top overhaul

[rturbett]

Can anyone give me a ballpark figure on the cost of a top overhaul for a 66 C?

At what compression numbers are you deciding its time to be done?  What would you consider to be an acceptable oil burn rate?

Are the numbers much different for an E or F?

 

Thanks,

Rob Turbett

[KSMooniac]

Cylinders for the E/F/J cost twice as much as the C because Lycoming is the sole source supplier of those.  The C jugs have some aftermarket options.  Minimum acceptable compression per Lycoming is 60/80, I believe, although many folks wouldn't be comfortable flying with those values.  Maximum oil burn rate per Lycoming is in the neighborhood of 1 qt/hr, too, and many folks wouldn't like that either.

I'd also add that a full cylinder replacement might not be warranted if you find a good shop that will work on jugs and only repair items as necessary instead of just swapping entire jug assemblies.  It is entirely possible that changing valve guides and making sure the valves seat properly are good enough, along with a cylinder hone and new rings.  I had this done on my cylinders last year for ~$1500 for all 4, plus new pistons (+$600) and one new exhaust valve ($150 I think).  (R&R labor not included)  New cylinders for me would have been ~$7500 + labor.

You can do some shopping here:  http://www.aeroinstock.com/products/Cylinders/45/0/product_cat/index.html

[GeorgePerry]

Quote: rturbett

Can anyone give me a ballpark figure on the cost of a top overhaul for a 66 C?

At what compression numbers are you deciding its time to be done?  What would you consider to be an acceptable oil burn rate?

Are the numbers much different for an E or F?

[mjc]

Quote: GeorgePerry

Usually Top Overhauls are performed because the compression on one or more cyclinders has dropped off. 

There are exceptions to this rule but for brevity sufice to say that "Perfect" compression is 80.  So good compression for a Non Turbo charged piston aircraft engine is typically in the mid to high 70's.  Anything in the mid to low 60's is not so good and anyting in the 50's = park it.  Just as important as the compressions is oil analysis.  If an engine has a cyclinder go from high to low compression its probably making metal.  Having the Oil looked at will verify this.

[GeorgePerry]

Agreed...One compression test does not make a bad jug.  But if there are multiple checks in conjunction with high oil consuption then it's probably time to do some maintenance.

[rturbett]

My intuition tells me that the cylinders should all be in the same gerneral range. If one or two show numbers very diferent, then you need to investigate.   Is there a particular cylinder on a mooney that has a reputation for wearing first?(Lycoming) 

Rob

[mjc]

George, thanks for clarifying your thoughts; I see now we agree. Also, I found the source of the 60/80="low compression" data, in Lycoming's Key Reprints (http://www.lycoming.com/support/tips-advice/key-reprints/pdfs/Key Maintenance.pdf):

A loss in excess of 25% of the 80 lbs., or a reading of 60/80 is the recommended maximum allowable loss. (Page 13)

Mike Busch isn't a fan of Lycoming's guidance and explains his thoughts in http://www.avweb.com/news/savvyaviator/savvy_aviator_56_before_you_yank_that_jug_197497-1.html.

As for all cylinders turning in similar compression readings, I've also heard that if one is widly different it may be an indication of a problem (especially if the compression loss is due to a valve leak). I don't know if any one tends to be more problem-prone than others. Problems with different areas of the baffling will affect different cylinders.

[rturbett]

Great article. That definitely increased my knowledge on cylinder compression.

 

on a side note, do you have to drink two bottles of that powerful laxitive before having the boroscope done?

[sreid]

Quote: KSMooniac

I'd also add that a full cylinder replacement might not be warranted if you find a good shop that will work on jugs and only repair items as necessary instead of just swapping entire jug assemblies.  It is entirely possible that changing valve guides and making sure the valves seat properly are good enough, along with a cylinder hone and new rings.  I had this done on my cylinders last year for ~$1500 for all 4, plus new pistons (+$600) and one new exhaust valve ($150 I think).  (R&R labor not included)  New cylinders for me would have been ~$7500 + labor.

 

[KSMooniac]

Steve, I used Midwest Aircraft Services in Newton.  (316) 283-5915  

They aren't a very sophisticated shop in that they don't have a web presence, but I'm satisfied with the work they did 3+ years later.

 I did the R&R in my hangar, and drove them to the shop since they were a relatively short drive for me.  I'm sure you could ship them easily from OP, KS too.

[sreid]

Sounds like they did good work for you, and the location is relatively convenient.  There doesn't seem to be anybody that does cylinder work around KC anymore.  Thanks for the contact info, I will give them a call.

Steve