Piston upgrade for O-235

[Delta Mike]

Hi all,

What advice is there on finding and putting in different pistons to a low compression (6.75:1) O-235-C2C?

This particular O-235 is on a Long-EZ in Durango, and with a Great American 62x62 climb prop it is unable to generate more than 2250 rpm static - rated takeoff rpm is 2800. Engine TSMOH is 870 hrs.

Several things were done to try to improve power:
1. New plugs
2. Tested all leads - OK
3. Adjusted valve clearances to spec (0.008" - were ~ 0.013" all round)
4. Tested fuel delivery / replaced fuel filters
5. Replaced standard air induction with ram air induction with oversized K&N filter
6. Checked Mags, reset internal timing / E-gap to spec
7. Installed LSE Plasma II to bottom plugs

All of these changes brought static rpm up to about 2270 rpm

Compression checks showed the #4 cylinder at 66/80 with leak through the intake valve. #1, #2, and #3 all read ~76/80. #3 also leaked intermittently through the intake going to 66/80 depending on which way the prop is moved during the check. Taking off the valve springs on #4 showed about 1/16" end play at the tip of the intake valve, indicating worn intake valve guide. Removing the piston showed the intake valve was not seating on about 30% of the circumfrence.

#4 and #3 cylinders are going to the shop for intake valve guide replacement (and whatever else they find out).

I am considering topping all four cylinders and putting in at least some 8.5:1 compression ratio pistons, like the -L2C model. At Durango's typical density altitude even the 9.7:1 compression ratio will only give 93 ponies at full rpm.

For those of you still reading,

Where is a good place to get the pistons?
What options are there in pistons - 5 ring vs 3 ring, forged vs cast, etc?
What are some pros and cons - do the intake or exhaust valves need to be replaced, or are they all the same for all of the O-235s?
Who else has done this type of change?

Feedback will be much appreciated, the bird is in the hanger.

Delta Mike

[easyrider]

Try these guys
http://www.lycon.com/
I know several people who have success with them
Regards
Easyrider

[spy]

  I run a 0-235 c1b (all stock)...and with a 60x74 prop...my static is 2550-2600...and it gets 2800 on full power  level flight ...is tach reading right?...
 2200 static on a 62x62 seels low...my old prop was a 62x68 :? ....and i got 2700-2800 statics...

[Joe Dubner]

Try these guys
http://www.lycon.com/
I know several people who have success with them
Regards
Easyrider

Someone responded that Lycon gave them credit for their O235 when they built his O320.  Alas, in my daily morning delete-the-Viagra-spam-postings duties, I accidentally deleted that post.  Would the poster please post it again?  And please accept my apology.

In my defense, I'd like to point out that it's early here (6 AM) and I haven't had my coffee yet :-)

I'm off to the Arlington EAA fly-in today -- back in a few.

--
Joe

[Drew]

Joe--that was mine that you deleted---but you essentially captured it in your text.

Cheers!

[Delta Mike]

I pulled all the cylinders on the O-235 and took them to a cylinder shop. All intake valves were leaking due to worn guides. All the exhaust valves were stretched (though not leaking) and the exhaust guides worn.

I'll be paying ~$300/cylinder to have the intake guides replaced, and the exhaust guides and valves replaced, and cylinders honed. The low compression (6.75:1) pistons will be replaced with medium compression (8.5:1) pistons like the L2C model.

Hopefully those changes will rev up the prop good.

[Drew]

What kind of CHTs were you running prior?

[Delta Mike]

There was only one CHT on the #4 cyl, and since the plane is new to me I do not have a history on it. The owner/builder's position is that everything was running fine.

I am upgrading the engine temp monitoring to a new EI UBG-16 with full EGH and CHT. They were kind enough to give me a rebate for my old single channel unit.

Right now I am debating weather to go ahead with my plans to make a diffused sealed plenum for updraft cooling or bite the bullet and install downdraft with NACA shoulder scoops.

Updraft benefits are oil pan cooling = no need for oil cooler, use of existing NACA inlet, no downtime for downdraft configuration, and mabye better cooling drag profile.

Downdraft benefits are better cylinder cooling, simpler baffle configuration, better warming of intake mixture, and better representation of CHTs.

I sure wonder how well the NACA shoulder intakes work given that it's the top side of the wing.

[Jack]

Hi all,

What advice is there on finding and putting in different pistons to a low compression (6.75:1) O-235-C2C?

This particular O-235 is on a Long-EZ in Durango, and with a Great American 62x62 climb prop it is unable to generate more than 2250 rpm static - rated takeoff rpm is 2800.

When your adding more power expect more heat output.  Regarding rated RPM, that's only when you have a constant speed prop and it's complexity.  With a fixed pitch prop your always inbetween a climb or cruise prop.

On setting your valves, be real carefull if you set them tight.  I would check them again after a flight and see if they closed up especially on the exhaust ones.  I set a couple of exhaust ones at .013 and they tightened up to a bit.

You might explore ram induction and an electronic ignition for more power without tweaking the pistons.

Cheers;

Jack