Gentlemen –
It is nearly impossible to replace a Permold starter adapter correctly in most aircraft without dismounting the engine.
Yes, it’s a pain, but it’s the only way to do it right.
Starter adapter studs are an interference fit in a thru-hole in the crankcase.
The interference fit damages the threads of the stud and the hole.
In addition to the interference fit, studs are installed with Loctite 271 – it makes the installation “permanent” and contributes to sealing the hole against oil leakage.
Instructions for removing a stud installed with Loctite 271 include raising the temperature of the assembly to about
400-degrees F to soften the adhesive. Nine times out of ten, removing a stud without heat will also remove aluminum from the threads – if the stud doesn’t break at the first exposed thread.
Nominal-size steel bolts – for example, AN5-40A – will not achieve proper thread engagement in a new stud hole, much
less a deformed one. Without proper thread engagement, correct fastener torque cannot be applied and maintained.
The overhaul manual (M16) lists a number of approved repairs for damaged threaded holes.
The starter adapter stud locations are not addressed.
Neal
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The problem for us is that the adapter is fixed to the block with studs. But we do not have enough room to withdraw the
adapter backwards and clear all of the studs – I think was two that wouldn’t clear. I can’t recall which, but once you look at it, you’ll see which ones they are. So – I removed the offending studs with a stud extractor – took a bit of doing as I assume the
studs are installed with super Loktite or similar, but they came out OK. Withdrew the adapter, and my Lame fitted a new shaft and spring which luckily for me was provided by TCM under a warranty claim. Meanwhile – removed the other studs, and then reinstalled
the adapter with a set of properly spec’d bolts (length etc critical of course) instead of the two above offending studs.
If the adapter ever fails again – it will now be a very simple job to remove the starter adapter.
I guess I should caution that I don’t know if what I did is endorsed by TCM – it may be, but I don’t know; I did check
with my LAME and he considered it fine, but your call of course here!