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Rebuild the O320 or trade up to IO360?

Mike D

Mike D

Well Known Member
So, I have 1900 hours on the o-320 150hp Lycoming on my -6a. Cylinders #2 and #3 are seeing low compression (tested cold = 65/80, 56/80, 42/80, 76/80)
Last year was 74/80, 49/80, 72/80, 78/80

Engine runs well. Full power, normal CHT and EGT. Bore scope looks good. Oil burn is 1qt/8hours. Looks like worn rings. (Hear air when listening in the oil filler)

Need to make some decisions.
Do I run and retest?
Do I rebuild the o-320.
Stroke it to a o-340?
Buy a used or new o/io-360?

I would like to keep the cash output low. But my intention is to sell the -6a in the near future when I finish up the RV-10. So resale is a consideration.

If I convert to a io-360, what changes am I looking at? Cowl fit issues? New high pressure fuel pump? Return fuel line? New fuel valve?

What if going to o-360? Will the cowl fit?

What would you do?
 
Definitely run and re-test. Rings rotate during running. Occasionally the gaps line up and cause low compression readings.
 
If you do the swap, and I don't recommend the change, you will need to change the following:

Both fuel pumps will need to be replaced.
New prop, if you are fixed pitch.
New exhaust
New baffles
The cowl should work fine, unless you go with a horizontal sump. If you do that, then you will have some fiberglass work ahead of you.
No need for a return fuel line.

Since you are finishing up a -10, it would be easier to stay with the -320. Upgrade to the -340, if you want more HP.
 
If you run and retest and aren't happy, you could just get a new set of cylinders and put them on, and check the cam and lifters at the same time. That will allow you to increase to at least 160 HP, but remember that you may need your prop modified for the extra HP.
 
Compression tests tell you very little about an engine and I like many others hacome come to think of them as largely useless.
Use a borroscope and check the cylinders and valves. This is becoming much more common in the certified world, sure we still have to follow the SB from CMI and Lycoming but I expect that will eventually change.
Anything you put into the engine you will get a lot less back when you sell. So if it runs good, sell as is.

Here is an old article on it:
http://www.avweb.com/news/savvyaviator/193486-1.html?redirected=1


Tim
 
thanks for the replies!!!

I will run and retest.

I don't want to do a top overhaul given the time already on the engine.

But not sure I will get much for the plane if the engine is run-out. Or it will be a much harder sell.

Seems engine prices have gone up significantly over the last several years.
I see 2008 cost for new o-360 at $18K and now they are at $28K. I know my income or investments have not gone up anywhere near that fast. :(
 
If you can't get compression up then I'd recommend just a rebuild of your 320 with maybe 9:1 pistons. The 340 crank kit costs a bunch and only gives you a MPH or 2 on the top end. Now if your crank fails inspection I'd consider the 340 for sure.
 
Sid Lambert said:
If you can't get compression up then I'd recommend just a rebuild of your 320 with maybe 9:1 pistons.....Now if your crank fails inspection I'd consider the 340 for sure.
Click to expand...

I have been thinking about this topic as well with an o320 e2d that has 2020 hours since new, but had cylinders upgraded to 160hp 600 hours ago. Some people tell me that I can go to 3000 hours in this configuration before I need a major overhaul. Not sure if I should have a teardown inspection or what.
 
CATPart said:
I have been thinking about this topic as well with an o320 e2d that has 2020 hours since new, but had cylinders upgraded to 160hp 600 hours ago. Some people tell me that I can go to 3000 hours in this configuration before I need a major overhaul. Not sure if I should have a teardown inspection or what.
Click to expand...

Read some Mike Busch on this subject and see if you still want to tear open a well running engine. Note the charts of engine failures after overhaul vs. the hours you have.....
 
flyingriki said:
Read some Mike Busch on this subject and see if you still want to tear open a well running engine. Note the charts of engine failures after overhaul vs. the hours you have.....
Click to expand...

It's the Mike Busch disciples that are telling me to go to 3000 ;) I already have read many of his articles and have seen the charts you speak of. It is very interesting information.
 
Upgrade your 320 to 340

Mike D said:
thanks for the replies!!!

I will run and retest.

I don't want to do a top overhaul given the time already on the engine.

But not sure I will get much for the plane if the engine is run-out. Or it will be a much harder sell.

Seems engine prices have gone up significantly over the last several years.
I see 2008 cost for new o-360 at $18K and now they are at $28K. I know my income or investments have not gone up anywhere near that fast. :(
Click to expand...

Mike,

One of the best discoveries I have found since taking over Titan is their IO-340. This is the same engine we install in all the Carbon Cubs and it is amazing. Everyone has dynoed over 180hp and if you put on constant speed prop the real bonus is its torque around 2300rpm. Its better that than a stock 360! One thing you might consider is to send into Titan, we will do a complete inspection and then can rebuild with a new 340 crank saving you thousands of dollars. If your 320 crank is in good shape I'll even buy it off you for a few bucks.

Visit www.titanengine.com and then contact me if you are interested.
 
Just as another data point, I tore down my O-320-E3D at just over 2800 hrs and every part met serviceable specs. These engines will easily run 3000 hrs when properly maintained.
 
So the question is do you want to overhaul an engine that may easily go another 450 hours for $20,000 then buy $20,000 worth of avgas to go the first 450 hours or buy 450 hours worth of avgas and overhaul when it may actually be necessary having only spent half the money in the same time....:confused:
 
Last edited:
Update:

I did not run and retest.

Bought a new borescope to replace my dental cam version.
End result is the piston pin is wearing a groove in the cylinder walls and causing the low compression test result.

I am pulling the cylinder and will rework or buy a new one.

b987.jpg


Engine and 1,2, and 4 all have 1991 hours
No3 (the bad one) only has 390 hours. :(

Here is no 2 for contrast. 1991 hours and still has crosshatch marks. (Virtical lines are reflections)
rxzy.jpg
 
Last edited:
Update:
The borescope turned out to be 100% correct.

The wrist pin was wearing a grove into the cylinder wall. In the second image, note the normal one on the right vs the worn one on the left.

This then pushed the piston to one side. This can be seen by the scrape marks on the piston side.

The grove is shallow, but it apparently caused a large drop in compression.

Turns out this cylinder was replaced 400 hours ago with a "cermichrome" cylinder. I was told these don't last too long. It will be replaced with a "cerminil" cylinder. Hoping to get a few hundred more hours out of this engine before an overhaul.

I am not an engine expert. This is relayed info from an IA who is helping me learn. If any of this is wrong info, please give me your experience.

5du5.jpg


sf22m.jpg


ut5q.jpg
 
I see two issues, Looks like you have the older thin wall wrist pins,these may have been superseded by the heavy wall ones. Lycoming has switched to silicone-bronze plugs in place of the aluminum.You could also use the Superior wrist pin with the smaller plug built in. Check with your IA. I could be Wrong and often am.
RHill
 
I was told my cermi-chrome overhauled cylinders wouldn't last long and they barely made it 860 hours. They were a bad deal. Going straight Lycoming cylinders per Ly-Con recommendation for them to work their magic on.
Good luck.
 
flyingriki said:
I was told my cermi-chrome overhauled cylinders wouldn't last long and they barely made it 860 hours. They were a bad deal. Going straight Lycoming cylinders per Ly-Con recommendation for them to work their magic on.
Good luck.
Click to expand...

How much extra does ly-con charge for their magic above the price of plain old lycoming cylinders?
 
Wrist pins

Thill is correct, Lyco did asks for thin wall pins to be changed to new thick walled pins, but of course this would requie all the pins to be changed or the engine would be out of balance with just one heavy pin. This is one of the problems when pulling an engine apart you spot things that have been working well but have been superceded.

Your AI advice is needed here. I think a Piper lost a piston in flight that resulted in the change to thick wall, and because I put in 8.5 rather than 7 to one pistons in my E2a I upgraded the pins.
 
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