Radiator/Cooling Fan fried '86 K75?

[Beemahdad]

Hi everyone
I am a proud owner of a used 1986 K75 after owning Japanese bikes over the last 30 years. In the 3 seasons I've had her, she's provided some incredible memories but as they say, it's not the destination...

My question is regarding the cooling fan on my radiator. When I first had her, I manually checked to make sure the fan spun each time I washed. A few days ago, after returning from a 1000Km mini iron butt tour, I went to check and I was surprised to see the fan is showing a lot of resistance. I have my suspicion that the fan motor is fried so am wondering if expert opinions agree or disagree with this.

So... what are the chances the motor is fried?

I don't want to take it apart and try cleaning if I know that it will not likely be salvaged and I have to order a new fan motor. With the limited good weather in Vancouver, BC, I don't want to sideline my ride longer than I have to.

I look forward to reading some replies.

Thank you

Sunny

 

[kentuvman]

Hi Sunny

Welcome to the K bike forum!

I have an '87 K75s - the cooling fan was shot - a common occurance on our bikes.

It was an easy repair - I recall draining the coolant - removing the tank & fairing to remove the radiator - performed the job on my workbench.

Beemer Boneyard sells the Bosch fans - I believe they give MOA members a 10% discount. eBay also has them.

Do you have a clymer or Haynes manual? You'll want one if you plan on doing your own repairs & maintenance. Thought I saw a used one for sale on our online flea market.

 

[Beemahdad]

Hi Ken
Thanks for your reply. I do have both Haynes and Climer and am comfortable doing the job. It seems like a straight forward job. If the fan will not spin freely by hand, is the motor 100% seized and beyond repair?

Sunny

 

[dbrick]

What happens is: the K75 has a very capable cooling system, and the fan rarely runs. Because it doesn't run much, the brush assemblies and commutator get dirty over time. When the thermoswitch turns the fan on, there's higher-than-normal resistance in the wiring. The brushes get hot; then the brush holders get hot. The holders are plastic, and they deform and the brushes jam into the commutator. Thus, the motor shaft won't turn (or won't turn easily) and the fan doesn't run.

I've heard of folks removing and repairing the brush holders, but most just replace the motor.

 

[128465]

It's a pretty easy fix---even for me...I've replaced one on each of my 2 K75S's so far.

Of course removing all the Tupperware on the 'S' models takes some time

For my first replacement the motor had seized completely but my most recent replacement was done more as a preventative measure when it started to squeal intermittently. When I removed it is still functioned properly and spun fairly smoothly but a wire did look a bit melted when I removed it from the fan assembly.

When I replaced the motor instead of the whole fan unit there was some minor soldering involved but the unit cost for the just the fan motor is cheaper and so is the postage as the motor is much smaller to ship. I had great service from
Euro Motoelectrics in Colorado

Good Luck!
Marilyn

 

[kentuvman]

Hi Ken
Thanks for your reply. I do have both Haynes and Climer and am comfortable doing the job. It seems like a straight forward job. If the fan will not spin freely by hand, is the motor 100% seized and beyond repair?

Sunny

Yes - as the others have said, the fan mechanism is a weak link in the K 75's infrastructure! Suggest replacing!

 

[98lee]

Welcome to the forum! Sorry to hear of your problem. It is common because the fan is called for so infrequently and like Dave said, it has plastic brush holders (I've heard that it is a defroster fan motor out of a Porche.

http://www.euromotoelectrics.com/Cooling-System-BMW-K-Bike-Fan-Motors-and-Assembly-s/5.htm

The hardest part of the job, once the fan is out, is removing the black plastic cover IIRC. Just take it slow. If you need further guidance, just ask here.

In the future, please include the year and model of the bike in question, IN THE TITLE. It makes it easier for others with similar problems to search for and it draws more responses. http://forums.bmwmoa.org/showthread.php?t=46057
I've added that info to your post.

 

[Beemahdad]

Hi again David, Ken, Marilyn, Lee

Thanks for all the great hints and advice. I'll go ahead and order the replacement motor and plunge in to replace the motor. It's good to know ahead of time whether I should invest the energy in trying to clean the thing or just replace it. Thanks for the direction you all have given me.

Sunny

 

[kentuvman]

Probably a good time to replace your coolant while you've got things apart if it has been over years - check hoses for integrity & same for coolant recovery reservoir & hoses back there.

 

[dbrick]

You're welcome, Sunny. Take a good look at the rubber hoses, too.

I'd also suggest you replace the radiator cap (the one on the radiator itself, not on the expansion tank). The cap has two valves in it - one to vent coolant out and one to allow coolant to flow back in when the motor has cooled - and the cap's now almost thirty years old. If either valve misbehaves, you risk harming the motor and you'll be pulling the tank again.

 

[kentuvman]

Forgot to mention - if you wind up replacing coolant, make sure you get a coolant that's compliant with this bike.

Some on this forum only use the BMW coolant - I use premixed 50 coolant / 50 water.

 

[oldnslow]

No one mentioned testing the motor before you tear into it! Cant remember which terminals on the fan relay to jump, but i just did the teat about a month ago, so search the forum for radiator fan test.

 

[Beemahdad]

Hi Dave and Mike
thanks for your recommendations.

Actually, I already flushed and replace the coolant at the start of the season but I will certainly look at replacing the hoses and rad cap also when I replace the fan motor.

Sunny