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Old 04-21-2013, 05:30 AM   #1
dirtsurfer OP
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Sub frame bolts

My recently acquired 78-79 R100RS seems increasingly to appear as a hastily assembled pseudo- barn find

Anyway whilst installing the battery I was singularly unimpressed with the nut and bolts fastening the top part of the sub frame. They protrude into the space where my tool box should go and the make inserting the battery a real challenge.

Then , today, I was looking at another thread; a bloke restoring his dad's RT and I found a picture of the same area and what appear to be countersunk bolts?




Woops , you have to click to see a larger image
circled in top R corner of picture.

I immediately went to my bike and undid the bolt to see if the hole in the frame would accommodate a countersunk bolt. It did not look like it.

Number 5 in this pic



MaxBMW fisch says it is countersunk. but not what size it is. Can anyone tell me what the dimensions of this bolt are?

Thanks
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Old 04-21-2013, 06:01 AM   #2
Rucksta
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You may have original bolts.
I don't remember seeing the countersunk bolts until mid '80s
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Old 04-21-2013, 06:47 AM   #3
squiffynimrod
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Both my 85 and 92 have the countersunk bolts.
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Old 04-21-2013, 07:18 AM   #4
CanadaBiker
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I just went through this on my '77 R100. Here are the bolts I removed. I think they are M8 x 25mm shank, 30mm total length?


I wanted new ones, so I ordered the ones you found from Max. They came as the countersunk bolts, but my subframe is not machined to properly take them.

I bought some at the hardware store, and used new plastic nuts caps from Max. But now that you mention it, it will be a bit more of a pain to remove the battery and such. I might at least turn them around. The plastic cap will accept some of the thread protruding past the nut. (or maybe I use the countersunk bolts, even though they don't sit properly, as it will give me even more room within the subframe)
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Old 04-21-2013, 07:56 AM   #5
boxerboy81
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I think it was 1981 on that had the countersunk bolts.
Loosen the upper battery clamp, tilt the battery backwards and lift it out. A more modern thinner battery might miss the intrusive bolts???
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Old 04-21-2013, 12:00 PM   #6
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Quote:
Originally Posted by CanadaBiker View Post
I just went through this on my '77 R100. Here are the bolts I removed. I think they are M8 x 25mm shank, 30mm total length?



I wanted new ones, so I ordered the ones you found from Max. They came as the countersunk bolts, but my subframe is not machined to properly take them.




I bought some at the hardware store, and used new plastic nuts caps from Max. But now that you mention it, it will be a bit more of a pain to remove the battery and such. I might at least turn them around. The plastic cap will accept some of the thread protruding past the nut. (or maybe I use the countersunk bolts, even though they don't sit properly, as it will give me even more room within the subframe)
On my /5 I cut the bolts down, used jam nuts over warpy washers and backed it up with green locktite. Gave me the additional clearance.
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Old 04-21-2013, 12:02 PM   #7
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Quote:
Originally Posted by CanadaBiker View Post
it will be a bit more of a pain to remove the battery and such.

You can access/remove the battery by taking the airbox off. To me, this is easier then removing it through the sub frame.

Where-abouts in Southern Ontario are you?
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headtube screwed with this post 04-21-2013 at 12:29 PM
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Old 04-21-2013, 03:00 PM   #8
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I just had a broken stud damn near kill me. Personally, I would not use stainless or titanium bolts bolts there. I have seen them break way more often than shock studs!

For a short while years back, I was getting paid to help with race bikes. Both a good friend and myself advised the bike rider and the owner of the bike the same thing. Unfortunately, he had a titanium bolt on one of his clip on's break at just about the fastest part of the track. Probably around 140mph. He was lucky he didn't get hurt worse but it did F one of his feet up. Permanently.
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Old 04-21-2013, 03:37 PM   #9
pommie john
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Last time I was in my local airhead workshop I remember being told that the subframe bolts are high tensile. I can't remember the grade, maybe 10.9 or higher.
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Old 04-21-2013, 06:19 PM   #10
ME 109
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my 81 has c/sunk bolts.
8.8 grade would be suitable and anything higher grade, better.

Just had a squiz at my subframe and thought it is probably the same as the earlier models, other than the c/sinking.
I would think it OK to have the earlier subframe modified to suit c/sunk bolts. It may be a little difficult tho' due to clearance between the two sides of the subframe.
Obtaining the correct angle of the c/sink would be important.
There appears to be a metal plate sandwiched between the pressed ends of the sub-frame tube. I imagine this would be to add strength to the c/sunk hole. Are the earlier frames the same?

Maybe just easier to find a high tensile bolt with a shorter/flatter head.......
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Old 04-22-2013, 04:05 AM   #11
dirtsurfer OP
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Quote:
Originally Posted by ME 109 View Post
......

Maybe just easier to find a high tensile bolt with a shorter/flatter head.......
Yep. I have some high tensile button heads around somewhere
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Old 04-22-2013, 05:45 AM   #12
CanadaBiker
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Quote:
Originally Posted by headtube View Post
You can access/remove the battery by taking the airbox off. To me, this is easier then removing it through the sub frame.

Where-abouts in Southern Ontario are you?
I'm way down south in Kingsville, just outside of Windsor. Are you near Toronto?
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