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Found Source of Metal


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At last annual, 15 Hrs tach time ago, my IO360A1A had metal in the filter.  It was running great with great oil pressure and temperature and good compressions.  After oil and filter I flew it fifteen hours without having to add oil, and running like a Swiss watch holding 81 PSI oil pressure and 179 degree oil temperature very steadily.  I stayed very close to home while doing this flying.  Within glide distance of the field most of the time.

At that point we drained a sample and cut the filter to find metal again.  It had been running so well that I was suspecting the prop Governor.   We sent the oil sample which took almost a month to reach the lab (thank you USPS,) and it came back with high iron which indicated a cylinder or rotating shaft.

 We started pulling cylinders and they all looked really good.  With cylinders off, we found the problem.  The second cam lobe from the front is severely worn down and that lifter looks as if someone has been practicing their use of a hammer and chisel.  

Our plan is to IRAN the cylinders and replace the cam and lifters and probably main bearings hopefully nothing further is found when we split it.

BTW, this is an 1100 hour engine that had a few years of setting still.  After setting still it had cylinders removed, everything inspected, cylinders honed and new rings then put back in service.  I would have to check my logs, but I think it has run about 85 hours since that point.

 

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Surprised they yanked the cylinders after just three years of sitting. If it was more than that and the overhaul is 20 ish years old I’d send it to jewel.  It’s a good idea to change the hoses and isolators anyway and the fuel system was sitting unused as well during that time. The price difference might not be that much and there will be considerable value added.

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The fuel system was gone through and AD’s caught up with at the time of the cylinder honing and ring replacement about 85 hours ago.  The engine was an overhaul about 1100 hours ago.  The original engine went a few hundred hours past TBO.  Don’t have the logs here for exact numbers.

 

IMHO, the cam lobe began wearing as a result of sitting.  Maybe had corrosion that led to flaking.  Lycoming cams are at the top.  Over a period of sitting the oil film goes away.  Cam to lifter pressure, due to the microscopic area involved result in a tremendous load as measured in PSI.  Flat tapped cam and lifters live a really stressed life.

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1 hour ago, 0TreeLemur said:

This is an excellent data point for those who inquire about buying aircraft that have been sitting for a few years.

On the other hand, my C flew for 3 hours total the two years before I bought it in 2007, literally ~300 yards from the bank of the Ohio River. Still no engine trouble.

There is literally no data available concerning how many hangar queens have trouble and how many do not . . . .

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23 minutes ago, MBDiagMan said:

It’s an excellent data point to exalt the advantages of a low cam.


Go IO550! :) (next time...) +1 for the low cam, and removable without the mOH.

My M20C with its O360 sat outside for two years unused... prior to my purchase...

It had so much carbon in one of its valve guides it stuck a valve within my first 10hours...

Without MS, or an engine monitor... I had very little knowledge of what was going on within the engine...

 

Swapping out the cam followers for DLC’d cam followers would be an interesting preemptive maneuver...

That probably requires pulling a cylinder at a time to swap out each follower...

The cratered followers are a known cause of machining off the associated cam lobes...

Post pics if you got em...  :)

PP thoughts only, not a mechanic...

Best regards,

-a-

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In my limited experience, it typically takes between 6 month to 18 months. First it just takes a break in the surface hardening on the lifter from corrosion, then its like a miniature pot hole that grows and starts to damage the cam. Its rare, but not totally unheard on Continentals, but of course much more common on Lycomings with Cam at the top. 

Like suggestions above, I'd seriosuly consider OH as well. 1100 hours isn't that much but years is just as important and an IRAN doesn't add any resale value to the plane/engine unlike resetting the clock on TSMOH. But IMO the deciding factors come down to how long you intend to keep the plane. If this is a forever like plane and you expect you'll be the owner through its remaining engine life then I wouldn't be in a hurry to OH at all - the # of hours are no longer important. I'd IRAN it as well. Bottom's can last a long long time if not damaged from metal - which could become an issue here too, but that remains to be seen till inspected.

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3 minutes ago, jwarren2 said:

Wouldn’t you want a DLC coated cam also ?

 

Unfortunately....

When you perfectly match the hardness of both surfaces... they tend to wear each other out at an accelerated pace...

Some oddity in metallurgy to explain that...

In this case... the surface of the cam follower is the culprit... its surface craters, while the cam is fine...

The cam stays fine, until the sharp rough cratered surface of the follower runs over it...

The oil can’t lubricate the cutting tool like surface...

PP thoughts only, not a metallurgist...

Best regards,

-a-

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As far as removing cylinders and changing tappets, I’m pretty sure due to their design that flat tappets require the cases to be split.

If your splitting cases, go ahead and overhaul, an overhaul does not require good parts to be replaced, a Lycoming SB does.

‘But odds are that if your splitting the cases your doing the work of an overhaul anyway.

‘An A&P is doing the work correct?

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3 hours ago, A64Pilot said:

As far as removing cylinders and changing tappets, I’m pretty sure due to their design that flat tappets require the cases to be split.

If your splitting cases, go ahead and overhaul, an overhaul does not require good parts to be replaced, a Lycoming SB does.

‘But odds are that if your splitting the cases your doing the work of an overhaul anyway.

‘An A&P is doing the work correct?

Yes the case must be split to change out the tappets, but splitting the case doesn't make it an overhaul. A major overhaul is a FAA legal defintion that requires replacing all the parts listed by Lycoming. Anything short of that is only an IRAN and doesn't reset the hours for TSMOH. 

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Yes A64, the case is being split to replace the cam and followers.  That’s the only way that the. operation can be accomplished.

No, A&P is not doing the work.  Two A&P/ IA’s are doing the work.  They are massively experienced and competent.

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On 3/6/2021 at 8:59 PM, MBDiagMan said:

It’s an excellent data point to exalt the advantages of a low cam.

Well, not actually. The low cams in Continentals have the same corrosion and spalling issues. And, add to that the cylinders have weak valves because the rocker arm is lubricated from below, rather than the top. Meaning the valve stems and guides do not benefit from oil flowing down over them like a Lycoming. This is most likely the reason that Continental cylinders last half as long as Lycomings. The lack of lubrication wears out the exhaust valve rotocoils quicker, and the lack of heat transfer wears out the valve guides quicker. 

Edited by philiplane
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50 minutes ago, MBDiagMan said:

I would have to look in the logs to confirm Yetti, but I think 2001.

I’ve got one from 2004 after a prop strike inspection.  No documentation on why it was replaced at the time.

What years you think are the “bad” ones @Yetti?

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6 minutes ago, Ragsf15e said:

I’ve got one from 2004 after a prop strike inspection.  No documentation on why it was replaced at the time.

What years you think are the “bad” ones @Yetti?

I probably should be tracking this better, but the trend is early 1990s to mid 2000s   There seemed to be a change of metallurgy.  don't think Lycoming would ever fess up to it.

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12 hours ago, MBDiagMan said:

Yes A64, the case is being split to replace the cam and followers.  That’s the only way that the. operation can be accomplished.

No, A&P is not doing the work.  Two A&P/ IA’s are doing the work.  They are massively experienced and competent.

Well, then what’s their opinion? Have you asked?

I just hope the crank isn’t damaged.

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