67 F N9634M

[merrja]

My engine was lightly flown for a few years after the overhaul... Consequently I was forced into another overhaul at 700 hours because the cam was slightly pitted ans started making metal after I had flown it 500 hours

[DaV8or]

My engine was lightly flown for a few years after the overhaul... Consequently I was forced into another overhaul at 700 hours because the cam was slightly pitted ans started making metal after I had flown it 500 hours

 

See, it's stories like this one that make me question how much Lycoming camshaft failures are really caused by corrosion. It seems to me that corrosion wouldn't take 500 hours to cause a failure. I would guess you would see metal in the filter in about 50-100 hours, maybe even less. I'm starting to think it's more of a metallurgy, heat and friction problem.

[ryoder]

See, it's stories like this one that make me question how much Lycoming camshaft failures are really caused by corrosion. It seems to me that corrosion wouldn't take 500 hours to cause a failure. I would guess you would see metal in the filter in about 50-100 hours, maybe even less. I'm starting to think it's more of a metallurgy, heat and friction problem.

I wonder if it's just crappy camshafts?

And forgive my ignorance but on a small block Chevy a camshaft swap is not a big deal. Sure it takes time but they can be replaced without even pulling the heads if done carefully. And cams are cheap. Why is it such a big deal in an aircraft engine?

[Shadrach]

It's not that big of a deal, just time consuming. A small block Chevy was never designed to fit under an aircraft engine cowling. An overhead cam aircraft engine would absolutely be designable if it weren't for the certification hurdles and low demand of our highly regulated, boutique market.

[bonal]

You have to split the case

[M20F]

You have to split the case

And take the engine off and put it back on.

[bonal]

An overhead cam engine would be great but would make for a longer length from the case to the top of the heads meaning a wider cowling to close it all in also now you have a more complex timing mechanism and you would be adding weight

[Shadrach]

An overhead cam engine would be great but would make for a longer length from the case to the top of the heads meaning a wider cowling to close it all in also now you have a more complex timing mechanism and you would be adding weight

Everything is a compromise.

[RobertGary1]

On the other hand a piston/jug replacement is not too intense on our engines but it's a full tare down on the Chevy.

[bonal]

Yep compromise

[carusoam]

Why is it not such a problem on Continentals...

Cam location?

Best regards,

-a-

[merrja]

I wonder if it's just crappy camshafts?

And forgive my ignorance but on a small block Chevy a camshaft swap is not a big deal. Sure it takes time but they can be replaced without even pulling the heads if done carefully. And cams are cheap. Why is it such a big deal in an aircraft engine?

Yes, I agree.  I'm thinking about getting a rebuilt from Lycoming since they have roller tappets.  Additionally I can trade in my 1967 crank case for a ~2005... I

[DaV8or]

Yes, I agree.  I'm thinking about getting a rebuilt from Lycoming since they have roller tappets.  Additionally I can trade in my 1967 crank case for a ~2005... I

 

Are you sure about that? I remember reading that Lycoming wouldn't accept any engine older than 10 years old for credit.

[RobertGary1]

36 years for overhaul. Doesn't apply to remain. Lycoming policy. http://www.lycoming.com/Portals/0/techpublications/serviceletters/SL%20L250A%20(7-29-2011)/Lycoming%20Engines%20Exchange%20Engine%20Core%20Policy.pdf

[DXB]

36 years for overhaul. Doesn't apply to remain. Lycoming policy. http://www.lycoming.com/Portals/0/techpublications/serviceletters/SL%20L250A%20(7-29-2011)/Lycoming%20Engines%20Exchange%20Engine%20Core%20Policy.pdf

Good info. I wonder regarding the reason for not overhauling older engines, but still providing full credit for the core exchange for a remanufactured engine?  Do they not reuse the older crankcases?

[DaV8or]

36 years for overhaul. Doesn't apply to remain. Lycoming policy. http://www.lycoming.com/Portals/0/techpublications/serviceletters/SL%20L250A%20(7-29-2011)/Lycoming%20Engines%20Exchange%20Engine%20Core%20Policy.pdf

 

Cool! Good to know.

[RobertGary1]

Good info. I wonder regarding the reason for not overhauling older engines, but still providing full credit for the core exchange for a remanufactured engine?  Do they not reuse the older crankcases?

 

Yes 36 years is an odd number. I believe both can include reused cranks, although the tolerances are tighter on the reman'd engine. 

 

-Robert