You are right on that. Alternator to WP so there goes that theory
Mine was not walking off the water pump pulley but rubbing on the lip of the alternator pulley. Once the tensioner bolt was changed along with new pulley (it was wearing due to the skewed belt) and pulley bearing no more wear.
When the car was recently serviced by a Ferrari 355 mechanic it had a full belt service and we replaced the adjuster and bearing for tensioning the alternator/water pump belt. We did not replace the casing perhaps I need to pull this off and have a look.
I had a look at the tensioner and it had a very slight angle to it in my opinion but not excessive. I do not see how this could affect the belt walking off the water pump pulley as the tensioner sits between the belt drive and the alternator. Perhaps the screw is damaged or the casing for the adjuster. It looks a pain in the backside to remove whilst on the car.
I had a look at the tensioner and it had a very slight angle to it in my opinion but not excessive. I do not see how this could affect the belt walking off the water pump pulley as the tensioner sits between the belt drive and the alternator. Perhaps the screw is damaged or the casing for the adjuster. It looks a pain in the backside to remove whilst on the car.
This thread is really helpful as it shows me all the parts that relate to the tensioner. And seeing the old one I can see the ware. Perhaps I should just bite the bullet and buy a new housing and the related parts required to replace everything.
It was a pattern 355 part from Eurospares but a well proven solution in the UK. It has all worked fine for a few hundred miles since the belt change and WP fitted. I think alignment to the same plane is the issue.
Have a look also at the alternator mounting hardware. There is some scope for misalignment if washers/spacers are in the wrong places.
I now know what the problem was that caused the auxiliary belt to travel off the water pump pulley. I have provided pictures for reference. This was a new pattern water pump that was fitted recently. On closer inspection it would appear that the Woodruff key that drives the pulley on the water pump had failed. This caused the pully to oscillate and throw the auxiliary belt. It also caused the water pulley shaft to fail where the pulley is bolted to the water pump and sheared off at the nut. Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
Very interesting and useful info. Thanks for post. Glad you got to the bottom of the issue and hopefully you’ll be back up & running soon.
Wow this exact same thing happened to my friends car as I was driving it. The nut sheared off and the belt came off.
On the pattern pump I used (supplied via Ricambi) the woodruff key was very hard to install flat into the pulley groove. You had to be very careful and it took a few goes to feel comfortable that the woodruff key was seated well in the groove.
Looks like the shaft was cut for a square key. Perhaps they inserted a shear pin instead of a square key, or a key of the wrong (soft) material. Hard to imaging shearing a key on a water pump unless there was some other problem. You now know what caused the belt problem. Next, what cause the key to fail?
The pattern pump I used was a half moon key. The one that failed on my friends car was from Eurospares I don’t think it was a half moon. The exact same thing happened though the nut sheared off and sent the belt flying. EDIT Just confirmed the woodruff key was the issue with the failed water pump from Eurospares. He changed to a brand new OEM pump due to no longer trusting the pattern part. I was skeptical about my pattern pump but seeing as the woodruff is the same as factory I installed it and no issues since.
