Interesting engine baffle observation...

[Lood]

Well, I certainly going to test it on my engine. My cylinders #1,2 & 3 are very close together, but #4 runs 25 - 30 deg hotter. It's probably not a big deal, ut it annoys me endlessly - more so, seeing that it is a freshly overhauled engine. I haven't done the Gami lean test to determine where #4 runs ITO mixture, compared to the other, but this wedge solution makes perfect sense tome WRT the airflow around the cylinder.

[Steve65E-NC]

This is an interesting stream.  My #3 has always been more hot than the spark plug probe problem would suggest.  I take off with JPI on #3.  In warm weather I have to keep the climb speeds over 125 mph to avoid going over 400 on #3 CH.  I think I will try the little piece of glued on silicon, per Bob's photos,  to open up the cooling passage behind #3.  I do a lot of work on my aircraft, under proper supervision, and feel comfortable with this experiment.  

 

Thanks.  

[Shadrach]

Actually, my name is Ross!

[Hank]

That's what happens when you disappear for so long. Welcome back!

[Oscar Avalle]

This is an interesting stream.  My #3 has always been more hot than the spark plug probe problem would suggest.  I take off with JPI on #3.  In warm weather I have to keep the climb speeds over 125 mph to avoid going over 400 on #3 CH.  I think I will try the little piece of glued on silicon, per Bob's photos,  to open up the cooling passage behind #3.  I do a lot of work on my aircraft, under proper supervision, and feel comfortable with this experiment.  

 

Thanks.  

It sounds ok. I will do the same with my #3. My #3 is very hot and this may help. I will report back once I am done.

 

Actually, Wasn't there somebody else who mentioned that he did the same and had a similar result? Or is it me that I am spending too much time around here...

[Bob_Belville]

As reported elsewhere, this trick cut my delta T for #3cyl CHT from +30/35 to +15/20. Today, at the suggestion of my favorite A&P, I make it a double thickness of standard sealing material. I'm anxious to see if that helps even more.

[Shadrach]

Oscar,

I look forward to another data point!

[Oscar Avalle]

I tried to do the same, but it seems that the design of the doghouse of the M20C (70) is different...

[M016576]

Ours, #1 is the hottest cylinder at all times

#1 used to be the hottest on mine until I removed that little plate in front of #1. Now it's 60 degrees cooler than before: typically in the low 310's. #3 gained about 5-10 degrees- it now sits around 340.

[Bob_Belville]

#1 used to be the hottest on mine until I removed that little plate in front of #1. Now it's 60 degrees cooler than before: typically in the low 310's. #3 gained about 5-10 degrees- it now sits around 340.

Byron, I suppose those temps are your 30-40 LOP temps @ 60% power? 

What would your CHT look like @ 75%, 100 ROP?

[jetdriven]

Bob,  thats 15-25 LOP at 65%, the 75% 10.0 GPH (low) and 15-25 LOP (high) LOP numbers are 360 on #3 and #4 at low altitude, and they push 380 at altitude.

 

The cowl flaps on our machine close tightly. I am convinced there is huge amount of excess air that goes into the M20J cowling with no where to go, our center top cowl fastener is missing right now, and on a 200 MPH IAS low pass, the spot where the fastener goes is bulged up almost a half inch.  Plus if you get a front crank seal leak, the oil blows out the front of the cowl behind the spinner onto the windshield.  If you reduced the inlet area by half it would lower drag and not affect CHT much.

[Bob_Belville]

Byron, thanks. your cowl is still more efficient than mine, with all I've done.

 

I came back from MRH Sunday @ 6000' OAT 60F. @ 60%,   8.0 gph LOP I was seeing cht2&4:357 cht1&3:373. OT @ 192.

 

2 days earlier going to MRH      @ 7000' OAT 56F   @ 75% 11.5 gph 100 ROP I got     cht2&4:367 cht1:377 ; cht3:388 OT 201 withe cflaps open.

later in the flight @ 10.5 gph, 71% indicated HP, the temps were all the same as @ 11.5.

 

OilT is very sensitive to cowl flap position. closing the flaps gradually results in a liner rise in OilT.

[bumper]

 

I should have mentioned that it's RTV'd (high temp) in place... If it were to actually come loose, what kind of mayhem do you think a 2X10MM piece of silicone rubber would cause?

 

[Bob_Belville]

Oh I dunno, it could get blown back and forth, sort of like a hail stone, gathering velocity and energy until it is finally able to punch hole in the engine case resulting in a catastrophic total loss of oil and eventually causing the plane to end up UDITWOF (upside down in the weeds on fire). Just sayin' :c)

 

bumper

"It" is a piece of 1/8" fg reinforced silicone baffle seal. IOW is "rubber". www.aircraftspruce.com/catalog/appages/siliconecowlseals.php?clickkey=12783

And to put it in place one uses a good sized screw drive or similar to open the space between the cyl and the sheet metal baffle behind #3. Slide the rubber in and when the pry bar is removed the rubber is firmly pinched holding the baffle wall a little further off the cyl. (My A&P/IA assured me more than once there is no stress to the cyl from this spacer or the act of inserting it. If one were to pry too hard it might be possible to crack the baffle sheet metal.)

[Shadrach]

Me thinks bumper is being sarcastic...

[Bob_Belville]

Well, I doubled up on the shim behind #3 cyl. but if anything that cylinder is now hotter relative to #1. I think I'll go back to 1 thickness of silicone seal. 

[Shadrach]

Careful Bob, that piece of baffle material is too big. It's preventing air from circulating around an area the width of 5 fins, plus creating turbulence around it. Look at the pic in my OP; it's very low profile (narrow). That big piece you have in there is probably killing 10% of your airflow around that cylinder. Hot spots are not a good thing.

[flyingvee201]

Careful Bob, that piece of baffle material is too big. It's preventing air from circulating around an area the width of 5 fins, plus creating turbulence around it. Look at the pic in my OP; it's very low profile (narrow). That big piece you have in there is probably killing 10% of your airflow around that cylinder. Hot spots are not a good thing.

 

Maybe use Ross' thin strip measurements and double stack it by gluing two thin pieces. Maybe use RTV temp stuff to glue the two thin strips together?

[Bob_Belville]

Maybe use Ross' thin strip measurements and double stack it by gluing two thin pieces. Maybe use RTV temp stuff to glue the two thin strips together?

The silicone fits very tight. I will pull the wide piece out an put a minimum wide piece back in. 

 

I suppose I should be a little concerned about transferring vibration from the engine to the whole baffle structure. I have some cowl cracks and believe I need to replace the 12 year old  Barry Engine Mounts. (The engine is sagging relative to the cowl.

[Shadrach]

Your engine is running hotter now?

[Shadrach]

Search "target EGT method". 25X25 is really kind of a lousy method. Took me a decade to break my Father of it...

[Bob_Belville]

Boy, I've tried to get modern with WOT & 2650 RPM for climb several times (25 square was SOP when I owned my 1st M20E 30 years ago) but even at 110-120 KIAS CHTs are pretty hot. Pulling back to ~ 25" seems to result in cooler CHTs @ the same IAS.

[romair]

Bob - is your fuel flow high enough at take off? That could be a cause for high CHTs.

Stefan

[Shadrach]

Max FF is not adjustable on the Bendix RSA. The only adjustment is idle mixture.

[Bob_Belville]

Bob - is your fuel flow high enough at take off? That could be a cause for high CHTs.

Stefan

Stefan, data from last flight: (from KIWI, elev 50') 29.4 & 2644; FF: 17.4

 

17.4 is typical of my max flow. Prop control was firewall, max RPM varies some from flight to flight, seems to be affected by Oil Temp. (IO360A1A)