Topic: joining case's using thread

[paddy paul]

  I was watching How it's made on the science channel this morning and they were showing how they build 4 cylinder airplane engines and when they put the engine case's together they put a line of thread all the way around the case after they put the bonding agent down.. Has any body ever heard of this before?   I never have come across this in any of my years working on engines, Gas or Diesel.  Is this a FAA type of thing or was it just a manufacturer's spec... They said it helped the engine from leaking oil at the case seams... could this be applied to our engines, I just thought it was really strange....... 

[CycleRanger]

Fascinating.  Apparently silk thread has been used to seal air-cooled aircraft engine cases for decades. 
I did not know that.  Googling finds a bit more info about the practice.

[mystic_1]

could this be applied to our engines, I just thought it was really strange....... 

Seems to me like that may throw off various clearances in the engine, Honda engineered things taking into account the thickness of the OE case sealant.

mystic_1

[paddy paul]

It did seem strange to me, the case's that they were assembling had a flat machined surface without a grove for the thread and it was a pretty thick one at that, I'm going to google it today when I get some time and try and see what the reasoning behind it is, as for doing it to my engine I think I will stick with the way Honda did it, plus How often to you actually see the case's leak there on these bikes, if they are put together correctly.

[mystic_1]

plus How often to you actually see the case's leak there on these bikes, is they are put together correctly.

True that, I've never seen a leak at the main case seam.

mystic_1

[Blackhorse]

As a former FAA certified A&P (airframe and power plant) mechanic and an instructor we used "00" silk thread on all our overhauls of Avco-Lycoming O-320 air cooled reciprocating engines at the crank case halves. The crankcases were machined as a butt joint (flat no over lap) as opposed to the overlapping joints we see in today's turbine engines. The joints were aligned with specifically located body bolts and the thread acted as a dam should any fluids try to leak past the gasket bond that was also placed in between the joint. This was the manufacturers requirement as per their overhaul manual, not the FAA's

[paddy paul]

Thanks, Black horse and Merry Christmas from the family, good to see another Robert Earl Keen fan...

[gane]

Have heard/used "carpet thread" w/sealer on English machines,(vertically split) but never encountered leaking w/just a light skim of sealant on Japanese goods. On all the japanese plain bearing 4's I'm familiar with the case halves are the holders for crank main bearing shells. Thus anything you put between them would affect bearing tolerances. in short, don't... My 2 cents. G