Cold #4 Cylinder

Greetings,

I've noticed that the #4 cylinder on my IO-360AIB6 runs colder than the rest of the cylinders; CHT ~30F and EGT ~90F colder than the hottest cylinder #3. (typ: 305/1310F @ WOT, 24.5 MAP, 2550 RPM, 11.8GPH, OAT ~65F)

I am using a custom plenum, and I have 1 washer installed between #3 and #4 and the rear baffle. The oil cooler is mounted on the firewall, and fed via a 3" duct located above #4 cylinder.

Compression on #4 was 78/80 at the last cond. insp. (Feb 2014).

The engine is an Aerosport power IO-360-A1B6, dual Lightspeed Plasma III, all Lycoming parts.

Any tips, tricks, sage advice from the hive-mind would be appreciated.

Cheers!

Brian

#3 only

The washer is not required on #4. I ended up fabricating a 1/8 x 2 x 3/4 spacer behind #3 instead of the washer. Very happy with the results so far.

I always move the injectors around until I get the most equal temps. First move the lowest temp to the highest temp, etc, etc. until you like your results.

Do you move the whole injector or just the restricter?

Cheers

I just move the inserts but you should make sure all 4 screens and holes are clean on the injector housings.

Injector?

I swapped injectors a while back and it made no difference -- not surprising as all of the inserts are the same size.

I'm going to remove the extraneous washer behind #4, and open up the space behind #3; will see if that makes any difference.

B

Well i'll be damned...

...there was no washer behind the #4 cylinder. I added two more washers behind cylinder #3, and it appears to have had NO effect.

Definitely a thermodynamicist to weigh in (Dan H. you out there? )

I have a firewall mounted SW 8406R oil cooler, fed with 3" SCEET from behind/above the #4 cylinder and butterfly valve set 1/3 - 1/2 open (Oil temp is 205F - 195F in this configuration @ WOT/2500RPM/7500ALT/60F)

So here's my thinking of things to try next:

1. Reduce the size of the duct feeding the oil cooler -- probably to 2". Switch out the metal box that Van's sells and make my own diffuser for the oil cooler (why not..)

2. Build a duct of some variety for the "exit" side of the oil cooler and dump the air between the exhaust pipes into the slip stream.

3. Go back to 1 AN960 behind #3

Have you done a leaning pull to track all EGT's (CHT) as the mixture is leaned? It seems like the CHT is cool because the EGT is cool. It might seem too rich, but the leaning process should help understand that.

If all the EGT's were the same, then it would seem that the CHT diff is either a differing sensor, or cooling is actually better on that jug.

Can you obtain such data or have it already?

Like Bill said, do a GAMI spread test to find fuel flows at peak egt for each cylinder.
My stock spread (.028 nozzles) was about .5 or .6 gph if memory serves.
There have been stock GAMI spreads reported that are much worse.

A call to Don at Airflow gave me a couple of nozzles (a .0275 and a .027) resulting in a new spread of .1 gph. I have seen my CHTs as close as 5F across all but that was unusual. Usually about 18F spread. #4 is coldest on mine too. I need to cut the #2 dam a little more.

As rzbill said, I would recommend a lean text and see if that cylinder is richer than the others. If so, that would certainly explain it. As long as temps aren't too hot, I would recommend that you equalize internal cooling (tuned injectors) and then try to equalize external cooling (baffles, oil cooler ducts, etc).

If your CHT is around 30dF from the others that is fine. Stop worrying.

If your GAMI spread (fuel flow not EGT) then the heat input is balanced and if the CHT is 300-340 LOP and say 360-380 when ROP???.quite worrying and enjoy.

Take an APS class and learn why!

As the others have said, do a mixture sweep. If #4 peaks last, install a slightly smaller fuel nozzle.

...there was no washer behind the #4 cylinder. I added two more washers behind cylinder #3, and it appears to have had NO effect.

Click to expand...

That just makes a big leak. There's been lots of discussion here about how to improve cooling at #'s 2 and 3 without a leak.

1. Reduce the size of the duct feeding the oil cooler

Click to expand...

Leave it alone.

2. Build a duct of some variety for the "exit" side of the oil cooler and dump the air between the exhaust pipes into the slip stream.

Click to expand...

Limited value if the lower cowl exit size is stock. The purpose of exit ducting is to port the cooler to an area of lower pressure (at or near the exit) than the pressure found within the lower cowl when the exit area is reduced.