Technical Faulty Fan/Impotent Impeller

[fiat500]

....all correct. I think there's meant to be what Axel Gerstl (Suvvern prices...1 Euro 20 each) calls "rubber pad" each side, touching the fan. In this example it looks like the steel shim washer was outboard of the one on the cone side. They could fit either side.
I've always thought they were positioned in a way to space the fan away if it was catching the cowling. But if that was the case I would expect them to be thicker, although there may be thicker versions. In reality they would only serve that function on the side nearest to the alternator.

I measured the length of the boss and the depth of the housing that it goes into and there's just enough clearance that they don't ground on each other even without the impeller sandwiched between. So my theory that maybe this conflict was preventing the fan being tightly gripped is wrong if my assembled engine is the same.. But to be safe I'm still going to pack the setup on my engine with this spare spacer as a precaution.

PS. My plastic washer needs a bigger hole.

I'm quoting myself just to fill in a bit more information. Someone on Facebook was struggling to get his impeller/fan tightly clamped to the alternator and it was snagging on the cowling. As from memory, I couldn't be sure exactly what components should be fitted and because I wanted to help and to fully understand this myself, I removed the assembly from an old engine which has probably not been dismantled before.

I was surprised to find that not only did it have two, very robust "fabric" washers, there were also three steel shims between the side of the impeller which faces the alternator and the clamping boss. As a set, these shims measure about 2mm.

The use of shims obviously prevents the fan from rubbing on the cowling and will not always be needed, nor if used, will there always be three of them. But this may be a useful point to record for future passers-by.

 

[Bleeding Knuckles]

I'm quoting myself just to fill in a bit more information. Someone on Facebook was struggling to get his impeller/fan tightly clamped to the alternator and it was snagging on the cowling. As from memory, I couldn't be sure exactly what components should be fitted and because I wanted to help and to fully understand this myself, I removed the assembly from an old engine which has probably not been dismantled before.

I was surprised to find that not only did it have two, very robust "fabric" washers, there were also three steel shims between the side of the impeller which faces the alternator and the clamping boss. As a set, these shims measure about 2mm.

The use of shims obviously prevents the fan from rubbing on the cowling and will not always be needed, nor if used, will there always be three of them. But this may be a useful point to record for future passers-by.

Hi Peter, I suffered the same predicament when assembling my bambino housing, even though there were only the two rubber/fabric washers the fit onto the rear half towards the alternator was rubbing badly so I had to obtain some 0.5mm shims to build up the required clearance. I did find that when fitting up the front half of the housing, it was necessary to 'dress' the bottom of the air intake tube to gain clearance for the fan otherwise it would rub a little. My fan did rock on the mounting slightly, but luckily when fully tight this stopped. It goes to show that there is a deal of trial and error to get it right.
Ian.