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Engine overhaul practices then and now?

 
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rwahlgren



Joined: 15 Aug 2003
Posts: 139

PostPosted: Tue Aug 07, 2018 10:35    Post subject: Engine overhaul practices then and now? Reply with quote

I'm curious how much has changed in overhaul practices on engines from back in the day they came off the assembly line, to the present?
I'm sure there have been various service bulletins that have updated parts and techniques to use during overhauls. And then there are non approved by the manufacturer, parts that are now used on some of the inline V engines like Merlin and Allison. How about things like sealers?
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kmccutcheon



Joined: 13 Jul 2003
Posts: 197
Location: Huntsville, Alabama USA

PostPosted: Wed Aug 08, 2018 08:40    Post subject: Re: Engine overhaul practices then and now? Reply with quote

rwahlgren wrote:
I'm curious how much has changed in overhaul practices on engines from back in the day they came off the assembly line, to the present?
I'm sure there have been various service bulletins that have updated parts and techniques to use during overhauls.


I don’t have experience with overhauling big engines, but I have done quite a few general aviation engines. You are correct about service bulletins/letters/instructions, issued by manufacturers, that introduce new parts, inspection techniques, materials and processes. Continental service literature, not including overhaul and parts manuals, forms a stack about 4” high; Lycoming is twice that.

rwahlgren wrote:
And then there are non approved by the manufacturer, parts that are now used on some of the inline V engines like Merlin and Allison.


In my GA experience, there are usually several sources for cylinders, pistons, rings, valves, springs, gaskets, etc. These all carry FAA Parts Manufacturing Approval, which is a combined design and production approval for modification and replacement articles that allows a manufacturer to produce and sell these articles for installation on type certificated products. I expect replacement parts for Merlins and Allisons should be similarly approved.

rwahlgren wrote:
How about things like sealers?


These have also changed over time. For example, most GA engine crankcase parting surfaces were originally sealed with a silk thread and Permatex No. 4. Some manufacturers have switched to newer sealants for this purpose. The important thing is to follow the manufacturers recommendations, otherwise you put your license at risk.
http://www.aero-news.net/index.cfm?do=main.textpost&id=c9a9aeb5-b68e-4724-834a-91d35f8e32e6

Continental publishes a list of approved sealants. Please see
https://www.cessnaflyer.org/maintenance-tech/item/815-continental-motors-inc-service-information-letter-sil-99-2c.html

Lycoming also. Please see
https://www.lycoming.com/sites/default/files/Alternator%20Crankcase%20Parting%20Surface%20Sealants.pdf
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