1992 R100RT TOP Fork Nut

b25bsaboy · Nov 12, 2016

good day,

started taking my front forks apart and all is going well. I am at the point that the large hex nut BMW part # 31 42 1 454 959 that sits on top of the upper bracket of the triple tree. Would someone on this board know what size this nut is, so that I can go to my local Princess Auto and get the proper socket. Thank you for your patience and wisdom

happy wanderer · Nov 12, 2016

Just pop the plastic cap off the top and measure it. Should be 36mm. Crow foot wrench works best. Or the one in the tool kit... with a rubber mallet.

20774 · Nov 12, 2016

On my /7, the nut is 36mm. Do you have a micrometer? Something useful to have...just measure across the flats. Or get your favorite crescent wrench, open it to fit, and go to the store and find something that fits that opening.

If it's like the /7, it will be a thin nut. Typically, the socket will need to be ground down to eliminate the inside chamfer...you need ever bit of bite you can get on the nut. If it's not like the /7, well, never mind!! :wave

happy wanderer · Nov 12, 2016

20774 said:
On my /7, the nut is 36mm. Do you have a micrometer? Something useful to have...just measure across the flats. Or get your favorite crescent wrench, open it to fit, and go to the store and find something that fits that opening.

If it's like the /7, it will be a thin nut. Typically, the socket will need to be ground down to eliminate the inside chamfer...you need ever bit of bite you can get on the nut. If it's not like the /7, well, never mind!!

Not sure it is Kurt. I did a where used search. It was only used on the R65, R80RT, R100RS, R100RT and R80. Did not see the /7 in the list but it could be same size only slimmer. I just popped my cap off and measured 36mm on mine but the flats are pretty big so no problem getting a normal wrench on there. Even easier with the bars off.

At first I was confused with the top nut which is 41mm I believe.

b25bsaboy · Nov 12, 2016

happy wanderer said:
Not sure it is Kurt. I did a where used search Kurt. It was only used on the R65, R80RT, R100RS, R100RT and R80. Did not see the /7 in the list but it could be same size only slimmer. I just popped my cap off and measured 36mm on mine but the flats are pretty big so no problem getting a normal wrench on there. Even easier with the bars off.

At first I was confused with the top nut which is 41mm I believe.

Just finished the dishes and went and measured. Answer is 41mm. Thank you, and will pay a visit to Princess Auto our equvilant to Harbor Frieght in the

.

88bmwjeff · Nov 12, 2016

b25bsaboy said:
Just finished the dishes and went and measured. Answer is 41mm. Thank you, and will pay a visit to Princess Auto our equvilant to Harbor Frieght in the .

I had trouble finding that size as well. I ended up ordering a really big open/box end wrench/spanner on the internet. I

lmo1131 · Nov 13, 2016

41mm... odd size, probably 40mm.

You don't have this tool in your roll?

happy wanderer · Nov 13, 2016

b25bsaboy said:
Just finished the dishes and went and measured. Answer is 41mm. Thank you, and will pay a visit to Princess Auto our equvilant to Harbor Frieght in the .

If that's the case the -190 part number you posted was for the top of the forks and the 41mm is for the center of the cross brace. Does it look like this?

b25bsaboy · Nov 13, 2016

happy wanderer said:
If that's the case the -190 part number you posted was for the top of the forks and the 41mm is for the center of the cross brace. Does it look like this? View attachment 59002

Double checked and it's part # 31 42 1 454 959 Hex Nut. Here is a picture and it is 41mm. Went to Princess Auto and with a low level impact wrench, off it came.

Do have a question for the masses, but I watched a Chris Harris and he reinstalled a spring retainer that has an o-ring. What he did was to rube alcohol on the o-ring prior to installing. As a retired factory representative who was involved in rubber polymers what is the purpose of this practice? This a new one on me and would be interested in why.

happy wanderer · Nov 14, 2016

Chris Harris loves using rubbing alcohol to make all things rubber slide together much easier and it does work very well for any rubber parts that you want to slide on easily. My preference is to use red rubber grease on most O Rings as it does the same thing, is an organic compound and actually helps preserve the rubber whereas alcohol dries it out a bit as it evaporates I would think.

b25bsaboy · Nov 14, 2016

happy wanderer said:
Chris Harris loves using rubbing alcohol to make all things rubber slide together much easier and it does work very well for any rubber parts that you want to slide on easily. My preference is to use red rubber grease on most O Rings as it does the same thing, is an organic compound and actually helps preserve the rubber whereas alcohol dries it out a bit as it evaporates I would think.

Thank you for the answer, as I thought alcohol might dry out the o-ring. I have always used a very small amount of synthetic grease and all is well.

Thanks to everyone chiming in on some of my questions which is much appreciated

🏍

b25bsaboy · Nov 14, 2016

happy wanderer said:
Chris Harris loves using rubbing alcohol to make all things rubber slide together much easier and it does work very well for any rubber parts that you want to slide on easily. My preference is to use red rubber grease on most O Rings as it does the same thing, is an organic compound and actually helps preserve the rubber whereas alcohol dries it out a bit as it evaporates I would think.

Thank you for the answer, as I thought alcohol might dry out the o-ring. I have always used a very small amount of synthetic grease and all is well.

Thanks to everyone chiming in on some of my questions which is much appreciated

🏍

lkchris · Nov 16, 2016

lmo1131 said:
41mm... odd size, probably 40mm.

You don't have this tool in your roll?

OP's bike is a 1992, which has a complete K-bike front end. It should be obvious it didn't come with a tool last used for '84s.

b25bsaboy · Nov 19, 2016

b25bsaboy said:
Thank you for the answer, as I thought alcohol might dry out the o-ring. I have always used a very small amount of synthetic grease and all is well.

Thanks to everyone chiming in on some of my questions which is much appreciated🏍

lkchris said:
OP's bike is a 1992, which has a complete K-bike front end. It should be obvious it didn't come with a tool last used for '84s.

Good point :banghead

happy wanderer · Nov 19, 2016

b25bsaboy said:
Thank you for the answer, as I thought alcohol might dry out the o-ring. I have always used a very small amount of synthetic grease and all is well.

Thanks to everyone chiming in on some of my questions which is much appreciated&#55357;&#56836;&#55356;&#57293;

As long as your synthetic grease is not silicone based no problems as long as it is never used anywhere around the fuel or intake systems. Even the tiniest amounts of silicone will contaminate your O2 sensor.

1992 R100RT TOP Fork Nut

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