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MG MGB Technical - Water Pump Replacement

Hi

Last week noticed coolant leak (true leak, not simply overfilling rad like last time).

Have traced it back to a leaking Waterpump, so ordered a replacement to fit over the weekend.

First time I've done it, any tips before I get my hands dirty?

Car's a 72 GT 18GG engine.

Many thanks

Darrel
Darrel

Darrel,

Its a fairly straight forward job. Radiator out to make room, don't force any really stubborn bolts - better to hit with a rust-breaker/thread loosening spray and wait (Onyx is popular over here). Whilst the pump is off its a chance to washout the floor of the block water jacket, an amount of crud often gathers there and it may loosen with a hose jet - same for area behind cylinder four, but careful about poking anything in there that may break and get lodged.

Thoroughly but gently clean thread holes before reassembly as well as mating faces. A little non-hardening gasket goo and final tightening of each bolt progressively in turn.

Depending on the kind of fan mounting you may find you will need grommets, bolts whatever depending on condition you find them in. Its important that the fan should be mounted in a balanced state so don't skimp here.

Good luck.
regards
Roger
Roger T

Scrape the block clean of any old gasket or sealant, and use Hermitite red (a smear spread out with a finger-tip, not great gobbets) and not that truly awful silicone muck on both sides of the gasket. Lay the gasket over the pump first to check the alignment of the holes, and trial fit the pump to the block for the same reason.

18GG is correct for a 68 to 71, a 72 model year should have an 18V. According to the Parts Catalogue they use different pumps, GWP114 in the former case and GWP117 in the latter. The catalogue also indicates they use different bolts, even though two are short and two are long in both cases. I fitted an alloy pump to an 18V and found one of the holes was offset by about half a hole compared to the block so needed filing out, also a boss on the pump had to be ground down before they would all fit.

Futher to Roger's comment there is a fitting kit for the fan comprising spacers, washers, grommets and locking tabs, if not bolts. Unless you know the condition of the grommets is good it's a good idea to replace these while doing the job.
Paul Hunt

PS and very important, you also need to compare the length of the two pumps! There are short nose and long nose pumps. Short nose pumps need a spacer between the pump flange and the fan, long nose must not have one or the fan can chew the radiator. You can get away without a spacer on a short nose but you have to turn the blades round the other way or they hit the engine.

This also reminds me that the fan blades have a front and a back, so even if you have the same length pump you still need to get the blades the right way round when refitting it. Ordinarily with metal blades the fan centre has several ribs radiating out from it, and the blades are rivetted to these. The correct way round is with the ribs on the radiator side of the blades, and this normally coincides with the outer corner of the leading edge of the blades being rounded more than the trailing edge. Plastic blades are usually a little easier to work out, having s relatively blunt leading edge and a thin tapered trailing edge, just like an aircraft wing, remember the fan rotates clockwise when you are looking in at it from the front of the car.

However if you had a short-nose pump with no spacer originally (like I did), and the new pump is also short-nosed, then the blades would have been the wrong way round to start with, and they must go back on the wrong way round unless you fit a spacer.

Have a look at http://www.mgb-stuff.org.uk/wn_coolingframe.htm and click on 'Mechanical Fans'.

And yet another thing occurs to me, the fan bolts must have a plain shank where it goes through the spacer tubes, this is essential for correct fan positioning and balance, if the bolts are threaded for their whole length the fan will almost certainly be positioned off-centre.
Paul Hunt

Paul/Roger

Many thanks for the very detailed responses. I really appreciate it.

Going to give it a go Saturday, will post back with how I got on.

Thanks again

Darrel
Darrel

I subsequently remembered that you can't switch between long-nosed and short-nosed pumps without also changing the pulley!
Paul Hunt

This thread was discussed between 28/07/2009 and 31/07/2009

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