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Prior planning for engine work

00Dan

Well Known Member
I am sorely tempted to pull the jugs on my O-320-A3A and replace my 7.0:1 pistons with 8.5:1, along with the heavy wrist pins of course. My research and prior posts here have made me comfortable with the idea of doing so on the narrow deck engine as long as I don’t go any higher compression that 8.5. I do have some considerations though before I do any such work. The elephant in the room is the engine itself. It is a 1978 overhaul with approximately 1900 hours on the bottom end now. I’m a cheap ******* so I hadn’t planned to overhaul it as long as it isn’t making metal or otherwise showing signs of age.

Obviously, if I buy a set of pistons and start pulling jugs it’s kinda up in the air what the inside will look like. It could be fine, and I install my new pistons and go have fun with my (relatively) cheap 10 HP upgrade. The alternative is that things look not so nice inside, particularly the cam and lifters.

In this hypothetical, let’s assume I pull a jug and find the cam is shot. At this point a case split seems inevitable. The question now is how to proceed. Unfortunately, I do not have any of the logs for the engine before the builder of my plane bought it in the 80s. As best I can tell, it was pulled from an Apache at 200 odd hours and then rehung on my RV-4. I can’t say what run it is.

As I see it, option 1 is to overhaul it entirely and work with what I got. This option includes either sending it off or learning to overhaul it myself. It seems this will probably be the highest cost option.

Option 2 would be an IRAN depending on how everything looks. Take it apart, clean it up, replace seals and toss it back together. Given the age of the engine it will probably end up close to a full overhaul.

Both options 1 and 2 provide the opportunity to properly convert the case to long stud and use hold down plates per the book.

Option 3 would be to get a replacement engine and sell/trade mine as a core. A mid-time engine could end up being the cheapest option, or it could end poorly given the “Pandora’s box” that are used (but not run out) engines. This option is complicated by the fact that I have a conical engine mount, limiting myself to attempting to find another ancient 320.

Are there options I’m not considering? Really all these problems can be solved with money (which makes it not a problem, right?) but I’d appreciate the opinions of others who have perhaps done this calculus before.
 
As someone who's just gone through a similar planning exercise on an O-320 built in 1992:

If you take a look at a 1978 camshaft that's done 1900 hours, you'll find some kind of defect on it which persuades you to go the rest of the way and bulk-strip the engine.

In my case there was corrosion pitting and early signs of fatigue on the tips of some of the cam lobes, and one of the exhaust valve tappets felt ever so slightly rough when I ran a finger nail over it, even though the engine had never made any metal. It might have run for another 300 hours, or it might have run for another ten hours.

I'll never know now, 'cos I overhauled it. I'll think about it again in 2000 hours time :D

These engines all have design lives. And yes, you can use condition based maintenance techniques to (sometimes greatly) extend their service, but they still wear out eventually.

With that said:

At more than 40 years old and nearly 2000 hours, I agree with your assessment that your overhaul (option 1) and IRAN (option 2) will probably be very similar costs, so you might as well go with option 1 and end up with a zero-timed engine at the end of it.

I don't like your chances of option 3. Good cores seem to be as rare as hens' teeth at the moment. And if your crankcase isn't cracked and your accessory case attachments are in good condition, you might as well keep them.

For mine:

I decided I'd rather have my O-320-D2A come apart at a time of my choosing than at a time of the engine's choosing. I was always going to do it eventually, so I wasn't saving money by delaying it, I was merely changing the date of the expenditure. Now I'll probably be too old to fly by the time I need to do it again.

I acquired two P-Mags, a Precision Airmotive Silverhawk EX320-2 fuel injection system (cheaper new than an overhauled certified Silverhawk system!), a high pressure engine-driven fuel pump, and a high pressure electric fuel pump from Vans. The cylinders only had 900 hours on them, so they got overhauled instead of replaced. One of the rods had a manufacturing defect that showed up in NDT, so it got replaced. Crankcase cracks in the saddle between Cyl 1 and 3 were repaired, then the case was decked and line-bored. The engine has been overhauled, zero-timed, and returned to service as an IO-320.

Very spendy, but a massive improvement! I'm very glad I did it.


- mark
 
What I did

While I was building my -4, I horse traded for a runout O320 H2AD from a local engine shop that was left over from a 172 engine upgrade. I had logs but never saw it run. I tore it down 100% and sent all the rotating steel and case out for eval /yellow tag overhaul. I was lucky, and all was within spec and usable..got tags for everything. I sent the cylinder assemblies out for the same, and settled on overhauling them with new valves/seats, ect. Did my mags and carb myself , put it all back together and ended up about 6-7K into it. Flying now for 10 years and 500ish hours and no issues at all. I think you would sleep better if you did the bottom along with the cylinders, as its not that bad to do and you'll know what you have when its done.
 
While I was building my -4, I horse traded for a runout O320 H2AD from a local engine shop that was left over from a 172 engine upgrade. I had logs but never saw it run. I tore it down 100% and sent all the rotating steel and case out for eval /yellow tag overhaul. I was lucky, and all was within spec and usable..got tags for everything. I sent the cylinder assemblies out for the same, and settled on overhauling them with new valves/seats, ect. Did my mags and carb myself , put it all back together and ended up about 6-7K into it. Flying now for 10 years and 500ish hours and no issues at all. I think you would sleep better if you did the bottom along with the cylinders, as its not that bad to do and you'll know what you have when its done.

This does make me think of a potential variation to option 3: buy a core and overhaul it while my current engine is still flying, then swap the two. This would certainly minimize downtime but cost would be up in the air depending on how many parts are serviceable (although that’s also an unknown with my engine so hard to accurately quantify in either case).
 
Before you do anything, check the crankshaft IAW Lycoming S.B. 505b (corrosion/pitting). This has taken quite a few crankshafts out of circulation.
 
Before you do anything, check the crankshaft IAW Lycoming S.B. 505b (corrosion/pitting). This has taken quite a few crankshafts out of circulation.

I performed this SB earlier this year and the crank bore was clean, so at least that part of the crank is okay.
 
A consideration I had in favor of option 3 (swapping engines) is down time. Global supply chains are pretty fouled up at the moment and will remain that way for the foreseeable future. This combined with reports that overhaul and machine shops are backed up tells me that if I pull my engine for a tear down I may not get it back for a while.

Where would it be worth looking to see what comes up? Any suggestions as far as reputable salvage companies or engine shops that may have running take-offs?
 
I'd be inclined to go with a DIY overhaul.

Why not purchase the "known" items early, then tear down the engine and see what else you need. For instance, you know you'll need 4 cylinders and pistons, so go ahead and get them. You'll need a gasket and seal set, so buy it and put it on the shelf. Buy a new oil pump.

Some folks go ahead and replace the cam and followers, regardless of condition. If you're that person, buy the components up front.

That way, when you do pull and disassemble the engine, your lead times will (hopefully) be driven by the machine shops plus a few bits and pieces like bearings.
 
I'd be inclined to go with a DIY overhaul.

Why not purchase the "known" items early, then tear down the engine and see what else you need. For instance, you know you'll need 4 cylinders and pistons, so go ahead and get them. You'll need a gasket and seal set, so buy it and put it on the shelf. Buy a new oil pump.

Some folks go ahead and replace the cam and followers, regardless of condition. If you're that person, buy the components up front.

That way, when you do pull and disassemble the engine, your lead times will (hopefully) be driven by the machine shops plus a few bits and pieces like bearings.

I like this option from a logistical standpoint as the next best thing to swapping. I am a bit concerned about how many runs are on the current crank and case, though. Despite not having the logbooks, the builder carried forward the times from logbook #7 when he bought it and started his log.
 
I spoke to a salvage operator who has a narrow deck 320 that was overhauled in 2009, IRAN’d in 2018 after sitting, then finally removed in 2019 after a forced landing. They claim no prop strike, but it’s been sitting in a warehouse in Texas for the past 2 years and the cylinders are rusty. On its face, it seems this engine could be a good candidate for honing the cylinders and maybe replacing the tappets but otherwise good to go (total time on bottom and cylinders is only about 20 hours). What am I missing?

A related question: would swapping engines need more than just a logbook entry? I have old recertification required operating limitations, would I need to get them updated first to avoid needing a DAR to come out?
 
Engine source

Check with the shops that do engine conversions on Cessna 172's. Penn Yann in NY is one, there are others. In the past they have been a source for core engines.
A reputable source will guarantee the case and crank to be serviceable. In that event the first thing to do is tear down the engine and send the case and crank out for certification/overhaul.
 
Check with the shops that do engine conversions on Cessna 172's. Penn Yann in NY is one, there are others. In the past they have been a source for core engines.
A reputable source will guarantee the case and crank to be serviceable. In that event the first thing to do is tear down the engine and send the case and crank out for certification/overhaul.

Is there any equivalent for old Pipers? My conical engine mount unfortunately rules out any Lycoming model off a Cessna. My quick search on this points me towards most of the old A and B model 320s either being swapped around by Piper owners in the field or snatched up by home builders back in the day (before the Dynafocal mount models became more widely available).
 
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