Jab3300 cylinder #6 running too cool...

[ldmill]

Question for the group. I've got 6 hours on my Waiex (N81YX) now and am into the tweeking stage at this point in time. My CHT levels for cylinders 1 - 5 are all in the 290 - 320F range during cruise at 2800 rpm range. However, cylinder #6 doesn't get any warmer than 230F. All six EGT's are between the 1270 and 1330F. Suggestions on how to deal with this? Should I rivet a small angled diverter(turbulance) plate in front of the #4 cylinder? It's a perfect straight shot back to #6, so I was opinioning that something to break up the flow path somewhat would help.

Thanks!
Lorin Miller

[N111YX]

I'd be skeptical of that reading, Lorin, especially with regards to #6. Could the last cylinder in the pack really be getting such an incredible blast of cooling air? Maybe, maybe not.

My hottest cylinders have been all over the place over the last 333 hours. My number 1 is always the coolest though and I attribute that to air blowing right on the sensor.

Good luck in experimenting!

[ldmill]

Kip - after much fiddling around with the baffles, I've been able to balance out my CHT's pretty well now. #6 reading was in fact correct. The air was blowing right over the front two cylinders and only hitting #6. I did have to rivet in air dams just above the split between #2/4 cylinders and #4/6 cylincers. I also did this between #3/5 cylinders as well as blocking #1 leading edge fins some. This slowed the air flow down/deflected it some- and created a high pressure area over the front two cylinders and forced air down between them. Interestingly enough, #2 was the hottest on the entire engine followed by #4. I've now got all 6 cylinders reading between 260 - 290 degrees on average. CHT's are never really an issue at this point. During a hard climb, I just have to watch EGT's more than CHT's now.

Oil temps are also well in control - stay at 187 almost all the time except for a very hard climb, then they will start up. Very tight baffling for the oil cooler.
Cheers!
Lorin Miller N81YX

[N111YX]

Great! See you at OSH...:)

Kip - after much fiddling around with the baffles, I've been able to balance out my CHT's pretty well now. #6 reading was in fact correct. The air was blowing right over the front two cylinders and only hitting #6. I did have to rivet in air dams just above the split between #2/4 cylinders and #4/6 cylincers. I also did this between #3/5 cylinders as well as blocking #1 leading edge fins some. This slowed the air flow down/deflected it some- and created a high pressure area over the front two cylinders and forced air down between them. Interestingly enough, #2 was the hottest on the entire engine followed by #4. I've now got all 6 cylinders reading between 260 - 290 degrees on average. CHT's are never really an issue at this point. During a hard climb, I just have to watch EGT's more than CHT's now.

Oil temps are also well in control - stay at 187 almost all the time except for a very hard climb, then they will start up. Very tight baffling for the oil cooler.
Cheers!
Lorin Miller N81YX

[fastj22]

Now that I've reoriented my Aerocarb vertically, it seems all the cylinders are getting even mixture and the plane has a lot more power. My EGTs are well balanced, but I am having issues with my #2 CHT too. Its higher by 50 degrees than the rest. I've cut down the fence on that side and its helped a bit, but still too hot, especially on climbout at full throttle. #4 and #6 are happy and cool.
I'm now thinking of installing some deflectors to slow some of the air right above #2 and direct it down on the head. I had done that previously between 3 and 5 and it helped a lot. I guess that's why its called experimental.

[fastj22]

Update.
I put a "choke" on the incoming air on 2,4,6 (left side pilot view). This forces air thru the #2 head fins and not over it. Most of the air was going over #2 to the back of the duct. I was expecting 2 to go cool and 4 and 6 to suffer. I was right. Before, #2 was hot and 4 and 6 where cool.
I then trimmed back the choke to allow more air over the #2 fins and put a small deflector between 4 and 6.
Improved. 2 stayed cool, and 4 and 6 were better but not great. But I'm making progress. I have now cut another 1/4 inch out of the exit to increase flow. Will fly tomorrow morning to see the results.

BTW, 1,3,5 are acting great. I think I have that side balanced.

[andrewp]

This is interesting - I was going to post a "WT Heck" type post about my poor Jab running too coll on 2,4,6. Actually it runs ok in cruise, but it is a real problem when I am descending when if I pull power back, #6 used to plunge below 212F. After fiddling with little deflectors and diffusers I managed to make it worse and then I had all 3 cylinders on the left side go below 200 as I was turning base to final. It has been kicking my butt as I can't do stalls and climb and descent testing now I have some smaller wheel pants on because the engine gets too cold (!). What a problem to have.

I just today have been adding more deflectors ... the more I tried to choke off #6, the more air when through #2 and #4. My last attempt has been to but a LOT more metal in the plate restricting airflow. As it sits, #6 is now too warm in cruise for my liking and #4 and #2 are still getting to cool, but it is a lot better so I know what I need to do to make it better. It is just a matter of tweaking, large and small.

The main reason for me writing was that this seems to have been something that has kicked in at 30+ hours, like my engine has finally broken in. I am so used ot it running hot that I am disturbed when it doesn't. In fact, at one stage today, I had four cylinders falls below 200 as I landed. On a 55F day. Give me a break. What a long way away from first flight this is. I was curious whether this fits anyone elses experience. Just seemed to be a little late in the game for my Jab to be making a behavioral change like this.

AP
#618

[daleandee]

This is interesting - I was going to post a "WT Heck" type post about my poor Jab running too coll on 2,4,6. Actually it runs ok in cruise, but it is a real problem when I am descending when if I pull power back, #6 used to plunge below 212F. After fiddling with little deflectors and diffusers I managed to make it worse and then I had all 3 cylinders on the left side go below 200 as I was turning base to final. It has been kicking my butt as I can't do stalls and climb and descent testing now I have some smaller wheel pants on because the engine gets too cold (!). What a problem to have.
AP
#618

Andrew,

I have a Corvair so maybe I should keep out of this conversation but I worried about mine running too cool as climb-out CHT's are 255 and cruise CHTs have been in the 200-225 range. But then the guys that build and teach us to build these engines ask the same question that you have asked yourself. That is, "what's the problem?"

I guess I could go about making it run hotter but if I leave it alone I'll like it better when the 100º days of summer return. Sounds to me like yours is getting close to where you want it to be.

Dale
N319WF

[andrewp]

I agree and would love to leave it alone, but I don't know what the bad side of falling below the 212F minimum cylinder temp for applying full power is. Makes it difficult to do touch and goes!

[DCASonex]

I had same with my 3300 and #2 tended to be second the hottest. Found that spiraling air from prop pushed air up and over cylinder #2 and over feed cylinder #6. Added sort of a dropped ceiling to baffle over area leading to cylinder #2 approximating clearance around cylinder #1. Now all cylinders within a 15 deg f range in cruise, but still see the effect somewhat during climb when ram air is reduced relative to spiraling air from prop. E-mail me if you would like a couple of photos.

David A.