85 K100RT Cooling Fan - Repair or Replace?

[montec]

To repair or replace the cooling fan motor?

I've narrowed down the new "noise" on my 85 K100 RT to the cooling fan.

I would describe it as a rattly vibration or squeal, but I'm not sure that truly describes the sound. I've attempted to share a video of the sound so that you can judge for yourself.

The noise seems to kick in when the fan is starting up and then intermittently while the fan is running.

I've checked the area to make sure the blade is not rubbing against anything (hoses, wires, debris, etc).

The motor turns easily by hand and will generate a bit of a rattle with the initial push.

I would credit that sound to the the small amount of free-play between the fan blade and the motor shaft.

The nice part of the riding season in Minnesota is relatively short, so I'd prefer to minimize the time spent down for maintenance.

It takes a bit of work to get the fan assembly removed so I'd like the insight of experience before I get started.

What are the most likely causes of this sound and is it an easy repair?

If the best approach is to replace the motor, does anyone have instructions or helpful hints on removing the fan blade and rear plastic cup from the old motor and reinstalling them on a replacement?

http://www.beemerboneyard.com/kfanmtr0427.html

http://www.euromotoelectrics.com/BMW-Motor-Radiator-Fan-K-models-1983-1995-p/fan-k427m.htm

Thanks in advance.

Monte
85 K100RT

 

[HFbmw]

radiator fan

Good morning,

I have had problems with that fan as well. Finally I replaced it with a fan from NAPA. Almost looks normal to have this black fan in front of the radiator instead of behind it! The engines are bullet proof! I had the original fan die on a trip to South Carolina. I was fine at 80 mph, however there was a major accident east of Knoxville and the coolant level blew the cap off the reservoir! So I had to get off that freeway quick. Cooled down and added water!

I have tried bone yard fans and purchased one but it only lasted 7000 miles or 9 months. Opted for a NAPA 12 inch fan and tied it to the front of the radiator. I would advise purchasing a new fan. Costs are $300 plus removing the air box and removing the old fan. While you are in there might as well purchase fuel line and replace that.

The BMW I have has almost 167,000 miles. No problems with the after market fan.

take care,

Tim Lindstrom,

 

[montec]

Thanks for the info Tim.

I haven't found anything that points toward a specific cause for my mystery noise, so I plan to purchase a replacement motor. At least that way I have it on hand when I get all the parts and pieces out of the way.

The $80 motor is much cheaper than the $300 fan assembly. The trick will be getting the blade off the shaft and remounting it in the fan bracket.

I replaced my fuel and vacuum lines last fall; otherwise it would be a good time to refresh those items as well.

Compared to a lot of K's on the road, mine is just getting broken in at 98,000 miles.

Thanks,
Monte

 

[mikeyork5]

Relatively easy job (an hour or two) - just did it on my K75. Bought the fan from Euro Motoelectrics. AS I recall it was around $80.

 

[pglaves]

"I would describe it as a rattly vibration or squeal, but I'm not sure that truly describes the sound. I've attempted to share a video of the sound so that you can judge for yourself."

Squeal says bearing, or brushes. Vibration says bearing. It is a barely repairable motor. Lube might help but temporary. I'd replace the fan. I did it once in a campground at Hungry Mother State Park, so a master shop isn't required.

 

[montec]

Thanks for the confirmation on the best resolution.

Any tips or tricks on removing the blade from the motor or should it slide off without too much effort?

Thanks,
Monte

 

[pglaves]

Thanks for the confirmation on the best resolution.

Any tips or tricks on removing the blade from the motor or should it slide off without too much effort?

Thanks,
Monte

It will slide off. Plan ahead to find/make a forked tool to pry with that will span about a 3/8 inch shaft.

 

[montec]

Parts have been ordered from Beemer Boneyard.

Now all I need is the time to get it done.

Thanks again.

Monte

 

[Roc-Roc]

I replace my fan on my 85 K100RS when it had 60k miles with OEM fan. It was still working when I sold the bike with over 225k miles. It wasnt very difficult to replace.

 

[montec]

As a follow-up to the original post, Paul was on the money (again).

The bearing was quite rusty looking and the shaft had noticeable free-play (1/16th inch gap).

The task was not terribly difficult, but did require a lot of time to get all of the pieces out of the way to remove the radiator to get to the fan. The blade swap was relatively easy and the new motor is much quieter.

Thanks again to everyone that offered advice and opinions.

Monte