Mont 4RT Burning out cooling fan motors ? Why

[jonnyc21]

10 hours ago, JustinC said:

I ran through the electrics check as per back of the Maintenance mannual.

The resistances all seem to check out OK (Primary coil, Temp sensor, ground checks etc  all ‘above and below’ the wiring harness (ie the harness checks are satis).

The only real ‘finding’ is that the manual spec for the resistance checks between the three yellow stator wires (each against the others) and in fact the impulse generator  wires (red and green) are 0.5-1 Ohm (at 20deg C) whilst when I checked them I was getting 1.5 Ohm approx (all of them consistent) but the day temp is perhaps 8 degrees. Not sure if the temp would explain the difference.

Im hoping the explaination is (as Miss said!) a faulty regulator so Ill fit a new one (along with fan motor and fan) and see what volts I get. If still too low - perhaps call the stator into question.

I would also check the fan motor by running it using a 12V battery to make sure it isn't the cause of the bad regulator as well. 

[on it]

IMHO    if its the regulator ? why is it only the fan motor burning out as as the regulator dose not make volts  just keeps them a constant voltage , Stator must be good as bike has electric power to run                                                                                                                                                                                       A sticking fan motor would draw more current to try to turn it but that in turn would draw more current /volts from rest of system ie fuel pump /ignition thus causing bike to stop /cut out ,

But  if  the  temp sender ( intermittent ) faulty ie not cutting fan OUT fan  motor will run continually causing over heating of fan motor as a fan motor is NOT built to run like that,,,, OR IF  the fan motor is/or running continually is the fault a coolant flow problem ?    causing the fan motor to work over time                                                    As for  Fan relay i think it only cuts fan motor volts off  for starting when the bike is hot ,to put all volts/current  to starting mode then cuts back in once started  sending volts/current  to fan motor  

Edited March 1, 2021 by on it
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[JustinC]

Thanks for your input On It.

The update from my end is this....

I found the system voltage with the bike running is 6 volts. From what Oz thumper was saying, I was hoping this might explain the burnt fan motors (x2) and that the cause of the system voltage being only 6 would be the voltage regulator. The only other finding was the stator resistance was a bit higher than spec (1.5Ohme rather than 0.5-1).

So I got a new (well new to me) voltage regulator and fit it today and ran the bike.... and it's STILL 6 volts.

So what would explain low system voltage?

I daren't fit a new fan motor if low volts is the problem and I havent found d a cause and fixed it.

Any thoughts? what to do or check next?

thanks

[JustinC]

Just to close the loop on this thread (with some embarrassment in my part!).

i fit a new voltage regulator (and fan motor and fan blade of course) and in the end couldn’t work out why the bike would run well and I’d only get 6 volts.

I could find no leaks to earth and figured the stator would work or not kind of thing (rather than put out ‘half’ volts.

Si wondered if I had a measuring error. So I got a new (borrowed) multimeter and ahem.. blow me.. the system volts was 13. So my multimeter faulty !

Much head scratching caused in necessarily!

thanks to those who chipped in !