Guys, I have a choice of two water pumps to use on my '50 OTS. I’m undecided on which would be the best to use. Can I get some opinions here?
The one on the left is a new C6746. Its hub means I’ll have to use a later fan. That’s okay, I have a nice example ready to go. I like the fact that the impellor shaft is of a larger diameter – thus taking a larger seal – but I don’t see any way to rebuild it when it eventually fails down the road. For instance, what holds the impellor and fan hub on to the shaft? I don’t see any slotted split pins on the impellor or fan hub. Is this all just a press fit? On a side note: this one came to me from one of the usuals. The bypass port boss face was unmachined or, as cast from the foundry. As a result, when test fitting the brass banjo to it, it was glaringly obvious that there wouldn’t be a water tight joint here. Not an issue for me as I was able to clean up the face using my mill but if I didn’t have access to one, I’d be highly… displeased.
The one on the right is C4938. Not new, but it has been rebuilt in the past few years. Correct for my year car and I do have a five blade cast aluminum fan and pulley to match. I’ve been told that these tend to leak though and the shaft is of a noticeably smaller diameter. Also, the rebuilder didn’t do the best job with maintaining the distance between the impellor and water pump body before drilling the shaft and fitting it with a tension split pin. The book calls for 0.015" clearance but I measure about 0.030 - 0.035" clearance. How critical is that?
So this is where I’m at. Anyone else here faced with different water pump choices? Does one cool noticeably more so than the other? Any other pros and cons for each?
I’m guessing that the later C6746 reproduction pump uses the later 1950’s-60’s sealed bearing. The impeller is a press fit, no key or split pin.
The snout on the early pump is a lot like a full-floating axle in a heavy truck. The fan hub and bearing mount to the pump housing and drive the impeller via a drive dog. So although the shaft is smaller in diameter, it does not carry the transverse loads from the belt drive, only torsional loads from the rotating impeller.
I would think the biggest difference is in the performance of the two fans, not the actual pump design.
The earliest pump had an impeller with four vanes on a 3/8" shaft with ordinary ball bearings, driving dog, spring and a graphite seal, same as the pushrod engines.
The later pumps had impellers with five vanes, and still with the 3/8" shaft and driving dog etc., but beginning with the 140 they were on a 5/8" shaft with integral bearings and seal, the hub and impeller pressed on.
The one with the four bolt hub is a later mid '50s to '60s version for 120 made with the 140 style integral bearing shaft. It appears to be the same as the one on my car, which has cooled it reasonably well for 30 years.
However, I did have to replace the integral bearing shaft once, which I got from one of the well known vendors, and not long after that my hub came off the shaft and the fan scraped the radiator. The pulling force of the fan pulled the hub off. Apparently the diameter tolerances of the 1960s era hub and 1990s era shaft were not quite compatible for a tight press fit. I drilled and tapped the hub for a set screw (UK = grub screw) and put a notch in the shaft for the screw to grip and hold it.
So unless you are going for those last few concours points, I would go with the later pump and six blade fan.
Also I would not trust the press fit of the hub, but would add a set screw.
Yes, at the very least the early fan will turn at a slower speed compared to later ones. The pulley on my early fan has an outside diameter of 5.5" as opposed to 4" on my new, later one. Something that could make a difference when idling in hot weather.
Thanks for the benefit of your experience on this Rob. I see that the shaft stands about 3/16" proud of the fan hub on this new, later pump. So, I’ll take your idea and simply drill through the shaft and press fit a split roll pin (1/8") leaving enough of the pin protruding from the shaft on each side to keep the hub on. I don’t want to have to remove the fan hub from the shaft if I don’t have to.
And yet, what is there to keep the shaft from pulling itself off of the impellor? I’m still reliant on the impellor/ shaft press fit?
I’ll answer my own question by observing that an old spare I have – C7452 – also has no pins on the impellor, so, I’ll speculate that all later water pumps had the impellor end fitted to the shaft with a press fit only.
okay, it depends what you mean by work best?
and have you increased the power of your engine in any way during the rebuild?
more power is more heat in my book and the later fan would be better.
I have had both pumps and fans on my 1951 car.
with the original 5 bladed pump and fan, my car did overheat on a cool, rainy day in England.
after installing the later pump and fan, I have not had a problem and the cooling is much more efficient.
the early pump has a different pulley as well and the fan turns more slowly…less cooling.
I’d love to use the early fan as it is much prettier but it does not cool sufficiently and my driving would need to be much more cautious.
Right, experiences like yours adds to my decision to stay with a later pump. I’m all for keeping the car original, but far less so if it means sitting on the side of the road waiting for the temperature or traffic to die down. I’d like to use the earlier pump, but the bolt circle diameter of the cast fan means not being able to use a pulley smaller than 5" turned on my lathe. Maybe down the road I could fabricate some sort of adapter if truly motivated, but for now the early pump, pulley and fan will continue to sit pretty on my garage shelf.
