Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Narrow pulley conversion

I can see the advantage of a larger engine pulley to get the alternator (another useful conversion) idle revs up but why a narrow pulley unless its to match the alternator one

The wider belt has a reputation for causing premature wear to the dynamo and water pump bearings. My 1954 Plus 4 retained the wide (3/4") belt but I was careful to not have the belt too tight.

Tony

I’m not sure the mechanism behind the excessive wear argument but I have read that in multiple locations.

To me it’s more compelling argument that the wider belt is a specialty item hard to find and the narrower belt you can find anywhere, and is easier to change.

Might the wider pulley setup cause excessive wear because the thicker belt allows one to make it tighter than it needs to be? So not so much causing the wear but rather setting conditions for it?

Yes, Nelson G, too much tension relative to the area of grip may be the reason, plus of course the availability issue. Availability is less of an issue now that most folk can buy from a belt supplier on the internet rather than hunt around motor factors.

Any other Plus 4 owner have a shelf filled with worn out water pumps?

Arwyn

Richard its not narrow pulley as in diameter its narrow regards the thickness of belt required...

Hello all - can anyone educate me about the proper water pump pulley for our TR4A engined plus 4s?

My nut is a nyloc, 1/2” across the faces (which would normall fit a 5/16” bolt). The shaft is 20 threads per inch.
This is clearly an unusual size but not unheard of. When I search alternatives I find that M8-1.25s are very close (20.3 TPI vs 20; major dia. 0.315 vs 0.313).

I bought a pack - when I try to hand turn it, it doesn’t really go easily - stops on first turn and I wound have to wrench it. My old nut just turns easily. Am reluctant to force this new nut.

Anyone encounter this before, and if so what did you do?

I've a narrow belt conversion on my 1968 Plus 4 and the nut that secures the pulley to the pump is 1/2 BSF.

Arwyn

Thanks Arwyn - I think my pump is a very old replacement. 1/2 BSF is 16 TPI. Mine is definitely 20 TPI.

I have a plan:

1. I managed to find a shop that sells 5/16-20 nuts - 4 on the way. Straight-eight.com, they specialize in Deusenbergs and pre-war cars.

2. A 5/16-20 tap is on the way. I’ll use it to chase the threads on my M8-1.25 nuts and then can compare.

Could always slice up some hex bar and make my own, but we’ll start with this. The fact that they even make a tap means this size has been used, albeit rarely.

Once am done with this pulley business I can get back to refitting my new crosshead. I’ve replaced the timing chain and tensioner, water pump rebuilt and back on. finishing my C40 rebuild now as well. Slow and steady wins the race.