[massey478]

Thank you, David! A good added step to remove carbon in the combustion chamber loosened when plug was turned. Especially true on engines that burn some oil. I had carbon get under a valve for a short time on a Cessna 150 I had changed the plugs on. A good run-up to full throttle cleared it fortunately. I have a 44 Massey Harris tractor that many years ago when plowing started making a knocking noise. Would not turn over after shut off. Motor was locked up. Of course a bearing(s) was expected as the cause but no problem found there. Head removal, very hard to break loose after the bolts were out, revealed a large piece of carbon had broken loose and got trapped between the piston and cylinder head, sticking the piston to the head when it stopped at TDC on that cylinder. Weird, but true! Made good Super Glue! Culprit for the carbon was again a worn engine doing light work during the winter, choke out starting and until warmed up, building up carbon then when spring plowing with the characteristic hard pulling involved happened it caused the carbon deposited from the light work to burn/ break loose. We always saw a good many sparks out the stacks on tractors when running at night until it cleaned up. Engines need to be worked once in a while to keep the carbon under control. I have been down the throttle plate/choke plate screw path several times also. Good thing most are brass!