Lotus Elan

Water pump hub/pulley

PostPost by: EPC 394J » Sun May 27, 2018 3:54 pm

So, there I was enjoying a drive with wifey. When a clunk from under the bonnet suggested something had become detached! Pulled over to find the water pump pulley, and hub, had departed the engine bay!

A few yards back down the road, I found said pulley, and was able to re-fit it with the one securing grub screw, through the hub to contact the shaft. About 15 miles later, same thing happened again! This time, I was unable to locate the pulley/hub.

Now some questions. Should I have been able to re-fit the hub/pulley ?cold?? Should it require heat to enable it to ?shrink? onto the pump shaft?

Secondly, the bearings on my water pump are definitely loose, so at some time in the not too distant, a new water pump will be required. (Though it?s working perfectly well at the moment.) Could the vibration from the loose bearings alone, act to eject the hub/pulley off the shaft, if it was correctly fitted?

I have an electric fan, so no fan was fitted to the pulley.

Any thoughts?

Very many thanks.

Andy
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PostPost by: promotor » Sun May 27, 2018 4:05 pm

The boss that presses on to the water pump shaft should be a tight fit although you won't need heat to fit it. I have found when removing them (with a press) they let go with quite a bang.

Have heard reports of replacements not being a great fit.
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PostPost by: StressCraxx » Sun May 27, 2018 4:09 pm

Interesting. Every water pump I have had used a shrink fit pulley. A setscrew does not have enough holding force to the shaft alone because of belt vibration and torque impulse from the crank. The shaft now has some damage from the pulley and loose setscrew, so shrinking a new pulley on will need some careful preparation of the shaft without making it undersize.

Drilling a dimple hole in the shaft and using a "dog point" setscrew with loctite may effect a temporary repair, but it's still a bit of a bodge.
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PostPost by: types26/36 » Sun May 27, 2018 4:14 pm

EPC 394J wrote:
A few yards back down the road, I found said pulley, and was able to re-fit it with the one securing grub screw, through the hub to contact the shaft.

Maybe I'm not understanding but what "grub screw" are you referring to ?
The water pump hub is a press fit onto the impeller shaft ......never seen a grub screw? has someone fitted a grub screw to try to fix a loose pulley?
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PostPost by: EPC 394J » Sun May 27, 2018 4:31 pm

This hub DEFINITELY had a grub screw!

So if that?s not original, then yes, it?s been bodged! :roll:

Maybe not by the PO. Maybe by a Lotus ?specialist?? :evil:
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PostPost by: 69S4 » Sun May 27, 2018 5:59 pm

I'll bet your wife was impressed :lol:

Never had or seen a grub screw on the water pump hub. They've always been a press fit that with a bit of care and some force you can adjust to line the pulleys up.
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PostPost by: EPC 394J » Wed May 30, 2018 10:26 pm

As I say, I ?lost? the pulley and hub. I?ve returned to the site of the departure, and have been unable to find it in the grass verge.

So. I?ve bought a new hub from a well known supplier, and exactly as expected, (and designed!) it is too tight a fit, to place on the pump shaft. The question I then have is.... Is there any chance, with heat etc, of me re-fitting the hub to the shaft in situ? Reading the workshop manual, it?s clear the whole assembly is built, using a press. Not possible with the front cover in place on the engine!

Have I any alternative to removing the engine?

My Lotus replacement chassis, has had a removable cross member fitted below the sump. But I?d rather just push a new hub onto the shaft if at all possible?

Very many thanks for any advice.

Andy
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PostPost by: gjz30075 » Wed May 30, 2018 10:45 pm

Maybe, you can heat the hub (oven, grille, oxy torch, whatever) and when it it plenty hot, spray the shaft
with the freeze stuff used to free up frozen bolts. Using oven mitts, fit the hub. This may be a two man
job.

Or,

Ream out the hub for a snug fit and use the grub screw(s) method to hold it in place.
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PostPost by: Bigbaldybloke » Wed May 30, 2018 11:59 pm

I?d polish the shaft then ream out the hub and fit it with a grub screw and the relevant grade of loctite (bearing fit?). It?s unlikely to shift, especially if you drill a dimple in the shaft for the grub screw to seat in.
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PostPost by: rgh0 » Thu May 31, 2018 11:13 am

You really need as tight an interference fit as you can achieve without destroying the bearing as you push it on if you want to fit a new hub without pulling the front cover. Heating the hub and freezing the shaft and fitting it quickly should get that fit you need with a light press fit which would just require a few light taps of a hammer to fit. Dont worry about going on to far as you can always pull it back with a conventional puller.

If you measure the hub bore and the shaft diameter accurately you can calculate the needed temperature difference to fit the hub with a few light hammer taps that will not damage the bearing.

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PostPost by: 2cams70 » Thu May 31, 2018 11:51 am

As a trial you could practise doing it this way on a scrap bearing shaft out of the car. You might want to compare the shaft for size too as there will be a reason for the bodge. If all ok press the pulley off and go for the real thing. You don't want to end up with the pulley shrunk on the shaft only half way - that would be pain. Check the shaft for burrs too. A small burr can create a big interference. I imagine there will be quite a burr if it's been secured with a grub screw in the past
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PostPost by: billwill » Fri Jun 01, 2018 1:24 am

The only proper way to do it is with the waterpump off the car, which with the original non-module pump means taking the front plate off the timing case, which is a head-off or sump-off matter.

Then the hub can be pressed on with a press or a big vice, pressing on the back of the shaft using a spacer, DO NOT PRESS ON THE IMPELLOR.

If you really want to try it on the car, I suggest reaming the hub out to a hammer-tappable fit, then drill right through the hub and shaft and secure with a split pin or thread the shaft hole and put a long screw right through. Like the other comments I doubt if a grub screw would do the job.
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PostPost by: 2cams70 » Fri Jun 01, 2018 2:32 am

There's no harm done experimenting on a scrap shaft to see whether you can heat the flange up enough to expand the bore sufficiently to slide it on. If you decide to ream the bore out to a sliding fit when cold I would not even bother with grub screws, etc. either. Just use the correct grade of Loctite retaining compound. It's designed to replace a press fit and it's only a water pump so not that much torque to transmit.
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