Checking cam lobes and lifters on a pre-buy

[ualdriver]

Messed up my first post on the forum and it deleted. Oops.

I'm looking at buying an airplane in the up and coming months. Two of the aircraft that I am currently looking at live in Florida and don't fly much- maybe a few hours per month. I'm concerned about corrosion, not so much on the fuselage or even in the cylinders as if it is there, I think it will be found by an A&P during a pre-buy. I am more concerned about the internal portion of the engine, in particular the camshaft, its lobes, and the lifters.

Is it a big job for an A&P, during a pre-buy, to examine the engine's (Continental O-360-es) camshaft, lobes, and lifters? Is it even possible? Does it make sense to even do such an inspection?

[CarlOrton]

I don't recall ever hearing about someone wanting to know if the cam is corroded. That said, a pre-buy is an attempt for a qualified person to find something fairly obvious. You *could* theoretically pay 'way more than usual to pull off a jug and take a look inside. If the engine has sat for awhile (like years), I can see where you might do that before starting it just to make sure you don't scuff something valuable. Even if you find nothing, that doesn't mean you're in the clear. As an example, an alternator or starter motor could be perfect right now, and this afternoon short out. No way of knowing that off the cuff.

Then again, a seller may object to having a cylinder pulled. That just opens-up opportunities to drop something in the crankcase, scratch something, etc.

Since it flies fairly regularly, if it ran OK (obviously no misfire, stuck valve, etc) and developed the power it should (full static RPM on ground, normal performance in the air, no odd temps), you're probably good to go.

[ualdriver]

I don't recall ever hearing about someone wanting to know if the cam is corroded. That said, a pre-buy is an attempt for a qualified person to find something fairly obvious. You *could* theoretically pay 'way more than usual to pull off a jug and take a look inside. If the engine has sat for awhile (like years), I can see where you might do that before starting it just to make sure you don't scuff something valuable. Even if you find nothing, that doesn't mean you're in the clear. As an example, an alternator or starter motor could be perfect right now, and this afternoon short out. No way of knowing that off the cuff.

Then again, a seller may object to having a cylinder pulled. That just opens-up opportunities to drop something in the crankcase, scratch something, etc.

Since it flies fairly regularly, if it ran OK (obviously no misfire, stuck valve, etc) and developed the power it should (full static RPM on ground, normal performance in the air, no odd temps), you're probably good to go.

I guess what I am trying to figure out is twofold:

1) On a Continental O-360-es, if one wanted to aggressively look for corrosion, is it even possible to get a good view of the entire camshaft? I assume all the lifters could be pulled.

2) If one is looking to buy an airplane that has been barely flown in the past year to year and a half, has been sitting outside on the ramp the entire time, is only flown maybe a few hours per month, is living in a corrosive state like Florida, how does that buyer approach the inspection of the engine during a pre-buy? I know an A&P can see "obvious" corrosion by pulling inspection panels, scoping the cylinders, etc., but how does a buyer know that a cam lobe and/or lifter isn't spalled?

[rick9mjn]

on adding to reply #2., do a google search for " eaa , mike bush , buying, webinars ", and also look up savvyaviator.com ... .. .good luck , good day , /rick

[WLIU]

Continentals don't have the same cam issues that Lycos do. Continental engines place the cam below the crank. Which gets them lubricated sooner on start and puts them where they get drips of oil from above while they sit. Yes you can have cam issues in a Continental, but it is much less likely. If the engine is run a few hours a month, you are likely good, even in Florida. In Florida I would look for corrosion on the prop and in the wings.

Best of luck,

Wes

[CarlOrton]

I guess what I am trying to figure out is twofold:

1) On a Continental O-360-es, if one wanted to aggressively look for corrosion, is it even possible to get a good view of the entire camshaft? I assume all the lifters could be pulled.

<snip>

I don't know about the 360, but on most, you have to split the case to remove the lifters, since they're flanged on the end. On my O-200, it's just an empty cam follower body...the hydraulic part slides into the lifter body from the outside, so, yes, the "lifters" can be removed, but the body into which they fit remains buried deep in the case. Such that you can't use that as an inspection port.

That's why I said to pull a cylinder; with a flexible borescope, you can then see down in there a bit. Whether you can see the entire cam or not depends on the number/type of webs on the inner surface of the crankcase.

As WLIU noted, you prefaced this with the engine being run only a few hours a month. As long as it was run in flight long enough to have the humidity boil out of the oil, you should be good. A ground run-up won't do it.

One last point, you could always take an oil sample (warm) and have it sent for analysis. The labs are VERY good at identifying the metal(s) identified in the oil and from where they came.

[WLIU]

The Continental O-470s have automotive style lifter bodies that you can pull out once the pushrods are removed. No case split required. I looked at a couple of my cam lobes that way. I do not know if the Continental -360's have that style lifter bodies. If they do, and you really really want to pay for the effort you could look at the cam by putting each cylinder at TDC, remove the rockers, pushrods, and pushrod tubes.

That said, the stated history is not scary.

Best of luck,

Wes

[cub builder]

As WLIU says, cam spauling is typically not an issue in Continental engines. It's not a matter of cam placement so much as a metallurgy issue. Lycoming uses a hardened steel follower on a hardened cam, so the cam follower doesn't hold oil on the face very well leading to corrosion if left sitting for long periods of time. The hardened face with pitting on the follower peels the cam lobes like a machine tool. Continental uses an iron face cam follower, which is softer material and holds oil much better. Even if the Continental cam follower is corroded, it typically won't damage the cam. The hydraulic lifter will take up the slack for wear, and you don't typically see any issues until you tear the engine down at TBO and find the face of the cam followers are dished out (concave rather than convex).

Additionally, my Continental O-360 manual shows that it uses a straight bore cam follower similar to the O-470. So, if desired, one can remove the push rods and pull the cam followers out through the cam follower bores. Takes the better part of the day to do. I wouldn't bother on a Continental, but I'm sure a shop will be happy to take your money to do it for you if it's your desire.

-Cub Builder

[ualdriver]

on adding to reply #2., do a google search for " eaa , mike bush , buying, webinars ", and also look up savvyaviator.com ... .. .good luck , good day , /rick

Rick. Thanks! I have done exactly all of the above, which is what sent me down this whole camshaft/lifter question, especially when he showed what corroded, spalled lifters and cam lobes looked like! Busch does great work, and I just bought his book, "Engines," which I hope to read over winter break. When he stated in one of his webinars is that corrosion is the major reason why engines don't make TBO, that's what made ask why lifter/camshaft/lobe inspections aren't done routinely.


Continentals don't have the same cam issues that Lycos do. Continental engines place the cam below the crank. Which gets them lubricated sooner on start and puts them where they get drips of oil from above while they sit. Yes you can have cam issues in a Continental, but it is much less likely. If the engine is run a few hours a month, you are likely good, even in Florida. In Florida I would look for corrosion on the prop and in the wings.

Best of luck,

Wes

Good info Wes, thanks.


I don't know about the 360, but on most, you have to split the case to remove the lifters, since they're flanged on the end. On my O-200, it's just an empty cam follower body...the hydraulic part slides into the lifter body from the outside, so, yes, the "lifters" can be removed, but the body into which they fit remains buried deep in the case. Such that you can't use that as an inspection port.

That's why I said to pull a cylinder; with a flexible borescope, you can then see down in there a bit. Whether you can see the entire cam or not depends on the number/type of webs on the inner surface of the crankcase.

As WLIU noted, you prefaced this with the engine being run only a few hours a month. As long as it was run in flight long enough to have the humidity boil out of the oil, you should be good. A ground run-up won't do it.

One last point, you could always take an oil sample (warm) and have it sent for analysis. The labs are VERY good at identifying the metal(s) identified in the oil and from where they came.

Good advice and thanks for the info. Oil analysis kind of confuses me a bit. Not the concept, just how anyone could really interpret the data from a single analysis. For example, if I did an oil analysis on an aircraft that sat around on a ramp in Florida, I'd likely expect high iron content, for example, just from microscopic iron (corrosion) being shaved off cylinder walls during the start. That kind of iron would be OK, but maybe the engine is making iron because of a bad camshaft lobe, right? How would an A&P know the difference?


The Continental O-470s have automotive style lifter bodies that you can pull out once the pushrods are removed. No case split required. I looked at a couple of my cam lobes that way. I do not know if the Continental -360's have that style lifter bodies. If they do, and you really really want to pay for the effort you could look at the cam by putting each cylinder at TDC, remove the rockers, pushrods, and pushrod tubes.

That said, the stated history is not scary.

Best of luck,

Wes

Thanks again Wes. Perhaps I shouldn't be as concerned. I just assume the worse when I see so many pointers that could plant the seeds of internal engine corrosion.

[CarlOrton]

Good advice and thanks for the info. Oil analysis kind of confuses me a bit. Not the concept, just how anyone could really interpret the data from a single analysis. For example, if I did an oil analysis on an aircraft that sat around on a ramp in Florida, I'd likely expect high iron content, for example, just from microscopic iron (corrosion) being shaved off cylinder walls during the start. That kind of iron would be OK, but maybe the engine is making iron because of a bad camshaft lobe, right? How would an A&P know the difference?

A good lab will reference your sample against fleet averages. Yes, ideally they will know YOUR engine better after several samples (to develop trending data), but one sample can still be compared to other similar engines.

When you submit a sample, you typically provide info on hours on engine, engine type, hours since last oil change, etc., so they can adjust the results in comparison with other like engines.

Regarding the types of material found in a sample, they will give a broad-range guess as to the source. As an example, they can determine the alloy. So, iron with nickel in it would come from a different component than iron with [insert metal here].

Most labs are relatively small, so if you document your unique situation (low avg run times, pre-buy, etc.) they can tell you that while a given material may be high in comparison to the fleet, x hours of flying is typically found to reduce those values. They're really pretty good forensic investigators!

[ualdriver]

A good lab will reference your sample against fleet averages. Yes, ideally they will know YOUR engine better after several samples (to develop trending data), but one sample can still be compared to other similar engines.

When you submit a sample, you typically provide info on hours on engine, engine type, hours since last oil change, etc., so they can adjust the results in comparison with other like engines.

Regarding the types of material found in a sample, they will give a broad-range guess as to the source. As an example, they can determine the alloy. So, iron with nickel in it would come from a different component than iron with [insert metal here].

Most labs are relatively small, so if you document your unique situation (low avg run times, pre-buy, etc.) they can tell you that while a given material may be high in comparison to the fleet, x hours of flying is typically found to reduce those values. They're really pretty good forensic investigators!

Great info, thanks again. I didn't realize they kept a database of similar engines but I guess that makes sense. We walked away from an aircraft that had trending high iron content over a two year period, but that oil analysis company did not provide a baseline comparison for other engines. That would have been useful information. I think Busch mentioned in one of his webinars that he recommends Blackstone for oil analysis.

[DaleB]

I used a cheaper place for my first oil analysis (AOA, I think?) and Blackstone for the most recent. Blackstone’s report and analysis is an order of magnitude better, well worth the slight extra cost.