The Cessna 120-140 Association Forum

Hope everyone had a nice Thanksgiving. I few questions to the collective brain trust.

1. After maintining my plane for over 15 years, I had never noticed a nipple on the passenger side of the intake manifold that's plugged with a screw. Very small; approx 1/4" OD. See photo. I don't want to take the screw out so I don't know ID or whether its a passage into the manifold throat. It appears to be cast into the manifold, so I don't think a previous owner added it. I don't see it in the engine diagram. Anyone have an idea what it's for?

2. I'm chasing an overheating probelm with rear cylinders. I've taped and caulked everyplace that looks like a path for air to escape. Between the cylinders the inner baffle has quite a gap - 3 finger's worth - between it and the case. I don't think this is the cause of my overheating; it's been that way since new and the overheating is recent. Still, I'm thinking about adding an extension to close up the most of the gap. Feedback?

3. Some of the cylinder fins near the exhaust valve on #4, and lower down near the barrel on #2 have a pink hue that I don't remember. Is this a sign of spot overheating?

Thanks for your insights.

Dave Sirota
N89654

I can tell you that my intake spider has ports on both sides, one used on the pilot's side for the primer. The passenger side port is plugged but it is a bigger plug than a 1/4" OD. Maybe someone used your plugged port for a manifold pressure gauge at one point?

Between the cylinders the inner baffle has quite a gap - 3 finger's worth - between it and the case.

Here's mine, o-200 engine. Are you missing a piece? See inner cylinder baffle article Neal Wright
viewtopic.php?f=10&t=1434

Some of the cylinder fins near the exhaust valve on #4, and lower down near the barrel on #2 have a pink hue that I don't remember. Is this a sign of spot overheating?

Here's my #2 exhaust before sending the cylinders in to Randy to work his magic years ago. Valve probably wasn't seating all the way or warped or some such thing that would impede valve cooling. I had that hue on the exhaust areas and not the intake areas. That copper line on top is for a manifold pressure gauge, installed moons ago by previous owner.

On item #2, with the recent cylinder overheating issue. Have you checked your intake runners for airleaks? The rubber collars/hoses? Also check the intake elbow, it's attached to the cylinder with bolts on opposite corners and over time the elbow can "bow" in the center, the intake gasket can suck in and cause an airleak. Usually more pronouced at idle than full power, but that may be one issue.

The picture that Dave Sbur provided is correct, the inner cylinder baffles should run tight to the case.

Those inter-cylinder baffles are part of the "Summerization" kit and not "required". Don't get me wrong, though, they are a good idea and my plane has them. You can see the whole kit (and caboodle) on page 134 of the parts catalog.

Thanks, everyone, for your suggestions. I'll be making the "summerization" bits this weekend and we'll see what happens.