water pump, Alaska 86 GMC Sierra classic 1500 4x4

[BJedi76]

My 350’s water pump was leaking out the weep hole, so I bought a remanufactured water pump and installed it. It wasn’t until I had everything back together, that I noticed that the pulley scraped on the pump & fan studs only fit backwards. I wasn’t exactly happy, but I managed to MacGyver it back together & even installed the pulley and fan. However, when I filled it with coolant, it was streaming from the weep hole.
I therefore, removed the: fan, pulley, power steering pump, alternator, and water pump AGAIN..!!! I returned it to the store for an exchange, however I upgraded to a “new pump”, rather than remanufactured one.
After installing the second replacement pump (and the other accessories!), I installed the fan studs (which installed properly, BTW ), but when I went to install the pulley and fan, the water pump fan studs didn’t lineup with the pulley or fan holes.


My question is, “ am I just seriously unlucky or is there a logical explanation somebody might be able to give?

 

[chengny]

Measure the bolt circle (distance across the face from one hole to the other - that passes through the center) on all three of them. Since the fan and pulley haven't been changed, you'll probably find the B.C. on the water pump driven flange doesn't match.



BTW - read this from Gates on initial water pump seal leakage.Sounds as if you had more than just seepage - but for future reference. Also it wasn't mentioned whether the engine was ever started. Sometimes the pump must be run at operating speed to bring the stationary and rotating halves of a seal into contact.

When a water pump is new, some seepage from the weep hole is normal as it takes some time for the mechanical seal to properly seat itself (break-in period). This is no cause for concern. Once the mechanical seal has seated itself, the seepage will stop. More pronounced seepage and drips from the weep hole after this break-in period or a large coolant bleed mark around the weep hole are abnormal and indicate impending water pump failure.

 

[idahovette]

Changed a lot of H2O pumps and NEVER had a replacement pump leak after I installed it. Always used NEW pumps and most had fit all hubs.(2 different bolt hole measurements)

 

[BJedi76]

Chengny;

measure the “bolt circle”?
what is a “bolt circle?

on all 3 what?

i don’t understand...



Idahovette;

why is there 2 different fan bolt patterns? what do i tell the parts store, to make sure i get the right one?
ie; air conditioning or not, California or federal, etc.

 

[idahovette]

In most cases the pumps usually have both bolt patterns, but I've dealt with NAPA almost exclusively and ONLY NEW pumps.

 

[Swims350]

take the old pump to the store and match it up.

I found ony m86 86 gmc 1500 with a 305 that it's water pump was different from say an 85 or so part number wise not sure why anything else because they all looked the same.

However I do know sometime in some vehicles there in 86 gm started with serp. belts, those would be reverse rotation or the older ones.


Mine went on without any issues. I have seen the ones with another set of holes in the pump for the pulley, reason being different would be different sized fan, cooling options or something along those lines. Some trucks had HD cooling some had regular, sometimes ac and no ac comes into play.

 

[chengny]

Chengny;

measure the “bolt circle”?
what is a “bolt circle?

on all 3 what?

i don’t understand...

The B.C. (on a 4 bolt flange) is simply the distance across the flange face between two diametrically opposed bolt holes. This image explains it better than I can:

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all 3

When you go to make everything up there will be 3 sets of bolt holes that need to be lined up in order for the bolts to pass through. Starting from the front and going back they are:

1. The fan's driven flange

2. The drive sheave (pulley)
h

You must be registered for see images attach

3. The water pump's driven flange

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On a side note. Note the bolts threaded into the pump flange above. It's not common practice (probably because it's not as factory) but I've been doing it for years now. Instead of using the factory arrangement of studs/nuts I just thread bolts in from the front. The flange on an OEM water pump is tapped to accept 5/16 - 24 NF bolts. Makes assembly a lot easier.

 

[K5_489]

The flange on my BBC reverse rotation water pump has a different BC than the standard rotation pump, and is a metric thread. Found that one out the hard way after getting the new motor installed, and the fan clutch wouldn't fit on. Ended up having to use the fan and clutch off the 350 in the '95 parts truck...