BMW K bikes (Bricks)

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1Back to top Go down    K100 gearbox on Wed Jul 03, 2013 12:38 pm

otto59


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Looks like I'm buying a used gearbox. What years and models will fit an 85 K100 rt? Is the rs the same? Only have 3 weeks to get it in for a road trip.


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2Back to top Go down    Re: K100 gearbox on Wed Jul 03, 2013 12:59 pm

keefk1100lt

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Just about any K series 'box should fit. Internal gear ratios are:-

K75 - Gearbox Ratios 4.50 / 2.96 / 2.30 / 1.88 / 1.67 : 1
K100 - Gearbox Ratios 4.50 / 2.96 / 2.30 / 1.88 / 1.61 : 1
K1100 - Gearbox Ratios 4.50 / 2.96 / 2.30 / 1.88 / 1.61 : 1

The 75 seems to have a slightly longer first gear but otherwise they're the same. Externally, AFAIK, they're identical.

    

3Back to top Go down    Re: K100 gearbox on Wed Jul 03, 2013 1:02 pm

otto59


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@keefk1100lt wrote:Just about any K series 'box should fit. Internal gear ratios are:-

K75 - Gearbox Ratios 4.50 / 2.96 / 2.30 / 1.88 / 1.67 : 1
K100 - Gearbox Ratios 4.50 / 2.96 / 2.30 / 1.88 / 1.61 : 1
K1100 - Gearbox Ratios 4.50 / 2.96 / 2.30 / 1.88 / 1.61 : 1

The 75 seems to have a slightly longer first gear but otherwise they're the same. Externally, AFAIK, they're identical.

There's one available here in Canada but he's not sure of the year.


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4Back to top Go down    Re: K100 gearbox on Wed Jul 03, 2013 1:12 pm

keefk1100lt

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I don't think the year should be an issue, more the mileage!

K gearboxes seem to be pretty robust, so as long as you know it came from a running bike, it should be OK.

    

5Back to top Go down    Re: K100 gearbox on Wed Jul 03, 2013 4:36 pm

Brad-Man

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Of course, if you get one from a paralever bike you could upgrade your rear suspension...

    

6Back to top Go down    Re: K100 gearbox on Wed Jul 03, 2013 5:40 pm

sidecar paul

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@keefk1100lt wrote:Just about any K series 'box should fit. Internal gear ratios are:-

K75 - Gearbox Ratios 4.50 / 2.96 / 2.30 / 1.88 / 1.67 : 1
K100 - Gearbox Ratios 4.50 / 2.96 / 2.30 / 1.88 / 1.61 : 1
K1100 - Gearbox Ratios 4.50 / 2.96 / 2.30 / 1.88 / 1.61 : 1

The 75 seems to have a slightly longer first gear but otherwise they're the same. Externally, AFAIK, they're identical.



I don't know where this figure of 1.61:1 comes from.
All the BMW literature gives the top gear as 1.67:1 across the K range.



I believe the gearbox internals are common to all K's, the only differences being the paralever lug and some models had painted boxes.

Even the K1 has the same ratios according to my BMW sales blurb.


Paul.


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'84 K100RS (0014643) (owned since '85), 86 K100RS (0018891) with Martello sidecar (built as an outfit in '88),
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7Back to top Go down    Re: K100 gearbox on Wed Jul 03, 2013 6:22 pm

keefk1100lt

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Hmmm... Interesting.

I got the specs from another forum, here:

http://www.motobrick.com/index.php?topic=321.0

Typo perhaps?

    

8Back to top Go down    Re: K100 gearbox on Wed Jul 03, 2013 8:59 pm

RicK G

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@otto59 wrote:Looks like I'm buying a used gearbox. What years and models will fit an 85 K100 rt? Is the rs the same? Only have 3 weeks to get it in for a road trip.

Any gearbox from a K75, K100 & K1100 will fit they are identical Ratios and all the different ratio is a myth started because some promotional litter-ature that came from BMW mistakenly had the K100 5th gear stated as 1.61-1 when it is 1.67-1.


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9Back to top Go down    K100 gearbox on Wed Jul 03, 2013 11:24 pm

otto59


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My replacement is leaving Ontario tomorrow. Hopefully have it within a week. Does anyone flush them out to clean them?


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10Back to top Go down    I would on Wed Jul 03, 2013 11:34 pm

ibjman

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Not having verifiable history on the used part, I would completely drain the current lube & refill with quality synthetic of the proper grade....I think I use 75W90?

Run it a couple of thousand then do it again (while hot). If no foreign materials are found, you're probably good to go.

PS: you never said if you dis-assembled the failed one for inspection.
Also, remember to save the defective parts for useable items inside.

    

11Back to top Go down    K100 gearbox on Thu Jul 04, 2013 10:18 am

otto59


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@ibjman wrote:Not having verifiable history on the used part, I would completely drain the current lube & refill with quality synthetic of the proper grade....I think I use 75W90?

Run it a couple of thousand then do it again (while hot). If no foreign materials are found, you're probably good to go.

PS: you never said if you dis-assembled the failed one for inspection.
Also, remember to save the defective parts for useable items inside.

Will do. I find running synthetics springs all sorts of little leaks. Non-synthetics I get none. Time will tell.


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12Back to top Go down    I would be suprised on Thu Jul 04, 2013 11:39 am

ibjman

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I'd be surprised if putting syn in the trans would create a leak unless the seal is already deteriorated. In that case you will want a new one regardless. + there are only 3 or 4 possible leak points. these are not known to be plagued with leaks.

For my part ......on second thought, make the 1st change with regular gear oil......it's less expensive and it'll only be in there for a couple of thousand miles. On the second change......use whatever gives you the most overall confidence. I use syn in my gearboxes because I tend to neglect future mx & it may be in there for the rest of my days.
Regards, Ibj...

    

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