Question for Paul McBride, the General Aviation News engines expert: I just installed an older Insight GEM 2 in my 1971 Piper PA-28-140D that I pulled out of my other Cherokee, which just got a JPI 900 upgrade.
When I removed it, the GEM 2 worked great.
On the first flight with the GEM 2 installed I noticed #4 CHT rose to 500 on climb out (OAT -3 up here in Canada) and the other three cylinders were 400 or just under. I pulled power and got #4 back to 400 (was still reading hotter than the other three) and headed back to the airport.
On my way back I tried full power again while being leveled off and #4 rose quickly to 500.
I landed, shut it down, pulled the plugs (which looked good), I borescoped and looked at the valves, cylinder walls, etc., and nothing looked obviously wrong. Baffling looks normal with no obstructions.
I did notice on mag drop #4 took the longest by about 10 seconds to see an EGT rise.
I also noticed where the exhaust exits the cylinder, it looks white and like it was running hotter than the others.
I haven’t hit it with a temperature gauge externally after it was running, but the cylinder was hotter than the others by touch.
I am thinking an air leak on the intake tube is causing a lean cylinder? Or maybe a crack in the cylinder wall? Or oil compression ring blocked? Maybe I should try ring flush?
Someone suggested the cam may be worn, so I could try and measure the valve movement. The cam was changed more than 20 years ago, with only 300 hours on it.
The plane lived in Northern Alberta during this time so corrosion shouldn’t be that much of a factor.
Engine is a Lycoming O-320-E3D Factory with 1,900 hours, but was pulled apart at 1,600 hours (20 years ago) and rebuilt (300 hours on engine since rebuild).
The problem cylinder is chrome and has 400 hours. All cylinders are P10 oversized. Magnetos are Slick and have 75 hours since rebuild. Plugs have been tested and cleaned.
The engine runs great and appears to make full power.
Any help would be greatly appreciated.
Thanks,
Tyler
Paul’s Answer: Tyler, I’d say that you have an interesting situation here, so let’s see if we can offer a few suggestions.
It’s too bad your aircraft doesn’t have a manifold pressure gauge because that may offer some hints as to what’s going on in the #4 cylinder. If you had a manifold pressure gauge and we suspect there is an intake leak somewhere, the manifold pressure at idle would be somewhat higher than if there were no leaks.
I did observe the one picture showing the exhaust stack gasket with some kind of sealant on it, which is not a good thing. I’d suggest this sealant was put on at some time in the past because there was blow-by at the exhaust flange, and someone thought they could correct this issue by applying a sealant.
No sealant of any type should be applied in this area.
There is a possibility that this leak could be causing an erroneous reading of the CHT on the #4 cylinder also.
There is another way to look for an induction leak and that is by using soapy water with a paint brush around the intake pipe where it attaches to the cylinder and also where it goes into the sump.
There also maybe a loose clamp on the intake hose where it attaches to the oil sump. Or the sleeve that is swaged into the sump where the hose attaches may also be loose.
When it comes to older aircraft, anything is possible so, as you can imagine, it also makes troubleshooting more difficult.
Looking at the photos you provided, I didn’t see anything alarming other than what I would expect for an engine with this many hours on it. I was looking for any signs of a clean piston dome, which would indicate a very lean mixture, but they all show deposits, which is normal.
So where do you begin to troubleshoot from here?
My suggestion is that you correct the exhaust stack gasket first, because we know that isn’t good.
Next, I’d check for induction leaks at both ends of the intake pipe on the #4 cylinder, making sure the hose at the sump is in good condition and the metal tube is not loose where it goes into the sump.
Finally, make certain that the hose clamps are tight.
I’d hope the probe wiring is long enough to allow you to move the #2 cylinder probe to the #4 cylinder just to check it to see if it still reads high on the gauge using the known good #2 probe.
Tyler, I don’t think there are any really serious issues here, but just some simple troubleshooting to check things out. This type of situation is not uncommon when dealing with aging aircraft.
For now, I’d forget all of the other suggestions you mentioned because I don’t think we need to dive that deep into troubleshooting the problem at hand.
I think the fact that the bolt for the induction tube collar is missing in the photo, might have something to do with the issue of running lean. It’s probably sucking air in past the gasket because the bolt is missing. Just my observation.
Perform a cylinder leakdown test, other issues could be at play, like valve seat leak, and piston rings not being sealed equally, Hope you find your issue.
Maybe if you installed the missing bolt it would make a difference .
It’s missing 4 cylinders.
is it using oil how’s the idle maybe rings on 4
Bolt missing on intake pipe flange on picture.
May be a good clue.
Jeff
It actually uses a threaded stud, and a nut on both intake and exhaust ports.
Continental uses a brass nut on the exhaust…they don’t rust or seize on the stud.
If you are looking for intake leak (vacuum)or sum sort of exhaust system leak use a simple automotive diagnostic tool (smoke machine) and smoke test it, introduce smoke into the intake tract or into the exhaust and as the test implies look for leaking smoke. Simple. Hope it helps as some leaks of this type are difficult to diagnose and resolve.
THE FIRST THING I WOULD DO IS REPLACE THE CHT PROBE.
Switch the sensor to another cylinder and see if the high reading follows?
That’s RTV high temp silicon, very common in automotive and appears to be holding just fine.
Sometimes used to seal imperfections, sometimes as a “to make sure”, doesn’t effect engine operations.
High temp is not high enough for this application. Red RTV is good up to around 600° F while exhaust gasses are typically around 1500° F.
I agree with Paul that this is likely a exhaust leak. An induction leak would have be to be pretty bad to cause a problem at high MAP, but well worth investigating to see if it is causing a very lean condition. The EGT on that cylinder would have been at or near peak, if that were the case.
Never put sealant on exhaust gaskets. It costs $15 for a new one. Yes the missing bolt is a big no go. The other elephant in the room are you baffle seals. Maybe quietly just take your plane to another AME and have it inspected firewall forward. Two red lights on one cylinder. What does the rest of the engine installation look like?
In the pic of the cylinder, it looks likea stud and nut are missing from the intake riser, left edge of the pic.
I’d recommend looking closely at the baffling at the #4 cylinder, especially the intercylinder baffle.
Jim H – BINGO!
Good catch!
In this case, it is a bolt that is missing.