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Lycoming 0-320-A2B Running Rough & Hot

Michigan
Hello!

My name is Thea and I recently purchased an Experimental PA-18-150 Replica. I am having a couple of issues and hoping to receive some insight on this type of motor and any quirks that people might know of! I do have quite a bit of time in Super Cubs (1200+ hours) as I am a banner tow pilot, but most of my time is in 180 HP 0-360s...

A little back story.. This cub was built in 1985 and only has a TT of 595 hrs. The previous owner had it for about 20 years and only put about 200-250 hours on it. Logs are complete and from them I can see that the motor was completely overhauled in 2009 due to a prop strike. At that time a new crank and cam were installed. All new chromed cylinders were installed. Since OH the engine only had about 100 hours put on it and then sat from 2016/2017 until the day I brought it home (8/2023).... luckily it was a short 15 minute hop.

Since getting it back to the shop. We have pretty much gone through everything we can before pulling jugs or doing anything more aggressive. We replaced all the oil lines. I sent out the carb and mags to get them overhauled - even though they had less than 100 hours on them. I installed a new Kellys Aero harness and replaced all the spark plugs.

Post upgrades, I have put about 12 hours on it. One issue I am having is the oil temps are progressively getting higher and are now in the 220 range. I do have a very old oil cooler and put in an order today to upgrade to a new Aero Classics one. I also discovered with this old case I do not have a vernatherm. That is also the next project to replace the current oil screen housing with an updated version that contains a vernatherm. I am also looking into changing out the screen to a filter via airwolf STC.. If anyone has any insight on that I'd love to hear it!

I guess my question is if there is anything else I should be looking at? or really any/all info people might have on this type of motor. Eventually I am installing a Dynon HDX system with full EIS... But for now all I have is oil temp & oil pressure. I do not know what my CHTs are running.


The second issue I am having is the engine seems to be running rough at the 2100 RPM range... This "roughness" was semi the reason I sent out the mags/carb and purchased a new harness. But even after those upgrades it seemed to improve some but definitely is still there. On take off with full mixture it runs great but soon as I start pulling the throttle back and hit the "2100-2150 RPM" range it runs rough. I only make about 2300 RPM on take off because I have a very coarse prop (already ordered the composite Sensenich ground adjustable prop - just waiting on delivery). I have determined this "roughness" improves drastically with leaning but I am having a hard time determining if it improves because the fuel/air mixture ratio is better or with the slight RPM rise from leaning it takes it out of that "roughness range." I am leaning towards it being a air/fuel mixture ratio problem but it seems a little strange to me that its only apparent at that certain RPM. I do have the square carburetor airbox and have heard that these have issues with not getting enough air... again if anyone has any insight on the truth/validity of that statement I'd love to hear it. I am open to upgrading to the dome style airbox if that is the case!


Anyway, sorry for the long winded post and thank you to anyone who takes the time to read it and offer suggestions!

Thea
 
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If you have slick mags they are notorious for internal timing issues right after overhaul/rebuild so double check the timing first that is quick and easy. Look closely at the primer system A leaky primer can cause the engine to run rough and leaning it will smooth it out. What is the RPM drop at 2400 rpm in cruise when you pull carb heat? It should be around 100-150 RPM if more you are running rich check the float bowl screws. As long as the airbox is in good shape I would leave it alone most likely not the issue. I am not a fan of Vernatherms, You most likely have a viscosity valve and they work fine. Don't throw too many parts at it until you have figured out what the real issue is.
DENNY
 
It would be easy to check the oil viscosity valve plunger and spring. I have replaced a spring and this seemed to help on a cub with a similar high oil temp issue.
 
If you have slick mags they are notorious for internal timing issues right after overhaul/rebuild so double check the timing first that is quick and easy. Look closely at the primer system A leaky primer can cause the engine to run rough and leaning it will smooth it out. What is the RPM drop at 2400 rpm in cruise when you pull carb heat? It should be around 100-150 RPM if more you are running rich check the float bowl screws. As long as the airbox is in good shape I would leave it alone most likely not the issue. I am not a fan of Vernatherms, You most likely have a viscosity valve and they work fine. Don't throw too many parts at it until you have figured out what the real issue is.
DENNY


Thanks Denny! Those are great suggestions... I actually removed the primer system.. Ive heard that they can be the cause of roughness and honestly in all my years of flying cubs I don't think Ive ever touched a primer so I just opted to take it out completely.

I also haven't noticed any higher than 150 rpm drops with carb heat checks, but next time I fly I will specifically look at that in cruise closer
 
It would be easy to check the oil viscosity valve plunger and spring. I have replaced a spring and this seemed to help on a cub with a similar high oil temp issue.

I will look into that. I am currently back to the drawing board & taking it apart in order to swing the motor back open.
 
I have the square carb box on 160 hp O320. No problems.


Sent from my iPhone using SuperCub.Org
 
One of the easier things you can do, is to perform the valve/valve guide clearance inspection and cleanup reccomended on all Robinson helicopters for Lycomings. (320 and 360)
Basically...coking can occur which will keep the valves from closing fully...easily verified by compression testing and if not bueno...then you drop the exhaust, pull the valves out, after dropping them into the cylinder, with the piston at bottom of stroke. basically you are dis-assembling the top end, one cylinder at a time and doing an minor valve job "in Situ". I've done this in a day many times and have found many engines with not enough clearance between valve guide bushing and valve stem.

This definitely cause a stumbling...it usually starts after 20 minutes of running and getting up to temp.

Anyhow...all you really are doing is running a reamer through the valve guide bushings to return them to proper clearance and clean things, real well and re-assemble.

The culprit is normally folks who aren't religious about oil changes...thus the oil being allowed to "coke" a bit...and the exhaust valve stem exposed to lots of hot yuck, becomes the lucky recipient.

Anyway, you can look up the service bulletin or ask a Robinson service center.

Easy to do and doesn't cost much...and helps lots of times with restored good compressions, returned power, improved cooling AND....NO MORE STUMBLE!!!

Steve
 
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To follow up on this thread... I fixed the high oil temps by replacing the oil cooler and installing a vernatherm. Since, this post my motor has still been running rough at that certain RPM range. It also has not been making power. I recently replaced by prop with the Sensenich ground adjustable and could only make 2400 RPMs at the lowest pin. Thats when we knew knew something wasnt right. I was 5 second from pulling a jug to inspect the cam when we found this up the tail pipe. The flame tube completely warped over in on itself and is covering the exhausts exit. I even stuck my boroscope up there and could see it was covering the hole. We are hopeful this is the power/RPM problem. Now trying to figure out if I replace just the muffler or entire exhaust system
 

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Goodness that problem has had dire consequences for many. I have a serviceable muffler with a low time heat shroud I could part with. I installed a hot rod muffler in its place. It’s a good way to go to forever avoid this problem as it has no baffles. It definitely gave me more RPM but as others have said it’s a lot louder in the cockpit. There not cheep but this also takes care of the muffler AD. This should have been caught at the annual inspection or last time the AD was complied with. Keep up the good work and get that cub back in the air. I had forgotten you have an Experamental cub, so it’s up in the air about AD’s. A condition inspection would be when this should have been looked at.
 
That is a semi common issue with the stock muffler and the reason for the required yearly inspection. When mine started to warp I just got a Hot Rod exhaust which has the baffle completely removed. My exhaust pipes are in good shape so it was a pretty simple fix. The Hot Rod exhaust helped with my CHT's on climb out and produces a lot of heat. the down side is they are loud!! I have had to prop start my planes more than once a primer system makes it easy. whenever you buy any plane it seems you always have to work through some issues. Sounds like you list is getting shorter, hang in there.
DENNY
 
Being experimental I would be tempted to see how hard it is to just cut the flame tube out completely. A good weekend snow day project.
DENNY
 
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If you decide to replace the system, I have a Vetterman exhaust system for an o320. I changed over to an o360. Less than 100 hrs on the Vetterman system.


Sent from my iPhone using SuperCub.Org
 
If you decide to replace the system, I have a Vetterman exhaust system for an o320. I changed over to an o360. Less than 100 hrs on the Vetterman system.


Sent from my iPhone using SuperCub.Org

I was going to suggest a Vetterman exhaust. That’s what I would do if I was experimental.
 
If you decide to replace the system, I have a Vetterman exhaust system for an o320. I changed over to an o360. Less than 100 hrs on the Vetterman system.


Sent from my iPhone using SuperCub.Org

Sorry! just seeing this! I’m not familiar with the Vetterman System.. Is it a similar set up as the sutton/rubbert? after some thought this past month it would be nice to move the muffler forward so that is where I was leaning! Nothing has been set in stone yet! Because of the holiday and everything else it’s just been sitting exhaustless waiting…

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This is what I'm using from Custom Aircraft, fits perfectly. I like the heat muff forward keeping access at the sides easier. https://www.customaircraft.com/systems.html

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It has been my experience that the Vetterman exhausts do not put out much cabin heat. You live in Michigan. I would recommend you consider a Sutton. They put out LOTS of heat for cabin and carb functions. If you live in the southern states Vetterman does make a fine product.

Bill
 
It has been my experience that the Vetterman exhausts do not put out much cabin heat. You live in Michigan. I would recommend you consider a Sutton. They put out LOTS of heat for cabin and carb functions. If you live in the southern states Vetterman does make a fine product.

Bill
While I have no experience with the Vetterman, I would suggest when comparing the pictures with it and the one which I've shown in post #18, the Custom Aircraft heat muff is closer to the cylinders (more heat). The exhaust temperatures cool down rapidly the further they are from the cylinders. I would speculate the Custom Aircraft would do a better job of heating the cabin. It does mine, but then I don't fly when the lake freezes over.
 
Every Cub I've flown, yes even J3, Pa11 and Pa15 have made good enough heat. Good enough to fly for hours at zeroF. My old Alaska buddy Stu convinced my years ago the the warm air comes out of the firewall heater box down by the floor and goes unnoticed under the front and rear seat and warms the tail wheel as it passes by. Put the heat where you need it and you'll be absolutely amazed at how much heat there really is. Even the J3 put out 125* air in front of the rear stuck.

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Glenn
 
I never had any issue with heat running Danes LEES on our A model Cub up in Alaska. I ran a long piece of SCAT under the front seat as Glenn depicts above, long enough for the rear seat occupant to use as a defroster for the side windows. The front did get a bit chilly when the biologist stuffed the hose into his jacket to keep the telemetry gear warm when operating at -30. Dress for Egress and no issue.
TR
 
I never had any issue with heat running Danes LEES on our A model Cub up in Alaska. I ran a long piece of SCAT under the front seat as Glenn depicts above, long enough for the rear seat occupant to use as a defroster for the side windows. The front did get a bit chilly when the biologist stuffed the hose into his jacket to keep the telemetry gear warm when operating at -30. Dress for Egress and no issue.
TR
Yup, I was taught to dress like you have to walk home

Glenn
 
Every Cub I've flown, yes even J3, Pa11 and Pa15 have made good enough heat. Good enough to fly for hours at zeroF. My old Alaska buddy Stu convinced my years ago the the warm air comes out of the firewall heater box down by the floor and goes unnoticed under the front and rear seat and warms the tail wheel as it passes by. Put the heat where you need it and you'll be absolutely amazed at how much heat there really is. Even the J3 put out 125* air in front of the rear stuck.

View attachment 105338View attachment 105339

Glenn
Is this a STC heat system? I’m thinking about running scat tube from the output opening along the floor to the rear edge of the pilot seat. Not sure how I will attach it. My feet get really hot and the PAX don’t get enough heat.

Thoughts and suggestions appreciated!

Robert
 
No STC required, all temporary

You need one of these. On mine it just slides down and is held in place by friction between the firewall pad and the " V " tubing

Screenshot_20240228-132534.png

I added this to direct heat up to the bottom of the panel on each side, it you drill some holes in the first flange on the sides you will still get some heat to your boots

Screenshot_20240228-132357.png
Other fittings are available also

Screenshot_20240228-133318.png

Glenn
 
Every Cub I've flown, yes even J3, Pa11 and Pa15 have made good enough heat. Good enough to fly for hours at zeroF. My old Alaska buddy Stu convinced my years ago the the warm air comes out of the firewall heater box down by the floor and goes unnoticed under the front and rear seat and warms the tail wheel as it passes by. Put the heat where you need it and you'll be absolutely amazed at how much heat there really is. Even the J3 put out 125* air in front of the rear stuck.

View attachment 105338View attachment 105339

Glenn
I'm sure you're well aware Glenn, but for those that aren't, be mindful of the heat being applied to the brake cylinders depending on setup. As they heat up, they can pressurize the brakes resulting in potential issues during the landing phase. The other setups I've seen that are similar had the hose pulled up close to the bottom of the front seat providing space from the brake cylinder/s.
 
Just went out and took some more pictures of my setup. I've done this on 4 different planes. Looks like my firewall flange is on that Wagaero sells and I have one screw holding it in place at the top. When I'm solo I just remove the back scat from the fitting, or you can make a plug to stick in the back hose and that also allows the backseater to choose how much heat the want. My wife stuffs her glove in it. I added a diverter to the " Y " and ran a cable to it so I can choose where the heat goes. This setup keeps me warm enough down to -20F. Hope this helps

Glenn

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Very helpful photos! Thanks for taking the time to post them. I like the simplicity and low cost.

Robert
 
Is this a STC heat system? I’m thinking about running scat tube from the output opening along the floor to the rear edge of the pilot seat. Not sure how I will attach it. My feet get really hot and the PAX don’t get enough heat.

Thoughts and suggestions appreciated!

Robert
I have the same problem my feet are almost always to hot. You don't need a STC. Just attach a length of scat tube and run it along side the stick and under the seat. If your heat box is flush on the inside figure out the hole size and just bolt a neck on the inside to attach the scat tube. https://www.aircraftspruce.com/catalog/eppages/tubingconnectors.php the winter If I get cold I still use the floor heater and the heat comes up behind my seat keeping my neck warm. I do have a additional rear seat heat box but that was made into a dedicated defrost heat last time the cub was recovered.
I'm sure you're well aware Glenn, but for those that aren't, be mindful of the heat being applied to the brake cylinders depending on setup. As they heat up, they can pressurize the brakes resulting in potential issues during the landing phase. The other setups I've seen that are similar had the hose pulled up close to the bottom of the front seat providing space from the brake cylinder/s.
Good thing to think about. I shot the scat tubing with a heat gun and it is over 200 degrees. I keep my brake fluid topped off and have never had a problem but it is something to consider. I did not add any holes for front heat, that radiant heat off the scat tube seems to do fine.
DENNY
 
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