Haven't been on at all in the past few months but got on to order some thermostats from Kat.
I am confident that I am the "poster child" of this thread at this point. I had the stock pump's gear let go back in October during a trip to Mississippi towing a Mustang. I changed it in the yard when we got there but didn't have access to a welder so I just stuck the Advance Auto pump in as is and went. It lasted until about mid April and I don't remember if it spun the gear or impellor. Since then I have put more water pumps in my truck than I have tanks of fuel, trying something different each time with nothing working so far. I've arc welded it and had the impellor break from around the weld, MIG welded and had the shaft break off at the weld on the gear side, welded with less heat both MIG and arc and had the weld break off the shaft or impellor. I've been wanting and trying to have it TIGed and one guy brought his MIG instead and thought he knew better, another that I left the pump with said he TIGed it but it had spatter marks on it from flux core MIG wire, and the machinist I took one to (which failed yesterday) cut a groove around the end of the shaft to get a deeper penetration, then he MIG welded it because he didn't have the proper TIG wire, and even worse he douced it in water as soon as he was done to avoid hurting the seals - at least he did it all for free since he wasn't sure if it would hold up.
Yesterday, I finally took one to the machinist I trust out near my old shop and I'm pretty sure his will hold. He also cut a groove on both sides for better pentration and on the impellor side drilled a hole along the shaft, taking half shaft, half impellor. Then he pre-heated the impellor, since it is cast, and TIG welded it, filling the hole and in the grooves on both sides. We kept cold wet rags around the outside of the impellor, gear, and housing to keep heat from soaking to the seals.
We discussed other options such as keying and pinning. The shaft is hardened and very tough to drill through; but carbide bits will do it. If you use a small roll pin perpendicular to the shaft I would worry that it would break, especially with some of the welds that I have broken. If you use a hardened pin it will hold up better but you need to make sure it is a very tight press fit to get it in. If it isn't and the interference fit breaks loose so that you are actually using the pin it will slowly beat itself up until it breaks. The other option is to drill half shaft and half impellor/gear running along the shaft to "key" it with a round hardened pin (similar to the Empire crank keying setup). Again you need to make sure it is a tight press fit and I would use green loc-tite (must be heated to 550* to get it to let go) to prevent it from ever coming out.
I think that the lower temp and especially faster reaction of the thermostats will also help cure the problem. I have been trying to let the engine get fully warmed up before doing any playing but even so they are breaking during or after me being hard on the truck. With the S480 single when it lights the truck takes about 2 seconds to go from 2500 RPM to close to 5000 RPM (typically breaking the tires loose regarless of speed) - I think that part of the problem is that hard of acceleration (change of speed and inertia of the impellor and water it is pushing) and the fact that the thermastats are closed or only partially open is causing so much pressure at 4000+ RPM that it just breaks the weakest part of the pump or the weakest weld. Believe me if you get the impellor to hold you will get the gear to break loose, and vice versa. I will try to report back on if the TIG welding and thermostats together solve this issue. I'm pretty sure I'm on water pump # 9 and the last 7 have lasted 6 days on average - so if I can get one to hold I think the same things should work for everyone else.
Weld them up, mod down the vanes, run the McRat themostats.
