#1 Rear Still Hot

[tomcomet]

So the factory remans are in and I have 30+ hours on them. The breakin went smoothly, temps and oil consumption are down and everything is going great except for my old nemesis - high #1 rear cylinder head temps. Argh!

Up here in Canada I am flying around in 0 to -20C and even then I am breaking 400 degrees on #1 rear often and have to crack open the rear cowl flaps. Not normal and not great!

Here is the data from a very recent flight on the NEW ENGINES:https://www.savvyanalysis.com/flight...1-9ec59eaf0ef8

I did have this problem though a little less pronounced with the old, original engines as seen here - https://www.savvyanalysis.com/flight...0-e62f33991d3d

Obviously, the fact that this problem has followed me through both sets of engines points to the fact that the root of my problem is NOT the engines at all. In our never ending quest to fix the snag we have checked and redone all the baffling in the rear, rerouted the air intake hose that was slightly over #1R and gone so far as to use the high heat sealant to caulk and attach the metal baffles to the cylinder heads forcing all air past the cylinder fins (there were a few openings and holes etc.).

A friend of mine (Hi John) has the identical year 337G and he has difficulty getting his engines hot enough this time of year and is constantly bragging about taking off with his cowl flaps closed. This, of course drives me crazy as I am bewildered how a seemingly identical piece of hardware can create such different results. Obviously all airplanes are different and mine is French after all so it is even more so BUT I really want to get to the bottom of this puzzle.

Help!

[tomcomet]

On both front and rear engine #1 & #2 start out colder for both EGT & CHT. The only difference on the front engine the temps all converge and stay together for the most part once warmed up whereas in the rear #1 just stays much hotter. Not sure if them initially being colder means anything or if that is normal?

[edasmus]

Are we positive the CHT is really 400....?? Just a thought here but have you tried swapping the CHT probe from the suspect cylinder to another cylinder and vice versa? Are these the same probes in the exact same locations from the previous engines? It would be an interesting experiment nonetheless. If swapping probes leads to the same temps, then you know the 400 is valid.

I know another favorite of Mike Busch is to check the flow of the injector for that cylinder. Maybe that single injector is all jacked up. Just a thought....

Good Luck my friend!

I feel your pain.

Ed

[tomcomet]

Originally Posted by edasmus

Are we positive the CHT is really 400....?? Just a thought here but have you tried swapping the CHT probe from the suspect cylinder to another cylinder and vice versa? Are these the same probes in the exact same locations from the previous engines? It would be an interesting experiment nonetheless. If swapping probes leads to the same temps, then you know the 400 is valid.

I know another favorite of Mike Busch is to check the flow of the injector for that cylinder. Maybe that single injector is all jacked up. Just a thought....

Ed

We have tried changing probes and the high heat issue does not move so it is not the probe. Yes, checking the injector is one of the next things on our list, however, these are all new GAMI injectors and that same cylinder had similar heat issues on the old injectors so not sure if that is going to help.

[edasmus]

OK, I was hoping you had the same old probes in the same locations on the new engines as in the old engines. If that were the case, I thought a likely probe issue but that would appear not the case based on your probe swapping attempts.

I agree it is probably unlikely your new GAMI injector has an issue but it would still be worth verifying. It's not impossible.

I'm guessing you have a relationship with Savvy Maintenance and Mike Busch.?.?

What do they say about that cylinder temp and what to attempt to do to solve the problem?

[DrDave]

A picture of all of the baffling around the engine would certainly be helpful.

Dave

[kilr4d]

Originally Posted by edasmus

OK, I was hoping you had the same old probes in the same locations on the new engines as in the old engines. If that were the case, I thought a likely probe issue but that would appear not the case based on your probe swapping attempts.

Also need to check the continuity of the wire from the rear probe to the panel. It's entirely possible it's chafing the way that cyl temp jumps around.

Also should put the factory cht probe on the #1 cyl to confirm temps.

[kilr4d]

Originally Posted by edasmus

Are we positive the CHT is really 400....?? Just a thought here but have you tried swapping the CHT probe from the suspect cylinder to another cylinder and vice versa? Are these the same probes in the exact same locations from the previous engines?

Originally Posted by tomcomet

We have tried changing probes and the high heat issue does not move so it is not the probe. Yes, checking the injector is one of the next things on our list, however, these are all new GAMI injectors and that same cylinder had similar heat issues on the old injectors so not sure if that is going to help.

Going forward with this thought, has anyone tested the continuity of the wire from the rear engine to the panel?

Did they re-use the harness from the old GEM or lay in a new harness?

[kilr4d]

Also, I neglected to mention rigging in my previous posts. Crucially important that pushing the mixture lever forward pushes the mixture control on the pump to the forward stop.

[kilr4d]

Originally Posted by tomcomet

A friend of mine (Hi John) has the identical year 337G and he has difficulty getting his engines hot enough this time of year and is constantly bragging about taking off with his cowl flaps closed.

http://www.reactiongifs.com/r/fgwv.gif

Originally Posted by tomcomet

Help!

Bunch of thoughts here; some of which you and I have discussed. I'll break it down into a few different posts.

[kilr4d]

Originally Posted by tomcomet

So the factory remans are in and I have 30+ hours on them. The breakin went smoothly, temps and oil consumption are down and everything is going great...

So I actually have more concerns about your front engine than your rear. The front engine on a Skymaster has better packaging (the cowl is tighter but better designed) from an airflow point of view but your front engine is running hotter than your rear.

Looking at the data I think there's one or two smoking guns and it's the fuel flows and possibly timing. I've attached two flights from this week; one yours and one mine so we have similar ambient temps, etc. The book calls for 18.1GPH takeoff fuel flows and the conventional wisdom has been to pad that a bit. Comparing the two, your front engine ranges from 17.6GPH to 17.8GPH at takeoff power and my front engine seems to stay at 18.3GPH. So the front needs more fuel.

The other thing to look at is ignition timing and the rate with which your cylinder temps rise. Your CHT's climb FAST and this can be an indication of timing that's advanced. As a matter of fact, I'm going to be checking my timing for the opposite reason; I think mine might be a degree or two retarded.

Action items:

1. Check fuel flows as per TCM SID using calibrated gauges.
2. Check timing using a digital angle finder, not just the analog dial with buzz box.
3. Let's park ours sided by side, decowl and compare baffle seals.

[kilr4d]

Originally Posted by tomcomet

Up here in Canada I am flying around in 0 to -20C and even then I am breaking 400 degrees on #1 rear often and have to crack open the rear cowl flaps. Not normal and not great!

Your rear engine is a completely different story and imho it isn't an airflow issue.

The rear engine (except for cyl#1) is way happier than the front....higher fuel flow, gentler CHT rise, consistently cooler temps, etc. From what I see the #1 cylinder is an isolated issue.

Action items:

1. Check fuel flows as per TCM SID using calibrated gauges.
2. Check timing using a digital angle finder, not the old buzz box.
3. Talk to GAMI about the #1 cylinder...confirm correct injector shipped and installed in correct cylinder.
4. Fly and record an LOP mag test. A bad plug or wire can cause high CHT's.
5. Clean injector and confirm flow from fuel injector block.
6. Check for vacuum leak in intake manifold to cylinder.
7. I hate to say it but also borescope the #1 cylinder just to make sure cylinder walls and valves look ok.
8. Let's park ours sided by side, decowl and compare baffle seals.

[kilr4d]

Originally Posted by tomcomet

Obviously, the fact that this problem has followed me through both sets of engines points to the fact that the root of my problem is NOT the engines at all.

Yeah, about that....it's time to try a different mechanic. Seriously. Sometimes all the problem needs is a different set of eyes.

I know it's a pain in the butt to get work done away from your home 'drome but there's a couple other guys around that should take a look at your plane. This needs a methodical process of elimination starting with the basics...fuel and spark.

[JAG]

I am with John - if you have eliminated the easy stuff (Indication issue), you need to look at Fuel, spark and timing.

Some great articles to read were written a few years ago by John Deakin on Avweb, and you can still find them:

https://www.avweb.com/news/pelican/182084-1.html
https://www.avweb.com/news/pelican/182179-1.html

These are just 2 links to get you started - but essential reading to bring focus to the relationship that fuel air mixture and spark have to do with you CHT.

Jeff