DXB Posted August 5, 2021 Report Share Posted August 5, 2021 CHTs on my mind. The things that make my M20C's O-360 potentially more powerful (Powerflow exhaust, variable timing on Surefly, Superior cylinders) do work, but may have come at the cost of more CHT headaches. It is now impressively a ~153kt machine at 70% power in the 5000-7000ft range, but I rarely get to use that power due to CHT concerns. On a recent hot summer day in cruise at 9000 at <65% power, I was running 21.3 MP, 2350 RPM, 8.5gph, with #2 and #4 CHTs in the 400-420 range. This was the coolest I could get it without cutting power drastically. On the climb, #4 usually exceeds 430, sometimes exceeds 450 despite my best efforts to get the nose down quickly after takeoff accelerate to >120mph before climbing in earnest, and #2 is second hottest in climb but 30 degrees cooler. Fuel flow is 17-18gph on takeoff consistently, and I have the richer carb. I've checked mag timing, obsessed over baffling, fixed an induction leak, and fiddled with throttle setting/carb heat ad nauseam, but this is the best I can get it. Some fun discussion points: 1. Lycoming O-360 operator manual says: "For maximum service life, cylinder head temperatures should be maintained below 435°F (224°C) during high performance cruise operation and below 400°F (205°C) for economy cruise power." They define performance cruise as 75% HP, economy as 65%. Why are hot temps worse for cylinders at LOWER power?? It seems to me that lower cylinder wall pressures at lower power would make high temps LESS damaging. 2. Mike Busch writes things like "set your engine monitor CHT alarm to 400°F or less (I have mine set to 390°F). When the alarm goes off , immediately do whatever it takes to bring the CHT back down below 400°F." Mike's writings are very clear and illuminating, but there are some points that seem a bit dogmatic and not supported with clear evidence. Our carb'd planes tend to run hot, and would relieve a lot of headache and cockpit distraction if we can feel comfortable with CHTs up to 435. Folks were cheerfully oblivious before engine monitors anyway - is this at least partly an over-monitoring issue? 3. What are the real risks of running CHTs in the low 400s in continuous operation or up to 450 in climb? A. Mike Busch says "I'm convinced that if every piston-powered aircraft was equipped with a modern probe-per-cylinder digital engine monitor that set off alarms anytime any CHT rose above 390F for Continentals or 410F for Lycomings, cylinder head-to-barrel separation fatalities would become largely a thing of the past." For our parallel valve O-360s, I think the cheap cylinder replacement cost and resulting ability to use first run cylinders has pretty much solved this problem also? B. Hot CHTs are more likely to damage exhaust valve guides, leading to burnt exhaust valves and a catastrophic valve failure. But are CHTs in the low 400's really so damaging to valve guides? My #4 has always been the hottest by far, and it is the only one that hasn't burnt a valve. The first one to burn was actually the coolest (#1) which never sees 400. Also borescopes are cheap and easy for owners and mechanics to use, and so there seems to be little excuse for not catching a burnt exhaust valve with plenty of notice. C. Having a higher threshold for concerning CHTs might make it more likely to miss a thermal runaway event driven by pre-ignition. Maybe, but an alarm at say 450 on my monitor does provide substantial warning still. Is this again an over-monitoring problem? D. Hot CHTs may make the crosshatch on the cylinder wall not last as long, leading to more blow-by and oil consumption. I'm still not sure how much difference 400 vs 435 makes in this regard. E. Anything I've missed? 3 Quote Link to comment Share on other sites More sharing options...
Mooney Dog Posted August 5, 2021 Report Share Posted August 5, 2021 Have you checked your internal baffling at all? Ive been working with a fleet of 172N with 180hp upgrade, o-360 variants and this summer we've watched them all hit 400-430f consistently. We ended up adding vents into the engine cowling to increase airflow which has brought temps down another 20F on average at the cost what appears to be 1kt of speed. Granted i havnt done any XC in them. 1- Keeping CHT below 400 is good for life of the engine. Should be relatively easy to keep those temps on an average day with good airspeed. I wouldnt be surprised to see 420 or greater in the climb. Higher if its Texas or Florida summers. More so this year with the triple digest in the Midwest. 2- I would set you alarm to in the warning zones for the engine personally. the 400 range isnt great, but its not "bad" for the engine, and isnt cause for heavy alarm. You should still strive to be below it though. 3- The risks are close to the same as any risk would be during a "full power" operation, maybe with a slightly higher chance of engine failure. I wouldnt put money on this though, i honestly do not know. All in all, CHT is a GREAT resource to help you get a full life out of your engine, but there's many many factors that can play into why you have a "hot" cht. I Believe Mike's point on having proper CHT and EGT measurements should be on every new aircraft (and i think they are these day). Remember most of our engine in aviation are air cooled, thus the faster the air moving around the engine, the cooler they will be most of the time, and that still relies that the air is actually moving around the engine, and not sneaking out someplace else. Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 5, 2021 Report Share Posted August 5, 2021 1) When did we see a cylinder head / barrel separation last? 2) Our operations manuals written back in the day… were printed too soon to meet today’s needs… 3) We typically use 380°F as a guide for CHT control… no matter who’s cylinders we are using… 4) This CHT guidance is based on the material, not the manufacturer… Aluminum. 5) Even there… is plenty of flexibility… the strength vs. temp curve has no strong inflection points we are trying to stay on one side or the other…. 6) What we are trying to avoid… as the metal gets softer with temp… the surface features will wear quicker at higher temps… 7) We like the hatched pattern in the cylinder walls for keeping oil distribution occurring as expected… 8) When cylinders wear they cost money to OH or replace… 9) So… that kind of covers Temperature and cylinder wear… a slow degradation over a long period of time…. 10) For destructive forces… look for things that increase ICPs… 11) Internal cylinder pressures can be a bit more destructive over a short period of time… 12) Some things that cause bad ICPs are similar to…. bad mag timing, too soon… or wrong fuel that detonates early instead of burning slowly… my favorite… <20°F OATs… and high pressure zones… (negative MSL numbers are like having a turbo on an NA engine…) 13) For warm OATs… it is important to select a heavier weight engine oil to match the environment… too thin, the oil won’t lubricate very well, and bearings have been known to spin out of their locations… a spun bearing, blocks the oil holes from doing their jobs… engine failure occurs briefly after that… 14) We have seen a couple of broken piston hardwares around here… always interesting to know what causes things to have happened… 15) Getting past that first 100hrs of engine ownership is a comforting feeling… the first 10hrs is as uncomfortable as possible… 16) Our engines are mostly oil cooled, including the back side of the pistons… yes, the oil is air cooled… 17) our cylinders are mostly air cooled, even the M20C circulates oil near the exhaust valves…. 18) Some O360s have stuck valves in the past… there are a few procedures to know more about the health of the valves… from reaming out the carbon deposits to checking the dimensions on things… the rope trick, and the wobble test… 19) The inside of the doghouse is as aero dynamic as a square block… somewhat brick like… 20) Basic clean-up of the dog house can only get you so far… new seals, fixed cracks, and the things between cylinders too… 21) This is where we go see the cowl guys… 22) We know there can be a cowl that allows us to fly our engines with cruise temps under 380°F on all cylinders… 23) It’s kind of a complex science. While cooling one cylinder better, we accidentally remove air flow from another… 24) It’s Ok to have warmer CHTs… 25) it’s not OK to have a Hot CHT and not know the cause of it… 26) The O360 adds to the challenge because it is a challenge to adjust fuel flow to each cylinder…. Some may get more than the others… one may not get the right amount… 27) Speaking of fuel flow… what is the max fuel flow you are seeing at SL at WOT? 28) Often around here… some engines are set up with a max FF that isn’t very ideal… call it suboptimal… 29) A simple case for IO550s… the same engine may have 25gph as a max FF setting, and another may be set at 30gph… the difference is the excess cooling available while producing the same 300hp… 30) Extra fuel flow is great for cooling cylinders… to a point where there is too much and the proper air / fuel ratio gets exceeded…. 31) I don’t have a feeling for… can an engine monitor tell you your oil flow around your valve stems has been blocked…. The CHT sensor isn’t there… a second TC in that fluid steam would be nice… Compare what you have to an engine that has what you want… There is nothing like climbing WOT to altitude with CHTs where you want them to be… PP thoughts only, not a mechanic… Best regards, -a- 2 Quote Link to comment Share on other sites More sharing options...
PT20J Posted August 5, 2021 Report Share Posted August 5, 2021 What kind of CHT probes do you have? Bayonet or spark plug gasket? 1 Quote Link to comment Share on other sites More sharing options...
47U Posted August 5, 2021 Report Share Posted August 5, 2021 How far open are your cowl flaps? Fixed or adjustable? Have you considered opening them up a little? Where does your oil temperature run? Are the oil cooler fins in good condition and do you know if all the galleries are flowing? I think it was @PilotCoyote who discovered a couple blocked galleries using a laser thermometer. Granted, hot oil probably doesn’t contribute that much to high CHTs, but it might help a little. Were your CHTs cooler before the SureFly was installed? Have you considered reprogramming it to fixed timing to see if it makes a difference? 3 hours ago, DXB said: Hot CHTs are more likely to damage exhaust valve guides, leading to burnt exhaust valves and a catastrophic valve failure. Last annual, I had low compression (62/80) on my #3 cylinder. There was evidence of heat stress on the exhaust valve and the guide had failed. Was it related to high CHTs? 2 3 Quote Link to comment Share on other sites More sharing options...
tmo Posted August 5, 2021 Report Share Posted August 5, 2021 5 hours ago, carusoam said: For warm OATs… it is important to select a heavier weight engine oil to match the environment… too thin, the oil won’t lubricate very well, and bearings have been known to spin out of their locations… a spun bearing, blocks the oil holes from doing their jobs… engine failure occurs briefly after that… This is one I don't get. It seems to me that the only moment the weight of the oil matters is at cold startup. After that, it's up to the engine to maintain the desired oil temperature, more or less (vernatherm, etc) - so both W80 and W100 will get to the ~200F and stay around there. When cold, I can see that too thick of an oil can be a problem - it won't get to all the places it needs to, cause pressure locks in radials, etc. But I can't see the oil being too thin / too hot, as never will it ever be at 200F, where it works best. FWIW, I put Philips XC 20W50 in my TSIO-360, because I fly too little to switch between W80 and W100 as dictated by OAT - but based on the above, why can't I just do W80 and be done with it? Educate me, please. 2 Quote Link to comment Share on other sites More sharing options...
DXB Posted August 5, 2021 Author Report Share Posted August 5, 2021 11 hours ago, Mooney Dog said: Have you checked your internal baffling at all? This is an area that I'd like to learn more about - my intercylinder baffles are definitely in place on each side and seem form-fitted around the cylinder head so it would be hard to malposition. I have heard about other specified distances between those baffles and the front and back end baffles that are connected by a tie rods at the bottom of the doghouse, but I've never fully grasped how to measure or adjust it! DB Quote Link to comment Share on other sites More sharing options...
DXB Posted August 5, 2021 Author Report Share Posted August 5, 2021 10 hours ago, PT20J said: What kind of CHT probes do you have? Bayonet or spark plug gasket? Bayonet (JPI EDM900 as primary, with factory probe /gauge removed) - I probably should swap another probe onto #4 at some point - that's the one where behavior got much worse after the exhaust and Surefly. 8 hours ago, 47U said: How far open are your cowl flaps? Fixed or adjustable? Have you considered opening them up a little? Where does your oil temperature run? Are the oil cooler fins in good condition and do you know if all the galleries are flowing? I think it was @PilotCoyote who discovered a couple blocked galleries using a laser thermometer. Granted, hot oil probably doesn’t contribute that much to high CHTs, but it might help a little. Were your CHTs cooler before the SureFly was installed? Have you considered reprogramming it to fixed timing to see if it makes a difference? I have the fixed cowl flaps on a '68. I've thought about how much work it would be to convert them to adjustable. Talking to folks with adjustable ones seems to indicate that they have to open them almost fully to get perceptible cooling benefit, so I wouldn't want them fixed in that position. My oil temps are great - 180ish in the winter, 190s in the summer, 200-210 only when climbing WOT on a hot day. I'm interested to learn more about the oil gallery issue though. Surefly was installed in the winter and I didn't notice much CHT difference after, but cool OATS may have masked it - Powerflow went on later that winter and I noticed a dramatic rise in #4 CHT. I wondered if #4's power was most impaired by stock old exhaust and so that's where the change was manifest, or the issue was that is was the poorest cooling already. I have wondered if it was a combinatorial effect between the Powerflow and the Surefly that gives me problem in cruise, when Surefly gives the advance, but the issue is also there in WOT climb at sea level, so that made me deprioritize changing the Surefly to fixed timing. Regardless, it's on the list as a last resort. 2 Quote Link to comment Share on other sites More sharing options...
Raymond J1 Posted August 5, 2021 Report Share Posted August 5, 2021 It seems to me that only the position of the flame front changes the T ° CHT, all other things being equal (OAT, IAS, MAP, Rpm,...). However, what causes the flame front to vary is the advance at ignition, the mixing ratio and the delay at the exhaust opening. Do you have a way to go back with Surefly (frozen ignition advance as for a classic magneto) and determine the influence of powerflow ? As Antoine says, thoughts only... Quote Link to comment Share on other sites More sharing options...
Mooney Dog Posted August 5, 2021 Report Share Posted August 5, 2021 8 hours ago, tmo said: This is one I don't get. It seems to me that the only moment the weight of the oil matters is at cold startup. After that, it's up to the engine to maintain the desired oil temperature, more or less (vernatherm, etc) - so both W80 and W100 will get to the ~200F and stay around there. When cold, I can see that too thick of an oil can be a problem - it won't get to all the places it needs to, cause pressure locks in radials, etc. But I can't see the oil being too thin / too hot, as never will it ever be at 200F, where it works best. FWIW, I put Philips XC 20W50 in my TSIO-360, because I fly too little to switch between W80 and W100 as dictated by OAT - but based on the above, why can't I just do W80 and be done with it? Educate me, please. It just has to do with the viscosity more than anything. 10w-30 and 5w-30 in theory work the same when hot, but in realty they're not. Those weights being for my car, not plane, but the same should apply. If someone knows better please correct me. 3 hours ago, DXB said: This is an area that I'd like to learn more about - my intercylinder baffles are definitely in place on each side and seem form-fitted around the cylinder head so it would be hard to malposition. I have heard about other specified distances between those baffles and the front and back end baffles that are connected by a tie rods at the bottom of the doghouse, but I've never fully grasped how to measure or adjust it! DB Well its more so if air has another path to go, it will go that path instead. And if the air can flow, it will flow, but if its restricted, it wont flow as much. 1 Quote Link to comment Share on other sites More sharing options...
Ragsf15e Posted August 5, 2021 Report Share Posted August 5, 2021 Two things… the Surefly shouldn’t be affecting it at all until it begins advancing somewhere around ~5000’ or below ~25mp although they don’t publish where the advance starts anymore. However, some people needed the extra gear for mounting the SF with the correct base timing. Are you certain the SF has the correct base timing? Did you need that extra “tooth”? Is your mag check at runup exactly the same for the SF and mag? EGTs raising and rpm drop the same? Second thing… if my chts were that high, my oil temp would be 220+. It’s interesting to me that your oil temp is reasonable while your chts are so high. Especially in cruise? 1 Quote Link to comment Share on other sites More sharing options...
jamesm Posted August 5, 2021 Report Share Posted August 5, 2021 (edited) I have the same CHT problems with my 67C particularly cylinders 2&4 are my hottest 420 and above sometimes on climb out. I my case this was before and after with a Surefly ignition and I have a stock exhaust. I have switched from a Insight G3 to EI CGR30C/P engine monitor no difference still have the high CHT's. I have tried everything with no success except changing the carburetor. It's very weird in my case sometimes it will be a hot summer day CHT temp are ok then it can be a cool winter day and CHT temps are off the charts. I believe M20Doc had posted that could be the carburetor. I think I have the 10-4164-1 Carburetor. Below are his comments I don't recall mooneyspace link to his direct post. Sorry for the Plagiarism Clarence, I really appreciate your input. In your opinion is worth changing out the Carbs? James '67C Edited August 5, 2021 by jamesm 1 Quote Link to comment Share on other sites More sharing options...
Prior owner Posted August 6, 2021 Report Share Posted August 6, 2021 1 hour ago, jamesm said: I have the same CHT problems with my 67C particularly cylinders 2&4 are my hottest 420 and above sometimes on climb out. I my case this was before and after with a Surefly ignition and I have a stock exhaust. I have switched from a Insight G3 to EI CGR30C/P engine monitor no difference still have the high CHT's. I have tried everything with no success except changing the carburetor. It's very weird in my case sometimes it will be a hot summer day CHT temp are ok then it can be a cool winter day and CHT temps are off the charts. I believe M20Doc had posted that could be the carburetor. I think I have the 10-4164-1 Carburetor. Below are his comments I don't recall mooneyspace link to his direct post. Sorry for the Plagiarism Clarence, I really appreciate your input. In your opinion is worth changing out the Carbs? James '67C I changed my carb recently… rather, I replaced the old 10-4164-1 with an overhauled one. Marvel tech said they set it up to flow 19.0 gph on the bench. I generally see FF above 18.3 on takeoff, and have even seen 18.9 a couple of times, if my FF instrument is to be believed with the boost pump on Thus far, it seems too much fuel for me- the engine surges and runs rough after climbing out from a 2600 MSL airport at summer temps. Leaning it immediately after takeoff to achieve smooth running is a chore and a little worrisome regarding the possibility of leaning it too much and losing some cyl head cooling, as the cyl temps don’t immediately change on the instrument- I’ll know I’m running too lean only after having run lean for about half a minute or so… And If I lean it out for takeoff instead, well, that has been a miserable experience for passengers, airport neighbors, and my nerves….I might be sending it back to have the flow reduced if carb performance doesn’t improve during colder temps. A carb that is too rich has you trying to figure out exactly where the mixture should be set for best power + extra fuel for cooling, but not so much fuel that it reduces take off performance. It’s a bit of a guessing game. I miss my old carb! 3 Quote Link to comment Share on other sites More sharing options...
Andy95W Posted August 6, 2021 Report Share Posted August 6, 2021 It sounds like you and Dev ought to swap carburetors. 4 Quote Link to comment Share on other sites More sharing options...
jamesm Posted August 6, 2021 Report Share Posted August 6, 2021 I have been hesitant because not knowing if I would for certain cut my CHT's by 30 degree's or more than I would probably do it. It's a lot of work to and logistically a royal pita to get people schedules to work out. Plus I haven't heard a lot people doing this so I not too sure if data is there support swapping out the carburetor. Quote Link to comment Share on other sites More sharing options...
jamesm Posted August 6, 2021 Report Share Posted August 6, 2021 I think a better solution is to fix the cylinder cooling and airflow distribution issue. It is documented by Mooney an article where air spilling out front of the cowl. however this would mean all kinds of paperwork. There doesn't seem to be legal and simple way to flight testing of modified baffling arrangement without having to deal with FAA. Who approved the design in the first place. Perhaps the Saber Cowl would lower CHT's on climb out. Quote Link to comment Share on other sites More sharing options...
cctsurf Posted August 6, 2021 Report Share Posted August 6, 2021 Sounds like you and I are running very similar engine setups. I have the powerflow, surefly, and superior cylinders on a c model. A little carb heat may help your CHT distribution immensely. Since I have had my jpi installed, as I just crack the carb heat, I can watch the difference between the chts drop to almost nothing. Normally, my cylinder 3 is quite warm of the others. If you look at the flight data I attached, around 30 minutes after startup, I finally set my mixture and open the carb heat a little. Notice the brown line, cht 3, actually falls below the others and the temps just around 380 for the flight, with a little messing around because I was messing around. I push as far LOP as I can to keep those temps cool... Like Mike says in his leaning webinar, lean to roughness and then bring it back 'till it's smooth. I can lean -WAY- more with that 4 deg C of carb heat than I can without it. Hope that helps. 2 Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 6, 2021 Report Share Posted August 6, 2021 @Sabremech’s cowl takes the square box, air flow inhibiting, sheet metal out… and replaces it with a modern curvy design to better handle airflow… Similar to what Mr. LoPresti did for the M20F to J conversion…. Note for TMO, somebody covered the details of oil labeling vs. reality… above…. The important part is to really know what oil you have chosen and what it does in the parts of the engine that get really hot, vs. where the thermistor is sitting… Note regarding Electronic ignitions and hotter CHTs when using the same timing as the magneto that was there before…. This is a known, often positive experience… 1) Ignition timing is selected by the airframe manufacturer in accordance with the engine manufacturer… based on real experience… 2) The magneto generates a good spark with the system that it has… 3) Spark strength is what is causing the higher CHTs… 4) The electronic mags have a stronger spark… 5) The stronger spark initiates the fuel burn slightly better than the good spark does… in a measurable way… 6) If you wanted to get a near identical performance of the good spark, using the strong spark… a simple adjustment of the timing should suffice… 7) The strong spark essentially burns more of the fuel inside the combustion chamber… giving it a higher conversion… 8) The strong spark is similar to advancing the timing further from TDC… using the magneto’s week spark… Great observation Coyote! There is always going to be a too rich mixture… for that we have the red knob… Having too high of a FF at sea level is a pain in the neck, sort of… Usually, people start pulling out the red knob on T/O using the (hmmmm…. There is a name for this ground level, mixture setting procedure…) Essentially, a good climbing, ROP setting… is in the 2-300°F ROP… more than that is excess cooling… heading for a mixture that may not burn very well…. Or skip.. Great conversation, I hope I added something of value… PP thoughts only, not a flame front scientist… Best regards, -a- 2 Quote Link to comment Share on other sites More sharing options...
47U Posted August 6, 2021 Report Share Posted August 6, 2021 What year did Mooney switch from the narrow deck O-360 to the wide deck? Does the wide deck run hotter by design? My narrow deck CHTs run around 330 in cruise. The only time I get over 400 is in the climb… if I don’t keep the speed up (120-130 IAS). Perhaps another factor, I was looking at a friend’s ‘68 G yesterday. Mooney switched the carb air source from the back baffle on #3 cylinder (on my ‘63 C) to in front of and below #2 cylinder on his wide deck O-360. His CHTs run hot, too. Example pics below. 3 Quote Link to comment Share on other sites More sharing options...
cliffy Posted August 7, 2021 Report Share Posted August 7, 2021 Thoughts- High pressure on the top of the cylinders and lower pressure on the bottom of the cylinders makes our air cooling work. Anything that raises the pressure in the lower section of the cowling lowers the flow through the cylinder fins and lowers cooling. Making sure all the sealing around the generator/alternator section in the front goes a long way to keeping the lower cowl area at a lower pressure. Another seal that gets forgotten is the hard rubber flap around the front section of the guppy mouth where it goes into the "guides" on the cowl front section. I've found numerous times that the rubber seal was not seated properly in the guide (especially the lower section) allowing high pressure air from the guppy mouth entrance to spill into the lower cowl area thereby increasing the lower cowl pressure and lowering the flow of air through the engine cylinder fins. 3 Quote Link to comment Share on other sites More sharing options...
DXB Posted August 11, 2021 Author Report Share Posted August 11, 2021 On 8/6/2021 at 11:48 AM, 47U said: What year did Mooney switch from the narrow deck O-360 to the wide deck? Does the wide deck run hotter by design? My narrow deck CHTs run around 330 in cruise. The only time I get over 400 is in the climb… if I don’t keep the speed up (120-130 IAS). Perhaps another factor, I was looking at a friend’s ‘68 G yesterday. Mooney switched the carb air source from the back baffle on #3 cylinder (on my ‘63 C) to in front of and below #2 cylinder on his wide deck O-360. His CHTs run hot, too. Example pics below. Interesting - I have the wide deck, but my ‘68C actually has the carb /cabin heat intake behind #3 just like your ‘63. Since my #2 and #4 run hot and #1 and #3 are never a problem, I surmised that that large carb air intake (where air just gets dumped overboard if carb and cabin heat are off) creates a pressure gradient that favors air flow over the right side of the engine. However, I’m told a hangar fairy made a completely illegal mod as an experiment to see if obstructing the majority of that intake behind #3 would help the left side of the engine cool better. I heard it made zero difference on a single brief trial flight. Quote Link to comment Share on other sites More sharing options...
DXB Posted August 11, 2021 Author Report Share Posted August 11, 2021 (edited) On 8/7/2021 at 8:00 AM, cliffy said: Thoughts- High pressure on the top of the cylinders and lower pressure on the bottom of the cylinders makes our air cooling work. Anything that raises the pressure in the lower section of the cowling lowers the flow through the cylinder fins and lowers cooling. Making sure all the sealing around the generator/alternator section in the front goes a long way to keeping the lower cowl area at a lower pressure. Another seal that gets forgotten is the hard rubber flap around the front section of the guppy mouth where it goes into the "guides" on the cowl front section. I've found numerous times that the rubber seal was not seated properly in the guide (especially the lower section) allowing high pressure air from the guppy mouth entrance to spill into the lower cowl area thereby increasing the lower cowl pressure and lowering the flow of air through the engine cylinder fins. Agree completely with these suggestions - unfortunately I already had the seals around the starter and alternator fully rehabbed a few years ago and have made sure that the front seal of the doghouse against the cowl is in good shape and sits snugly in the channel designed for it all the way around. Edited August 15, 2021 by DXB Quote Link to comment Share on other sites More sharing options...
Mkruger2021 Posted August 11, 2021 Report Share Posted August 11, 2021 On 8/4/2021 at 10:01 PM, carusoam said: 1) When did we see a cylinder head / barrel separation last? 2) Our operations manuals written back in the day… were printed too soon to meet today’s needs… 3) We typically use 380°F as a guide for CHT control… no matter who’s cylinders we are using… 4) This CHT guidance is based on the material, not the manufacturer… Aluminum. 5) Even there… is plenty of flexibility… the strength vs. temp curve has no strong inflection points we are trying to stay on one side or the other…. 6) What we are trying to avoid… as the metal gets softer with temp… the surface features will wear quicker at higher temps… 7) We like the hatched pattern in the cylinder walls for keeping oil distribution occurring as expected… 8) When cylinders wear they cost money to OH or replace… 9) So… that kind of covers Temperature and cylinder wear… a slow degradation over a long period of time…. 10) For destructive forces… look for things that increase ICPs… 11) Internal cylinder pressures can be a bit more destructive over a short period of time… 12) Some things that cause bad ICPs are similar to…. bad mag timing, too soon… or wrong fuel that detonates early instead of burning slowly… my favorite… <20°F OATs… and high pressure zones… (negative MSL numbers are like having a turbo on an NA engine…) 13) For warm OATs… it is important to select a heavier weight engine oil to match the environment… too thin, the oil won’t lubricate very well, and bearings have been known to spin out of their locations… a spun bearing, blocks the oil holes from doing their jobs… engine failure occurs briefly after that… 14) We have seen a couple of broken piston hardwares around here… always interesting to know what causes things to have happened… 15) Getting past that first 100hrs of engine ownership is a comforting feeling… the first 10hrs is as uncomfortable as possible… 16) Our engines are mostly oil cooled, including the back side of the pistons… yes, the oil is air cooled… 17) our cylinders are mostly air cooled, even the M20C circulates oil near the exhaust valves…. 18) Some O360s have stuck valves in the past… there are a few procedures to know more about the health of the valves… from reaming out the carbon deposits to checking the dimensions on things… the rope trick, and the wobble test… 19) The inside of the doghouse is as aero dynamic as a square block… somewhat brick like… 20) Basic clean-up of the dog house can only get you so far… new seals, fixed cracks, and the things between cylinders too… 21) This is where we go see the cowl guys… 22) We know there can be a cowl that allows us to fly our engines with cruise temps under 380°F on all cylinders… 23) It’s kind of a complex science. While cooling one cylinder better, we accidentally remove air flow from another… 24) It’s Ok to have warmer CHTs… 25) it’s not OK to have a Hot CHT and not know the cause of it… 26) The O360 adds to the challenge because it is a challenge to adjust fuel flow to each cylinder…. Some may get more than the others… one may not get the right amount… 27) Speaking of fuel flow… what is the max fuel flow you are seeing at SL at WOT? 28) Often around here… some engines are set up with a max FF that isn’t very ideal… call it suboptimal… 29) A simple case for IO550s… the same engine may have 25gph as a max FF setting, and another may be set at 30gph… the difference is the excess cooling available while producing the same 300hp… 30) Extra fuel flow is great for cooling cylinders… to a point where there is too much and the proper air / fuel ratio gets exceeded…. 31) I don’t have a feeling for… can an engine monitor tell you your oil flow around your valve stems has been blocked…. The CHT sensor isn’t there… a second TC in that fluid steam would be nice… Compare what you have to an engine that has what you want… There is nothing like climbing WOT to altitude with CHTs where you want them to be… PP thoughts only, not a mechanic… Best regards, -a- Well, I think you have pretty much covered it! MK 1 Quote Link to comment Share on other sites More sharing options...
DXB Posted August 15, 2021 Author Report Share Posted August 15, 2021 On 8/5/2021 at 8:06 PM, PilotCoyote said: I changed my carb recently… rather, I replaced the old 10-4164-1 with an overhauled one. Marvel tech said they set it up to flow 19.0 gph on the bench. I generally see FF above 18.3 on takeoff, and have even seen 18.9 a couple of times, if my FF instrument is to be believed with the boost pump on Thus far, it seems too much fuel for me- the engine surges and runs rough after climbing out from a 2600 MSL airport at summer temps. Leaning it immediately after takeoff to achieve smooth running is a chore and a little worrisome regarding the possibility of leaning it too much and losing some cyl head cooling, as the cyl temps don’t immediately change on the instrument- I’ll know I’m running too lean only after having run lean for about half a minute or so… And If I lean it out for takeoff instead, well, that has been a miserable experience for passengers, airport neighbors, and my nerves….I might be sending it back to have the flow reduced if carb performance doesn’t improve during colder temps. A carb that is too rich has you trying to figure out exactly where the mixture should be set for best power + extra fuel for cooling, but not so much fuel that it reduces take off performance. It’s a bit of a guessing game. I miss my old carb! I imagine a stop could be placed on your mixture cable, either at the panel side (ideally an easily removable one) or a change in how it attaches to the carb, that would give you a very slight decrease in fuel flow at the full rich setting? It doesn't seem worth the time, expense, hassle of pulling your carb again. Also this is very interesting information for me - my 17-18gph leaves my #2 and particularly #4 running hotin , but on the O-360 it sounds like enriching to 18-19gph under many conditions causes other problems. It makes me less inclined to pull my carb. Quote Link to comment Share on other sites More sharing options...
DXB Posted August 15, 2021 Author Report Share Posted August 15, 2021 On 8/6/2021 at 12:14 AM, cctsurf said: Sounds like you and I are running very similar engine setups. I have the powerflow, surefly, and superior cylinders on a c model. A little carb heat may help your CHT distribution immensely. Since I have had my jpi installed, as I just crack the carb heat, I can watch the difference between the chts drop to almost nothing. Normally, my cylinder 3 is quite warm of the others. If you look at the flight data I attached, around 30 minutes after startup, I finally set my mixture and open the carb heat a little. Notice the brown line, cht 3, actually falls below the others and the temps just around 380 for the flight, with a little messing around because I was messing around. I push as far LOP as I can to keep those temps cool... Like Mike says in his leaning webinar, lean to roughness and then bring it back 'till it's smooth. I can lean -WAY- more with that 4 deg C of carb heat than I can without it. Hope that helps. Thanks - I've heard this partial carb heat technique does improve mixture distribution for some folks - unfortunately I've messed with it ad nauseam in cruise without significant effects - it does change the distribution slightly but I think somehow #2 and #4 get much worse cooling airflow on my setup so that is the overarching effect. I have noticed some benefit of very slightly cocking the throttle plate in helping my #4 run cooler in initial takeoff climb, presumably by improving mixture distribution, but the effect seems inconsistent. Quote Link to comment Share on other sites More sharing options...
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