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K100-forum.com » Technical, repair and troubleshooting » Engine and transmission » Frame to transmission bolts

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1Back to top Go down   Frame to transmission bolts Empty Frame to transmission bolts Wed May 17, 2017 11:53 am

Filmcamera

Filmcamera
active member
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I recently managed to destroy second gear during some spirited riding on the twisties. Whilst I could have the gear repaired by undercutting the dogs in the end I decided it was cheaper and probably easier to buy a used transmission. 

I found one on eBay from a 1993 K1100RS which looked great when I got it, the splines etc are almost new. 

Yesterday I installed it and all was going great until I came to refit the M8 bolt on the RHS that goes through the frame into the transmission. Try as I might I could not get the M8 bolt to screw in. On closer inspection (I took the transmission back out again) I discovered the hole had been repaired with a M6 helicoil. A M6 bolt screws in no problem. 

The rest of the transmission looks perfect and shows no sign of having been down or anything like that. 

So I am looking for a little advice. Should I try and remove the helicoil that is in there and retap the hole for an 8mm or should I just install a 6mm bolt and ignore it? 


Frame to transmission bolts YjUdLV

    

2Back to top Go down   Frame to transmission bolts Empty Re: Frame to transmission bolts Wed May 17, 2017 12:19 pm

Filmcamera

Filmcamera
active member
active member
Rechecking the correct bolt is a M10 1.5 and the helicoil that is in there is for a M8 1.25

I do have both a M10 1.5 tap and also a M10 1.5 helicoil so I might try taking out the old helicoil and just re-tapping a M10 1.5 thread first.

I will admit it makes me a little nervous

    

3Back to top Go down   Frame to transmission bolts Empty Re: Frame to transmission bolts Wed May 17, 2017 2:19 pm

club_c

club_c
Life time member
Life time member
If it were me I'd repair the threads to the original size. The clever engineers at BMW put it there at that size for a reason and who are we to quevestion zem?  Vee shall ask zee quevestions here!  You're right there so not a big deal to make the repair. My 2 cents worth... (read my signature)


__________________________________________________
"There's never enough time to do it right, but there's always time to do it over."

1988 K100RS SE VIN 01477554
    

4Back to top Go down   Frame to transmission bolts Empty Re: Frame to transmission bolts Wed May 17, 2017 2:29 pm

Filmcamera

Filmcamera
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active member
Yep, that is what I am doing, I tried just tapping with a M10 tap but no luck so I had to use a helicoil.  Seems to be pretty good.  The only issue is I did not go quite deep enough so I cannot get the original bolt totally flush with the frame but a washer or two will fix that.

    

5Back to top Go down   Frame to transmission bolts Empty Re: Frame to transmission bolts Sun May 21, 2017 3:10 pm

Filmcamera

Filmcamera
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active member
I did manage to drill out the M8 and install a M10 helicoil and reuse the correct size bolt and now the bike is all back together and running well.  So far I have only done one quick shake down ride to test out the new transmission but it feels great!

    

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