360 Threw My Water Pump Belt..Again

I threw my water pump belt last week, 330 miles after it was tensioned as part of a heat exchanger replacement. I assumed that I under tightened the belt. Although the belt still looked good, I got a new one, as well as a new belt tightening bearing. I replaced it this weekend, but the belt was thrown again during the test drive. I haven't opened up the access cover yet, but I'm wondering if anyone else has experienced this?

During replacement, I noticed that my water pump pully was loose; I could wiggle it back and forth. That must have been the reason I threw the belt. It made me wonder; did I tighten it correctly when I last replaced the water pump? I couldn't tighten it without the shaft spinning, so I hit it for a second with my impact until it stopped wiggling. When I replaced the belt bearing, I positioned it so it was just kissing the belt.

I hope that I didn't wear the water pully journal; that thing is expensive.

 

Perhaps. But the current pump only has 330 miles on it.

 

It engaged the key. The problem, I think, is that I couldn't tighten the pulley nut fully without the shaft spinning after I installed the pump. I thought that I would tighten the pulley nut after I installed and tightened the belt. But I forgot. That's my theory anyway. The pulley nut was as tight as I could get by holding the pulley. The pulley would spin, but there probably was some wobble.

I need to pull the cover and confirm that the belt slipped again, but I lost power steering and charging, so I assume that's the case.

BTW, how are you supposed to fully tighten the nut anyway?

 

This may have happened. Or more likely, I failed to ensure that the pulley was torqued properly and the key slipped off during operation. In any case, I'm going to have to replace both the pulley and water pump because the shaft and journal are ruined. Expensive mistake.

 

Thanks for your advice, Rifledriver. I was reluctant to use my impact for fear of damaging the bearing, but I'll use it next time. I also didn't realize that the belt bearing went on the inside of the belt; I found it on the outside and kept it there.

I use the Android App Carbon Drive to measure belt tension frequency. Even though the app is for bicycles, I've found it much more consistent and easy to use than other apps designed for cars. I also use the Challenge Stradale specs that Ratarosa shared (around 120 Hz, I think), rather than what's in the manual (around 100 Hz?).

 

Reinstalling my new/used pulley, I now find it likely that this is what happened. While the new key fits loosely into the new water pump shaft groove, it's a tight fit into the pulley groove. Even bench fitting the key into the pulley groove is challenging.

Is there a hack for aligning the pulley with the key before tapping it in? Since the key groove in the pump shaft doesn't extend the length of the shaft, I can't fit the key into the pulley first. Is widening the pulley groove entrance a viable option? What have you all done?

 

That did it.

I dried a little blue thread locker on the back of the key and took a mini file to the key way. Then, ensuring maximum light, I kept eyes on the key as I lined it up and gently tapped the pulley in. I didn't think it was moving until I noticed that the threads were extending out. I used an old nut to push it in deeper, and then finished with a new nut. Whew!

I thought that installing a pulley would be easy, but the Ferrari put me in my place.

 

Whatever works, right? I didn't want to glue the key onto the water pump shaft, and I didn't think grease would hold it tight enough. A little thread lock onto the bottom of the key, followed by an hour dry time kept the key in place as I maneuvered the pulley. I'm sure the professionals have a better way, but I didn't have a professional with me at the time.