Long-EZ Engine Power

[Delta Mike]

Hi all,

 

I am looking for knowlege on fixing an O-235 power problem in a Long, and I think the Canard Zone > Flying > Engines > Lycoming forum is too buried to get visibility.

 

That said, 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 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

[Kent Ashton]

How has this engine/prop combo performed in the past? Is the airplane new to you?

 

I'm an east-coast flatlander (775' field elevation) but it seems to me that at your field elevation (6675'?), even a new engine would not make 2700 static RPM. At your elevation and at the 2250 RPM you're turning, the engine might only be making 60 or 70% power--just a guess. Perhaps some folks who fly at your elevation will comment.

 

You might check that the carb butterfly opens fully at WOT.

[Delta Mike]

Hi Kent,

 

The airplane is new to me, so I have to figure out what to expect from it in its new home. For starters, I expect to get at least 2400 static at this elevation.

 

The butterfly valve in the carb is opening up full, thorttle arm fully against stop.

 

Any knowlege on putting L2C pistons into a C2C?

[Kent Ashton]

If you can get ahold of "Top End", a book published by Light Plane Maintenance, the book has a good discussion of whether to top an engine or overhaul it. If your's is a high-time engine since a (real) major overhaul--more than say 1500-1700 hours--I wouldn't just top it, I'd do a major overhaul. They are not hard to disassemble, send all the parts out for inspection/overhaul, and (with some A&P help), reassemble.

 

However, O-235 parts are said to be a fair amount more expensive than O-320 parts because there were far more O-320s made. If you decide to do a major overhaul, I would suggest trading the engine in for an O-320.

[rviglierchio]

I just got off the phone with a Long EZ multiple builder, long time flyer who told me he once had a prop of that brand and couldn't wait to get it off the plane. It may be a contibutor to the overall problem. I've been researching props and it seems to come down to either Hertzler or Catto for best performance. Good luck.

[Kent Ashton]

I just got off the phone with a Long EZ multiple builder, long time flyer who told me he once had a prop of that brand and couldn't wait to get it off the plane.

I had a Great American prop on a Cozy III O-320. Seemed to run just fine. Great American had a good reputation for many years. Heck, it was just a sturdy, well-made wooden prop; I don't know why someone would have great difficulties with that. Of course, you had to get the right pitch and size.

 

Yeah, a person might get better performance out of a more modern thinner, carbon fiber/wood airfoil. Doesn't sound like the prop is his problem.

[Delta Mike]

All four cylinders are in the repair shop right now. They were all leaking at the intake valves using the solvent in cylinder test.

 

Apparently the Lycomings are pretty sensitive at the full power end to leaking intakes. The blowback through the intake pipes must mess up the distribution or something.

 

It also turns out there is no problem putting in higher compression pistions. There are some differences with the low compression cylinders, like non-tapered, non-nitrided walls. The repair shop said that would not be a problem, except for possibly higher oil consumption, which he said was good for the rings anyway.

 

I'll put out a post when everything's back together.