Bulk Strip?

[SGM]

Looking for advice

 

I noticed a Cherokee for sale with about 300 hours remaining before hitting TBO hours.  However it recently had a full "Bulk Strip" incluing new bearings, gaskets, camshaft, internal bore etc at a cost of $10k (which was roughly half labour).  

 

The comment from the seller was "The engine can go past the TBO for all ops other than Charter which I doubt you will need.   Especially as it has had a recent extensive overhaul.  We can't understand why it was not zero timed at the overhaul."

 

For the purposes of comparing other aircraft for sale, how much life in hours would it be reasonable to assume a bulk strip gives?

 

 

[440032]

Start with a look at CASA AWB 02-1 issue 1 - On condition maintenance.

 

 

[old man emu]

Wish I could get an engine bulk stripped for 10K of which half was labour.

 

On reading that, I'd want to know the reason for the bulk strip. It usually means there's been a prop strike.

 

 

[onetrack]

The bulk strip could have been for a condition other than prop strike - bore corrosion sighted, metal fragments in filter or sump, or just the owner reporting a strange and unusual noise, and initiated a bulk strip as a result, trying to find the noise source.

 

As I understand it, only the manufacturer can produce a zero-timed engine. A ZT engine has every single engine component inspected to ensure it meets factory specifications, and components which do not are replaced with new or fully reconditioned components.

 

A ZT engine is produced with a new engine S/No and data plate, and may even have factory component upgrades, making it a different model of engine.

 

Nothing wrong with running an engine "on-condition", particularly when you know it has had a sizeable number of its major moving components replaced.

 

But you must be aware that in a bulk strip, some components such as the crankcase are likely to be original, and may not provide the same level of reliability as a factory ZT engine with a new or reconditioned crankcase.

 

Continental state the differences quite clearly -

 

http://www.continentalmotors.aero/Rebuilding_Benefits/

 

 

[Yenn]

My understanding is that a bulk strip could be done just because the engine is of a certain age. CASA require a bulk strip of old engines because there is deterioration of seals and other things, due to age rather than wear. I guess that this may be an old engine, which has not been used all that much.

 

I would assume that the condition of the bores would have been checked during the bulk strip, but not necessarily for wear, just visible corrosion, also the camshaft.

 

It is probably a Lycoming and one of the common failure points for them is the camshaft. It would be bad practice to return to service an engine with corrosion on the cams, but I don't know if there is any guarantee.

 

I would suggest that you read the engine logbook, which should detail work done. Maybe even talk to the maintenance organisation.

 

 

[SGM]

Thanks guys...The reason given for the bulk strip was "rough running at 1000RPM,  which was caused by Cam lobes having deteriorated - dual lifter lobes".  Engine is O-320 E2D.

 

 

[onetrack]

A$10K is a pretty cheap overhaul for an O-320 E2D. I'd have to say they spent the bare minimum, and only replaced the basic components, such as the faulty camshaft, the rings and bearings, and seals and gaskets.

 

http://www.airpowerinc.com/productcart/pc/TLEngineDetail.asp?catID=33&prodID=9853

 

 

[facthunter]

You usually have to do the followers at the same time as the camshaft and since the problem is fairly common I doubt you would get serviceable second hand components. I doubt a reputable shop putting an engine into a VH plane would allow anything out of tolerance to go back in the engine but if it was never installed in a certified plane the issue doesn't arise. I would contact the shop, and see what they have to say about the engine's condition. (and get it in writing) If they say "we just did what was asked" don't assume it's in good shape. Speculating...  Why is it on the market?  If the plane that it came from has another motor you can pretty much assume THAT was advised and reach your own conclusion about the value of this engine as a useable product.. Just because it's had $10,000 spent on it doesn't even guarantee it's worth that figure. or worth any figure at all.  This is the nature of aircraft stuff. Nev

 

 

[Thruster88]

Thanks guys...The reason given for the bulk strip was "rough running at 1000RPM,  which was caused by Cam lobes having deteriorated - dual lifter lobes".  Engine is O-320 E2D.

 

When the cam lobes "deteriorate" the metal ends up in the filter. Working as an AME I have seen two cases this year (lycoming). Running on condition requires a. Compression test pass

 

                                       b. No metal in filter

 

                                       c. No excessive oil consumption 

 

                                       d. A LAME who is prepared to stick their neck out.

 

I don't  think this engine will be any better of due to the bulk strip in regards to running on condition.

 

 

[old man emu]

You won't see a long-necked LAME unless the LAME has been maintaining the aircraft since Pontius was a pilot.

 

 

[facthunter]

 People usually sell a plane with the sort of hours this one has left as with much less it is virtually "out of hours". "On condition" means that it must reach a certain condition to be entitled to an EXTENSION of Permitted Operation beyond the normal TBO.. Any engine may be unserviceable at any time( like an annual or 100 hourly) or even as result of feeling the compression and having it checked any time, If it doesn't pass certain tests like a leakdown, static run power test noise or rough running etc It can be returned to service when that "fault" has been satisfactorily rectified to run out the original TBO time  which may include being eligible for "on condition" extension if it meets the criteria THEN. A zero time rebuild would have to meet tighter criteria and would be around $40 K PLUS. Cylinders  (assemblies) are around $13k each depending on model of 320 you have, If they need replacing.  If the motor has been rebuilt twice at TBO TT 4600 hours, I would seriously consider not doing it for the 3rd time . Nev

 

 

[Yenn]

This was not really what CASA would define as a bulk strip. It was repairs to camshaft and no doubt followers.

 

There is no need for rings to be replaced. It is possible to pull the cylinders and pistons off without disassembling them, therefore no need to re ring. But that would not happen with a bulk strip.

 

 

[facthunter]

With very worn camshafts the metal has to go somewhere and that's through the oil pump and the filter at least. Some could also end up in the accessories drive case. The engine would hopefully be flushed and cleaned and the bores checked for scratches. You wouldn't necessarily do the rings, but I probably would but it all adds to the cost.  Be surprised if there wasn't "some" bore corrosion. There's an engine and prop log book and all flights should have been recorded. Nev

 

 

[SGM]

Thanks everyone.. I will pass on this “bargain”

 

 

[Mike Borgelt]

Read Mike Busch on engine reliability. He has an interesting seminar on engine failure rates. Significantly worse in first 500 hours after new or re-build, settling down nicely after that to well past recommended TBO.

 

I'd not replace a well running engine with good compressions, oil pressure  and no metal in filter, just because it hit TBO.

 

TBO is to cover the manufacturer's and CASA's backside, not yours. Mike is a very experienced U.S. A&P (LAME).

 

 

[facthunter]

There is a situation were the weak not so well built, prove so and remove themselves from the flock/equation to come back as rebuilt and perhaps perpetuate the unreliability statistics of recently worked on engines, and so on.

 

   . After perhaps 50-100_ hours any particular engine doesn't get better with use and once deterioration starts to happen, it's at an increasing rate. Valve guide/stem wear is checked regularly on  Lyc /cont engines and is requiring of rectification at a certain wear limit regardless of hours done. Valve to guide clearance is critical for valve seat life, and to avoid stem breakage. on ANY  (piston) engine.

 

   Engine life long term is very dependent on usage pattens. Regular long trips in a dust free environment with no para drops etc. and the initial build has to be right.  Nev