I have a 3.8 that does not charge well at idle after the generator was done. But up the RPM by 300 and it charges great.
I don’t know what has happened over the past 60 years with this car. It has the double groove belt.
my question is, will the double grove pulleys from the 3.8 and 4.2 interchange? or are offsets different.
If they will interchange, what are the pulley sizes for the crank and Water pump. I would like to measure mine and see what I have, then if I can get a slightly larger pulley, do that so I can spin the generator faster. Generator pulley only comes in one size from what I can see.
Also, if the water pump can have a slightly smaller pulley, I would like to do that for better cooling.
My crank pulley is about 131 mm diameter X 35mm deep, the water pump is about 144mm in diameter X 47mm deep and the generator is about 80mm in diameter X 31mm deep. These are within about 2mm I would think. I am measuring in the car, so they may be slightly off.
I can’t help with any pulley size information, but my 3.8 must have had a change in size of at least one of them because niether the 3.8 nor 4.2 belts would fit. One was too tight and the other ran out of adjustment when the generator met the frame rail. IIRC, the grooves were the same size and spacing so no issues there. Back then (70’s) it was a bit harder to track down parts in NZ so I just had the pulleys turned down to take a regular V belt; never had any issues with slipping\squealing, and replacements were easier to source from regular suppliers, although I never had to replace that one. Pity I never did it to my 4.2, as it threw a belt on journey, had to be trucked to the next town and await a new belt, which took a couple of weeks. Then a 400 mile round trip to pick up the car and repair. A single V belt would likely have been available locally.
Hi Burton, I went through all of this about a year ago and it turned into a bit of a sh*t show with one thing leading to another … a new too tight fan belt resulting in a destroyed generator having to be replaced with an alternator etc.
One more thing…I did search for different belts as I hoped to find one that would work and compiled some other dimensional info that might be helpful…
Duplex Pulley Belt Number Circumference Outside Circumference
as stated in parts catalog as measured
C19523 (for Mk2) 940 mm 949 mm
C19524 1010 994
C19525 1050 1044
C24291 (for 4.2) 1100
Steve! I had the same problems, that’s why the Generator was rebuilt! Tight belt, destroyed rear bearing. In order to fix that problem I spaced out the generator bottom slightly and now with a longer belt the tensioner works and it sits correctly.
Just finding out if there are other dimension pulleys available seems to be the hard part. My pulleys are the same size as yours, so looks like we do have the same set up. By why belts don’t fit and the generator spins just a little too slow is still the big question. I think the 4.2 crank pully may be a little more shallow, I just don’t know its diameter. I could build a spacer… if the pulley was slightly smaller, then the smaller belt may fit, but the generator would be slower. So hopefully I could make a 4.2 fit, and it would have a slightly larger diameter.
Generators are always set so that at idle they provide very little if any charge …… that is why when the lights are on and you rev the engine you get a “flare” in the lights and better lighting …… I’m not sure of the reason the generators work this way but someone with better electrical knowledge will be able to give you the technical reasons
I have a bone-stock 3.8 E-type with its original date-coded generator (rebuilt, of course) and I can tell you from four decades of experience that the generator absolutely does not charge the battery at idle. Your system is performing normally.
Go for a drive, get those revs up and if the amp meter goes positive you’re okay. Find something else to worry about.
[quote=“REBUILD61OTS, post:6, topic:421420”]
… I’m not sure of the reason the generators work this way
A Generator spins at low speed so it doesn’t come apart at high Rpm don’t change the pulley unless only your grand mother is driving it
The hot rod boys will tell you that things happen above 5000 rpm
Birds nest
When these cars where designed they didn’t figure on 2 hour traffic jams and Craig tape decks
We don’t drive these cars enough so if your really worried about charging, drive it more or
Use a 3 phase charger from time to time , you can leave it on it will float charge
Or get an alternator
IMHO Cheers
You guys are great. I am still curious about pulley sizes, just because I am a curious guy. So if anyone could ever tell me about it, I would love to hear about it!
All I know is the 3.8 generator and the 4.2 alternator setups required different-length belts. I don’t think the crank pulleys were different, nor was the water pump pulley.
I think…
The alternator pulley was smaller, IIRC, and the alternator being mounted higher likely was the reason for the longer belt.
Jim the other difference is that most generators ( other than mill spec) used sintered bronze oillite bushes ….all alternators I’ve seen use full ball race type bearings …… and this is also why the pulley is smaller so that they can spin at higher speeds
Yep Lucas called that “special equipment” same with the stuff put into Rolls Royce etc…… they also did distributors with ball races ….I think the mark V at least had them
You reminded me: the generator for my parents Silverstone race car, also had ball bearings front and back. The case was also multiply drilled for lightness…
