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Thread: 100 HP 0-235 Overhaul

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    100 HP 0-235 Overhaul

    How possible is taking a 100HP O-235 and upgrading it to a higher horsepower rating by switching parts that need overhauling?

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    Re: 100 HP 0-235 Overhaul

    Didn't know they made a 100 hp O-235. I think they are all 108, 110, 112, 115, 118 or with an the sparrowhawk STC, 125 hp.

    Oh, I see the C1A only had 100 hp due to RPM. Should not be a problem to get 125 hp out of it.
    “The only difference between reality and fiction is that fiction needs to be credible.” - Mark Twain

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    Re: 100 HP 0-235 Overhaul

    Quote Originally Posted by Turd Ferguson View Post
    Didn't know they made a 100 hp O-235. I think they are all 108, 110, 112, 115, 118 or with an the sparrowhawk STC, 125 hp.

    Oh, I see the C1A only had 100 hp due to RPM. Should not be a problem to get 125 hp out of it.
    Since you brought it up, does that include the C1? And is there a website or some other source for the info? Sorry guy, just being lazy and it's one of those things at the bottom of my list of things to do for my project.

    Thanks.

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    Re: 100 HP 0-235 Overhaul

    Quote Originally Posted by TerryM76 View Post
    Since you brought it up, does that include the C1? And is there a website or some other source for the info?
    The Sparrowhawk STC for 152's changes the -L2C's 8.5:1 pistons to the -F1's 9.7:1 pistons. All you would need to do is look in the Lycoming IPC and get the part # for the 9.7:1 pistons. No STC required for E/AB. Pretty easy upgrade except you might to change the prop to match new power output.
    “The only difference between reality and fiction is that fiction needs to be credible.” - Mark Twain

    “If you can't dazzle them with brilliance, baffle them with bull$hi+.” ― W.C. Fields

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    Re: 100 HP 0-235 Overhaul

    http://precisionengine.home.mindspring.com has a cylinder upgrade STC. Not required for a homebuilt, but there is some mods that the case needs to put the high compression cylinders on if done right. Knowledge costs something. You can always just parts catalog the 125hp stuff out of the lycoming book

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    Re: 100 HP 0-235 Overhaul

    Quote Originally Posted by Turd Ferguson View Post
    The Sparrowhawk STC for 152's changes the -L2C's 8.5:1 pistons to the -F1's 9.7:1 pistons. All you would need to do is look in the Lycoming IPC and get the part # for the 9.7:1 pistons. No STC required for E/AB. Pretty easy upgrade except you might to change the prop to match new power output.
    Sometimes I forget the leeway permitted with E/AB and get wrapped around the axle trying to find the certificated solution. Gets difficult at times living on both sides of the fence. Always learning something new.....makes it fun.

    Thanks.

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    Re: 100 HP 0-235 Overhaul

    I am flying a 0235 C-1 in my RV3 and have two others for future need. The older low compression 0235's are a lot different than the newer higher compression engines like used in the Cessna 152. One thing the cylinder tie down bolts are different and the case is much stronger. I don't think you can convert to 125hp. You probably can convert to 108 but I don't know for sure what would be required.

    After looking at the above referenced STC to convert a C2C to a higher horse power I still would get a newer case rather than converting a older C Series. By the time you do the case mods and yellow tag you could probably buy a newer used L2C case. That is if the goal is anything higher than 108/115hp that use the cylinders with 3/8 inch tie down studs. The higher compression cylinders use alternating 3/8 and 7/16 studs and have a choke bored cylinder versus the older low compression straight bore.
    One other important point the newer 0235's have dyna focal mounting versus the older c series which use conical mounts.
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    Last edited by ddsrph; December 15th, 2016 at 04:19 PM.

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    Re: 100 HP 0-235 Overhaul

    Quote Originally Posted by TFF View Post
    http://precisionengine.home.mindspring.com has a cylinder upgrade STC. Not required for a homebuilt, but there is some mods that the case needs to put the high compression cylinders on if done right. Knowledge costs something. You can always just parts catalog the 125hp stuff out of the lycoming book
    He (Bill Scott) did my cylinders at my overhaul,,,, a real artist, smoothest engine I ever flew. IO360 in Mooney 1970 M20E. I highly recommend him.

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    Re: 100 HP 0-235 Overhaul

    Crankshafts can be serial numbered for different hp ratings.

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    Re: 100 HP 0-235 Overhaul

    Quote Originally Posted by Nemo View Post
    How possible is taking a 100HP O-235 and upgrading it to a higher horsepower rating by switching parts that need overhauling?
    This brings up an interesting point similar to one I raised several years ago on Supercub.org. This was before I even knew of a STC. My question back then was it possible to take 0235 L2C pistons and rings, which are much cheaper that the ones for the C series, and mill some off the top to decrease compression but still keep it higher for a little extra HP but not too much to over stress the un-altered C series case. Also by keeping the older cylinders it wouldn't require larger tie down studs. This would provide more HP, decrease cost dramatically for the much cheaper pistons and rings and require no case mods. The consensus was it would work but I never pursued it further. If you take a four ring c series piston and connect it side by side via the piston pin to a L2C piston the L2C is about 1/8 inch taller. You could mill off part of this for a midrange compression ratio. Any thoughts here?

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    Re: 100 HP 0-235 Overhaul

    Quote Originally Posted by ddsrph View Post
    This brings up an interesting point similar to one I raised several years ago on Supercub.org. This was before I even knew of a STC. My question back then was it possible to take 0235 L2C pistons and rings, which are much cheaper that the ones for the C series, and mill some off the top to decrease compression but still keep it higher for a little extra HP but not too much to over stress the un-altered C series case. Also by keeping the older cylinders it wouldn't require larger tie down studs. This would provide more HP, decrease cost dramatically for the much cheaper pistons and rings and require no case mods. The consensus was it would work but I never pursued it further. If you take a four ring c series piston and connect it side by side via the piston pin to a L2C piston the L2C is about 1/8 inch taller. You could mill off part of this for a midrange compression ratio. Any thoughts here?
    So now how thick is the top of the new piston, will it be balanced, and how much practice do you have with engine out in what ever you are flying. Lots of stress on those pistons....The Continental A75 piston has a waffle pattern on the back side the A65 does not for example. If it is experimental you can do what ever you want, bit I would stick with some form of stock configuration be it C series or L2C and leave it at that. Save the custom machined pistons for the drag strip where you only run for a minute or two.

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    Re: 100 HP 0-235 Overhaul

    Quote Originally Posted by proppastie View Post
    So now how thick is the top of the new piston, will it be balanced, and how much practice do you have with engine out in what ever you are flying. Lots of stress on those pistons....The Continental A75 piston has a waffle pattern on the back side the A65 does not for example. If it is experimental you can do what ever you want, bit I would stick with some form of stock configuration be it C series or L2C and leave it at that. Save the custom machined pistons for the drag strip where you only run for a minute or two.
    I never said it was the thing to do. It would require a lot more research by an experienced engine person/persons to determine if it was a good idea. Some people just stick in unaltered L2C pistons or so I have been told, which in my opinion is definitely a bad idea. Here is a photo I have showing the difference between the height of the C and the L2C pistons. If the L2C piston is thick enough at the top to take some off and still leave it as thick as the lower compression C piston it may be a possibility. It's just an idea I had but have never really checked into whether it is a good idea or even possible. I found a great very low time engine and the issue with me became something I had no further interest in.
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    Last edited by ddsrph; December 18th, 2016 at 05:27 PM.

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    Re: 100 HP 0-235 Overhaul

    You would need to cut a couple of pistons open and measure. Pretty common race engine mod. My question is why bother? If it's not certified, I would not run the fourth ring; common for O-290Gs. The bigger studs are for reliability, I would probably want them. I have a friend who's Tomahawk had a cylinder come loose. Some studs broke and pulled others

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    Re: 100 HP 0-235 Overhaul

    I know I originally posted about O-235 engines, but how do you de-rate an O-200 to a C-90, (so I can swing a longer propeller)? The person I have asked about this seems to think it is just the different cam, because the crankshaft is the same.

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    Re: 100 HP 0-235 Overhaul

    Quote Originally Posted by Nemo View Post
    I know I originally posted about O-235 engines, but how do you de-rate an O-200 to a C-90, (so I can swing a longer propeller)? The person I have asked about this seems to think it is just the different cam, because the crankshaft is the same.
    turn less RPM? Smaller carb throat or different carb, restrict throttle movement. Any or all of above assuming it's experimental

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