BMW Airhead Drag Bike

[Dexter]

Part 2 of the swingarm mounts, cut up some more plate and added a gusset and walked the welds fully underneath and round over the top as well.

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Had enough of groveling about on the floor so to aid the setup of the swingarm etc the bike now sits on a new B & Q bench thing that father Christmas left.....

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Next up was sorting the rim to hub offset break out the string line and straight edge....

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Ended up with a 10mm rim offset to get the tyre in the center of the swingarm, this should still have clearance to the plunger tube but this is sort of dependant in how much the rear tyre grows when inflated, the bits of BMW gussets will now need to all be removed from the inside of the swingarm but thats a mega grinding job so need to work up some enthusiasm.....

Last part was the sorting out the swingarm side strut mount, we wanted to reuse the BMW bracket so some careful cutting with a thin disc then a reposition - the the new location around 15/20mm further back and weld into position.

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Making a long weekend over the BH so hope to get the rear hub and rim off the the wheel builder .... could be on 2 wheels soon.....

[Dexter]

In swingarm news the gussets were removed not the best job for a hot Sunday however needs must final weding of the pivot tube is still outstanding though.......

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expensive scrap

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[Dexter]

So bit of an update while we wait for the rear wheel, started to look at mounting the mangement box and then the coil pack.
Wanted to fing a place to hide its location as this should be a fit and forget so easy access was not the first priority. Ended up finding a space so its hidden inside the tank used some thin mild steel plate and made some folds to give it some more strenght have a look at the photos this may help..
Oh and yes that is 9000 on the box guess the engine will sound good at those
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Ok so next up was the coil bracket

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Then it was on to some rubber action but first set up the forks and using a cable tie as a marker finished off the final true up of the front wheel and tightening of the spokes.

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Ok so about that rubber... fitted the new rim tape then lubed up the tyre and managed to get this over the first part of the rim, threaded in the new tube then the difficult bit or it was for me... again bit more lube got the valve through then with some home made levers the tyre slipped into place well not really slipped but you get the idea. Popped up to the local garage and pumped it up, tyre came up nice on the bead - jobs a good un.

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Final job was to drill off some air holes in the front drum casting...

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Next up need to make up a drum steady and the drum casing has a sleeve pressed in for spindle location but it's 14mm and I am running a 17mm spindle so be on teh phone to moto-bins Monday see if they can help

[Dexter]

Next up was the battery mount, based on the origonal location but just added a keeper plate plan to add a front keeper as well found a nice srap with a turn buckle which should suffice. The lithium battery is just for trial as the ingnition system is total loss and from what i have heard they are good at most things but not suitable for my application.

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On the front spindle Moto-Bins could not help on this occasion - part no longer avalible so it looks like our trusty machine shop is back in business, not sure if we will make a new bush from scratch or machine out the current one to size.......leave that for another installment.

[IndianaSlim]

Thanks for the update!

[Dexter]

Hi IndianaSlim - more progress.......

The rear wheel was finally done and my able assistant picked this up for me while langrished by a pool in sunny spain

looks nice and they have managed to get the offset I needed, if I get some time now i am back will try to marry the tyre to the rim.

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Getting excited.......

[BUKNEKK4D]

In for more, this thing is looking killer.

[Dexter]

Hi Buknekk4d

Thanks using your first post on this lots of updates coming this weekend so hope you like them.....

[BUKNEKK4D]

I run Jap bikes myself but I sure appreciate a nice airhead.

[Dexter]

Next progess update

Re fitted the swingarm with the wheel mounted, clearance seems good but until the tyre gets mounted and some final checks fingers will stay crossed.

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[IndianaSlim]

Have you considered beefing up your swingarm?

[Dexter]

Hi Indianaslim

Not really thought on these lines but like the picture is this something you have any experience of ? I guess its depend how much power is being put down.....

Getting into a stride now... ok a brisk walk

Finished off the battery holder used the ali solder again really like this stuff.
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Then after the cock up on the valve hole couldnt wait for the replacement tube to turn up ( so impatiant) so stuck the tyre on the wheel just to take a look - the drag tyre with soft sidewalls was so much easier then the front to get on. So as this was only a tempoary fit its not 100% conclusive however the clearances to the swing arm look good and there is ample room to restore a gusset arrangment to the spindle area.

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Next up we had bought a universal set of rearsets quality was good and they have the ability to move the actuation point about which look as if it might be handy, the plan was to use the origonal rear peg locations to bolt these up but its never that simple. The fixing bolt which fiited within the peg was not even close to being a good fit so we made up a spacer

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[Dexter]

New tube has arrived so this was fitted this morning and then we were on 2 wheels, tyre to swing arm tube now we have some air in there is a bit close for comfort so looks like the grinder is coming back out for some action.

The forks have been fitted but without the new bearings so very much jury rigged for this trial, forks went through various iterations as we experimented with ride height. At this stage all we wanted to acheive was the desired ride height so the faring could be mocked up and then look at making mounting brackets so dont take too much notice of the forks at this stage as the day progressed we have come up with what we hope will be the final solution just need to sort out the springs.









So that fairing.... we started by pulling it passed the barrels and then spent ages getting the right stance bits of wood and boxes....ready to mark up the section which would be cut round the barrels we would keep these as small as possible at this stage and look to do teh final fitting when all the mounts are in place





Next up the front mount was made up using some already tapped holes in the headstock.



Cut outs for the barrels



And sort of mounted to the bike

[555]

Also remember that rear tire will "grow" when it gets hot. Look at a video of a drag car and you can size the tire increase in diameter.

[IndianaSlim]

Also remember that rear tire will "grow" when it gets hot. Look at a video of a drag car and you can size the tire increase in diameter.

Under power the rear of a BMW "jacks up", which may give that rear tire more clearance.

Dexter, my experience is all '73-'77 BMWs. In the search for better handling the things I've done were:
billet top clamp and fork brace to firm up the forks
frame braces to reduce flex
swingarm brace to reduce twist.

In your case maybe the swingarm brace is the one that may have the most value.
Thank you for posting all of this, I'm digging it!