Hi All

Replacing crank seals and bearings in a 240 because it smokes excessively from exhaust and had less oil in the gearbox on draining it after 4 trials.

My question is which way round should the left hand inner crank seal go in?

The one in the bike was fitted spring / open / concave face towards the middle of the engine also on the picture attached (from an old italian magazine test) although not a good image looks like it may be in this way too.

 

But exploded diagrams of the engine show the seal flat side with numbers on it facing inward towards the middle of engine / crank chamber.

 

The reason I ask is that I have completed rebuild and run up engine and it still smokes badly at high rpm ,Is it still sucking oil from gearbox as seal is in the wrong way round?

 

Also as a addition ,when fitting the centre gasket I wasn’t that happy with its fit but thought it was just a bit poorly made and it seemed to seat nicely as I closed the cases down.

Later I found an additional centre gasket in the gasket set ,turns out there are two types!  Does anyone know what the difference is between the two?

 

Cheers Roy

 

 

 

Traditionally the spring/open side always faces inwards, but ive seen a few engines (some older Japanese stuff) that specifically call for the reverse on the transmission oil side.

Edited February 24, 20251 yr by faussy

The spring/open side faces inward so that when pressure is applied from the compression of the fuel mix in the bottom end it energises the seal.
If it is the other way around only the spring/material strength is what is creating the seal which should be enough to keep out the air or gearbox oil which is not under a relatively high pressure.