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AC motor problem

A

archermatt

Member
I was driving around the other night and one of my friends noticed a knocking sound from the right side of the motor. The oil pressure went up about 10psi then the knocking went away and the pressure went back down to normal. Motor was running kinda rough when the knocking started to happen but not bad. ANyone have any ideas on what it could be?

Matt
 
What kind of engine is it?

When was the last time you changed the oil? Maybe it is low or a piece of trash was clogging the oil passages?
 
It's a straight valve 540 Lycoming. I had just changed the oil and now I can tell it's not running on all it's cylinders so I wonder if it's getting spark to that one cylinder. I can hear a mild clunking noise and it's running rough when I went out to the yard a little while ago to tighten all the bolts on it. It only has like 80 hours on the motor.
 
Run a compression check first, go from there.

Might look closely at the cylinders. I do know cylinders that separated from the bases. The fins on all the cylinders should be fairly close to parallel. If one head seems to be sitting out of line with the others, that might be something to look at.
 
I went through it last night. Everything looks fine from the outside, no leaks or gaps in the cylinders and I'm not smelling any fuel so I think they are getting some spark. I'm definetly not an ac mechanic,lol. Next time I'll convert her to a car motor but don't have the cash to do that. Anyone know of a good mechanic near palm bay/melbourne?
 
Maybe you just had some bad fuel. I'd fill the tank with fresh gas, and maybe add some Sea Foam
 
A compression check is a good start. Pull the top plugs on each cylinder and turn that baby over by hand for several revolutions of the propeller. It should feel the same through out. If you find a tight or binding spot, you could have a problem. What that would indicate would mean pulling the cylinders off at least to trouble shoot. Borrow a compression tester or visit a parts store and they often will rent one cheap. Leave all the top plugs out and screw the gauge into one hole. Turn the motor over and get three or four readings on each cylinder. If you have a bad jug, you will know.

But I would call a mechanic at an airport or Jurnigans and tell them what happened. Ask for an opinion.

I never experienced a spike in pressure, just always the opposite. mwood might be on to something.

If it is running rough then smooths out, that is a sign of a stuck valve. Have heard of the valve seats unseating and dropping back in. Especially if they were reamed out when installing.
 
I didn't notice you said it went UP 10 pounds. I misread and thought it had dropped TO 10 pounds.

Drain the oil through a paper towel and look for slivers of bearing material.
 
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