Thor engine mount loosening

by Had Robinson

The engine mounting bracket which connects the engine to the lower two mounts on the frame WILL eventually loosen.

Six 6mm cap screws hold the bracket to the engine.  They also hold the crankcase halves together.  Unfortunately, Polini did NOT use threadlock on these critical fasteners.  The intense vibration of the engine and the pull forces of the starter will work together over time to loosen these cap screws.

At 250 hours, a Thor 130 experienced loosening of the upper cap screw.  Two of the other six were also beginning to loosen!

Polini Thor loose engine mount

As the uppermost cap screw loosened, it began to rub against the flywheel and became very hot from the friction, hot enough to deform the screw and make it impossible to insert a hex bit into it.  When a loose cap screw touches the flywheel it can also distort the screw hole, which it did here.  This will weaken the ability of the fastener to hold the mounting bracket securely to the engine.

capscrew damaged by flywheel

THE FIX: The front of the engine will have to be exposed, the flywheel removed, and the cap screws removed and reinstalled with blue threadlock.  If any of the screw holes are damaged, a HeliCoil may be required.

HOW TO PREVENT: The first time the starter is replaced, perform the fix above.