Fan belt sizing

[bystander]

I agree with Tony, the top pulley is the problem. If you change it for an early coil engine one (the long one - later types are shorter, and will sit further back from the radiator, but would probably be efficient enough anyway)) the problem should be sorted, and the fan belt you already have will fit comfortably. If fitting a reproduction pulley make sure the bushes are bronze and not brass, otherwise rapid wear may ensue.

[Reckless Rat]

Leave it loose too.

[Parazine]

Once, years ago, I made a top pulley with a small AC pair of ball races fitted. Took ages but it was nice and it's still running, my friend owns the car today.

[AustinWood]

Belts always run to the highest point so it is important that the face of the pulley is slightly convex, it must not be concave.
If you look at the old overhead shafting as used in mills etc, they don't have any lips on the pulleys. They just depend on the pulley faces being convex so that the highest part is at the centre.

[jamesheath]

Tony,

I had no idea the mag pulley was different! - Now you point it out the difference is really obvious - the mag pulley has a dia of around 52mm and the coil one is around 38 - a big difference!

I seem to have a spare coil pulley kicking around, so I'll fit that (ug - now I need to remove the radiator).

   

(I'll be in touch for more bits soon!!)

Thanks again for explaining the mystery!

James

[Tony Betts]

Hi james,

You are half way there.

You have gone from a mag pully to a very late coil pulley.

It will ctr the belt, and should slacken the belt. but it will move the fan away from the radiator.

Either fit a spacer, or keep an eye on the higher risk of over heating.

This is why I sed originally there must have been 3 sizes of belt.

It could be the mag belts that the workshop have supplied forever as mag engine. Could actually be for very late coil???

Thanks tony