Just completed my 200,000 mile timing belt change, changing the water pump and all the idler pulleys, the hydraulic tensioner, belts, etc.

I noticed a strange design . . . the replacement water pump pulley has equally-spaced teeth, to mate with the timing belt, around the entire circumference of the pulley. The original, Volvo pulley, however, skips a tooth every after every third tooth and, at one point, after every second tooth.

A very strange design, but apparently purposeful.

Any ideas as to why this design?

My 850 water pump was the same way, missing a tooth here or there, thought it was a weird design, but pump wasn't leaking and otherwise seemed fine, so I let it be. Clearly manufactured that way.

Teeth not broken--was manufactured this way. Will take pictures and post today. Like the vibration explanation.

most interesting, newer seen before, could you put in a pickture?
have done about six TBs on four cars (2x850-94,V70D5-06,V402.0T3-03) and five pumps but no such odd thing ever.
br Tapsa

Posted photos:





Did a second timing belt change this weeked on friends '98 V70 AWD, and it had the same pulley design.


Ken

Hi, having over 20 years volvo...
never seen something like this.
has obviously been manufactured this way.

I would think a homogenous tooth design would
tender the most critical timing belt.

Thanks for the pickture
Tapsa

Not sure if you noticed, but I added a note at the end of the pictures . . .

That same weekend I also did a timing belt change on a 98 V70 AWD and it also had this unusual pulley design.

Also, Googled "Volvo 850 water pump pulley missing teeth" and got these prior mentions:

http://volvoforums.com/forum/volvo-850-16/water-pump-questions-39323/
http://www.matthewsvolvosite.com/forums/viewtopic.php?t=8803&p=185236

Most interesting! The weight savings are almost nill. If my garage were a little warmer, I would pull the cover off my Tbelt and inspect my 1996.

If the teeth are not broken, perhaps the original design was used to avoid harmonic vibration or noise.

Many tire treads vary as you go around their circumference

Take a closer look and see if the teeth actually broke off the old pump. The belt ribs are quite hard.