The engine overhaul

[aviatoreb]

20 hours ago, Bob_Belville said:

+1, you beat me with this reply, ask your A&P shop, he deals with guys all the time who want to fix a prop with duct tape or similar.

Didn't they send a man to the Moon with duct tape?  Heck why can't you fix anything with that.  I bet a little bit on the leading edges is a de-icing product.  And you can stop gap landing gear cracks with duct tape.  And you can brush your teeth with it too - prevents cavities.  Or if you get a cavity, just wrap the tooth in a little duct tape.  Most people don't know that trick.

 

[Yooper Rocketman]

2 hours ago, aviatoreb said:

Didn't they send a man to the Moon with duct tape?  Heck why can't you fix anything with that.  I bet a little bit on the leading edges is a de-icing product.  And you can stop gap landing gear cracks with duct tape.  And you can brush your teeth with it too - prevents cavities.  Or if you get a cavity, just wrap the tooth in a little duct tape.  Most people don't know that trick.

 

Gitmo, sorry for the thread drift but I couldn't resist.

 

[N201MKTurbo]

I've been doing some reading this morning and it seems like tappet spalling is not caused by corrosion or wear, but by sub surface fractures caused by impact. This can be caused by the hydraulic lifter not keeping the tappet in contact with cam. Or the valve sticking and not following the cam.

Tappets all have a hard surface weather it be by case hardening, nitriding or DLC coating. Spalling happens when impacts to the hard surface transmit excessive shear forces to the softer substrate causing shear fractures of the substrate.

So from this, Cam Guard will do nothing to prevent spalling.

I'm not a metallurgist, so if anybody out there has more expertise on these things please chime in. 

[Bartman]

I'm sure you can get away with a lot in Alaska, but I don't think my IA or the local FSDO would approve those repairs.

Notice the rifle mounted on the left strut

[Guest]

Just now, N201MKTurbo said:

I've been doing some reading this morning and it seems like tappet spalling is not caused by corrosion or wear, but by sub surface fractures caused by impact. This can be caused by the hydraulic lifter not keeping the tappet in contact with cam. Or the valve sticking and not following the cam.

Tappets all have a hard surface weather it be by case hardening, nitriding or DLC coating. Spalling happens when impacts to the hard surface transmit excessive shear forces to the softer substrate causing shear fractures of the substrate.

So from this, Cam Guard will do nothing to prevent spalling.

I'm not a metallurgist, so if anybody out there has more expertise on these things please chime in. 

I wonder if there is a relationship between those engines with spalled lifters and those who have not done SB388?  It still doesn’t explain those that fail before reaching the hours in the SB.

Clarence

[N201MKTurbo]

1 minute ago, Bartman said:

I'm sure you can get away with a lot in Alaska, but I don't think my IA or the local FSDO would approve those repairs.

Notice the rifle mounted on the left strut

But it will get you by till the next annual. That's assuming this airplane gets annuals.

[N601RX]

The other thing that changed a few years before all these failures started occurring is the amout of lead in aviation fuel was reduced by half. 

When I overhauled my engine a few years ago I purchased a new cam and had it modified with the centrilub STC. They drilled a couple of small holes in each of the cam bearing journals and then a couple of small holes on the rising edge of each lob. The camshaft is already hollow and they also plug each end.  This allows the cam to fill with pressurized oil from its bearing journals and put that oil directly on the face of the lifter where it's most needed. 

http://www.centri-lube.com/technologies.html

Edited December 17, 2017 by N601RX

[N201MKTurbo]

Just now, M20Doc said:

I wonder if there is a relationship between those engines with spalled lifters and those who have not done SB388?  It still doesn’t explain those that fail before reaching the hours in the SB.

Clarence

It is hard to say. I've only done a couple of engines in my life so I don't have broad experience with failures. Do you see more spalling on exhaust lifters than intake lifters?

Could it be that people are not setting the valve lash properly and the lifters are out of range in some conditions?

[gitmo234]

The thread drift is quite alright. I enjoy this stuff. I'm a bit of a data nerd. I'll miss the gigantic sign telling me what I want to know because I'm busy reading up on the inner-workings of the problem. Does camguard work? what is the actual cause of engine failure? stats? etc to infinity. 

Its clear though. My engine was jacked and had been for a while. Slowly rushing to failure. I focused on one thing at a time. I had it looked at by a half a dozen people and places. All gave a thumbs up. If I had "zoomed out" a bit on the chart the trend was visible. Oh well. We win some and we lose some. My Cessna was a 1956 continental O-300 with an absolutely ancient overhaul. Ran pretty decently. This had a less ancient but still old overhaul and had problems. When you put it all on red, sometimes you get lucky. 

Either way. The good stuff here is that I was prepared. I didn't have a specific engine fund built up that far yet, but I did have the means. So this means I get a 0 time engine soon. What this also means is I have a wonderful opportunity to get intimately familiar with that engines personality and how it runs. It's not a guess for me or anyone else. If its oil burn increases... I'll know. I am confident in the work of the shop doing my overhaul and so far, it's been more than I couldve asked for. Regular phone calls, pictures, etc. 

So honestly, this is a good thing. 

My only concern now is a 6 hour cross country being the break-in flight. If all goes well that's probably pretty awesome. Six hours steady flight is probably good for it (from what I've been reading)

 

[aviatoreb]

9 hours ago, Yooper Rocketman said:

Gitmo, sorry for the thread drift but I couldn't resist.

 

The definitive duct tape picture....

 

[aviatoreb]

8 hours ago, Bartman said:

 

Notice the rifle mounted on the left strut

That’s for air to air combat.

[cnoe]

I've been doing some reading this morning and it seems like tappet spalling is not caused by corrosion or wear, but by sub surface fractures caused by impact. This can be caused by the hydraulic lifter not keeping the tappet in contact with cam. Or the valve sticking and not following the cam. Tappets all have a hard surface weather it be by case hardening, nitriding or DLC coating. Spalling happens when impacts to the hard surface transmit excessive shear forces to the softer substrate causing shear fractures of the substrate. So from this, Cam Guard will do nothing to prevent spalling.

I'm not a metallurgist, so if anybody out there has more expertise on these things please chime in. 

 

 

With all due respect I don't believe it can be fully explained by that. I too have been reading about this subject for FOUR YEARS and the condition you describe may indeed be a major contributing factor but falls under the category of poor metallurgy. There is heat-treatment that penetrates well below the surfaces of the cam and tappets, and then there is the surface treatment. If the depth of the hardening isn't deep enough (or hard enough) it's like driving a truck over an asphalt road which causes the substrate to give a little. This can indeed cause surface cracks but isn't necessarily due to "impact" or "sticking valves"; it's due to improperly hardened base material.

 

But don't rule out minor corrosion (flash rust) as a problem as well. There's a reason why trainers have a lower incidence of cam/tappet spalling and it's directly related to the time between flights. Planes that sit for many days between flights simply don't fare as well and it's likely due to surface degradation and subsequent startups. For this problem anti-corrosive additives and engine dehydrators may provide some relief. It should also be noted that Continentals have a significantly lower incidence of cam/lifter spalling (as their cams sit low in the crankcase where lubrication is plentiful unlike the Lycomings). The real cause is very possibly a combination of factors for some, and a single issue for others.

 

FWIW, the camshaft pic Byron posted in this thread showed both the "intake" lobes as being affected but not the exhaust lobes. This make sense since those lobes see double-duty with the opposing intake lifters. I believe there is some hope with the new tool-steel/DLC-coated lifters.

 

Also, my engine shop highly recommends Camguard but it's certainly no cure-all. Still it's pretty cheap insurance compared to the cost of splitting a case.

 

These are just my observations. YMMV.

 

 

 

 

[jaylw314]

On ‎12‎/‎11‎/‎2017 at 10:55 AM, gitmo234 said:

The main bearings have a lot of ware on them as well. The crankcase has several loose fitting through bolts and sings of fretting. Overall this is a tired engine in need of this overhaul.

  Did everyone else miss this?  In one of his webinars a few months ago, Mike Busch mentioned how properly torqueing the through-bolts was crucial to proper function of the crankshaft bearings.  If loose, the bearings can loosen and even rotate, which could cause a catastrophic loss of oil to that bearing.  It makes me wonder if that was the root cause of part or all of the engine condition.

[gitmo234]

Updated call from the shop. some of my terminology may be off so forgive me if something doesnt make sense:

Fuel Servo: hasn't been touched since the 80s apparently, needed an overhaul to bring up to standard

New cam shaft required

New followers

Needs a new prop cable

Prop governor - inspected and no surprises... overhauled

crankcase - no updates since the 1980s. There was a mod or fix to prevent it from vibrating/rubbing/etc that wasnt done. this is being done

accessory case - needed to be re-machined

oil pan/sumps -tubes flow through them and there are some seals and lining that were leaking badly - overhauled

overhauled cylinders to be installed.

Prop itself - eddy inspection, seals replaced (small leaks) but overall GREAT condition. they did some basic work on it and said it looks brand new.

 

Plus side: prop came in way under what was expected. Downside: Fuel servo wasnt expected to be as bad as it was. 

 

[jetdriven]

What’s the cost for this overhaul, also is The shop using the Lycoming DLC lifters?

[gitmo234]

48 minutes ago, jetdriven said:

What’s the cost for this overhaul, also is The shop using the Lycoming DLC lifters?

Right now I’m running roughly $24k when it’s all said and done. I believe they are those lifters. He gave me the option but said he strongly recommends brand new lifters/followers when the other parts are replaced. I went with his recommendation

[jetdriven]

The DLC lifters are brand new and the newest design from Lycoming. I would confirm firmly those are in there. Don’t be @aaronk25 and find out after it spalls again at 250hr that they cheaped out and used reground or off brand lifters. 

[aaronk25]

Hey jetdriven, easy now it was the POS lycoming brand new camshaft that failed not the lifter. I would have, the first time around opted for new lifters to match but bulldoc engines put in reground lifters. However that shop and Jewel both said they were done with new lycoming lifters. Jewel said when it comes to cam and lifters Sam and David Jewell said “don’t use either cam or lifters new from lycoming”. Now that was 3 years ago and I haven’t asked them about the newer revisions lycoming is now producing but one thing was clear and that was both shops saw failures with lycoming parts.

I’m currently at Jewels recommendation running both cam and lifters reground and hardened from ASL. 400 hours great oil analysis. I offered to pay the upcharge and he talked me out of it.



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[bradp]

Aide from metallurgy issues, aren’t  there two major design differences that both at least correlate with the Achilles heels of these engines (cam / lifter interactions):

1) Lack of lubricantion to the cam - sits high defies gravity 

2) lack of lubrication to the valve guides

[jetdriven]

1 hour ago, aaronk25 said:

Hey jetdriven, easy now it was the POS lycoming brand new camshaft that failed not the lifter. I would have, the first time around opted for new lifters to match but bulldoc engines put in reground lifters. However that shop and Jewel both said they were done with new lycoming lifters. Jewel said when it comes to cam and lifters Sam and David Jewell said “don’t use either cam or lifters new from lycoming”. Now that was 3 years ago and I haven’t asked them about the newer revisions lycoming is now producing but one thing was clear and that was both shops saw failures with lycoming parts.

I’m currently at Jewels recommendation running both cam and lifters reground and hardened from ASL. 400 hours great oil analysis. I offered to pay the upcharge and he talked me out of it.



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Thanks for the update, A.  

[aaronk25]

You got it man! Hey did you iron numbers get inline?


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[N6758N]

11 hours ago, gitmo234 said:

Right now I’m running roughly $24k when it’s all said and done. I believe they are those lifters. He gave me the option but said he strongly recommends brand new lifters/followers when the other parts are replaced. I went with his recommendation

Again, it's the tappet bodies/followers that go bad, NOT the lifters. Everyone here keeps saying the lifters spall. They are talking about a separate component. Lifters don't spall, tappet bodies do. The lifter is inside the tappet body and connected to the valve via pushrod. The tappet bodies and cam are  what need to be replaced. The lifters should be too because they are cheap enough. 

[Guest]

9 hours ago, N6758N said:

Again, it's the tappet bodies/followers that go bad, NOT the lifters. Everyone here keeps saying the lifters spall. They are talking about a separate component. Lifters don't spall, tappet bodies do. The lifter is inside the tappet body and connected to the valve via pushrod. The tappet bodies and cam are  what need to be replaced. The lifters should be too because they are cheap enough. 

Separating pepper and fly shit.  For most people tapped body and lifter are interchangeable.

Clarence

[Gary0747]

How often do failing cams and lifters show up in the performance of the aircraft?  Ie. speed and rate of climb.

[carusoam]

1 hour ago, Gary0747 said:

How often do failing cams and lifters show up in the performance of the aircraft?  Ie. speed and rate of climb.

When the moon surfaced tappet body grinds through the hardened surface of the cam lobe, the valves don't open and close as well as they need to...

hence the power performance falls off, and metal shows up in the oil filter.

T/O distance and climb rate will be directly effected by the HP change as it declines.

oil ananylis is probably the best way to find it before the power changes.

PP thoughts only, not a mechanic...

Best regards,

-a-