Prop hub/flange

[Chopperman62]

Are there any known problems with the crank or prop hub on the VW engine?

[Neil Spooner]

It’s the weakest part of the engine. In my mind the “Peacock” shrink fit flange on the nose of a stock VW crankshaft is an accident waiting to happen, especially on an aerobatic aircraft.
The nose of the crankshaft was designed to support a pulley driving a fan and dynamo. Where the bolt goes in to the nose of the crank reduces the thickness of the crankshaft to about 3mm.
My Nippers utilise the “Force 1” hub obtainable from Great Plains or Hummel Engines in the USA. You will need to have the crankshaft ground with a 3 degree taper to accept the hub, and have the crankcase nose machined to accept the front bearing. This creates a strong conventional support for the prop.
There are quite a few reports of crank failures.
For the ultimate engine use the Force 1 hub, counterweighted crank and Nicasil cylinders as per G-ONCS & VICA.

[Neil Spooner]

If you do keep the “normal “ flange use the lightest prop you can find. Hercules are very good.
Phots show the nose of a stock crank being crack tested.
The owner of this engine has to sign a disclaimer before I will release it.
Failure usually occurs either at the key way or the groove for the circlip.
Unusually this crank has had a taper ground for a tapered flange. Most of them are shrink fit. The flange can only be removed a few times before the flange is scrap due to insufficient pinch.

[Neil Spooner]

These are photos of the nose of the crankshaft that came from G-ARXN which shows what happens when the pinch is insufficient. The flange and shaft have been fretting. The disturbing thing is that the “tinkerer” had had problems removing the flange and had drilled a hole down the side of the crank & flange…..and the reused the assembly. The hole doesn’t show in these photos.
This crankshaft would have failed fairly soon if I hadn’t condemned the whole aircraft due to multiple issues after the previous owner had been tinkering.