Water pump impeller clearance question

WABOOM

Hey guys, I need to know about the impeller clearance on a 308 water pump. Im confused.

The service manual says it should "protrude .007 -.017" beyond cover face"

Protrude is not a great way to describe being below a surface or a depth / clearance. Is that what they mean?

To further confuse me is the info I read on the restoration site about having .080" clearance between the impeller and backing plate.

This water pump is from Kanter and has .045" between the impeller and the back cover. See picture.

What do you think?

Thank you in advance

GrimGreaser

There's a gasket between the case and the backing plate that needs to be taken into account. Hence the protrusion specified by Hudson. Looks like Kanter just pressed the impeller flush to the shaft end.

WABOOM

Ok, the gasket is .040 so that puts me close to .080 total that is on the water pump article from the restoration site.

I was afraid the clearance would mess with the efficiency of the pump. Makes sense now.

Thanks man. Gonna go paint this pump now.

WABOOM

KenU_Tx

The manual is CORRECT in stating the impeller should protrude 0.007-0.017" BEYOND the gasket face of the pump casting, so that when the gasket is between the pump and the back plate the clearance between the impeller and the back plate will be about 0.023-0.013" when bolted to the engine block ( the gasket will compress some). I put one of the China pumpd from Kanter (Rebuider's Choice) on a 51 Hornet, and it would run hot at idle and low speed......the 0.080" clearance on the China made pumps is excessive, allowing high pressure coolant to cross back over to the low pressure side, thus reducing the pump pressure in the block...... The higher the pressure in the block, the higher the boiling point........when pressure is too low in the block, hot spots start creating vapor pockets or bubbles that reduce heat transfer.....the vapor pocket grow in size, forcing coolan t to flow out the over flow tube on radiator and the cylinder head temperature climbs. I took the China pump out and put a rebuilt pump with the correct 0.017" protruding pimpeller and about 0.013 impeller to back plate clearance , and the 51 Hornet ran cooler without blowing off coolant at idle and low speeds.

WABOOM

Damn.

railknight

Does Kanter have its stock of Hudson, "big-6," water pumps rebuilt in China?

WABOOM

I don't know. They are new production by Rebuilders Choice. I didn't find anything in, or on the packaging that says country of origin. The casting has a P on the inlet side of the body.

The article I referred to that mentions .080" clearance was written by Rudy Bennett.

I may have been mistaken. I don't think it was on Ken Cates site.

I wonder why there is such a discrepancy on the desired clearances?

KenU_Tx

https://openforum.hetclub.org/discussion/comment/254528#Comment_254528

There is NO discrepancy on the clearance in the Hudson manuals.....I t exists only in writeups you may have seen written by other people.....Have no idea where they came up with such a huge clearance for the impeller to back plate, if indeed that is what they were referring to. I never seen that reference you mention anywhere.

Geoff

All 1948 and later water pumps are the same, apart from details in the construction, and the specifications are for the impeller to protrude .007" to .017" BEYOND the surface of the pump body. Not recessed below as in your picture. Hence the gasket will compress and there will be virtually NO clearance between the impeller and the backing plate when assembled. On the Jet the pump bolts directly to the block, with no backing plate.

WABOOM

Thanks for your input and help. Looks like I bought an out of spec pump. I painted and installed installed a few days ago. Im going to order one from Dale Cooper tomorrow and at the first hint of trouble I'll remove the Kanter pump.

Im not wanting to parrot bad information (if indeed it is bad info) . I did find the article but won't link it.

It's in the Water Deflector Tubes and Modified Water Pumps article on Glowplugs site.

Geoff

I would send the pump back to Kanter and demand your money back, and send them the specifications as in the workshop manual - .007 to .017" protruding beyond the surface of the pump. Or if out of warranty then simply dismantle the pump yoursedf, and press the impeller on to the correct distance.

WABOOM

You're right. I'm sending it back. I'm gonna take it out this weekend.

Btw, doesn't spacing the impeller closer to back plate just increase the blade gap at the front of the body?

Geoff

Yes, that is correct.

WABOOM

But I assume that would be bad thing for coolant flow. Right? I'm not gonna do it , I'm just wondering.

Geoff

I really don't know! I just set up for the correct specs and have never had a problem.