Poor Starting 912iS

James Porter

Change the Gearbox

After 2 years of fault finding we eventually changed the gearbox and this cured the poor starting problem.

This problem seems to be known by BRP-Rotax but they are not telling anyone.

It seems that when the Gearbox is Manufactured / Assembled using Belleville washers, the tension is too

tight. This caused too much load on the engine, which prevents it spinning fast enough to allow a normal

start. Once the engine has started and warmed up it will start OK, until it cools down. I know a weird fault

but it all makes sense now.

Hope you get it sorted,

Regards,

Malc

Buckminster Gliding Club

Saltby Airfield

Lincolnshire

UK

Hi James,

What was your gearbox tension? Does your engine have a black colored or gold colored starter?

The gearbox belleville washer tension has no bearing on the engine load. The gearbox and engine are separate entities in this case. The tension in the gearbox will only affect that portion and is controlled by shims.  The shaft in the gearbox is on two bearings. Up front by the prop flange and back above the main case. The only way the gearbox could cause a load change is if one or both bearings were bad which personally I have never seen unless there had been a severe prop strike.

If the tension in the gearbox is way too low then it tends cause wear on the gears and dogs. I haven't seen one come from the factory too low and have never even heard a rumor of such.  Gearbox tension I see in the field is 440 - 495  in/lbs. (460 - 485 being average)