Waterpump query

Post Mon Mar 19, 2012 1:19 am

Is the below statment true?? Seen it on another forum.

''Water pump, tensioner pulley and timming belt every time always together NEVER do just one. The reason is once you release the tension on the belt and tensioner pulley (held in place by the water pump) is drastically reduces the life of the belt and bearings in the tensioner''

Post Mon Mar 19, 2012 1:25 am

I think that would only apply if the water pump was on the timing belt.

All E30 engines (AFAIK) the water pump is on the aux belt and you don't need to touch the timing belt to replace it.

Post Mon Mar 19, 2012 1:26 am

Its on a '89 325i sport.

Post Mon Mar 19, 2012 1:29 am

Yeah the water pump is driven by a v-belt, not the timing belt.

Post Mon Mar 19, 2012 1:30 am

Ah ok thanks Mr Dink.

Post Mon Mar 19, 2012 1:32 am

Sorry just remembered, on the m20 you do have to release the tension on the timing belt to get the water pump off, so yes you should do them all at once. Doh!

Post Mon Mar 19, 2012 1:35 am

http://e30world.com/engine/BMW-E30-timi ... water-pump

Post Mon Mar 19, 2012 1:37 am

Ok thanks for the link.

Post Mon Mar 19, 2012 2:21 am

mr_dink wrote:Sorry just remembered, on the m20 you do have to release the tension on the timing belt to get the water pump off

Really ?

I've changed 2 water pumps on M20's and never had to touch the timing belt tensioner......

Post Mon Mar 19, 2012 7:59 am

mr_dink wrote:Sorry just remembered, on the m20 you do have to release the tension on the timing belt to get the water pump off, so yes you should do them all at once. Doh!

You were right the first time. You don't need to touch the timing belt to change the water pump on an M20.

The link referred to even says, "it is recommended to change water pump at every second timing belt change."

My view FWIW is that if the pump needs changing and you know the belt is good, you can do the pump on its own. If the belt needs done, do the pump while you're in there.

You don't need to take the bottom timing case cover, pulley, damper etc. off to do the pump, but everything you need to take off to do the pump has to come off to do the belt.

All in all, unless the belt is recent, probably best to do both at the same time, but it's not necessary.

Post Mon Mar 19, 2012 9:01 am

On an M20, the static end of the belt tensioner spring pushes against the water pump, so removing the pump will also remove the tensioner spring and its locating pin.
This doesn't, however, affect the tension of the timing belt in any way, as the tensioner spring is only used to tighten the belt before the tensioner pulley is locked in place, but it does cause problems when trying to fit a new water pump, trying to keep the paper gasket in place, fit the bolts and compress and locate the spring at the same time, especially if the bonnet is still on the car.
If the belt is half way through its life, I'd change it anyway, or, there's no reason why the pin and spring can't be left off of the car until the next belt change is due.
The only part of the OP statement that is true is that it is considered bad practice to re tension a timing belt that has been slackened off.