squirt, the problem is rings or piston.
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Joined: Feb 2017
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Shade Tree Mechanic
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Shade Tree Mechanic
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A leak-down test is another way if you have the equipment to perform it. This test will pin-point the issue whether intake/exhaust valve, head gasket/cracked head, or rings.
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I would bet on an eletrical//ignition problem.
Last edited by Chev Nut; 04/22/17 08:12 PM.
Gene Schneider
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Shade Tree Mechanic
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Shade Tree Mechanic
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Burned valve symptom is generally a rough idle the smooths out at about 35 mph or so.
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Joined: Jan 2002
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possible, but if a valve sticks 98% of the time it is an intake and then it would back-firethroughthe carburetor.
Gene Schneider
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Joined: May 2002
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Backyard Mechanic
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Backyard Mechanic
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I agree with Gene. Sounds like late timing or ignition. I've had several burnt exhaust valves at the same time over the last 45 years and the most that happens is that you can hear the exhaust suck in air w/rough engine run. Early timing would cause back firing through the carb. Late timing causes cylinders to fire after the exhaust valve starts to open and that can cause a back fire(s). Also, plug wires on wrong cylinders can cause back firing and really rough running.
Check that the plug wires are installed correctly and/or try advancing your timing (turn the distributor counter-clockwise) and see if it smooths out.
Mike
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Shade Tree Mechanic
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Hello and thanks all. So over the weekend I left the door open which in turn ran the battery down. Now sometime before we got it someone converted it to a 12 volt system. What do I find when I go to charge the battery? a 6 volt battery. I replaced the battery with a 12 volt and truck runs great. Now my next question is what weight oil do I put in the transmission?
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Odd that someone would convert an electrical system to 12 volts, then install a 6 volt battery.
How are you able to tell the vehicle was converted to 12 volts ?
1951 Chevy Styleline Deluxe 2 door sedan / purchased from second owner 6-19-2000.
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