I have a -6 that #3 & #$ are overheating at full power on takeoff. They go over 410 before pattern 800'. I have to throttle way back and let them cool for about 2-3 minutes then I can climb at will. I have tweaked and sealed the baffling all I can. Its the tightest baffling I have ever seen (and as an active AP, I see a lot of them). I installed an (temp) eight inch long 45 degree angle at the rear of the outlet tunnel and it seemed to help. So I then removed that and cut out a two inch by eight inch section of the rear of the tunnel trying to add outlet area. It made it worse. Now what.
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cylinder head cooling
- Thread starter 49clipper
- Start date
AlexPeterson
Well Known Member
Hours and hours of reading in the archives...
on this one. Airspeed, fuel flows, OAT. 410 doesn't sound high depending on some of those factors.
Search for cylinder in the title section and you'll stay busy reading for quite some time.
The temps you show for climb many would consider enviable...
on this one. Airspeed, fuel flows, OAT. 410 doesn't sound high depending on some of those factors.
Search for cylinder in the title section and you'll stay busy reading for quite some time.
The temps you show for climb many would consider enviable...
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cyl head temps
They are not enviable to me.
fuel flow on takeoff shows 13.2 gph
I just calibrated that so it may be showing a tad high. the book says it should be slightly less than that, I think its getting plenty of fuel. Its burning 9.25 gph in cruise at 8000' and 75%pwr.
They are not enviable to me.
fuel flow on takeoff shows 13.2 gph
I just calibrated that so it may be showing a tad high. the book says it should be slightly less than that, I think its getting plenty of fuel. Its burning 9.25 gph in cruise at 8000' and 75%pwr.
It has happened where the Lycoming inter cylinder baffels have been omitted. You do have those right?
Not running an O-320 7:1(150hp) Upgraded to 8.5:1(160hp) with 150hp jetted carb?
Throttle arm is hitting the wide open stop when pushed full fwd (enrichment) ?
Mixture arm hitting the full fwd stop when full fwd?
Timing checked?
100LL/Mogas/Auto gas/Auto gas with ethanol?
FP/CS prop?
Not running an O-320 7:1(150hp) Upgraded to 8.5:1(160hp) with 150hp jetted carb?
Throttle arm is hitting the wide open stop when pushed full fwd (enrichment) ?
Mixture arm hitting the full fwd stop when full fwd?
Timing checked?
100LL/Mogas/Auto gas/Auto gas with ethanol?
FP/CS prop?
Kyle Boatright
Well Known Member
Your temperatures are fairly typical for an RV-6 or 6a. You might drop the temps on #3 and #4 by installing air deflectors in front of #1 and #2. In my case, a deflector in front of #1 resulted in a 30 degree drop in CHT on #3.
My air deflector on #1 is about 1.25" high.
My air deflector on #1 is about 1.25" high.
cyl head temps
yes , of course I have the intercylinder baffles and I even rtv's the 1/16" gps
Yes, throttle arm hitting stop
yes, mixture arm full at stop
like I mentioned, I checked the timing at 5hrs and now its 13.5.
100LL, nothing added. no leaning (no ethanol)
FP sensenich
No conversion, 8.5 :1 engine
O-320-D1A with precision carb
(I do have a concern with the carb, though. At altitude (as high as 8K), I cannot lean but very slightly or I get an immediate rpm drop, like its already lean. About three clicks out on the cable and I can see a drop on the rpm (digital). I suspect it is running lean. Never had an engine that did not take a lot of leaning at that altitude. Without my egt working, that leaves me guessing.
yes , of course I have the intercylinder baffles and I even rtv's the 1/16" gps
Yes, throttle arm hitting stop
yes, mixture arm full at stop
like I mentioned, I checked the timing at 5hrs and now its 13.5.
100LL, nothing added. no leaning (no ethanol)
FP sensenich
No conversion, 8.5 :1 engine
O-320-D1A with precision carb
(I do have a concern with the carb, though. At altitude (as high as 8K), I cannot lean but very slightly or I get an immediate rpm drop, like its already lean. About three clicks out on the cable and I can see a drop on the rpm (digital). I suspect it is running lean. Never had an engine that did not take a lot of leaning at that altitude. Without my egt working, that leaves me guessing.
cyl head temps
Kyle,
What kind of dams, vertical against the fins or what? How high? How much hotter did #1 get after the dam?
I just did one takeoff and saw 440f at 800' climbing at 100mph. I don't think thats normal.
Kyle,
What kind of dams, vertical against the fins or what? How high? How much hotter did #1 get after the dam?
I just did one takeoff and saw 440f at 800' climbing at 100mph. I don't think thats normal.
The ramps on the upper cowl (top) are not glassed on the inside (center of aircraft). I do not see any opening on the other side though, so there is no where for the air to go, if it entred the ramp. I don't see how that could affect it.
I think I will investigate that carb and make sure it has the right jet. That is a very good idea. According to the fuel flow, it is getting plenty of fuel. It seems to agree with the Lycoming charts.
Initially, #4 was the hottest cylinder and I installed a 3" tube from the 3" hole for the oil cooler (above #4) forward 7" to almost #2 and that moved the hottest cylinder to #3 improving #4 cooling a lot. I was losing all the cooling air to the oil cooler.
Jim CFI/AP/IA
Kyle Boatright
Well Known Member
Unless you're in an RV-4 (they cool extremely well), you're gonna have cooling problems on extended 100 mph climb outs. Lower the nose a bit. As I mentioned in another thread, 110-120 knots works for me.
The cylinder blockers go right up against the cylinder head fins. If you look into the cowling of numerous spam cans, you'll find similar devices. Again, mine is about 1.25", but you may need a taller or shorter version. People often just put a temporary piece of aluminum duct tape on there and try different heights to optimize things.
The impact of the cylinder blocker on #1's CHT's was negligable - 5 degrees, 10 degrees, something like that.
I would get the EGT fixed, look at those numbers. I suspect you will be drilling the jets before this is over.
I'd bet on Carb
Your #3 and #4 being 60 to 85 degrees higher, plus your experience of not being able to lean, indicate to me a too lean carburator. I've experimented a fair amount with the O320-D1A and various carbs and found the jet needs to be about .095 or .096 minimum. Mine needed .099. Mixture at cruise is nearer the rear (lean) than the full rich position.
I believe the proper part number for the carb is 10-5217 or 5017 (memory not serving me now) but do a search her on this site and you'll find the proper part number. Use a reamer, not a drill bit to make the jet larger. do it in small increments taking care to be sure it is straight and secure on the drill press. then fly it and see if that doesn't do the trick.
Good luck
Ron
N8ZD
Your #3 and #4 being 60 to 85 degrees higher, plus your experience of not being able to lean, indicate to me a too lean carburator. I've experimented a fair amount with the O320-D1A and various carbs and found the jet needs to be about .095 or .096 minimum. Mine needed .099. Mixture at cruise is nearer the rear (lean) than the full rich position.
I believe the proper part number for the carb is 10-5217 or 5017 (memory not serving me now) but do a search her on this site and you'll find the proper part number. Use a reamer, not a drill bit to make the jet larger. do it in small increments taking care to be sure it is straight and secure on the drill press. then fly it and see if that doesn't do the trick.
Good luck
Ron
N8ZD
Kyle Boatright
Well Known Member
Wouldn't a too-lean carb cause all cylinders to be excessively hot? I would think airflow is the issue in this case, because there are such large differences between cylinders.
With a FP prop the engine is way over square on Takeoff. Not really a problem unless too lean. Lower Altitude means more power, more gas needed. If he is lean on Takeoff the CHTs will go up but not necessarily the same amount depending on several things, mixture, OAT, IAS, ALT, cylinder location, baffeling, etc. My bet is on too lean. The giveaway is the cruise lean symptoms and the questionable FF gauge accuracy.
cyl head temps
First off,
thanks for all the quick replys. I know you guys who own rv's have a world of knowledge about them specifically that helps.
Kyle, I agree, since I am only having problems with 3&4, it makes me think of airflow also.
Also, I will try some air dams before next flight. That sure would be a simple fix.
I will adjust my climb. Being new to the RV, I was not sure the technique on climbout. It climbes so well at 100, I just did that till pattern altitude, then went to a cruise climb of about 125-135mph. The cruise climb works fine once i cooled the cylinders down.
Ron, My carb number is 10-5217. I will have to check the engine tcds to be sure its correct. It came with the engine from lycoming but that doesn't mean its right. Thanks for the data on the jets, I will definety check that out. Doesn't make any sense that at 8000' it doesn't want to lean. Sounds lean to me.
I just went out and checked the ramps in the inlets. They are open on both sides, but go no where. I guess I don't understand those.
I will also recheck the timing and controls since I will have the cowling off again. Thanks for all the replies.
Jim
N189EM RV-6
First off,
thanks for all the quick replys. I know you guys who own rv's have a world of knowledge about them specifically that helps.
Kyle, I agree, since I am only having problems with 3&4, it makes me think of airflow also.
Also, I will try some air dams before next flight. That sure would be a simple fix.
I will adjust my climb. Being new to the RV, I was not sure the technique on climbout. It climbes so well at 100, I just did that till pattern altitude, then went to a cruise climb of about 125-135mph. The cruise climb works fine once i cooled the cylinders down.
Ron, My carb number is 10-5217. I will have to check the engine tcds to be sure its correct. It came with the engine from lycoming but that doesn't mean its right. Thanks for the data on the jets, I will definety check that out. Doesn't make any sense that at 8000' it doesn't want to lean. Sounds lean to me.
I just went out and checked the ramps in the inlets. They are open on both sides, but go no where. I guess I don't understand those.
I will also recheck the timing and controls since I will have the cowling off again. Thanks for all the replies.
Jim
N189EM RV-6
Kyle Boatright
Well Known Member
You really do need to glass in one end or the other of both ramps. The opening provides a good path for air to escape the baffles without any benefit.
AlexPeterson
Well Known Member
Only if the baffle seal material doesn't ride up and down the ramps. Each case seems to be a bit different, depending on installation details.
Having #3 and #4 too hot can easily be mixture distribution. That seems to be classic lycoming based on many posts on this forum. Two cylinders may be running closer to peak heat output than the other two from a mixture point of view. When you get the egt's running it will help diagnose this immensely. Much in the archives about that also. It is hard to believe how uneven the mixture distribution seems to be in these engines. See:
http://www.n66ap.alexap.com/Mixture_article.htm
for a bit of discussion on this(added some carburetor charts).
Additionally, your total fuel flow at full throttle, near sea level does seem to be low. I believe around 14.5 gph or so for a 160 engine is correct. That may bring the temps down a little.
I don't know of any RV's (except as Kyle has noted, perhaps some -4') that can climb at 100 mph in the summer and not roast.
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vlittle
Well Known Member
This is a common problem: high CHT on take off and lack of leaning capability in cruise. Solution is to re-jet the carb. Several of my RV friends, plus myself have done this with good results. AeroSport did my engine and they rework my carb under warranty.
It's related to the efficient induction system of the RV's, I think.
Vern
As others have already posted, I also believe you have a carb that is causing a lean condition. Your GPH reading is not all that high for takeoff power. Also , at 8000 ft you should be able to lean enough for at least a 150 degree EGT change. 200 deg. is not unusual.
The reason for your confusion about air leaking through the inlet ramp is because it depends on how the baffling and baffle seals are installed (this is one of the problems with in the on line RV community.. there is lots of different ways to do things. Sometimes multi pal ways that are right.)
Some builders install the baffles so that the seal of the fwd sides does not lay on the ramp but instead seals against the inner surface of the cowl (this is how the RV-4 was done because of the cheek cowl. The proper way to do it is to install the sides so they meet the cowl just outboard of the air inlet opening. Then trim the baffle side to clear the ramp and install seal so that it seals on the surface of the inlet ramp. If done this way there is no leakage path through the inlet ramp.
I believe you have a combination of things.
1) It sounds like this is a new airplane with possibly a new or freshly overhauled engine? If so you need to learn that RV's are much more tightly cowled than certificated airplanes you may have worked on. During the breakin period you can see temps higher than you would like (the CHT's you are seeing aren't all that bad for an engine breaking in cylinders). You didn't mention what instrument you are using to read the temps?
2) The previously mentioned air dams for in front of cyl 1 & 2 will help lower the temps of 3 & 4.
3) Your fuel flow and inability to lean much at altitude indicate to me that you are running leaner than ideal.
Put all these together and you have higher than desired temps (sometimes it only take one of them).
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cyl head temps
I don't know if you guys saw my last post on another thread. Problem solved today on the high temps on 3 & 4. Kyles suggestion on the dam on #1 seemed to do the trick or most of it. I first made it 1.5" tall, which did wonders, then trimmed it to 1.25", which was way better. Now ! is the hottest but not bad. I climbed out this afternoon (after mods) and kept full power in to 3000', which is what I could not do before. Temps never got over 392 for #1 and the rest were about 365 thru 385. In cruise, they stay down around 330 avg with #1 just slightly hotter than the rest by about 5f.
Now for the rest of the story. I rechecked timing, throttle, mixture, and everything else and found the mixture cable had slipped and was not going full open. I had just checked that a couple of hours ago! Redid adjuste and now it acts like it should. I can lean at altitude like normal. I also put a plate over the 3" oil sceet tube over #4 cylinder rear baffe and drilled a 1.5" hole in that. Oil stayed right at 185f for the entire flight no matter what I did. No problem with that. OAT was 85f on the ground and about 75f at 6600'.
Thanks for all the advise.
Jim
I don't know if you guys saw my last post on another thread. Problem solved today on the high temps on 3 & 4. Kyles suggestion on the dam on #1 seemed to do the trick or most of it. I first made it 1.5" tall, which did wonders, then trimmed it to 1.25", which was way better. Now ! is the hottest but not bad. I climbed out this afternoon (after mods) and kept full power in to 3000', which is what I could not do before. Temps never got over 392 for #1 and the rest were about 365 thru 385. In cruise, they stay down around 330 avg with #1 just slightly hotter than the rest by about 5f.
Now for the rest of the story. I rechecked timing, throttle, mixture, and everything else and found the mixture cable had slipped and was not going full open. I had just checked that a couple of hours ago! Redid adjuste and now it acts like it should. I can lean at altitude like normal. I also put a plate over the 3" oil sceet tube over #4 cylinder rear baffe and drilled a 1.5" hole in that. Oil stayed right at 185f for the entire flight no matter what I did. No problem with that. OAT was 85f on the ground and about 75f at 6600'.
Thanks for all the advise.
Jim
