WOT Question

standfirmrasta

standfirmrasta

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Last year I changed my leaking engine clean coolant pump for a service exchange pump.

After fitting, I discovered that the old belt was too long!! (turned out that the pulley on the new pump was of a smaller diameter) called the supplier up and he said just to purchase a smaller belt for crank to pump, which I did.
The alternator belt from pump to alternator had enough adjustment.

Question is, will this smaller diameter pulley have an effect on my rev counter reading? (i.e. smaller pulley making alternator spin faster therefore affecting rev counter reading)

My recommended WOT is 3900rpm I am now getting 4200rpm.

Thanks Andy
 
alternator has (AFAIK) nothing to do with rev counting, so shouldn't be a problem.

Now, higher revs could be related to something else. Mind you higher spinning alternator may not be a v.good idea, but I suppose they have a reasonable range of revs they operate properly.

V.
 
virtuvas said:
alternator has (AFAIK) nothing to do with rev counting, so shouldn't be a problem.

Now, higher revs could be related to something else. Mind you higher spinning alternator may not be a v.good idea, but I suppose they have a reasonable range of revs they operate properly.

V.
Click to expand...

Firstly where is alternator mentioned as a problem apart from needing adjusting for belt
Secondly Tacho readings come from alternator....

Different size wheel on water pump I'd be worried too much cooling at lower revs? Although I guess the thermostat would take care of that..
 
Last edited:
KevB said:
Firstly where is alternator mentioned as a problem apart from needing adjusting for belt
Click to expand...
oops, should reply with 3hrs sleep, sorry...

KevB said:
Secondly Tacho readings come from alternator....
Click to expand...
new to diesels, would've thought there was something else to trigger from, but since there's no ignition distributor or anything electric/electronic alternator will do...
 
scottie said:
The pulley ratio between crankshaft and alternator are what matters water pump is only an idler in this case
Click to expand...

I'd agree with this - the surface speed (contact area) of the belt to both the crankshaft pulley and alternator pulley will be the same as respective diameters are unchanged. So alternator tacho output should still be correct and thus engine would seem to be over-revving? Coolant flow will be quicker, but probably immaterial as presumably there will be a thermostat controlling engine temperature? IMHO of course! :D
 
Actually, just re-read...

Is the crank to water pump one belt and water pump to alternator a second belt? That would change things somewhat... The ratio of both the crank to pump AND pump to alternator will have changed!


Yes this is correct,not too bothered about the pump but am concerned about the revs.
Am I understanding that the ratio change will affect the alternator hence the different rev readings?
 
I'd say 'yes' the revs will be wrong! :o

It may be mitigated slightly as you'll now be driving alternator from a smaller pulley so this ratio will have changed too. The difference here will likely be less however (probably bigger ratio between flywheel and pump than pump to alternator) so I'd expect the alternator to be running faster and thus reading higher revs than actual. You'd need to do the calculations to be sure, but have a look here:-

http://www.csgnetwork.com/pulleybeltcalc.html

Might help to compare the actuals before and after if you have the old pulley to compare with?

Also, perhaps read this:-

http://www.technologystudent.com/gears1/pulley2.htm

Is it possible to swap the pulleys on the old and new water pumps?

I've upgraded alternator in Land Rover on two previous ones from 65A to 110A, but always swap the pulleys too to keep rotations correct.

Regards,

Robin
 
Sorry assumed (don't ) that is was a 3 pulley on single belt

With the the alt being driven from the water pump then yes the tachometer reading will be out and if he pulley driving the water pump is smaller it will increase tachometer reading

What engine and rev counter do you have

Some tachometers have an adjustment so you may be able to calibrate it.
 
Hi thanks now seem to be getting near to my own theory.

Yes the water pump is driven by a tensioned belt by the crank,the pulley on the water pump is now smaller in dia than the original.
The alternator is driven by its own pulley attached to the pump pulley and must be travelling faster as a result of the smaller water pump pulley.

Engine VP KAMD 43 P.
Rev counter also VP.
 
The revs will absolutely be wrong if you change the diameter of the waterpump pulley on the KAD43.

I would not accept changing the belt becouse I got the wrong pump from my supplier.

Agreed its a mess finding the right pump and pulley but its possible to get it all correct.
/Michael
 
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