> Jensen Healey & Jensen GT Tech > Cooling > The JH Water Pump

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Mark Rosenbaum

Joined: 03-12-2005
Location: Kingman, Arizona USA
Posts: 532

Originally posted August 2004.

I've been looking at JH water pumps recently, and have learned a few things of interest which are presented below. My examinations involved only a limited number of water pumps, so some of my conclusions may be incorrect.

I will note here that the Lotus part number system uses the prefix letter to indicate a significant change (revision) to a part, while the suffix letter indicates the part's manufacturer. Unfortunately Lotus could not always be bothered to use their own system correctly.

Water Pump A907E0743W, others.

The JH parts books I've seen state that the JH used the same water pump (Jensen part number 93659) throughout its career. Whether this is true or not, the part -- and presumably the Lotus part number -- clearly changed during JH production, as is demonstrated below.

In addition to the water pumps used for the JH, there are several versions designed for use with Lotus cars having 907/910/912 engines; of these, some will doubtless work on the JH, while others may not. For lack of better terminology, I'm currently calling these the 1-extra-port, 2-extra-port, and many-cast-brackets varieties. I also have a few part numbers which may, or may not, relate to these pumps: D907E0743W (cars without air conditioning), C907E0878J (cars with air conditioning), D912E9274J.

The Lotus 907 engine's water pump consists of several subassemblies: a cast alloy housing, a shaft seal, a cast iron impeller, a shaft-and-bearing assembly, a pulley hub, and (for the early pumps) a circlip. What I know about these parts is presented below.

Water Pump Housing A907E0219Y.

I have not yet seen a sample of this casting, but presumably it resembles the drawing in the parts book. Apparently this is the only housing variant with provision for a circlip to hold the shaft-and-bearing assembly in place. I do not know the location of the cast-in boss for the seal failure drain hole.

Section A14 para. 4 of the JH shop manual states that the circlip -- and by implication this housing -- is used on 'early engines only'. It is left for the reader to decide which of the shop manual's several definitions of 'early' applies in this particular instance.

Water Pump Housing B907E0219Y.

In this casting, there is no provision for a circlip and the cast-in boss for the seal failure drain hole is at the bottom of the pump. It appears otherwise identical to the drawing in the parts book.

Water Pump Housing B907E0219G.

In this casting, there is no provision for a circlip and the cast-in boss for the seal failure drain hole is at the _top_ of the pump. This casting also has an added boss and hole just below the thermostat housing, and would be suitable for a 1-extra-port water pump as mentioned above. In my case, though, there is no spigot for a hose, and the hole is sealed with a small freeze plug.

This particular housing is part of the water pump on my car, presumably installed by some previous owner. As best I can tell without disassembling things, the number cast into the housing is B907E0219G. However, according to the Lotus part number system, there should be no significant differences between casting B907E0219Y and casting B907E0219G, so conceivably the first letter in the part number could be an E, F, or G.

[UPDATE 09 Sep 2004: A water pump that appeared visually identical to the one on my car was recently offered for sale on eBay. I made an inquiry of the seller, who informed me that the casting number on their pump was E907E0219G. From this I conclude that the pump on my car is most likely an E revision unit.]

[UPDATE 08 Oct 2004: The water pump in my car has a SECOND seal failure drain hole on the bottom of the pump, in addition to the one at the top of the shaft housing.]

I presume that this housing was designed after the end of JH production and was intended for use only on Lotus cars, perhaps as part of an improved water pump with better flow characteristics. If so, this might explain why my car's cooling system, which (so far as I know) is otherwise parts-book stock, works well even in ambient temperatures of 100^F.

Water Pump Housing C907E0219G.

In this casting, there is no provision for a circlip and the cast-in boss for the seal failure drain hole is at the bottom of the pump. There are some dimensional changes compared to B907E0219Y: (a) the thickness of the engine-block flange has increased from 0.215" to 0.256"; (b) the width of the flange sealing surface has increased from 0.280" to 0.330"; and (c) the thickness of the thermostat housing flange has decreased from 0.275" to 0.250". Clearly this pump would offer a better seal to the engine block than a B907E0219Y housing.

Impeller A907E0220Y.

This is a conventional six-vaned impeller that to my eye looks like cast steel rather than the more usual cast iron. It's fairly heavy (maybe 0.5 pound?), measures slightly under 3" diameter, and is a press-fit onto the 0.5" end of the shaft-and-bearing assembly. The design seems quite unsophisticated even by 1970s standards, and doubtless could be considerably improved (i.e. more flow for less power). While there are a couple of letters and numbers cast into the vaned surface of the one impeller I have examined closely, there was nothing that seemed to relate to a Lotus part number.

Normally there is only 0.020" to 0.030" clearance between the impeller vanes and the pump housing, so if any debris in the coolant reaches the water pump, it can get caught by the vanes and dragged against the housing. A hard material would abrade the housing very quickly, reducing the water pump's efficiency, perhaps even to the point that it quits operating entirely. I have an externally beautiful water pump housing that has been rendered useless in just this way.

Shaft-and-bearing Assembly A907E6033W.

Probably due to the precision of assembly required, this item is furnished only as a unit. The shaft is 4.794" long overall, and consists of an 0.625" diameter end about 3.05" long, an 0.500" diameter end about 1.25" long, and a relief section about 0.48" diameter in the middle.

The bearing cylinder is 1.180" diameter and 1.532" long and presumably is pressed onto the larger-diameter section of the shaft at the time of manufacture. There are two circumferential grooves on the cylinger, one for the circlip, the other for some unknown purpose. Presumably all late-production bearing cylinders are grooved to accept the circlip required by 'early' engines. In the examples I've seen, whatever bearings are inside the cylinder are lubricated with a yellow grease. Each end of the cylinder is closed by a rubber seal bearing a four-digit date code in (probably) a year-and-week (YYWW) format.

According to section A49 para. 1 of the shop manual, between the removal of the circlip and (approximately) engine number #11345, the bearing cylinder was a loose fit in the pump housing and had to be secured with Loctite, while for later water pumps it was a press-fit into the housing. The Lotus part number system would have required a revision change for the water pump assembly, and (if and only if treated as a separate entity in their manufacturing process) the machined pump housing, but not the raw casting (unless other changes were made to it at the same time). It is uncertain whether Lotus bothered to follow their own system for this change.

Pulley Hub A907E6096Z.

The early version is a turned steel disk some 2.59" diameter and 0.313" thick. Rising in the center of the disk is a round boss 0.916" outside diameter and 0.600" thick overall, which is bored to permit a press-fit on the 0.625" end of the shaft-and-bearing assembly. The hub has four equidistant 6mm x 1.0 threaded holes on approximately 2.20" centers (probably intended to be 56mm). Later versions of the hub are 4-lobed-cloverleaf in shape.

There doesn't seem to be anything at all special about this hub. I'd imagine that anything that could be made to fit, if combined with a suitable fan and pulley, would serve. This opens up many possiblities, for example, the fitting of readily available viscous-coupled aftermarket fans.

Thermostat Cover A907E0479Y, B907E0479Y, others.

These are light alloy castings without cast-in numbers. In the JH, engines up to #2760 used A907E0479Y while later ones used B907E0479Y. Both versions bear the same Jensen part number, 91485, in the online parts book. GTs use a different part whose outlet heads to the right of the engine, rather than the front, but I don't have a GT parts book on hand and thus do not have any part number for that version. From photos, there are additional variations used in Lotus cars.

The JH parts book drawing does not show a boss under the neck of the cover, but this boss is present in all the actual parts I have seen. Some of these have a 6mm stud installed there, others do not. There does not seem to be any need for this stud on the JH, but perhaps some early 907-engined Lotus required it, and thus the part was changed. So, as supposition and without proof, I wlll presume that bossless covers are A907... parts, those with the boss and without the stud are B907... parts, and those with boss and stud are C907... parts.

In any event, this is what I've discovered to date. As always, I welcome any additional information and/or corrections.

Attachment: water pump 1.jpg (Downloaded 225 times)


Joined: 03-13-2005
Location: Monmouth, Illinois USA
Posts: 33
While dismantling the engine, the bolt directly above the pulley on the waterpump snapped off.  I can not get the pump off and was wondering if that bolt is threaded into the housing or what exactly is not allowing me to pull it off.  any ideas?


Jensen Healey
Super Moderator

Joined: 03-11-2005
Location: San Anselmo, California USA
Posts: 983

I had the same problem and it was just good old fashioned rot caused by dissimilar materials, water, and not changing the antifreeze. I had to drill it out.


Jensen Healey
Super Moderator

Joined: 03-11-2005
Location: San Anselmo, California USA
Posts: 983
Is it time for my yearly rant on antifreeze? I have removed the head from my spare motor and it's water passages were completely plugged at the head gasket! The white deposits fill the area around the cylinders on the low side. This is the second motor (out of four) that has been clogged like this.

Come on folks! Put some new green stuff mixed with distilled water in there every year and keep your cooling system working. Don't use the orange long life stuff.

If you have summer overheating issues, reduce the antifreeze to 15% and add a bottle of Red Line Water Wetter.


Greg Fletcher

Joined: 03-11-2005
Location: Lake Nacimiento, California USA
Posts: 421
Good point Kurt! It's always so sad to see this kind of damage that can easily avoided by some simple maintenaince. Remember that a very small amount of anti-seize on those bolts can go a long way in keeping them from snapping off at a later date.

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