Airing the cylinders

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That was probably me..

By using a special sparkpug adapter that can be connected to compressed air (available from autosupply or sears, in a compression testingkit), pressure can be applied to a cylinder when the valves are closed (at Top dead center). Usually this test is used to look for leak down past the rings or through the closed valves, but in the case I mentioned, I also used it to find what cylinder(s) were leaking gases back into the coolant.. When I pressurized the offending cylinder, air bubbled up through the coolant.

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Yup, and the tool is also essential for the task of replacing valve guide seals. With the cylinder "aired up", one can remove the keepers & springs to access the seals without dropping the valve(s) into the cylinder...:waving:

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And with no air and the seals removed, you can do the wiggle test.

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wowza.

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You can change the valve seals without air. Just feed a length of 1/4" nylon line into the spark plug hole with the piston near the bottom of it's intake stroke. Then turn the crank until the piston comes up against the nylon rope and tie the wrench that you turned the crankshaft down so the piston won't move. Check to make sure the piston is coming up near the top of it's compression stroke. You can tell that because the two rockers will be free to wiggle a bit. Go ahead and do your work on that cylinder, remove the rope and repeat on the next cylinder. I've used the rope method several times when there was no air available or no adapter handy. I've tried it a few years agoon a GL1100 just to make sure it worked on that engine when I posted this method the first time.

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why is this method necessary to change the valve seals? also do you use the same piece of rope to tie down the crank with?

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exavid wrote:

You can change the valve seals without air.

Click to expand...

Good tip, exavid...I wouldn't have thought of that in a million years...on my own! :clapper:

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I didn't either, I learned it from an aircraft mechanic almost fifty years ago.

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NO different rope...although i guess it could be if it was long enough..but no you don't want to do that..

When you remove the springs that hold the valves in place the valves will fall down into the cylinders and turn..the rope or air keeps them seated so they won't turn in place. If they turn they may not seat back tight as wear and carbon etc. is different all around the valve seat. Also jsut don't want them falling in and dingin up anything and the seat of the valve. At least that's what I thought/think.

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ahha so the rope in the cylinder is coiled in the cylinder
head itself to prevent valve movement..veryy interesting.
thx for clearing that up. so then a rope that does not fray
to leave particles of crap in the cylinder should be used.

gumby

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Not much chance of rope debris being left behind and even if there was it would soon be gone once the engine fired up.