EGT Temps Out of Control

[Keeta182]

Question: What can cause EGT's to be as much as 180-200'F difference in one cylinder to the next?

Engine: 0-470-R with 700 hours in C182L
One Pilot plane for past 800 hours
Known facts: JPI data recorder has told us this....
1) EGTS have risen as high as 1690
2) Fuel flow at 1600'F is 12.0 gph
3) Cylinders 1 and 3 are the ONLY ones running exterme heat
4) Cylinders 4 and 5 are operating normal
5) Cylinders 2 and 6 are very COOL both in EGT and Cylinder temps
6) Consistent now for some time
7) Only way to keep cylinders 1 and 3 under 1500'f is with a FF of 15 gals
8) At 13 gph temps spread are 1300 on 2 and 6 and 1500' (aprox) on 1 and 3 with 4 and 5 right in the middle - on a graph its like looking at 3 lines as the two cylinder pairs are almost identical each time
9) JPI set up has been checked for proper wiring and calibration
10) Burned up Cylinder 5 at 600 hours - replaced, then cylinder 5 and 3 failed 92 hours later. Cylinder 1 was operationg normal prior to this event.
11) When carb heat is applied all EGT temps tend to normalize to a consistent and acceptable temp

Can this be a CAM issue?
Can this be a fuel flow issue?

I have spent hours reading all types of info and find it very inconsistent as a whole so now I hope you pilots may shed some light on why this has occurred.

Thanks in advance to any answers!

 

[gismo]

Question: What can cause EGT's to be as much as 180-200'F difference in one cylinder to the next?

Engine: 0-470-R with 700 hours in C182L
One Pilot plane for past 800 hours
Known facts: JPI data recorder has told us this....
1) EGTS have risen as high as 1690
2) Fuel flow at 1600'F is 12.0 gph
3) Cylinders 1 and 3 are the ONLY ones running exterme heat
4) Cylinders 4 and 5 are operating normal
5) Cylinders 2 and 6 are very COOL both in EGT and Cylinder temps
6) Consistent now for some time
7) Only way to keep cylinders 1 and 3 under 1500'f is with a FF of 15 gals
8) At 13 gph temps spread are 1300 on 2 and 6 and 1500' (aprox) on 1 and 3 with 4 and 5 right in the middle - on a graph its like looking at 3 lines as the two cylinder pairs are almost identical each time
9) JPI set up has been checked for proper wiring and calibration
10) Burned up Cylinder 5 at 600 hours - replaced, then cylinder 5 and 3 failed 92 hours later. Cylinder 1 was operationg normal prior to this event.
11) When carb heat is applied all EGT temps tend to normalize to a consistent and acceptable temp

Can this be a CAM issue?
Can this be a fuel flow issue?

I have spent hours reading all types of info and find it very inconsistent as a whole so now I hope you pilots may shed some light on why this has occurred.

Thanks in advance to any answers!

The first thing I'd suspect is improper probe placement. The EGT probes should be a minimum of 2 inches (3 is better) downstream from the cylinder exhaust port. If they are closer than that the probes may be sitting in gas that's still burning. I'm not used to seeing EGTs above 1550 on NA engines and 1690 is way beyond that which is one reason I'm thinking the probes might be too close. Even if all probes are equally close, a small difference in mixture or timing could put those two probes inside the exhaust flame tip while the others were just beyond it.

If that's not the cause you might have an induction system leak near those cylinders or your ignition (or valve) timing might be retarded. An exhaust valve leak would be another possibility.

FWIW, the absolute EGT values aren't all that important at cruise power settings, the delta from peak EGT is what counts. That said, such high numbers suggest that the two problem cylinders are operating at or near peak EGT which is not a good thing.

 

[rainsux]

It could also be probe problem. Swap them around and see if the problem moves.

Could it be a cam problem? Possibly, but away too early to be sweating that ...


Borescope the cylinders, taking a close look at the exhaust valves.

 

[Tom-D]

Did just start doing this ?

 

[Dan Thomas]

A cylinder burning oil can have a higher EGT. What do the sparkplugs from those hot cylinders look like?

Dan

 

[N2124v]

How about engine baffling? Blowing cold air around.?

 

[Keeta182]

Thanks for all the great input to date....

Here is what we know as of today...
1) All egt probes were in correct alignment and distance to head of exhaust manifold
2) Compressions on #2 are low, all others are high 60 to low 70's
3) BAffeling and cooling is good
4) Issue has been getting worse slowly and decidely for the #1 and #3 cylinder


So now that I have stirred the curiosity here is additional items found today....

Iw ent with my gut to check the lifter and see if we were ok on gapping. Spec is .080 to .200 (big huh?) for the valve tolerances. Right out of the gate we saw Cyl 1 exhaust at .270 so we thought...AHH Eureka!...alas that was not only thing we found. See attached photo...

So what we have here is a definate lack of tolerances from the cam shaft to lifters maintained...

The question is for me now is how did this cam shaft cause this damage and how did the lifters fail when all parts were new 700hours ago...I am trying to understand now is my flying creating an issue or exsaperating one already there? The thought is there are corrosion rings and pits halfway up the lifter so was this the inital cause? The engine flew very little for 100 hours over 4 years then 100 plus hours the last 6.

At this point I am merely wanting to help anyone else see the symptoms before it gets away and causes a catastrophic issue

 

[Keeta182]

Update:

The cam is "lapping" as it has been described. The lifter on #1 exhaust looked like it was beaten with a ball peen hammer until it cried! Some similar aspects to #3 as well. The gap tolerances were close to .300 (spec is .080 to .200) for valve gap to rocker. So the temps increasing over time were due to continuous wear down of the lifter pitting and cam pitting from "slapping" rather than a smooth roll against one another. This created improper firing and opening instances in exhaust and intake tolerances. It appears the cause was corrosion that occurred while the plane was sitting dormant prior to my use. It has no less than 125 hours a year for the past 5 years but it only had 100 hours over 4 years (studying logs now to see how long a period it sat without running at all) prior. The lifter walls showed corrosion pits that were apparent. It went from a high humid location to dry location at the 100 hour mark. Logs indidcate lifters and cam were new at OH, but I have no knowledge of shop or mechanic that did work.

So even though signs indicate a good overhaul was done, you can't fight mother nature and the law of physics.

To see a pic of the lifter go to http://www.hci3.com/gallery/signature-interiors/12562225

Thanks to you guys who responded, always great to stir a pot of knowledge.

 

[Hiperbiper]

# 2 and #11 would make me look at the Fuel flow gauge as in-accurate if this is what you use to set your mixture. Also #11 would lead me towards fuel/induction problems. Cam wear can't be fixed by carb heat (I don't think).

If you leave it full rich do you see the same issues or is this when you wind out the mixture?

You stated # 5 "burned up" and then #5 and #3 "failed". How did #5 die each time? Exhaust valve erosion? Soft or dead rings? Scored cylinder?

When you state JPI has been checked for proper wiring and calibration was this done by JPI or their rep?

Chris