Corrosion Pitting on Cam (or Crank?) on o-470R What to do??

[JoseCuervo]

Three cylinders were low compression on my annual inspection, on an engine (0-470R) with 1000 hours. So, we decided to replace all 6 cylinders (based on the logs, we don't think they were new/overhauled at the last overhaul. Wasn't quite clear., and 1 had already been replaced 150 hours ago.)

So, we got the 6 cylinders in, and when the old ones got removed, "corrosion pits" were discovered on the crank (is that the same as the camshaft??).

The shop is suggesting we IRAN the crank and other parts, put the cylinders on, and go on toward TBO as opposed to doing a complete overhaul.

What is the suggestion on which way to proceed?

Thanks.

 

[Stewartb]

Topping (replacing/servicing cylinders) would not expose the crank journals for inspection. I suspect they see pits in the cam. Repairing that will require splitting the case and then you're most of the way to an overhaul. The rule of thumb I was taught is that if you can feel cam pits with a fingernail the cam needs to be replaced or re-ground. I'm not a fan of grinding cams but the big deal will be splitting the case. There are no cam bearings in an aircraft engine. When you hear guys mention align boring that means the case meeting faces are milled and the cam and crank seats are bored round. You can see the problems you'll face if you have to split the case for a cam. Get more info and get another opinion from a mechanic you trust. If it's any consolation it's likely that lots of engines in the fleet have some pitting and we just don't know about it. Good luck.

 

[GlennAB1]

So, we got the 6 cylinders in, and when the old ones got removed, "corrosion pits" were discovered on the crank (is that the same as the camshaft??).

No, the crank actuates the pistons, or vice versa. The cam actuates the valves.

 

[Checkout_my_Six]

depends....if the cam has pits just replace the cam and tappets.

While it's open you could have things inspected....but where to draw the line? It soon becomes an overhaul if everything gets inspected.

 

[charlie]

The engine must be disassembled to change the cam. The best way to proceed is to have it disassembled and inspected and get a price to do an IRAN (just fix it) or a major overhaul and make the final decision based on the Cost. Right now you are on the hook for the labor plus a lot of parts made necessary by the tear down plus the cam, tappers and cylinders and in addition anything else found to be unairworthy Chances are it will be economically impractical to do the IRAN. You are starting out north of $15K not including removal and installation. Charlie Melot Zephyr Engines

 

[JoseCuervo]

The engine must be disassembled to change the cam. The best way to proceed is to have it disassembled and inspected and get a price to do an IRAN (just fix it) or a major overhaul and make the final decision based on the Cost. Right now you are on the hook for the labor plus a lot of parts made necessary by the tear down plus the cam, tappers and cylinders and in addition anything else found to be unairworthy Chances are it will be economically impractical to do the IRAN. You are starting out north of $15K not including removal and installation. Charlie Melot Zephyr Engines

Thanks.

Getting a quote of +$3500 to do the overhaul vs the IRAN.

Looks like I might as well go for the Overhaul at that rate.

 

[Tom-D]

So, we got the 6 cylinders in, and when the old ones got removed, "corrosion pits" were discovered on the crank (is that the same as the camshaft??).[/QUOTE]
No they are not the same.
Corrosion on the exposed crank is not a cause to split the case.
But I'd inspect farther. now that you can see the CAM, is the lifter creating a wear path all the across the cam lobe. If it is, the lifters are dished. the cam and lifters should be replaced if they aren't smooth and pit fee.