BMW K bikes (Bricks)


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Vitamin K

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So as my K morphs into its next incarnation, I am only looking to trim the tail down next week and install my cafe seat.

I have searched and can't seem to get a clear answer to whether it is okay to mig weld my hoop to the subframe while the engine and electrics are still mounted on the bike. Will it fry the bikes electrics? Do I need to remove everything from the frame just to mig the hoop?


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Father, Monk, Artist, Rider of the K

Current Ride:
1985 K100RT (slowing morphing into... "something")

Past Rides:
1970 R50/5
1975 R90S
1982 R65LS
    

Two Wheels Better

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A mate of mine welded on his rusted and broken K100 centre stand some years back and the bike wouldn't start again. He'd fried the ECU. It's a good thing the local dealer had a secondhand one available - at the time $600 - which he sold to him for $300. That might answer your question.


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'77 R75/7-1000cc, '87 K100RS, '93 K12 Big Block, '94 R100 Mystic, '03 K1200GT, '04 R1150RT, '06 K1200R, '07 K1200R & '09 K1300GT
Two Airheads, three Bricks, an Oilhead and a trio of new K's.
    

Vitamin K

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That is exactly my concern. Now I'm starting to think about just taking it down to the frame and might as well powder coat it while I'm at it. Seeing how I planned to to have it somewhat apart for two weeks, I might as welll have it all apart for a month.


__________________________________________________
Father, Monk, Artist, Rider of the K

Current Ride:
1985 K100RT (slowing morphing into... "something")

Past Rides:
1970 R50/5
1975 R90S
1982 R65LS
    

Two Wheels Better

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Paint or powdercoat is nice, and it'll look sweet once done, but you really only need to disconnect both the pos & neg battery straps to be sure. The 'puter sits in a plastic box (unless you've already modded that bit) and will be totally isolated from electrical shock brought on by welding.


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'77 R75/7-1000cc, '87 K100RS, '93 K12 Big Block, '94 R100 Mystic, '03 K1200GT, '04 R1150RT, '06 K1200R, '07 K1200R & '09 K1300GT
Two Airheads, three Bricks, an Oilhead and a trio of new K's.
    

Vitamin K

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@Two Wheels Better wrote:Paint or powdercoat is nice, and it'll look sweet once done, but you really only need to disconnect both the pos & neg battery straps to be sure. The 'puter sits in a plastic box (unless you've already modded that bit) and will be totally isolated from electrical shock brought on by welding.
No... no electric mods yet.

Just so I understand this correctly (even though you said it quite clearly)... If I disconnect the pos and neg on the battery, I won't fry the computer when I mig weld the hoop?

The short story is that I am not quite ready to the fully pull apart of the bike. I need to make some "rolling changes" first. In December it will all come apart and the frame (as well as other parts) will be cleaned and sent for powder. This is also when I will do my electrical mods (i.e. aftermarket speedo, and a robmack tgpi circuit).


__________________________________________________
Father, Monk, Artist, Rider of the K

Current Ride:
1985 K100RT (slowing morphing into... "something")

Past Rides:
1970 R50/5
1975 R90S
1982 R65LS
    

floyd

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As long as your battery is totally disconnected you'll be right - as therell no longer be a circuit for the magicelectrons to flow through (from the frame) and break anything.

Whenever welding anything on any vehicle, disconnect the battery.


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K100 with lots of K1100 bits - mongrel of a thing...
    

MartinW

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And as an extra precaution always have the earth lead on the welder as close to the weld site as possible.
Regards Martin.

    

Vitamin K

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Thank you all very much!

I'm going to do it. It's a big next step for me to take with the bike. I know once I cut it, there's no going back, but getting this question answered gives me a boost in confidence that I won't damage it (unless my weld is somehow bad Laughing ).


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Father, Monk, Artist, Rider of the K

Current Ride:
1985 K100RT (slowing morphing into... "something")

Past Rides:
1970 R50/5
1975 R90S
1982 R65LS
    

RicK G

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VIP
Disconnect the earth on the battery and unplug the ECU and ICU then put the earth clamp close to the weld and you stand zero chance of damaging anything except the frame where you are welding.


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If everything seems under control then you aint goin fast enough:- Mario Andretti
Bikes 1986 K100RT, 1993 K1100 LT, 1994 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 & 1976 SR 500 Yamaha for now
    

Vitamin K

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I can do this.
I can do this.
I can do this.

(Positive re-enforcement)


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Father, Monk, Artist, Rider of the K

Current Ride:
1985 K100RT (slowing morphing into... "something")

Past Rides:
1970 R50/5
1975 R90S
1982 R65LS
    

club_c

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Come on, how hard can it be??



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

1988 K100RS SE VIN 01477554
    

Dai

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What Rick says. If you're really paranoid then pull the plug from the back of the alternator too. By disconnecting everything you're giving yourself exactly five minutes extra work and a lot of anti-paranoia protection too.


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'83 K100 upgraded to K100RS spec
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California,
'03 Suzuki Blandit GSF600SK3 (NFS any more because wifey has claimed it)
    

Vitamin K

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@Dai wrote:What Rick says. If you're really paranoid then pull the plug from the back of the alternator too. By disconnecting everything you're giving yourself exactly five minutes extra work and a lot of anti-paranoia protection too.
Yeah, I'm pretty much going to disconnect everything. But... now I'm starting to wonder if I even need to weld a hoop. There is the existing bar that goes laterally across the the frame which the inner part of the mudguard/wheel well bolts on to. Does the force of the shock put too much stress on that lateral bar? Is the hoop really neccessary?

If not, I'm inclined not to weld a hoop and just cap the open frame on each side and then let my cowling hang over it just enough to cover it. I have seen some frames where the person left the ends of the cut sub frame open and installed those little indicators in the frame, but I don't to do take that approach.

I am a week away from starting my tear down for which I will start a thread. I have tasked my nephew with the job of taking lots of photos of what I am doing so I can share with you all my joys and frustrations (which will be many), as well as get feedback from the community. I mean really... What's the point of geeking out if you don't share that geekness with other geeks of similar interest?


__________________________________________________
Father, Monk, Artist, Rider of the K

Current Ride:
1985 K100RT (slowing morphing into... "something")

Past Rides:
1970 R50/5
1975 R90S
1982 R65LS
    

AndrewP

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@Vitamin K wrote:
@Dai wrote:What Rick says. If you're really paranoid then pull the plug from the back of the alternator too. By disconnecting everything you're giving yourself exactly five minutes extra work and a lot of anti-paranoia protection too.
Yeah, I'm pretty much going to disconnect everything. But... now I'm starting to wonder if I even need to weld a hoop. There is the existing bar that goes laterally across the the frame which the inner part of the mudguard/wheel well bolts on to. Does the force of the shock put too much stress on that lateral bar? Is the hoop really neccessary?

If not, I'm inclined not to weld a hoop and just cap the open frame on each side and then let my cowling hang over it just enough to cover it. I have seen some frames where the person left the ends of the cut sub frame open and installed those little indicators in the frame, but I don't to do take that approach.

I am a week away from starting my tear down for which I will start a thread. I have tasked my nephew with the job of taking lots of photos of what I am doing so I can share with you all my joys and frustrations (which will be many), as well as get feedback from the community. I mean really... What's the point of geeking out if you don't share that geekness with other geeks of similar interest?
Hi Vitamin K,

I bolted the hoop using the existing cross member, but you will need to weld a cross member to the front of the hoop ( next to tank ) to stop the hoop twisting left or right. You could weld tack a lug that would sit inside the existing frame so it wouldn't slip left or right.If you do it this way you can add longer hoops with different seat colours etc ?? have you got the hoop as yet ? found it difficult to sort this simple item.

    

Vitamin K

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I don't think I worded my question very well. sorry.... Sometimes a picture is better...


__________________________________________________
Father, Monk, Artist, Rider of the K

Current Ride:
1985 K100RT (slowing morphing into... "something")

Past Rides:
1970 R50/5
1975 R90S
1982 R65LS
    

Dai

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Life time member
Life time member
Yes, yes, yes, yes. That pressed steel bracket is not designed to carry the suspension forces. You can cut it out and replace it with a tube of the same diameter and wall thickness as the frame, but make sure your welder knows exactly what he's doing. Not recommended as a home job unless you've built frames before and understand the forces involved.


__________________________________________________
'83 K100 upgraded to K100RS spec
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California,
'03 Suzuki Blandit GSF600SK3 (NFS any more because wifey has claimed it)
    

Vitamin K

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Thank you. That is what I needed to know... and now I also see what AndrewP meant with his reply.

While I have not built frames before, I am capable of running a nice bead with my MIG. From what I have seen on just about every other k cafe bike, that pressed bar plus the welded hoop should be enough support... So it looks like I am welding the hoop.



Last edited by Vitamin K on Mon Oct 02, 2017 5:09 pm; edited 1 time in total (Reason for editing : additional information)


__________________________________________________
Father, Monk, Artist, Rider of the K

Current Ride:
1985 K100RT (slowing morphing into... "something")

Past Rides:
1970 R50/5
1975 R90S
1982 R65LS
    

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