Technical Using 3-hole water pump on 4-hole block

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Technical Using 3-hole water pump on 4-hole block

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Last year I rebuilt the water pump and whilst this was a fair old challenge, it was very satisfying to repair something that would cost me about £400 new.

But almost immediately I was getting a leak from the carbon seals at a rate which won't be manageable once the van is on the road. I will look into this and I'm sure it's just that I haven't put the seals in at the right distance from the rings that they bear on. But I've seen suggestions that there is away to adapt the engine to fit the easily available, much less expensive pump from the earlier 850 engines.

I've speculatively bought a brand new, 3-hole one for £51...a significant saving over the 4-hole versions. It prove to be a waste of money, but I'm hoping someone can help me by explaining how they have fitted one to the 4-hole engine.(y)
 
How many variants were there..?

Just one style for each block..??

I seem to recall I posessed an 850 pump years ago.. bought but never used


( have you approached the spares fella in Southern Italy?)

Charlie
There seem to be two types. A helpful chap on Facebook just posted an image of his modification. It seems both types use the top two tappings in the block. An adaptor plate has the four corresponding holes with a central, lower stud welded to the plate...it looks fairly easy to achieve so I'll give it a try and post here.
 
With acknowledgement to Goran Crv via Facebook.
 

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Last year I rebuilt the water pump and whilst this was a fair old challenge, it was very satisfying to repair something that would cost me about £400 new.

But almost immediately I was getting a leak from the carbon seals at a rate which won't be manageable once the van is on the road. I will look into this and I'm sure it's just that I haven't put the seals in at the right distance from the rings that they bear on. But I've seen suggestions that there is away to adapt the engine to fit the easily available, much less expensive pump from the earlier 850 engines.

I've speculatively bought a brand new, 3-hole one for £51...a significant saving over the 4-hole versions. It prove to be a waste of money, but I'm hoping someone can help me by explaining how they have fitted one to the 4-hole engine.(y)

I know this is an old thread but anyone looking for inexpensive 4 bolt type water pumps might check out:-
www.oldtimer-shop.eu/parts/fiat-850-sport-coupe-spider-gbc-903cc-engine-water-pump-4-bolts (this co. seems to have them for Euro 54.90)

Hth,

Al.
 
The thought of fitting the wrong pump deliberately sounds like a horrible idea.
The adaptor plate has to be a particular thickness to support the stud, but that moves the impeller outwards in relation to the water passageway in the block. That might be a problem. You also now have two sealing surfaces instead of one, so potentially more leakage possibility.

Fiat had spent some time designing the pump for their engine. Impeller type, shape and position all have an effect in the way coolant is moved around, as does the speed of rotation. Differences from original spec can cause various issues, including,
Coolant can be caused to 'froth' if it cannot go where pushed, or if pushed too hard.
Overheating can result if coolant does not move enough.

Does the 'modification' put the pulley out of line with the rest? Or is the adaptor plus gasket specific to put a shorter pump in the correct alignment?

If a good quality, correct spec pump is available, if mine, I'd be paying the price.
 
Hi F123C.

those 4 bolt pumps are for the engine block in a seat 133 with the vertical surface flange where as the 900t has the angled bolt flange, if you use it on the 900t block (angled flange)then the fan will not line up with the rad cowling.

Tim
 
Hi All20201013_194620.jpg
this is an image of the angle of the main 3 types of pump, the top and bottom ones are 3 and 4 bolt standard 843 and 903 pumps respectively, both fit the angled bolt face.
the middle one is the 133 type to fit the square vertical bolt face,
Tim
 
I can now back up everything said previously about the differences with the three-hole pump. The one I bought has smaller waterways and pipe spigots. The impeller is different and these aftermarket versions have a different, but possibly better arrangement of the water-seals.

None of the parts seems directly interchangeable with the Fiat four-hole pump. But looking indside one has been a relatively expensive, but useful insight into the mechanics of these things. This has helped me to dignose what exactly is wrong with my pump and has possibly given me a solution, as described elsewhere.
 
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