What to do for an O-320 to correct shortfalls. (2024)

stewartb said:

Mill the case and align bore. Grind and balance the crank. Balance the rods. Use cylinders with triple cut valve seats , balanced pistons, and flow matched. Pitch the old cam and buy new. Re-face and plate the cam followers if they check out. Have the hydraulic lifter bodies tested for leak-down. When back on the airplane use a gutted muffler to let it breathe better. The 320 is a great engine. Narrow the spec tolerances and pay attention to details. Make it better.

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I really like this thinking! Study two words above for all the work: align and balance

stewartb said:

Mill the case and align bore. Grind and balance the crank. Balance the rods. Use cylinders with triple cut valve seats , balanced pistons, and flow matched. Pitch the old cam and buy new. Re-face and plate the cam followers if they check out. Have the hydraulic lifter bodies tested for leak-down..

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Sounds as though you don't have this engine yet. If it has an early "light" case, the case halves can frett (Fretting refers to wear and sometimes corrosion damage at the asperities of contact surfaces. This damage is induced under load and in the presence of repeated relative surface motion, as induced for example by vibration.) which will require Milling the case and align bore. This effects the lengths of the push rods and fit of the timing gears. Unless the cam followers are low time throw them out and get new. The mushroom can break off ruining your day. I know of two instances of this happening on O-540s. It makes for sudden silence if it's the intake. Both planes fortunately made it to an airport. I believe that they are the same parts on the O-320.

stewartb said:

Mill the case and align bore. Grind and balance the crank. Balance the rods. Use cylinders with triple cut valve seats , balanced pistons, and flow matched. Pitch the old cam and buy new. Re-face and plate the cam followers if they check out. Have the hydraulic lifter bodies tested for leak-down. When back on the airplane use a gutted muffler to let it breathe better. The 320 is a great engine. Narrow the spec tolerances and pay attention to details. Make it better.

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I prefer a standard crank over a grind. I measure them prior to sending out for overhaul and won't let them grind if within spec. More overhauls left in it and less cost.

I asked some major engine shops about replacing the cam and they say there are as many new cam failures as old.

Cubs use A and B series O-320s. Conical mounts with the carb in the cent of the sump.

Not sure what shortfalls you may be talking about, ran one over 9000 hours in a glider tow SuperCub. Only reason we pulled it was that it spun a bearing. I don't even remember pulling a cylinder in the 10 years ~ 3000 hours I flew it. The only real problem we had was exhaust gaskets, changing them was almost a preflight item.

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With the exception of the "H" models, the cause of cam failures is not lack of lubrication while the engine is running and there is nothing you can do to change the design to fix the cam from corroding for lack of running other than dosing the oil or pickling the engine.

In addition to line and bore, I would recommend pinning the main bosses. I always put in new cam and new lifters, triple grind the valves, polish, flow match the intakes and exhaust and triple grind the valves.

DENNY said:

Exhaust valve guide ware is a major problem, even with hardened stems. I don't know if adding oil lines to cool the guides would help if you had a cool running engine to start with but is something I would consider trying. You could do a wobble test every 100 hours to see if it helped.
DENNY

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This site wont let me post the link But if you go to
precisionengine dot home dot mindspring dot com slash engine3 dot htm you'll get there or do a search for "the rest of the story Lycoming" and look for the mindspring url.

THIS WILL BE AN EYEOPENER.

Here's a link to the article. I've never cared for how these guys write.

http://egaa.home.mindspring.com/engine3.htm

Not a member of the site? There's an easy fix for that.

The single best change I ever saw to reducing CHTs on a well maintained Cub was switching from a conventional muffler to a gutted muffler. I'd expect the E valve temps received the biggest change associated with that. Maybe they should explore why some airframes have more issues than others when they share the same oil distribution?

rickg5106 said:

This site wont let me post the link But if you go to
precisionengine dot home dot mindspring dot com slash engine3 dot htm you'll get there or do a search for "the rest of the story Lycoming" and look for the mindspring url.

THIS WILL BE AN EYEOPENER.

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You can't post a link till you have been here a while. Spammers log on and and post links to all kinds of stuff they are selling.

I read that site years ago when I had an issue with valve guide weat on an O-360. That is not a common issue. Treat the engine correctly and it will serve you well. It is an air cooled engine made of steel and aluminum that expands and contracts at different rates. I have seen people taxi to the end of the runway on a cold morning and pour the coals to it and go. The Lycoming O-320 and O-360 engines are very dependable engines. You can find anything on the internet. I would suggest getting the Sacramento Skyranch Manual which was written by someone who rebuilt engines and study thefailures and their causes. Way more information than you ever need as an operator but sounds like you would find it very interesting.

The Sacramento Sky Ranch engine manual is available from EAA, for those who may be interested in adding it to their bookshelves.

https://www.eaa.org/en/eaa-shop/homebuilders_corner/2251692100000__Sky_Ranch_Engine_Manual