R

RV8R999

Well Known Member
Continuing from my other thread...

Added the washer as suggested to the #2 baffle to create a space between the inlet baffles and the flat section of the #2 cyl and sealed any other gaps.

Still the #2 CHT wants to go high very quick. It is manageable with climb speed but I don't think it should be at 410 before I even taxi to the run-up at idle the whole time (600RPM). It cools right down at 130MPH but is still 30-50 deg hotter than the others.

Timings been checked
Baffles checked
Washer Inserted
Air Damm removed

EGTs are all within 50-100 of each other with #3 often the hottest and in the 1200 deg range during T/O and climb. At 160 MPH 8500FT and 60% power CHTs are 315, 375, 330, 346 FF is at 18.6gal/hr

Oil temp remains between 165-185 all phases of flight.

Another washer maybe? I'm perplexed...
 
I do not have all of the history from your previous threads so this may have already been discussed. It appears that the numbers do not add up, for the level of CHT's that you are reporting the oil and EGT's look low. Have you verified the accuracy of the probes and the programming of the instruments reporting this info?
 
Honestly I have not done that other than a correspondence check between all 4 CHTs after the engine is shut down. I watch all the CHTs slowly fall and eventually they are all within 1 or 2 degrees of each other in the 100's and below until ambient temp is achieved. I know this doesn't really prove anything definitively but it was a data point.

I might try as suggested swapping the #4 with #2. Next easiest thing I suppose.

thanks
 
(This may have been mentioned previously.)

The engine will run cooler across the board after it is thoroughly broke in, there may not be a problem other than it is so new.

This is dumb observation reflecting a dumb omission with my cowl, but are the inlet rams installed in the top cowl? I flew without them for more than a few years and finally installed them last year. They probably do help with air flow across #1 and #2.
 
18.6 GPH at 60% ???

I don't think that would be a combustible mixture! I would double check the settings in your FF software. Almost like it needs to be divided by 2.
 
Hot clyinder

Check for a possible air leak into #2 cyl. This could be at either end of the intake tube. If #2 is going lean, then that could explain why it is getting hot very quickly, and running so much hotter than the others.
 
Ken, give us two good photos, cylinder and baffles above and below the cylinder.

The possibility of an intake air leak or a CHT probe error are both good suggestions. However, I can't reconcile either with this previous post....

With the cowling completely removed all CHTs hover around the 280-290 region with #2 being the lowest. When I run-up to higher power setting with cowl removed #1 and #2 are the coolest by 15 degrees or so. This alleviates any concern I might have had about something WRONG with the #2 cyl.

As soon as I put the cowl back on the #2 goes to low 400s even at even very low RPM so I'm convinced its a baffle issue.

.....but I'd still check them.

Hang in there.
 
DanH said:
Ken, give us two good photos, cylinder and baffles above and below the cylinder.

The possibility of an intake air leak or a CHT probe error are both good suggestions. However, I can't reconcile either with this previous post....

With the cowling completely removed all CHTs hover around the 280-290 region with #2 being the lowest. When I run-up to higher power setting with cowl removed #1 and #2 are the coolest by 15 degrees or so. This alleviates any concern I might have had about something WRONG with the #2 cyl.

As soon as I put the cowl back on the #2 goes to low 400s even at even very low RPM so I'm convinced its a baffle issue.

.....but I'd still check them.

Hang in there.
Click to expand...

AHA! The ever present illusive and mysterious pattern of air flow under the cowl.

I will never forget a seminar at OSH by Sonja Englart. She mentioned a cooling issue with a 6 cylinder engine and solved it by tufting and video recording air flow under the cowl. A minor baffle modification cured whatever the issue was.

She was so impressive, I bought her book "Efficient Powerplant Installation Piston Engines".

That probably was the intent of seminar and I was hooked. :)
 
Ken, check the baffle between cylinders #2 & #4 below the cylinders.

I had a friend with a Lancair Legacy with an O-320 engine who had similar problems, who finally found the lower baffle was not seated properly. Maybe this is your problem.

Hope you nail down the gremlin(s) soon.
 
I'll take some pics and post.

Joel - good thought but I double/tripled checked them as well.


I agree the CHT probes themselves seem unlikely in that the temps all match and track together until I'm at high power during climb or with the cowl on at idle.

Dan similar to your set-up I have a 4-1 exhaust (in fact you sent me the name of the company who welded yours). I do not know what the difference in area is between the 4-1 at the cowl exit compared to the combined area of the standard vetterman exhausts. Is it possilbe I'm choking my exit area a bit with the larger diameter exhaust? Dunno. Add to this my oil cooler does sit at the bottom of the engine mount on the left side nearly touching the lower cowl bottom which may be blocking cooling flow exit. I think on most set-ups the oil cooler is mounted on the firewall or at the #4 baffle, each of which is out of the exit flow path.
 
CARB Jet

Can someone point me in the right direction for the procedure to increase main jet size iin CARB.

What experience is out there with carb jets and high CHTs. I've read some past threads..very interesting.

Thanks
 
Ken,
Carb jetting and cowl exit area would affect all cylinders. The oil cooler location is unlikely to be a factor. I know you double checked, but let's take a detailed look at the #2 baffling, and the cowl inlet region too.
 
Well went to the airport...removed all the cowling (again) and checked all the baffling. Every hole is filled with RTV and the cyl baffling which wraps around the bottom of the cyl fins is very tight with no visible gaps along the sides.

Of course my camera was on my desk at work collecting dust...grrrrr

I'm not totally convinced of how I have the fwd side inlet baffle material working but to test this out I put the cowl back on and used Gorilla Tape from the inlet ramps to the inlet baffle sides.

and double checked all baffle material was tight against the cowling in all areas and it was very tight, even in the corners.

I started the engine and in just a few minutes at idle #2 was into the low 400s. This just doesn't make sense.

I took off with a climb speed of 130mph and CHTs stayed below 410 up to 8500ft with WOT. at 8500ft I went to nearly WOT (I can't go full cause the prop will overspeed). Once temps were stabilized I noted CHTs and EGTs were 336,375,345,365 and 1134,1175,1142,1168 respectively. I then leaned to about 8.4 GPH and noted EGT rise to 1430,1456,1427,1463. These numbers tell me my Carb Jetting is probably ok and that #2 is not overly lean as would be indicative of an induction leak (which I checked for). I was not able to swap out CHT probes cause when I put the firewall forward together I went crazy with adel clamps and it would have taken me a long, long time to undo all of those to unwind the excess wire.

I measured the outlet/inlet ratio (accounting for the 4-into-1 exhaust). The outlet area is smaller than inlet in a ratio of .96 (50 sq-in outlet to 52 sq-in inlet).

While I'm flying I can see the upper cowl bulging in between my skybolt fasteners at the top indicating a significant pressure differential across the upper cowl at the firewall.

The continuity equation requires mass flow in = mass flow out (in a closed system) the reduction in density due to heat transfer necessitates either an increase in exit area or increase in exit velocity. No ratio can exist which optimizes the velocity recovery of the exit air and the area throughout the entire flight envelope as they are competing constraints. My limiting factor is the #2 cyl at idle during the long taxi to runway 05 from my hangar as temps are already in the 410-415 range before I even do a runnup. Once airborne I can manage CHTs with A/S. On the ground I'm hosed...nothing I can do except shut down. I'm considering adding an additional 13sq-in to the outlet area to give me a 1.2 out/in ratio. This may allow the engine to breathe better and keep CHTs down during climbs and while on the ground.

Knowing the inlet velocity and the temp of the cooling air at the exit would be helpful

As usual this has been done many times with results covering the full spectrum.
 
RV8R999 said:
.....I measured the outlet/inlet ratio (accounting for the 4-into-1 exhaust). The outlet area is smaller than inlet in a ratio of .96 (50 sq-in outlet to 52 sq-in inlet).

While I'm flying I can see the upper cowl bulging in between my skybolt fasteners at the top indicating a significant pressure differential across the upper cowl at the firewall.
Click to expand...

If it were my airplane, I would get more air flowing through the engine by creating more exit area.

This of course is a controversial subject. Minimum inlet and minimum exit areas equate to minimum drag, say the experts. But consider this. After screwing around with 3 different engines with various cooling issues and various cowl mods to cure them, my cowl now has an inlet area of 45.5 inches and an exit area of 118 inches, a ratio of inlet to exit is over 2. That's ridiculous but guess what, it works.

Is it more draggy? Probably but not much, the airplane will match or exceed Van's numbers at 75% power. I made it to 10000' in 8 minutes 8 seconds yesterday with no cooling issues whatever. :)

Another thing to consider with regard to the standard Van's cowl inlet to exit ratio (which according to some experts should be 1:1.1) is that there is no adjustment for the different engines that will fit under that cowl. A 200 HP angle valve engine creates more heat than the 180 HP parallel valve engine, yet the air flow situation is the same with regard to area and ratio.

Just my 2 cents worth....and its probably worth less than that. But I know what works here and what does not.
 
I don't know Ken - let's look at this from a really simplistic standpoint. All four cylinders are in the same cowling, with a certain inlet/outlet ration, and three of them are cooling fine. One is hot. Changing the cowl is going to affect all of them. Logic says you are likely to see the same bias on that cylinder. Something is unique there. I ALWAYS suspect an deal with instrumentation before I attack anything else in a system - years of flight testing has taught me that until you know the instrumentation is right, everything else is guess work.

Yeah, it's a pain to unbundle the wiring, but until you swap sensors around, you haven't nailed that leg of the fault tree. You're doing some very good and detailed troubleshooting, and documenting it well. Why not do it all?

What's easier - unbundling the wires, or carving up the cowl?

Paul
 
i agree with you Paul, but while #2 is the hottest all 4 are getting hot at idle, significantly hotter than this engine did 9 hours earlier installed in my other plane with the same probes and instrumentation.

You are absolutely correct about needing valid instrumentation, I'm just not sure how to really do that with installed probes. How do I calibrate a CHT probe from 100 to 500 deg without removing the entire system from the plane? With thermocouple probes I've never seen a failure manifest itself with a change in the slope of the volt/temp curve. They either fail or they work - in my experience anyway. I'm sure I'll hear how I'm wrong in a few seconds :)
The fact is at ambient all of my probes are within a couple of deg of each other (oil temp, CHT, EGT, Carb Heat, my fire detector, and cabin temp). I've noted this correspondence through ambient temp swings from 40 to 100 degrees and the correspondence remains the same and matches the ambient temps. So without question all my temp probes are functional at the low end of the curve. When the engine is running they all track smoothly upward in a steady and predictable rate, its just that #2 has a steeper slope. They all react similarly to changes in that the temps rise and fall correctly with power, airspeed and fuel flow, its just that #2 is closer to the margins than I like.

I'm going to do some more research on the probes before I decide to pull them.

As always thanks for the insights!

Ken
 
I agree with Paul that it is a bit premature to start hacking up the cowling. That would be treating the symptom (high CHT) without finding and fixing the root cause of the high CHT.

Maybe I missed this, but has there been a good check for an induction leak? The pressure differential across the possible leak areas is much higher at low MP (idle) than at higher MP (climb or cruise). Thus it is possible that an induction leak in #2 would have more impact on the ground than in flight. I have no personal experience with induction leaks, so I don't know if a too lean cylinder at idle could cause a significant CHT increase or not, but I think an induction leak is worth ruling out.

Some folks will spray solvent around the ends of the induction tubes when the engine is running, and look for changes in rpm. But it would be a lot safer, and probably just as effective, to use the output pressure from a shop vacuum to pressurize the induction system and spary soapy water on the outside, looking for bubbles. The MP gauge should probably be disconnected before doing this test, as it may not be designed to handle pressures above ambient.

Also, it could be useful to check CHT probe accuracy in boiling water. You know they read about right at ambient temperature, but you don't have any accuracy data at higher temperatures.
 
"I started the engine and in just a few minutes at idle #2 was into the low 400s. This just doesn't make sense."

I agree that this seems impossible, I don't think you could get the temp up that high in a few minutes at idle even if you had the cyl wrapped in a blanket!
 
Kevin - I considered an induction leak but after inspection and closely watching EGTs during start at idle and in flight the values are too close to account for a 40-60 deg cht split. Plus, I ran the engine with the cowling off and all CHTs, including #2 remained in the high 200's and within 10 deg of one another and stabilized. Although i cant say they are calibrated to a standard (such as BP of water) the probes do correspond to one another through a significant temp range up to an above the BP of water. I've wondered about the termination of the probe wiring but eliminated this as I used the same hardware for all my thermocouples.

This cowling off test focused my efforts on the baffling. I checked the baffling and improved a couple of areas.

I appreciate the inputs, it is really very helpful thanks!

Ken

PS. I would never HACK-UP my cowl but rather make a series of very precise cuts to an exacting specification :)
 
It is probably worth getting several other experienced RV builders and one or more A&Ps over to take a look at things. Sometimes you can look at something so many times you stop seeing it. Maybe some fresh eyes can see something you have missed.

Do you have an engine data recording capability? When you run the engine on the ground with the cowling on, does CHT 2 increase steadily, or is there a sudden spike in temperature? After take-off with a high CHT 2, does it decrease smoothly as you get more air flowing over it, or does it come down suddenly?

If you run on the ground at low power for a few minutes with cowling on, then shutdown without ever going to high power, then remove and inspect spark plugs, what do you see? Do the plugs on #2 look any different from the ones on other cylinders? The colour of the plugs may give a clue as to whether there is a mixture difference between cylinders at low power.

Swapping #2 and #4 CHT probes seems like the next good thing to try though, as we still don't really know whether you've got an instrumentation snag, or a real CHT issue.
 
While I prob will not be able to swap the two probes due to wire length I can move the #2 probe to the #4 cyl without any trouble.

During all tests temps rise/fall in a very smooth, steady and predictable fashion.
 
Check your electrical connections at the probe. Sometimes if the two "insulated" connections contact each other they can cause an intermittent short that causes higher readings. Take a pair of pliers and gently squeeze the connections to make sure there is no slop.
 
The saga continues:

Removed the cowlings and inspected (again) for induction leaks, air leaks, etc..

No visible induction leaks. I did plug a few small gaps in baffling with RTV but nothing significant.

I noticed my fuel flow lever wasn't quiet getting to full rich (about 1/32" gap) so I adjusted the cable.

swapped the #2 Probe with #4 and cranked the engine. Nope...probes are fine. The high temp stayed with the #2 cyl (but with the #4 probe) and values were consistent.

I'm going to work more on the inlet baffling. I'm still not really happy with the seal along both sides of the inlet ramps (mine are filled with foam) but even when I thoroughly tape these off the temps go high on the ground.

I did fly for an hour and a half doing nothing but Touch and Goes. Worked on full stalls a bit. A couple of times was able to put it down on all three to the point I was actually surprised I had landed already but mostly I tended to bounce it in. Wheels landings really work well with flaps from 20-40. No flaps and the plane just wants to float, float, float, float (I came in over the fence at 90mph for the no flap). This plane does not like to slow down in the clean configuration...not a bad thing to complain about huh?!

10 hours TT and loving it :)
 
RV8R999 said:
The saga continues:

<<<snip>>>

10 hours TT and loving it :)
Click to expand...

Are there some experienced builders at your home field who would spend a half hour or so reviewing your installation? Start with the top cowling attached, then take a look with the top cowl off, then take a further look with the bottom cowll removed. You might find something that way.

Alternately, since this issue is isolated to one cylinder, I'm inclined to believe you have an induction leak or possibly a fuel injector that isn't flowing properly. I can't tell from this thread, but is your airplane fuel injected?
 
How do I check how much oil is getting to the head and what is the spec?

it is a carb engine. EGTs are all very close within 50 on the ground.
 
You just might have a bad cylinder; it happens. I would wait for twenty or thirty hours before you pass judgement. One time I had a brand new Lycoming cylinder that was always hotter then the rest. Close inspection showed that all the fins between the top and bottom spark plugs were blocked. I had to drill the gaps out and removed more then a tablespoon of casting sand.
About this time ECI and Superior started making parts and Lycoming quality control started to get better.
 
Results

Finally got back to the hangar after a week of travel...

I tested the #2 CHT Probe by connecting it to the back half of a soldering iron using a pair of vice grips. After letting it sit for 15 minutes it read a steady 396 deg. I connected the same iron to the #4 CHT probe in the same location using the same vice grips and allowed it to sit for 15 minutes. This read 401 deg. Repeat on #1 and #3 with 397 and 399 respectively. I'm comfortable my probes are working just fine.

The idle mixture was a little lean so I adjusted that as well.

I double and tripled checked every possible location of an induction leak on #2 and could not find a thing.

I removed the cowl and ran the engine at idle. 25 minutes later CHTs were 295, 283, 297, 301 respectively. #2 is actually the coolest without the cowling installed with EGTs within 20 deg of each other. Nothing wrong with this cyl

Double checked the P-mag and slick timing

Then I removed the oil cooler exit scoop I made. My oil cooler is mounted horizontally between the lower engine mount bracing on the left side. The scoop nearly touches the bottom of the cowling and helps turn the oil cooler air out toward the cowl exits. I was always a bit concerned this might be blocking cooling flow for the cyl.

Ran the engine at idle and 20 minutes later CHT were 333,390,388,369. When I ran the engine earlier prior to removing the scoop and whenever I went flying the #2 would rise to the 400's in 5-10 minutes and was easily the hottest by 30 degrees. I didn't get a chance to go run-up and fly yet but I will first thing in the morning. I'm hoping this is the problem. I'm sure the baffling is good...fingers crossed!

Ken
 
Fixed!

Flew today after having removed my oil cooler exit scoop.

This did the trick. All CHTs below 400 by the time I was through the run-up and during flight CHTs were 312, 345, 350, 348 oat at T/O was 94 deg. Much more balanced. Surprising the unintended consequences we face when experimenting.

The interesting thing with removing my oil cooler scoop was oil temps actually stayed cooler. I never saw oil temps above 180 during a slow high power climb. Mostly the temps were in the high 160's. This is with 1/2 of the 3" sceet tube blocked off. I'm going to verify my oil temp probe calibration but it is the same probe I've been using for a couple of years and I tested it when I bought it new. I did notice prior to engine start this morning oil temp was indicating 76 deg while CHT, EGTs, Carb heat were 92 deg. I found this to be strange since the engine sat all night and all temps should be ambient and very close to each other, especially with the plane sitting in a hangar out of the sun.

Thanks for all the advice during my troubleshooting!

Ken
 
Congratulations!

Glad to hear you solved the problem. What a great feeling that is!

Can you share some photos of the oil cooler setup so we can learn more about the offending component?
 
Oil Cooler Scoop Photo

Here you go...

The exit area of this scoop is about 10 sq in which is a little choked since it should nominally be a little over 12 sq in with a 3" inlet. However, I used this oil cooler engine combo in my previous plane with a very similar mounting configuration and was always blocking the inlet (even during 100 deg OAT days) to keep temps at 180-190. So my experiment was to intentionally choke the exit which worked well in the RV8, except that the location of the oil cooler and scoop really blocks the left side exit air and caused my #2 (and to a lessor extent #4) CHT to be abnormally high.
34ilsaa.jpg
 
in the never ending effort to keep those temps from climbing too high during idle....

Removing my oil cooler exit helped but I'm still seeing the #2 and #4 creep near the 400's before I even taxi to the run-up. I looked closer at the baffling portion that wraps around the lower cyl fins and noticed the opening between the inter-cyl baffle (the one that comes with the engine) and the fwd wrapped portion creates an opening which is at least 15-25% less in area for #2 cyl than the others. #4 has the next smaller opening. This is the space that all the cooling air has to pass through to get to the lower cowling and eventually out.

This helps explain why my oil temps are so low during flight (150-170s) even though I'm blocking off a portion in the cooler inlet. If the #2 and 4 cyl are overly choked because those openings are too small than more air is finding its way to the oil cooler.

I didn't modify the baffles at all but do not recall if we were required to size those wrapped baffles or if they came pre-cut, bent and drilled? Anyone remember?

Not sure why 2 and 4 would have smaller areas than 1 and 3 by design???

Thoughts...

Ken
 
Ken,
I spotted the different exit sizes when fitting new baffles and more or less equalized them. Don't recall any instructions to do it. No matter; I have several cooling experiments in the works. Nothing to report yet.

Take some pictures up under the cylinders and around the front of cyl 2.
 
For what it's worth............

I just experience this in my 6. Number two was starting to climb ahead of the others, leaned quicker too. Pulled the induction tube, it was leaking, problem fixed.
 
Dan, thanks for the feedback and look forward to result of your experiments.

This is the only pic I have now of the #2 underside baffling.
20k9lah.jpg
 
induction leak

Chuck - can you explain what you mean by "pulled" the intake? What did you discover? I've checked the #2 induction tube, sealed the flex coupling with RTV, checked the integrity of the intake gasket, ensured proper torque values, checked the primer lines and fittings. Plus the #2 runs the coolest when the cowling is removed and never goes above 280-290 but goes to near 400 in just a short span with the cowl on. I've repeated this test several times now. I have a great seal around the upper baffles in front, sides and back. The cyl is fine, runs in low 300's during mid cruise flight.
 
CNEJR said:
I just experience this in my 6. Number two was starting to climb ahead of the others, leaned quicker too. Pulled the induction tube, it was leaking, problem fixed.
Click to expand...

I had a cracked intake tube on cyl 2 earlier this summer too. My tubes came from Aerosport and they provided a free replacement. Hmmm.
 
Much Better

I blocked off more of my oil cooler inlet (3/4 of the inlet is now blocked off) and still the highest temps were only 180 during slow WOT climb. Most of the flight temps were in low 170's high 160's. Wondering if I even need an oil cooler?

I removed more of the baffle damm in front of #2 cyl fins and used a fine file to round off the edge and increase the gap from baffle to cyl fin to about 1/8" (also have a washer between the baffle and the cyl at the screw location).

Temps were much more balanced during flight with #1 the coolest by about 15-20 deg and 2,3, and 4 within about 5 degrees of each other.

2 & 4 still get hot on the ground but not as bad. I'm starting to wonder if the wood prop blocks most of the airflow while on the ground since it is very thick near the hub and probably doesn't push much if any air??

All in All things are working well.
a9phr4.jpg
 
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