CHT at 400 Degrees on 1 cylinder

Tom-D

Tom-D

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Tom-D
Re-Build on a 0-300-A, all baffling is new and tight, all new Superior Cylinders, yet #2 runs 400 Degrees while all others are at 350 +-
Sniff test produces no change in RPM ( no induction leaks)
Mag checks are 50/50 RPM on both mags.

I disabled the primer, #2 now runs at 340 Degrees while all others are +- 10 degrees

WHY ?
 
I assume you’ve swapped the sensors to check the easy stuff first?
 
denverpilot said:
I assume you’ve swapped the sensors to check the easy stuff first?
Click to expand...
Yes, leads were swapped, the 400 degrees stayed with #2. (several times)

All things were set to original, flight tested, and #2 ran 400.
First flight after I disconnected the primer #2 ran 340.

My theory, is we took away the leaking primer fuel, and it runs normally. (leaner)

Am I right?
 
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More likely that the primer is somehow allowing extra air in, causing that cylinder to run lean. (Cracked nozzle? Chafed through spot on the primer line? Bad brazing?) Running too rich usually results in lower CHT, not higher.
 
slacktide said:
More likely that the primer is somehow allowing extra air in,
Click to expand...
No chance. Nozzle is new, lines are new firewall forward. Primer pump never checked.

These are #2 lines with a #60 orifice in the primer nozzle, no way that much of a leak will cause a 50 degree rise in CHT.
 
Do a Gami lean test, figure out what your fuel distribution is.
When you do a mag check, check EGTs, they should go up.
 
teejayevans said:
Do a Gami lean test, figure out what your fuel distribution is.
When you do a mag check, check EGTs, they should go up.
Click to expand...
The 0-300- isn't fuel injected. Plus I'm not certain how to do the GAMI test.
 
Tom-D said:
No chance. Nozzle is new, lines are new firewall forward. Primer pump never checked.

These are #2 lines with a #60 orifice in the primer nozzle, no way that much of a leak will cause a 50 degree rise in CHT.
Click to expand...
And yet disabling the primer line to that cylinder only solves the problem.

Somehow you were getting extra air through that particular primer line and it was running too lean.

Think about this: if there was an issue with the primer system that was causing extra fuel to leak in during operation, it makes sense it would effect all cylinders hooked up to the primer system. Maybe I’m missing something, but I’m not seeing a scenario where a single primer nozzle gets fuel while the others do not.
 
Some engines only have one primer nozzle, as was the case with my 66 Cherokee 140. It isn't clear if that is the case here but sounds like it.

Where did you disconnect the primer? If at the cylinder, try at the primer itself. Plug it off, then unplug and see if you get the CHT rise with excess air.

The o-ring inside the typical primer is easily replaced and you can test it in a bucket of water for leaks.
 
Fearless Tower said:
And yet disabling the primer line to that cylinder only solves the problem.

Somehow you were getting extra air through that particular primer line and it was running too lean.

Think about this: if there was an issue with the primer system that was causing extra fuel to leak in during operation, it makes sense it would effect all cylinders hooked up to the primer system. Maybe I’m missing something, but I’m not seeing a scenario where a single primer nozzle gets fuel while the others do not.
Click to expand...
The primer on the 0-300 goes into the Y pipe and not to any individual cylinder.
It's location is directly below the #2 cylinder.
It is the only primer on the engine it only feeds 2,4,6 cylinders.
Prior to disconnecting this line #2 ran 50 degrees hotter at all power settings. after disconnecting this line #2 runs with in 10 degrees of all other cylinders.
These pictures show the "Y" pipes on each side of the 0-300, only the left side has a primer.
Picture 1 shows the primer nozzle on the "Y" pipe.
second picture shows the proximity to #2
Third show no primer on the right side.
 

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Ray Eaker said:
Some engines only have one primer nozzle, as was the case with my 66 Cherokee 140. It isn't clear if that is the case here but sounds like it.

Where did you disconnect the primer? If at the cylinder, try at the primer itself. Plug it off, then unplug and see if you get the CHT rise with excess air.

The o-ring inside the typical primer is easily replaced and you can test it in a bucket of water for leaks.
Click to expand...
The primer nozzle only has a #60 drill hole as the orifice for the spray nozzle, how much of a leak can that cause.
And I disconnected at the gascolater, which is prior to the primer pump, so the system was never really open to allow unrestricted air to enter.
 
Ray Eaker said:
SThe o-ring inside the typical primer is easily replaced and you can test it in a bucket of water for leaks.
Click to expand...
The two plunger "O" rings are easy to replace, but the "o" ring that shuts off the gas flow when the primer is locked not so easy. But that is next, total re-build of the primer pump.
 
Tom-D said:
The primer on the 0-300 goes into the Y pipe and not to any individual cylinder.
It's location is directly below the #2 cylinder.
It is the only primer on the engine it only feeds 2,4,6 cylinders.
Prior to disconnecting this line #2 ran 50 degrees hotter at all power settings. after disconnecting this line #2 runs with in 10 degrees of all other cylinders.
These pictures show the "Y" pipes on each side of the 0-300, only the left side has a primer.
Picture 1 shows the primer nozzle on the "Y" pipe.
second picture shows the proximity to #2
Third show no primer on the right side.
Click to expand...
I must be missing something, or just become too used to dealing with primer systems on radials, but where in those photos is this primer nozzle?
 
slacktide said:
More likely that the primer is somehow allowing extra air in, causing that cylinder to run lean. (Cracked nozzle? Chafed through spot on the primer line? Bad brazing?) Running too rich usually results in lower CHT, not higher.
Click to expand...

The amount of air that could travel through that tiny line is negligible. It's a .125" OD line with a .065" inside bore. The intake runner on that engine is around 1.5" ID. The runner's cross-secional area is 535 times the tubing's. And that makes no allowance for the massive increase in wall drag of small tubing. I would estimate that the primer line would supply much less than a thousandth of the intake's air. And then add the fact that the primer nozzle has an orifice hardly bigger than a human hair!

Common intake leaks come from a loose hose clamp, or a cracked intake gasket or warped flange. A high CHT can also be caused by a leaking exhaust gasket squirting hot gases at the CHT probe. Found that once.
 
Tom-D said:
The 0-300- isn't fuel injected. Plus I'm not certain how to do the GAMI test.
Click to expand...

The GAMI test has nothing to do with being fuel injected or carburated. Of course, you can't do much to change the results on a carburated engine, other than find and correct defects like bad intake manifold seals and such.

http://www.gami.com/gamijectors/leantest.php
 
slacktide said:
The GAMI test has nothing to do with being fuel injected or carburated. Of course, you can't do much to change the results on a carburated engine, other than find and correct defects like bad intake manifold seals and such.

http://www.gami.com/gamijectors/leantest.php
Click to expand...

This engine operated normally while on test cell, there are no intake Leaks, but #2 runs 50 degrees hotter when installed on the aircraft, and did so for 1.5 hours, (3 half hour hops) then when I disconnected the primer system, it runs normally, all cylinders at 350 +- 10
 
My owner informed me today that #2 failed twice prior to the overhaul. (1100 hours)

So the discrepancy is with the aircraft, not the engine. And the only thing that makes any difference is the primer
 
FWIW on any typical engine installation any of the probes could be getting some sort of cooling either from being tied to something or air passing by it.

For that matter a probe could read hotter than others if its in a tight area or near something much hotter than what its supposed to be measuring.
 
There's an old joke about the guy who goes to the doc because every time he does this, it hurts. This thread so reminds me of it. Install the primer, temps go up. Remove the primer, temps go down. Install the primer temps go back up. ..so its the primer system in some fashion. Do you have a hand vacuum pump or something you can fit over the nozzle the see if there really is a leak in the system?
 
Who cares how it runs? That engine is so pretty it'll get you home on its looks alone!
 
Chip Sylverne said:
There's an old joke about the guy who goes to the doc because every time he does this, it hurts. This thread so reminds me of it. Install the primer, temps go up. Remove the primer, temps go down. Install the primer temps go back up. ..so its the primer system in some fashion. Do you have a hand vacuum pump or something you can fit over the nozzle the see if there really is a leak in the system?
Click to expand...
new pump on order.
 
Ray Eaker said:
Couldn't the oring(s) in the pump be replaced? Or is it an electric pump?
Click to expand...
The 2 "O" rings that are on the plunger are easy to replace.
But what prevents the pump from leaking is not.
 
Tom-D said:
My owner informed me today that #2 failed twice prior to the overhaul. (1100 hours)

So the discrepancy is with the aircraft, not the engine. And the only thing that makes any difference is the primer
Click to expand...

As I was reading this.... Kept wonder if the primer line somehow interfered with airflow over #2's cooling fins? Funny how it worked on the test stand and not in the plane.

Was baffling and air flow the difference between the test stand and the actual mounting within the plane?
 
NordicDave said:
As I was reading this.... Kept wonder if the primer line somehow interfered with airflow over #2's cooling fins? Funny how it worked on the test stand and not in the plane.

Was baffling and air flow the difference between the test stand and the actual mounting within the plane?
Click to expand...
Primer lines go from the gascolater up the firewall, to a fitting passing the fuel thru the firewall then a line to the pump, then back out thru the firewall the same way, then down the firewall and forward under the cylinders to the "Y" pipe and primer fitting.

baffling is all new and tight. but airflow on the stand is never the same as in the cowl, and flying.
 
Just to give an example of how much air will flow through a small hole - in modern automotive systems, a hole the size of half a mm will be obvious in lambda correction values.
If I felt like running numbers, I could tell you how much the EGTs would increase for given manifold pressure and the size of the hole.
It's more than you think.
 
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