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O-320 150hp top end overhaul

SC3CM

SC3CM

Registered User
Engine has 1200 or so hours on it.

For someone who has never gone through this process before what are some of the gotchas that can come up? Aside from finding out you need to redo the whole engine...

I'm figuring the cost to be about 5-6k. Is that in the right ball park?

Rene
 
First thing to look @ is the Cam.

If bad; things go downhill real quick.

Your figures should work.

Varies with location.

Might be high?
 
right. If cam is bad then I'm off by about $18k, unless Tim's bedliner STC applies to engines as well :roll:
 
If your cylinders have "issues" like half of mine did and you end up with new or new to you then take a hard look at growing some ponies and converting to a 160... glad I did.
 
OLDCROWE said:
If your cylinders have "issues" like half of mine did and you end up with new or new to you then take a hard look at growing some ponies and converting to a 160... glad I did.
Click to expand...

I actually thought about that and keep ending up with the thought that if I'm doing that much I might as well come out with a major overhaul, but really think it's early for that and a waste of money because there still should be a lot of life left in this thing.

Rene
 
SC3CM said:
I actually thought about that and keep ending up with the thought that if I'm doing that much I might as well come out with a major overhaul, but really think it's early for that and a waste of money because there still should be a lot of life left in this thing.

Rene
Click to expand...
Rene,

I had some pitting and cold start scaring and a medium low compression cylinder that would have been marginal to hone and a LOW compression cylinder that had barrel slap worn to bad to hone out and they were already one-over. I was really happy with the results, this was done at 1300 hours +/-. Cam lobes were fine but I had the lifter faces dressed too. All in I think about $6500 including the CC STC. also replaced the engine mount bushings per the STC. I'm confident this engine will easily purr to 1000hrs on this top and then be an easy overhaul, or at least so my ace mechanic says.

Kirby
 
SC3CM said:
Engine has 1200 or so hours on it.

For someone who has never gone through this process before what are some of the gotchas that can come up? Aside from finding out you need to redo the whole engine...

I'm figuring the cost to be about 5-6k. Is that in the right ball park?

Rene
Click to expand...
Rene,

Price out new cylinders and selling your old cylinders VS overhauling yours. Don't forget to keep the right parts if you go new.

Tim
 
To buy 3 new cylinders is about what it costs in the end to overhaul 4. Then like above just sell yours. Pistons are 100 ea, so it depends a little on if you can use your old ones. Are your cylinders std.?
 
FIRST... tell us why you think you're into a "top overhaul" and then we can probably offer some positive thoughts!
 
Order the jugs as a matched set. If cam is bad have case line bored before you put it back together. Total rebuild without new crank, mags, and carb should be around 15-18 grand.
DENNY
 
I just got my O-320 back. Upgraded to 160hp, Bendix mags rebuilt, carb rebuilt, had the case pinned at the mains, line bored, factory new cam, factory new lifters, new Lycoming jugs, rods and pistons balanced, and the cylinders ported and polished, 20,000.
 
irishfield said:
FIRST... tell us why you think you're into a "top overhaul" and then we can probably offer some positive thoughts!
Click to expand...

My engine has always had more blow by than others, but was consistent. Typically I run it at 6 qts and don't overfill. In the past 50 hours the blow by has gotten much worse. At high RPM I can coat the plane in oil in an hour flight when I normally would have had just enough to wipe the gear legs and the belly. Inside the cowl is dry and clean and there is no oil leaking anywhere but the breather tube.

I'm hoping the mechanic goes in and finds nothing major, but I don't want to chase a problem. If there's a chance there is more than one thing wrong I'm more comfortable just getting it resolved now. If it's just one simple thing, great. If I go in more educated on what the possibilities are, then I can make better decisions when any issues come up.
 
That sounds just like mine. Last fall mine was going thru a qt every 4 or 5 hours most of it was going down the side of the airplane. This was when I found out that me exhaust valve guides were worn out, and #3 would not even hold compression. Is this common for the guides to leak so much they are pressurizing the crankcase and blowing the oil out?
 
btracy said:
Is this common for the guides to leak so much they are pressurizing the crankcase and blowing the oil out?
Click to expand...

It's not an uncommon problem. I've seen it happen in just about every make and model engine out there. Sometimes new guides and exhaust valves, a quality hone job on the cylinder (if it's within specs) and new pistons and rings is all it takes to make it good to TBO. And other times you've just found the tip of the iceburg. :smile:

On a mid time engine, I usually pull the rods as well so I can check rod bearing wear and crank wear, and get a chance to balance everything properly to make for a nice smooth engine.

-CubBuilder
 
SC3CM said:
My engine has always had more blow by than others, but was consistent. Typically I run it at 6 qts and don't overfill. In the past 50 hours the blow by has gotten much worse. At high RPM I can coat the plane in oil in an hour flight when I normally would have had just enough to wipe the gear legs and the belly. Inside the cowl is dry and clean and there is no oil leaking anywhere but the breather tube.

I'm hoping the mechanic goes in and finds nothing major, but I don't want to chase a problem. If there's a chance there is more than one thing wrong I'm more comfortable just getting it resolved now. If it's just one simple thing, great. If I go in more educated on what the possibilities are, then I can make better decisions when any issues come up.
Click to expand...
What does the inside of the exhaust pipe look like? Oily/wet or clean exhaust color?

Have you had a wobble check done to check the valve guides?

What are your compression check readings? While performing the compression check, where does the air leak out? Listen to the exhaust, breather and carburetor to determine where the leak is located.

All of these questions need answers before a conclusion can be determined and before the cylinders are pulled. For example, suppose that the compression is good and the valve wobble is within limits and the exhaust is dry, you may just be able to get away with an oil separator on the breather. I'm not saying that this is the case. Just a possibility.
 
a worn guide won't pressurize the crankcase.... worn rings do. a worn guide will let oil be sucked into the combustion chamber... even from the exhaust side due to valve lap
 
Start with the cheap stuff and work your way up to the expensive fixes. I had an old 0-320 narrow deck start those exact symptoms shortly after an overhaul and shortly after an annual, went from a quart in 12 to a quart in 3 or 4, The case was getting pressurized and blowing all of the oil out the breather. After doing a top on it I discovered that during the last annual the gasket on the oil screen case got put in backwards, $1.65 later I was back to where it should have been. And that young mechanic is now working elsewhere. I never want to learn that again.
 
We did some cheap stuff, but also decided to put on an Airwolf air/oil separator and replace two cracked cylinders that were found. I'm not an expert but I'm thinking this will make a difference.

The cracked cylinders were a bit of a surprise. I don't think I abuse the engine, but it was #3 and #4 which are always hotter.

The good news is I found the problem before it got really bad, it's not really going to cut into the good flying time, and I'll save money on oil and cleaning supplies :)

Rene
 
Rene, Do you have a four cylinder CHT installed? If so, your temperatures should always be less than 400 degrees. The middle 300s are better. If your temps are higher, you should look carefully at your baffles. There should be no place where the air can bypass going through the cylinder fins. I have found gaping holes which are so large that it is easy to look right past them. How about behind the ring gear where the opening allows the alternator belt to clear? How about the seals between the baffles and the cowling?
 
Pete, I have a nice JPI which helped find out there were some cooling issues on the back cylinders, so we re-did the baffling and the cooling is much better now. Unless I'm flying with Seaworthy who can't seem to fly below 2500 RPM I'll typically run nice and easy in the 2200 RPM range. Temps in cruise are below 380 on the hottest. The only time I'll see hotter than 380 now is on a steep/extended climb. More work could probably be done on the baffles but it's a LOT better than it used to be.

The plane should be back in the air in a week or so. If you want to meet up and have a look I'm open to suggestions.

Tim, the cylinders dug into the retro wardrobe budget so you are going to have to invest in a good pair of sunglasses or change one of the letters in the t-shirt you stole from Jim.
 
Rene,
Seaworthy and I are thinking about flying to Crow Island soon. My restrictions are flown off, so I'm anxious to test out Bill's seaplane puddle. We could compare baffles there.
 
beezerboy said:
a worn guide won't pressurize the crankcase.... worn rings do. a worn guide will let oil be sucked into the combustion chamber... even from the exhaust side due to valve lap
Click to expand...
Worn exhaust guides will pressurize the case and wont cause oil consumption except what leaks through them when the engine is stopped. There isn't enough suction or enough time during the overlap period to pull any appreciable amount of oil through. Intake guides will suck oil and wont pressurize the case. Yes, rings are the primary offenders.
 
MT12 said:
Start with the cheap stuff and work your way up to the expensive fixes. I had an old 0-320 narrow deck start those exact symptoms shortly after an overhaul and shortly after an annual, went from a quart in 12 to a quart in 3 or 4, The case was getting pressurized and blowing all of the oil out the breather. After doing a top on it I discovered that during the last annual the gasket on the oil screen case got put in backwards, $1.65 later I was back to where it should have been. And that young mechanic is now working elsewhere. I never want to learn that again.
Click to expand...
Can you explain the screen gasket causing these symptoms? All the gaskets I've seen lately have two little holes so it can't get installed backwards, years ago there was only one. I don't understand it causing these symptoms.
DRL
 
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