Water pump question

[MarkyB]

Anyone know how far from the gasket surface the impeller is on the 1098 water pump?
Any opinions about whether it makes much difference?

[PSL184]

Not very far from memory - I could go measure one in the garage later, but, as long as it clears the body I can't see its all that important....?

[MarkyB]

Don't bother, it turned out to be the fan belt that was making the noise, not the pump.
I did think that an impeller that didn't fill the cavity wouldn't pump as well as one that did though.

[stuart_k]

I do know that there are 2 pumps depending on the casting of the 1098 block, one with a short impellor and one with a longer one. I only found out when I ordered a new one and it didn't fit as it fouled against number 1 cylinder. You can get an idea of how much they stick out from the picture below:[frame][/frame]

[MarkyB]

Nice one, thanks!
The bad news is the pump I have "in stock" is the short impeller.

However it does have the cast iron impeller not the stamped tin one.

[kittyfell]

It will be fine, don't worry.

[MarkyB]

What are you basing that on?
I can't see how an impeller in a bigger space is going to work properly.

[kittyfell]

The small impeller will pump more than enough water, most of the time it is cavitating wildly anyway. Later engine ran the pump and fan more slowly, and the impeller was made larger for the 1275 engine.

[hotrodder13]

which one should i have on my 1275 it came with the shorter one on but i swaped it for a longer one is this right thanks tom

[MarkyB]

Aha! cavitating, I never considered that.
In fact not since I used an outboard which was years ago.
My memory is that if the prop starts cavitating forward progress is impeded to put it mildly. Bad news with an outboard but cunning design when applied to an engine water pump.
I guess a different sized pulley was used to change the pump/fan speed.