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Thread: Experimental 0235 Question for Engine Experts

  1. #1

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    Experimental 0235 Question for Engine Experts

    I have an idea that may be a bad one but would like to hear advice from those in the field of engine mods/STC's. I have no
    interest other than personal use. Would it work to take the newer 0235 three ring pistons, mill off some of the top surface to
    reduce some of the increased compression ratio that the L2C's have but leave enough to boost the 0235C series HP, within the
    limits the case would allow. This would accomplish two things: Slight increase in HP over the 108 and allow use of the much
    cheaper L2C pistons and rings.

    Jim Miller
    Thanks eskimo77 thanked for this post

  2. #2
    Cub Builder's Avatar
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    Yes, it could work. The bores are in fact the same. I'm sure you already know that the C series has smaller studs, etc, but the bores are the same, so as long as you leave sufficient material at the head of the piston for heat, there's no reason why it shouldn't fit. You wouldn't be the first to simply install a set of L2C pistons in a C series engine. I would recommend installing the L2C wrist pins as well. They are a different part number which often times means they have a different wall thickness in the wrist pin. I don't have a set available right now to measure, but could verify with my machinist who does have most of my old parts laying around in his shop.

    -CubBuilder

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    I had a old L2C piston and placed the piston pin half way in and joined a C series piston on the other half. The L2C was about 1/8" taller
    at the top accounting for the increased compression ratio on the L2C. It was thick enough to take off most of the 1/8" if not all but leaving
    some to boost the C series horsepower should be easy to calculate. I am suprised that someone hasn't developed a STC for this.

    JM

  4. #4
    cubdriver2's Avatar
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    Quote Originally Posted by Jim Miller View Post
    I had a old L2C piston and placed the piston pin half way in and joined a C series piston on the other half. The L2C was about 1/8" taller
    at the top accounting for the increased compression ratio on the L2C. It was thick enough to take off most of the 1/8" if not all but leaving
    some to boost the C series horsepower should be easy to calculate. I am suprised that someone hasn't developed a STC for this.

    JM
    C85 and 0200 piston do the same thing but you have to clearence the C85 piston or sparkplug insert when using it with the 0200 rod and crank.

    Glenn

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    Quote Originally Posted by cubdriver2 View Post
    C85 and 0200 piston do the same thing but you have to clearence the C85 piston or sparkplug insert when using it with the 0200 rod and crank.

    Glenn

    Glenn
    One thing good about the 0235's is they all have same rods and crank. It would be interesting to hear from people who have
    used the un-modified L2C pistons in the C-series engines. If they worked OK then my idea would work even better due to less
    stress on the engine case from the less than L2C compression ratio.

    JM

  6. #6
    Lowrider
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    Just a thought, but would a thicker head gasket do the same thing without machining the piston head? Not sure how much CR you are trying to get rid of but you could figure out what you need to get the compression ratio down where you want it. Cheaper pistons and a little more power seems like a good thing.

  7. #7
    skywagon8a's Avatar
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    Quote Originally Posted by Lowrider View Post
    Just a thought, but would a thicker head gasket do the same thing without machining the piston head? Not sure how much CR you are trying to get rid of but you could figure out what you need to get the compression ratio down where you want it. Cheaper pistons and a little more power seems like a good thing.
    Lowrider, This is a Lycoming engine. The heads are fixed to the cylinders. There is no head gasket.
    N1PA

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    Lowrider
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    OH...thanks!

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    7shannon's Avatar
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    Also I have read a few places that there are automotive piston rings that will fit the O235 piston, does anyone have part numbers for them? I have a C1 that came with my PA11 project that I plan to use.
    Kevin Shannon

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    I have a o235C/110hp at 2600rpm..What mechanical difference between o235C and o235C1???

    Don

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    7shannon's Avatar
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    Don, the cam and the carburetor are different

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    Steve Pierce's Avatar
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    I have the piston ring part numbers somewhere, I will look. Jason can ask Doug and Dan Stewart.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

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    7shannon's Avatar
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    Thanks Steve, the Hastings catalog lists 4 3/8 dia rings in 3/32 compression and 3/16 oil rings, looks to me like those should work.
    Kevin

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    I have a 0-235C P20 and am looking for a set of rings, I can find automotive rings the right size, but not with the wedge lock. Is it possible to machine the grooves to fit standard automotive rings. This is for an experimental engine.

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    Jim, what's your present compression ratio? What compression ratio would you like to use?

    I'll run the numbers on the power increase.

    C85 pistons on an O-200 crank give 8.68:1 for about a 7% increase over an O-200 piston.
    I like 9.5 pistons for a 9.76% increase (and they will still run OK on premium mogas).

  16. #16

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    How about high compression cylinder/piston assemblies on C-Series 0235. Bush the larger 7/16" base holes. Derate manifold pressure to say 25" max.??

  17. #17

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    I heard that you can put a 0360 jug set up on the 0235 motor to increase the hp. Would this actually work? I have an airboat with a 0235-C that I found out was converted into a 0235-L2A. I currently have a bad cylinder and was just going to replace it but once I heard this I had to ask the experts to see there thoughts. I am thinking if this would work I would want to try it to see what the increase in hp would be. Any thoughts?

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    Still trying to keep the thread alive. I've got a C2C with only 350 since major but sat for 10 years. Owner told me he pulled the prop through a couple times a month to keep the rust off the cylinder walls......ugh! Good news is the cam looks perfect. Bad news is that I'm P10 and the rings are more than ridiculous! Anyone with alternative ring #'s, experience with the L model piston rings, etc. the information would be welcomed.

  19. #19

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    [QUOTE=cubdriver2;553146]C85 and 0200 piston do the same thing but you have to clearence the C85 piston or sparkplug insert when using it with the 0200 rod and crank.
    I didn`t have to clearance anything when I built my C-85 to O-200 it was a straightforward swap, I did have to check the throw of the rods to the case but mine cleared with plenty of room and made my C-85 a really great little engine

  20. #20

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    I would consider L2c pistons and rings.

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    That would definitely be the most reasonable solution, and as luck would have it also the most beneficial. Just haven't been able to find much information on how well it works, whether guys are actually shaving the extra bit of compression off the piston, or whether they are just doing the substitution with no problems? I guess just looking for some experienced guidance. Also laughing at myself a bit here.....the airplane sat for 10 years and I was so worried about the cam (which looks perfect by the way) that now the cylinders are my problem. Paint was wore off the heads so no idea if they were oversize. I either get the award for being the most conscientious and safety minded A&P, or an award for being a paranoid idiot.

  22. #22

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    I have a home made straight exhaust system on my O 235. would a cross over system provide a noticeable power increase? Don't have $$ to waste.

    Don

  23. #23
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    Any real world experience follow up to share on this? Building up a set of cylinders and looking for a little hand holding, PM's appreciated. Jim

  24. #24

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    I'm looking at similar options for my 0-235-C1B. I'm also curious about whether anyone has follow-up experience with this. I'm in the middle of re-doing my engine and this might be a good opportunity to complete these modifications since the through bolts on the case would need to be reamed out to the larger 7/16 diameter from the higher compression engines.

    Biggest questions I would have would be:
    - Would any other parts need to be swapped (i.e. Propeller, etc.)
    - Would the engine still be able to run with premium mogas?

  25. #25

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    There is an STC to go with the L2C cylinders and pistons on a C2C as I recall, biggest difference for the C1 to C2C is prop bushings and slick mags.

    The STC calls for machining the case for the larger thru studs and corner studs. The stud kit alone is more than $1000!

    Another issue is the prop. If you have a 76AM-2, it is limited to 6.75:1 compression on the O-235. I suspect there is a vibration issue with the prop and higher compression ratios.granted you are Experimental, so you can EXPERIMENT.

    Just an FYI, piston part numbers for the O-235 6.75:1 compression are 73851, 14B23919 or 14B28072. I think that last part number is a 3 ring piston.

    I was lucky to find a set of usable used pistons that came out of an engine being overhauled.


    Sent from my iPad using Tapatalk

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