Hi All,

I weird issue has popped up recently. I have had three different planes come in with a 912ULS for an annual. When I took the crankcase locking pin bolt out (8mm) it wasn't an issue until I went to screw in the locking pin. It threaded down to the last several threads very easy, but then got very hard to turn and it wouldn't go all the way down into the "V" to lock the crankshaft. What these three planes had in common was the use of 100LL. I believe the lead over time had clogged up the threads. So first thing is "DO NOT USE A THREAD TAP / CUTTER" to try and open the threads. Use a thread chaser. It will clean and re-shape the threads, but won't cut into them. Take the 8mm x 1.25mm thread chaser and apply either some grease or a tad of copper anti-seize and work it down into the clogged threads. Move it back and forth out of the bad thread area until the threads are all restored / cleaned. Do not use a heavy Godzilla strength and force it down inside. Just work it back and forth. The regular locking pin should screw down inside easily. For all my years doing this I have never had this happen then the last two months I've had three engines like this. 

You are supposed to remove the 8mm bolt at each annual to check the gearbox friction torque and you use this when working on the gearbox at times.....  i.e. replacing the small crankshaft gear and 42mm nut. 

Here's a picture of a 6mm and an 8mm thread chaser you can buy on Amazon. So far it's worked well.


10232_1_Rotax Thread Chaser.jpg (You do not have access to download this file.)

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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