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Old 06-09-2006, 11:26 PM
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small block chevy water pump problem

Hi everyone!!
I thought I,d run this past you all and see if anyone has had this happen.We've been running small blocks the last 3 or four years and have had waterpump failures.They range from the hub walking forward to the shaft to actually breaking off.The night the shaft broke we think that we picked up a rock or something and the fan was bent and that is what started it since then we even had a new fan hub made with a .004 press fit on the shaft and they still move.We turn the engine at about 6500 this is a dirt track car.We ran it all year and no problems then we put a shroud on and it started again! A friend of mine tinkers with ultralights and thought it might be a harmonic problem.Has anyone had this happen and how did you fix it? Thanks in advance this thing has really got me bugged!!
i

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Old 06-10-2006, 07:42 AM
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The only problems I have ever had with a water pump was with rebuilt units. Are you running new pumps? Did you purchase a high flow performance pump? Have you considered under drive pulleys?

Vince
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Old 06-10-2006, 07:04 PM
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Quote:
engineman posted:
"we even had a new fan hub made with a .004 press fit on the shaft and they still move."
I'm not clear. What moves? The hub or the shaft? As in uneven fit (for hub) or bearing play (for shaft)?

What length of hub are you running? At 6500rpm, I hope it's minimal and not excessively long. Aside from this, I think it's possible to have uneven airflow mass from the shroud (should be equal distance from shroud edge to fan blades tips and also all blades should be equally deep into shroud). If it's significantly not, then more stress could be placed on one quadrant of fan, and therefore wp shaft, causing extra stress. Balancer could be failing and giving excessive torsional "rebounding", but I would think it would have come apart by now. What type of hubs/pulleys/belt drive to water pump?

PS: I broke one W/P shaft clean off. Put new W/P on my 79 SBC, with a worn out 350. Then slung a fan blade 3 months later. Ran it regardless. 6 months later built a SBC 383 stroker, used the same "almost new" W/P, right behind my brand new (now old) $250 4-row HD radiator. Yep, the W/P shaft broke and slung the fan right thru the new radiator. Previous shaft flexural stress from running with a missing blade? Yep, I'm sure it was.

..K20
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Old 06-10-2006, 11:28 PM
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Have you been running the same fan all along? Adding the shroud has obviously increased the load. Is the fan bolted straight to the pump or spaced out?
I know the old Z28s and LT1s used to rev hard in standard trim but I've had fan and alternator fan failures below 7 grand.
I'm assuming you've checked pulley alignment & runout. Check your belts for thickness or angle variation. I put new belts on an S2 Bentley 16 years ago and it vibed above 3g due to a 3/4mm variation in thickness.
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Old 06-11-2006, 08:27 PM
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...

Gentlemen,

Thanks for your posts. Here is some more info. By walking, i mean that it appears that the hub is wobbling on the shaft, and as the engine runs.the hub moves forward towards the radiator. We are running a 3 in. spacer between the hub on the water pump and the fan. The fan speed is close to engine RPM. The fans are metal and are 6 blade and 16 in. in Diameter. They are RACING water pumps with alum. castings.Some of the water pumps have a powered metal hub. A couple of the pumps we've had, have billet flanges with a set screw "Very Beefy". I made a copy of the "beefy" version out of tool steel and made the ID hole .004 smaller than the water pump shaft. The shafts measure .746 .The pump that i am having probs. with ran all last season, the shaft broke on it, we think because the fan blades were damaged by a rock. I removed the hub from the broken shaft, checked the ID hole which measured .742, pressed it back on another water pump, shaft size .746. The hole was not egged or bell-mouthed. This hub lasted 1 race before it slid it's way to the end of the shaft ,but didn't come off. We put a spare pump on with the same arrangement and ran a full show this Sat. with not a problem. I hope this helps as i said before this is really bugging me...

Thanks in advance..
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Old 06-11-2006, 11:26 PM
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Doc here,

Had a Vette in here that did that last year..

What I did was put a laser pen from the pulley of the pump To the other two pulleys and shot a beam through the center grooves..

Turns out the pump pulley (The part where the bolts go through the center) was canted about 1 degree forcing the load forward and at an angle..It went through 3 pumps before we found it (all within a few hundred miles) Tossed the pulley assembly and installed new pump..has been fine every since..

Another idea...Carefully put your hand behind the fan..how Much airflow do you have back? If little or none, the blades may be bent back , changing the pitch ever~so~slightly..actually pulling the blades forward at extreme RPM"s and wearing out the shafts..I mention this because you say it got worse after the shroud was installed..(wind tunnel effect..) ..just a shot to look for..

Doc
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Old 06-12-2006, 02:53 AM
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I'd also consider losing the spacer to get the fan closer to the pump, the re-shroud to suit. Thats a lot of load hanging out there at six ana half.
The centreline of a factory clutch fan is only about an inch and a half out.
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Old 06-14-2006, 10:16 PM
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Thanks to all some very good points the length of the fan extension is a concern we are going to try to alter it the problem though is the longer shroud tends to start moving around and it is tough to keep it from striking the fan without extensive bracing.Secondly if we get damage to the front end that shroud can cause alot of damage and become a terrible pain, if we run a smaller fan or increase the clearance we lose the effect.But I do think some of these are worth trying.
Thanks again to all
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Old 06-15-2006, 08:23 AM
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do you have any vibration problems in the engine? had this problem turned out to be a balance problem after swapping flywheels.
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