Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Underdrive Pulley

Latest little bolt on addition to my Crossflow is an underdrive pulley.

It's a smaller diameter main crank front pulley - supposed benefits are:

1. Alloy, so stronger than the original welding steel (they have a habit of breaking up)
2. Smaller diameter means that the Water Pump and Alternator spin at a lower speed so less strain on them
3. The reduced spin of the ancillaries can possibly relate to an increase in usable bhp due to less draw.
4. Reduced weight of the front pulley will help her spin up a bit quicker (same as the lighter flywheel)

Fan belt is OK on furthest setting, so ordered a shorter one so I get a bit of play. Fitted an alloy water pulley at the same time.

Interesting. Could this not have an impact by overheating by not circulating the coolant as quickly?

Unlikely - if you think, a standard car is cooled effectly at tick over (850rpm) - most of the time the engine is revving around 2-3000rpm - more than ample.

If the car was 'hot running' or had an ECU with a stack of battery draining electronics, then there may be issues.

Shhhhh!
I need him to save up for a radiator next 🤣🤣

That'll be the next christmas present to me

🤣🤣🤣

I too would be a little concerned not just with coolant flow but with charge rate as well. It could be that at idle the charge warning light comes on. During heavier electrical loads the alternator regulator will attempt to drive the alternator harder leading, maybe ironically, to greater belt loads. This can also lead them to make a noticeable whine until the rotor speed approaches at least 2500 rpm

Finally the smaller pulley will offer less traction to belt due to reduced surface area in contact with same leading to possibility of belt slip and increased wear.

If the new pulley is just a modest reduction you may get away with none of above issues but worth being wise to possible consequences.

Don't worry - lots of research done before purchase!

Remember, this is a 1972 Crossflow - so little electrical drain. I have the addition of electronic ignition, but also have LED lights all round. Fan has been removed and converted to electric but only tends to come on if I'm running for 30+ mins on the drive. I do have a new uprated alternator.

Everything was running fine at 850rpm this afternoon - ammeter showing charge and Voltmeter showing 14+V. Slitght drop when I bunged the heated seats on, but I got this with the old pulley as well, so no great shakes Charge light stayed off.

Belt it right at its length limit so going to wait till the shorter one arrives before I test on the road.

1972 4/4 with heated seats, now there's posh !!!

Dead posh!

I had all the seats retrimmed (as the original leather was on its last legs) and thought I'd have heated pads stuck in at the same time - all in cost £760 (£40 for the heated seat panels) which I thought was money well spent. With the uprated heater I plumbed in, it's now very comfortable!





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