Water pump clearance

[Sheepdip]

The book says set the cover gasket to measured clearance + 10-25thou. So if my measured clearance is 3 thou, I need a gasket between 13 and 28thou, so a 20thou gasket would be correct?

I ask because my engines have always run hot and my mate reckons he uses the thinnest (10thou) gasket regardless as closer running improvespump performance.

Any ideas?

Paul

[NickA]

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Sheepdip wrote:

The book says set the cover gasket to measured clearance + 10-25thou. So if my measured clearance is 3 thou, I need a gasket between 13 and 28thou, so a 20thou gasket would be correct?

I ask because my engines have always run hot and my mate reckons he uses the thinnest (10thou) gasket regardless as closer running improvespump performance.

Any ideas?

Paul

We're only talking a few 10ths of thou's so I don't really believe that's going to make much difference to the pumps performance. I'd rather give some margin for error and go for the bigger tolerance as you really don't want the top bolt touching the cover.

[Bob Heritage]

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Hi Paul

I have recently O/H my water pump, had the impeller skimmed to the minimum off(4thou) and my clearance was still 35thou, I put the lot in 60thou giving me 25thou clearance. My theory was that the pump is drawn into the jack shaft by the angle of the teeth and after the recent problems of jack shaft seizing I didn't want to put more restrictions on than necessary. Although I believe that the less gap the more efficient for moving water. Maybe look elsewhere to solve cooling issues rather than moving minimal extra amounts of water.

Bob

[Sheepdip]

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Hi Nick and Bob, thanks for thoughts. I've set it as per book too as I've heard of people having problems with bolt head touching, but still curious as to whether this is a factor in the "some run hot" saga - there aren't many other places to look!

I was intrigued by an earlier reply to inlet manifold where it was noted "use just a smear of gasket goo". I confess to being liberal with the stuff and now wonder how much this bulks the gasket out.

Thats a big clearance Bob, skimming the impeller shouldn't impact it tho as the top of impeller will still be the same place.

Paul.

[alan_thomas]

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I have also rebuilt my pump recentlyand I think the weak point in the procedure ismeasuring the gap.

The cover is held in place by 3 bolts and it is very easy to bolt down the cover (just to hold not tighten!) on the wonk so that the gap varies according to where you measure it. The difference between 3 thou and 30 thou gap isn't much of a misaligment so take a lot of time to ensure the measured gap is the same all the way around the cover.

I agree with Bob in that I would always err on too big a gap rather than the risk of the cover rubbing on the pump and also agree that this gap does not cause overheating.

- Alan

[Andrew S]

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Picking up on Bob's comment, is the water pump shaft pulled downg durin operation? Can the shaft touch the cover at a later stageafter measuring everything?

Andrew

[Sheepdip]

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I would have thought the pump would be pulled down - I can check on my other engine. Re clearance, I cleaned a lot of the gunge off the side of the cover so it would easily slide down, then I rocked it on the water pump center bolt, insertinga feeler until it rocked no more. Also did same loosely tightening bolts. Worryingly, even if I overtightened bolts the jackshaft still turned easily with no sounds of rubbing....

Also fitted a new bottom bush as slop in old - wish I hadn't bothered cause I reckon there was more slop in the replacement.

[les M]

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Paul

My understanding of the workings of the water pump are , that in reality the pump onlymoves the water using the vanesto crate thecentrifugal forces. (The pump is the most basic design of all centrifugal pumps that I have ever seen, I would expect the maximum possible discharge pressure available from the pump could be in the region of 10/15" water gauge) Therefore in theory the closer the pump vanes are to the cover the greater amount of water could be moved. Providing that the vanes have a clean square edge, vanes that are not square edged will not push the water as efficiently. So thats what I think about these pumps.

My pump has always been setat 10/14 thou.max.


Les.

[Sheepdip]

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Hi Les - so you don't think Stag pumps are cutting edge technology then? Sounds like everyone thinks set it up by book so thats what I'll do.

Cheers

Paul

[Bob Heritage]

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When you turn the impeller nut you can lift the pump out if you are lucky, therefor when turning the opposite direction it must pull down. My gap is quite big I know,but I have put the same thicknessgaskets back as I took out. I tried tightening the bolts evenly with a spanner until the jack shaft stopped turning, meaning the pump was fully inserted and the bolt was touching the cover, then loosened the bolts and measured again when finger tight as per manual. My understanding of the 6 and 12 vane pumps is that the 12 vane are like 12 bats and the 6 vane are like 6 spoons, that is why many say the 6 vane scoops more water.

Bob

[Sheepdip]

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yes, I thought about your comment after my reply Bob, you're right the gear cutwill impart some vertical pressure but would have thought downwards. I'll check my other engine.

You're right about the different impellers - the 6 vane has curved blades like a turbine, teh 12 vane are straight and look like they bat the water around!

Paul