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Thread: Can use some advise swapping o-290 with O-320

  1. #1

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    Can use some advise swapping o-290 with O-320

    Im confused which is easy to do. I have a rebuilt O-320 150 hp I am upgrading from an O-290. 1950 PA-18 certified. I have a sky Tec flyweight starter and that is all so far. Would like to keep it as light as possible, but dont have deep pockets... Converting gen to Plane Power alternator, or is the a better way to go? Anyone have any suggestions on what rear mounting lightweight rear oil cooler, and the best way to mount it for the best cooling. Also any other suggestions on a good exhaust that is in the 2k range. Is Sutton good? And any other mods I might need would be greatly appreciated. I seem to be reading some rear mounted coolers are having high cht issues. The stc on the alternator says I need a rear mounted, and with the Sutton exhaust. Also will the conical O-290 engine mounts work? In the Wag Areo STC it does not say it but the Cubcrafters does..dynafocal. Cubcrafters says I need to change my cowling? I opted out of making it 160 and kept it a narrow A2A but it dyno's out at 162.

    I have been flying my Super Cub for years this is the first engine so I'm at a loss. Getting all my info from here. I want power that I can afford. Thanks in advance.

  2. #2

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    I am not a fan of the rear mounted oil cooler, robs cooling air from #4 and makes it a pain to work on the mags. Check out the B&C alternator. I prefer the Hot rod muffler, but if I lived in the South I might get the Sutton to get the heat off the firewall. Did you upgrade the fuselage?
    DENNY
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  3. #3

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    Sutton exhaust is about 6 lbs lighter than the Piper exhaust and gets rid of the 50 hr AD. If your FSDO will do a Field Approval and 40 amps is enough, the B&C L40 alternator is what I’m using.


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  4. #4
    aktango58's Avatar
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    Atlee hot rod will also remove the AD on muffler. That said- heat on firewall good or bad for you? If you are not wanting heat on the firewall, Sutton would be my choice for weight reasons.

    Alternator: If you are a 'basic' cub with very little electrical, B&C gear drive alternator is about as small and light as you can get.

    Put your oil cooler where it will fit best. There is a reason so many got moved back.
    I don't know where you've been me lad, but I see you won first Prize!
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  5. #5

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    I have a Scott and Cleveland brakes. On the Wag Aero STC it does not say anything about a fuselage upgrade. It calls for dual pulley trim on the Cubcrafters..unless I am missing something. I can see how it will be hard to work on the mags. But I cant afford the 4500 Power Flow at this time.

  6. #6
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    I've converted an L-21B from an O-290D2 to an O320 (160 hp), with a lightweight starter, rear mounted oil cooler, alternator, lightweight underseat battery, Atlee hot rod muffler, and a new nosebowl (no oil cooler hole). I had to use the rear mounted cooler to make room for the SkyTec HT starter, which if I recall correctly, was the only model available at the time (~2001). You may not have to move the oil cooler with newer model starters, but I'm happy with the result. The resulting installation was ~30 lb lighter with 25 more hp. The climb improvement was, um, noticeable.

    I use a restrictor plate to partially cover the oil cooler to get the oil temperatures up and keep the CHT on #4 down. CHT temps are manageable with this setup. Once the restrictor plate is in, far and away the most important thing is to make sure you have good baffle seals, cover the gaps around the nose of the engine, "ramps" for cylinders 1 and 2, seal the hinges, etc., - there's lots of discussions on this in other threads. If you re-use the O-290 baffles, you'll need to fill in a couple of gaps around the cylinders, particularly the big gap at the bottom rear of #3. After doing all this, peak CHTs for #4 went down 30 deg.

    The Atlee hot rod muffler is really really loud in the cockpit. If I had to do it again, I'd consider the Sutton.

    I like the SkyTec HT starter. Some newer models are a pound or two lighter, but the HT has a kickback clutch and anecdotally seems more durable than the ultra lightweight ones.

    The Odyssey battery mounted under the seat really swings the prop. The cables are shorter, but you still should use high quality ones. Use a direct ground cable to the engine - don't rely on the stubby braid on the engine mount. Bogert makes them to order if you don't want to do it yourself.

    The alternator is a field approval of a Niagara kit (Denso automotive alternator) - no longer available from Niagara, although Denso alternators are easy to acquire. I doubt I could get the equivalent approved today.

    We retained the O290 carburetor (an SP3 I think). Going to an SP4 requires changing the lower cowl. I've had no trouble with my carburetor setup.
    Last edited by sjohnson; 02-24-2020 at 05:58 PM.
    Idaho drinks more wine per person than any other state in the country.
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  7. #7
    S2D's Avatar
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    Quote Originally Posted by aktango58 View Post
    Atlee hot rod will also remove the AD on muffler.

    You have that in writing somewhere?
    I may be wrong but that probably won't stop me from arguing about it.

  8. #8
    SuperCub MD's Avatar
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    Quote Originally Posted by S2D View Post
    You have that in writing somewhere?
    I have the letter and amoc, should be easily obtainable from atlee if needed.

    To the original question, what is your'50 PA-18? Is it a 18-125 or 18-135? Check the data plate,or is it a 18 converted to a 135? If it is a later model the 320 is a bolt in replacement,but the 320 requires a heavier engine mount, which is not a big deal. Everything else (exhaust, accessories) should bolt right up.

  9. #9
    AkPA/18's Avatar
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    S2D,
    Careful on the above claim. This guy who shows up out of nowhere claiming to be a supercub doctor.
    http://thrustline.com/

    Takeoffs are optional--Landings are mandatory
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  10. #10
    aktango58's Avatar
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    Quote Originally Posted by AkPA/18 View Post
    S2D,
    Careful on the above claim. This guy who shows up out of nowhere claiming to be a supercub doctor.
    Maybe he just likes to fondle the cool parts?
    I don't know where you've been me lad, but I see you won first Prize!

  11. #11

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    The hot rod is LOUD outside of the plane also!! My friends say they know it is me before they see the plane and I tend to fly real low!!! However, I do have have noise canceling headsets. So lets talk about cabin or more important CARB heat and what you get off both!!!! This may take a bit of work but we should have enough people with both Hot Rod and Sutton with carb probes to give us some input on carb temp rise. That is most the most important issue. If one of the smart guys want to post some stuff about carb icing/carb heat it would help.

    DENNY

  12. #12

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    Quote Originally Posted by sjohnson View Post
    I've converted an L-21B from an O-290D2 to an O320 (160 hp), with a lightweight starter, rear mounted oil cooler, alternator, lightweight underseat battery, Atlee hot rod muffler, and a new nosebowl (no oil cooler hole). I had to use the rear mounted cooler to make room for the SkyTec HT starter, which if I recall correctly, was the only model available at the time (~2001). You may not have to move the oil cooler with newer model starters, but I'm happy with the result. The resulting installation was ~30 lb lighter with 25 more hp. The climb improvement was, um, noticeable.I use a restrictor plate to partially cover the oil cooler to get the oil temperatures up and keep the CHT on #4 down. CHT temps are manageable with this setup. Once the restrictor plate is in, far and away the most important thing is to make sure you have good baffle seals, cover the gaps around the nose of the engine, "ramps" for cylinders 1 and 2, seal the hinges, etc., - there's lots of discussions on this in other threads. If you re-use the O-290 baffles, you'll need to fill in a couple of gaps around the cylinders, particularly the big gap at the bottom rear of #3. After doing all this, peak CHTs for #4 went down 30 deg.The Atlee hot rod muffler is really really loud in the cockpit. If I had to do it again, I'd consider the Sutton. I like the SkyTec HT starter. Some newer models are a pound or two lighter, but the HT has a kickback clutch and anecdotally seems more durable than the ultra lightweight ones.The Odyssey battery mounted under the seat really swings the prop. The cables are shorter, but you still should use high quality ones. Use a direct ground cable to the engine - don't rely on the stubby braid on the engine mount. Bogert makes them to order if you don't want to do it yourself.The alternator is a field approval of a Niagara kit (Denso automotive alternator) - no longer available from Niagara, although Denso alternators are easy to acquire. I doubt I could get the equivalent approved today.We retained the O290 carburetor (an SP3 I think). Going to an SP4 requires changing the lower cowl. I've had no trouble with my carburetor setup.
    Thanks I was just thinking about the Atlee Dodge. But all the advise has locked in me buying the Sutton. Great advice with all of this! Thanks for taking the time.

  13. #13

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    Its a 125 and it is a later model 320...came out of an 1985 Lancair. I am still going to get the dyna mount $800 feel better knowing my engine is going the same place my airplane is. Thanks man!

  14. #14

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    Thanks - that is what I am doing. Sutton B&C ordering today.

  15. #15

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    On the rear-mounted oil cooler, we have a hard time keeping the oil temp up in the winter. Even on hot summer days, the oil temp tops out at 170 degrees in cruise. From what I understand, you want more like 180.

    As far as the 1950 cub, does the tail number end in "K"? Ours is a K series; originally had flaps, 13 ribs, one wing tank, O-235, no electric.

  16. #16

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    In ends in Victor and did come with flaps. All it says on reg on everything is PA-18. I have been wondering about that for a while. I have everything but the baffle and rear oil cooler. Any suggestion on a brand? Thanks!

  17. #17

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    I have a rear mounted oil cooler, I put thin washers between the cooler and the baffle. This gives me a nice slot that I can slide a simple metal plate in front of the cooler. Make a few, how wide you go depends on ambient temp. I was flying a few days ago and blocked off 80 percent on the cooler worked great at 10-15 degrees.
    DENNY

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  19. #19

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    Awesome thanks Denny! This really helps!

  20. #20
    SuperCub MD's Avatar
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    Quote Originally Posted by Dumdum View Post
    Its a 125 and it is a later model 320...came out of an 1985 Lancair. I am still going to get the dyna mount $800 feel better knowing my engine is going the same place my airplane is. Thanks man!
    You have a A2A right? That is a conical engine, you need a conical mount. You need a stock mount for a Pa18-150. It will be the same as your 125 mount but built heavier.

  21. #21

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    Quote Originally Posted by SuperCub MD View Post
    You have a A2A right? That is a conical engine, you need a conical mount. You need a stock mount for a Pa18-150. It will be the same as your 125 mount but built heavier.
    Perfect timing. I was just talking to Alaska Airframes, He said I can use my 125 mount that they are the same. He said Piper used the same with 125, 135 and the 150hp. The Wag Aero STC says to replace with PN 12351-12. I can not find a number on my mount. Alaska's is PN 1235-102 so is the Univar. Now the question is will my o-290 mount be ok? Thanks for your help

  22. #22
    SuperCub MD's Avatar
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    It's been a long time since I converted one, but I seem to remember the 125'135 mount was lighter. Those mounts became obsolete around 60 years ago. Very few still exist, but you could still have a original. The stc requires a new heavier mount be installed. It will be up to the IA that is signing off on your installation to determine if you have the correct mount.

  23. #23

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    There's an old AD out for checking early Cubs converted to 150 with original mount, the 150 mount with the .049 wall tubes has a finger patch welded on for identification.
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  24. #24

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    Quote Originally Posted by Dumdum View Post
    Perfect timing. I was just talking to Alaska Airframes, He said I can use my 125 mount that they are the same. He said Piper used the same with 125, 135 and the 150hp. The Wag Aero STC says to replace with PN 12351-12. I can not find a number on my mount. Alaska's is PN 1235-102 so is the Univar. Now the question is will my o-290 mount be ok? Thanks for your help
    As mentioned previously, if your mount has welded on finger patches it should be ok. If no finger patches you will need a new motor mount like Mark said
    I did the same swap to my 51 Cub a couple hundred hours ago


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