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Lycoming SI1029D thread lubricant

Hello,

Lycoming says in its SI1029D that the studs threads should be lubricate with oil and STP or Parker thread lube.
I couldn’t find what is STP or Parker thread lube.
This SI is quite old, what is the good lubricant to use nowadays?

Thank you
Thomas

LFPE

Try searching “STP oil treatment “ and you will find it.

Quite a few performance engine builders use A 50/50 STP and engine oil mixture to lubricate bearings as they assemble engines, apparently it’s sticky enough to stay put and lubricate the bearings until full oil pressure washes it out.

Thank you for your reply.
Just to make sure it is about lubricating the cylinder base stud threads so as to torque wet well.
Thomas

LFPE

I don’t have an answer but I suggest great care in this area. Over-torquing cylinder studs is a prime reason for cylinders coming off in flight, and it happens a lot because many mechanics don’t know the difference between dry torque and wet torque. Where e.g. dry torque is specified, using any lube will result in a large over-torque.

The fact that somebody is asking this question at all is a big concern, because anybody working on engines ought to know all this immediately.

Administrator
Shoreham EGKA, United Kingdom

Yes or not asking any question is a maybe also a big concern.
I don’t say that for me as I am not a mechanic.
Thank you

LFPE
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