Engine OH Questions

[Paul_Havelka]

Sorry for the NEWB question but I haven't been able to find a direct answer yet.  I have seen where ac that have had prop strikes only end up getting the bottom end of the engine OH due to money issues since the insurance the individual had only covered the cost of that part of the repair.My question is what exactly differentiates this from a major?  Is it just that the cylinders were not replaced with new or OH units?

[carusoam]

There are top OHs... typical for an engine that is flown for all out speed... exchanging cylinders as needed...

Then there are the usual OHs... typical of an engine that has been used up over 2k+hrs....

Specific to prop strikes... there are procedures to follow... including how to define what a prop strike is... grass stains on the tip, or stones imbedded in the blades... bent parts like cranks that can be measured at the flange, stand out really well... cracked parts, sneak past the external visual inspection...

What used to pass for proper inspection has left a few props departing the plane... surprise!  A sudden change of thrust combined with a change of WnB...

Then there are all kinds of situations where an engine has had work done on it for one reason or another...

To really be confused... look up the definitions of OH, factory new, factory reman, factory OH, field OH....

How do you feel about who built your engine? Or in the case of the plane you are looking at... who did the inspection, how, What parts were replaced... there will be records and receipts that are easy to read...

Some people like this level of control... others can only afford so much...  Then there is the factory that couldn’t build a decent valve train... or the other one that couldn't control the metallurgy of a key component like the cam...

This is a lot to take in at first...  

What is your preference?

I went with a mid time engine, hoping to get years of flying out of it before having to answer the question... 

Then somebody bent my prop back with an errant piece of ground... call it a ground strike or a prop strike... it starts an expensive chain of events to make proper again...

The required inspection leaves the engine open to replace some worn parts... so while you are in there...

I went factory OH...

Best regards,

-a-

[Shadrach]

33 minutes ago, Creekrat said:

Sorry for the NEWB question but I haven't been able to find a direct answer yet.  I have seen where ac that have had prop strikes only end up getting the bottom end of the engine OH due to money issues since the insurance the individual had only covered the cost of that part of the repair.My question is what exactly differentiates this from a major?  Is it just that the cylinders were not replaced with new or OH units?

Time in service? Calendar Age?  These are very important factors in determining how to proceed after prop strike.

 

[Paul_Havelka]

Was just perusing different ads and saw this one and it piqued my curiosity.

 

1000 on lower end overhaul 1950 on first run Lycoming cylinders (1950 SMOH)

 

My preference is mid time for when i buy

Edited March 17, 2019 by Creekrat

[carusoam]

Want some more goofiness...?

The goofy part of a Top Overhaul... is its name.

On a horizontally opposed engine... it’s a boxer, punching outwards...

How do the cylinders become the top?

The bottom of the engine is an oil pan, not much to OH there...

The back of the engine has a few things that could wear, or break during a ground strike... gears, oil pump, mags...

The front has the prop... that gets a prop overhaul to account for updates... there are better procedures than OH when it comes to GA props in the US...

 

With 1k hrs on the bottom, and 2k on the top... there isn’t much of the system left... look into the details of when it may need a new alternator, starter, vac pump or prop Governor....

One important measurement of determining how long this engine will keep running.... is how often it has been flown over the past few years...

Is it seeing 100hrs each year? A fair amount...

Has it been sitting idle? 10 hrs since last April, nothing since May?

PP thoughts only,

-a-

[M20F]

Lycoming and Continental both list what is required for a major overhaul this is a paperwork exercise.  IRAN can be the same but it is not a major overhaul. 

Example.  You put 4 brand new cylinders on plane.  Fly for 1hr and have prop strike.  You do the bottom but because the cylinders were 1hr you do not replace exhaust valves on a lycoming.  It is now IRAN and not a major.  Difference is just what goes in the book. Why would anyone rebuild 1hr old cylinders.

Let’s say you do a major but don’t do the accessories.  Now you have an engine with 2000hr mags on it.  A lot of people wrongly equate the major with making all things new hence the non-standard phrase “firewall forward”.  

So in your case how old were the cylinders and other parts of the engine when it occurred.  If they were all new then a bottom could be essentially the same as a major. 

In short it depends and you really need to dig through all the log books to evaluate.  

Edited March 17, 2019 by M20F

[Shadrach]

7 hours ago, Creekrat said:

Was just perusing different ads and saw this one and it piqued my curiosity.

 

1000 on lower end overhaul 1950 on first run Lycoming cylinders (1950 SMOH)

 

My preference is mid time for when i buy

In that case, I would price it as timed out but run it on condition.  There’s absolutely no guarantee either way.  I wholly disagree that the engine doesn’t have much life left just because of the times you’ve mentioned.   Airplane engines don’t care anymore than any other engine how many hours they are run.  The internal components don’t get weak (if they did they wouldn’t be reused for factory remans).  People have almost religious beliefs when it comes to engine times and overhauls. I’m of the opinion that a perfectly good running engine is likely to remain a perfectly good running engine if it’s regularly serviced with good lubricant, used regularly and operated within temperature specs. Time in service is an overrated metric of health, especially compared to a splitting the case and inspecting it. Who cares about time in service if you can inspect the internals.

Edited March 18, 2019 by Shadrach

[Yetti]

Lower end is crankshaft and rods.   Upper is push rods and cylinders.

 

Edited March 18, 2019 by Yetti

[Shadrach]

4 minutes ago, Yetti said:

Lower end is crankshaft and rods.   Upper is cam and cylinders.

Not true. It depends on application. Auto builders consider anything within the short-block to be bottom end. So the cam can be part of the top end or bottom end depending on which side of the head gasket it’s on.  In aviation, anything within the case is considered bottom end.

[Andy95W]

I'm with Ross.  The differentiation is whether or not the case is opened.  You can replace all the cylinders (top overhaul) and never open the case.  When you do open the case (bottom end) lots of other ADs and SBs come into play and the cam and lifters get replaced if necessary.

[Guest]

6 hours ago, Creekrat said:

Sorry for the NEWB question but I haven't been able to find a direct answer yet.  I have seen where ac that have had prop strikes only end up getting the bottom end of the engine OH due to money issues since the insurance the individual had only covered the cost of that part of the repair.My question is what exactly differentiates this from a major?  Is it just that the cylinders were not replaced with new or OH units?

Hope this helps and assuming you’re talking about Lycoming engines.  When a prop strike happens you must comply with AD2004-10-14 which drives compliance with SB475. This may or may not require removal of the engine, it certainly does not require splitting the crankcase.  This is the minimum required.  Most people and insurance companies with go further and remove the engine, split it, do the above AD and SB as well as SB533.

An engine overhaul is done to the engine overhaul manual and the parts replacement as called out in SB240, again this is the minimum requirement to be called an overhaul.  Most reputable overhaulers will go much further.  The paperwork and parts list provided with the log book describe what was done, again if the paperwork is done well.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf/0/9fa5e5f8683a0a4686256e9b004bc295/$FILE/041014.pdf

https://www.lycoming.com/sites/default/files/Crankshaft Gear Modification and Assembly Procedures.pdf

https://www.lycoming.com/sites/default/files/SB533C Recommended Action for sudden Engine Stoppage%2C Propeller_Rotor Strike or Loss of Propeller_Rotor Blade or Ti (1).pdf

https://www.lycoming.com/sites/default/files/Mandatory Parts Replacement at Overhaul and During Repair or Maintenance.pdf

Clarence

 

[Yetti]

5 hours ago, Shadrach said:

Not true. It depends on application. Auto builders consider anything within the short-block to be bottom end. So the cam can be part of the top end or bottom end depending on which side of the head gasket it’s on.  In aviation, anything within the case is considered bottom end.

Lycoming 4 cylinder aircooled airplane engine.  Focus Danielson

[Shadrach]

13 hours ago, Yetti said:

Lycoming 4 cylinder aircooled airplane engine.  Focus Danielson

My mistake.  I thought you were genuinely trying to add to the conversation, not to just be contrarian. Carry on.

Cam is definitely part of the bottom end of a Lyc 4.

Edited March 18, 2019 by Shadrach
spelling

[Yetti]

45 minutes ago, Shadrach said:

My mistake.  I thought you were guinely trying to add to the coversation, not just be contrarian. Carry on.

Cam is definitely part of the bottom end of a Lyc 4.

I have edited my original post to meet with your specifications.  Hopefully you can sleep better tonight.

[Shadrach]

12 hours ago, Yetti said:

I have edited my original post to meet with your specifications.  Hopefully you can sleep better tonight.

Thanks sunshine! Hope you slept well too!

Edited March 18, 2019 by Shadrach

[Yetti]