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MarioThePlumber

BMW Airhead Build Adventure

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Forks are about halfway built but no pics yet... That said, I decided to do the trickiest part today and mount the cylinders.

 First was installing piston rings and then getting the pistons in the cylinders

71FA342D-D64A-4F2E-B4E4-830FEA879E3F.thumb.jpeg.e4d37cfb6315ef397467c04c440851d5.jpeg

Next, get all the o-rings ready and apply a thin layer of gasket maker to the base of the cylinders; I have about 20 minutes before that hardens to install the wrist pins, cylinders, heads, and pushrod/rocker assemblies

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First one on and torqued.

02A2BF32-A658-491F-929E-8D5B4F7244F2.thumb.jpeg.58f293bad48a98965db52ce3a36496ec.jpeg

 Second on and torqued.

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11 minutes ago, BushPig said:

Still following.

Jeeze I miss street.

It's only fun on a dual sport. So many wheelies, so many two wheeled knobbie drfts on overcooked decreasing radius corner entries.... no seriously i about ate shit hard on saturday. 

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12 minutes ago, Doctor Impostor said:

It's only fun on a dual sport. So many wheelies, so many two wheeled knobbie drfts on overcooked decreasing radius corner entries.... no seriously i about ate shit hard on saturday. 

I cant decide.

I have three styles I'd choose from.

A DRZ is one.

A naked such as a bandit or a CB400-900 is another

Or even go the other way and do a CT110 build.

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8 minutes ago, BushPig said:

I cant decide.

I have three styles I'd choose from.

A DRZ is one.

A naked such as a bandit or a CB400-900 is another

Or even go the other way and do a CT110 build.

701E, you'll thank me later, unless you're inseam challenged

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16 minutes ago, Doctor Impostor said:

701E, you'll thank me later, unless you're inseam challenged

I am unfortunately. and too expensive.

Edit: I think a dualsport or street bike would be good. Just cant be F'd doing proper dirt rides anymore.

Seems like 2hrs riding = 1hr with the hose and then airfilter and oil etc and fixing what you broke. Tinker more than you ride.

Edited by BushPig

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On 2/15/2016 at 7:24 PM, MarioThePlumber said:

Some time around March 2015, I noticed the BMW acting strangely. When coming to a stop, if I pulled in the clutch, the bike would rev to 3000 rpm and stay there. The only way this would stop is if I didn't pull in the clutch until the bike was at idle. I also noticed excessive smoke out of the right exhaust.

 

I immediately stopped riding and let the bike sit for a few months, searching the forums for any information. I couldn't find anything that fit my description exactly, so in July, I decided to tear down the right side of the engine.

 

July, 2015: A picture is worth a thousand words.

207EA94A-9D38-493A-80DA-AB191D61460E_zps

 

E336B2EB-7427-4EBB-A9AD-DC7A48B6F3E6_zps

I found pieces of the wrist pin circlip in the oil pan. I believe it failed, rattled around the space between the oil ring and skirt, and then blew threw the skirt. Luckily, I didn't find any evidence of con rod or crank damage. I replaced the cylinder and piston, making sure to replace all the small parts as well.

 

Finally, I should have a working motor, and I got to ironing out the small stuff. I bought new points, and a timing light. I set the advance, properly adjusted the carbs, and took her for a spin. It ran like a new bike!

Ach du lieber! Ouch!

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58 minutes ago, MarioThePlumber said:

Forks are about halfway built but no pics yet... That said, I decided to do the trickiest part today and mount the cylinders.

 First was installing piston rings and then getting the pistons in the cylinders

71FA342D-D64A-4F2E-B4E4-830FEA879E3F.thumb.jpeg.e4d37cfb6315ef397467c04c440851d5.jpeg

Next, get all the o-rings ready and apply a thin layer of gasket maker to the base of the cylinders; I have about 20 minutes before that hardens to install the wrist pins, cylinders, heads, and pushrod/rocker assemblies

359094A9-218D-442D-9ECC-2B0A029536C5.jpeg.455603edcb8c3f082323267bea4003ea.jpeg

9C75FFE3-AD8C-407C-BE30-2E5028BDE955.jpeg.6ee49bcce1e2b52eb986526cc8746aaf.jpeg

592854F2-6794-4E42-BF87-E98B642A93D9.jpeg.98e982131f4767c2dee4fd2202d7100b.jpeg

A7B6FB47-3B3F-4DE9-B5C9-F3CAF1774228.thumb.jpeg.fee753006a25f82d69b628313acfa8ee.jpeg

First one on and torqued.

02A2BF32-A658-491F-929E-8D5B4F7244F2.thumb.jpeg.58f293bad48a98965db52ce3a36496ec.jpeg

 Second on and torqued.

Nice Bimmer Mario! Happyness is a fresh engine.....

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It’s nice having daily updates: forks installed, routing spark plug wires, front wheel and caller installed, rebuilding the carbs.

61E2ED77-0489-435C-988A-7718E99699B5.thumb.jpeg.2f5ceee0f33b09a7d3a93c60316c6b82.jpeg

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 It’s starting to look like a motorcycle!

Tomorrow should be finishing the carbs, continue with the front brake, and hopefully I can get to cables and what not.

I’m guesstimating I’ll be finished next week.

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One week later... still not done.

 Front brake is operational! Fork oil added and top caps torqued, carbs have been rebuilt and installed, all cables are in.

186E07D5-0855-4805-BA57-05E3E543FF97.thumb.jpeg.b0ab152b22059d468ad6c43f79d2791b.jpeg

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Still got a few things to finish up... fuel line and tank, valve adjustments, ignition timing, drop oil pan.

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On 7/16/2020 at 5:15 PM, MarioThePlumber said:

One week later... still not done.

 Front brake is operational! Fork oil added and top caps torqued, carbs have been rebuilt and installed, all cables are in.

186E07D5-0855-4805-BA57-05E3E543FF97.thumb.jpeg.b0ab152b22059d468ad6c43f79d2791b.jpeg

D6C0F5AD-9D44-4BD7-8C15-29071BF9FB09.jpeg.f0664bd631295b41bf4e423485866448.jpeg

F93C04BC-B35B-46B0-976F-6312276DFD6C.jpeg.65743dd8f78850f0a03b00d984108058.jpeg

0815C66E-4BD9-4D3A-A67B-D628C12BCE65.jpeg.e727eac13a976830931b866050170fc8.jpeg

Still got a few things to finish up... fuel line and tank, valve adjustments, ignition timing, drop oil pan.

What's the hydraulic reservoir thing on top of the frame? Clutch, or brake?

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7 hours ago, RichieGoatGruff said:

What's the hydraulic reservoir thing on top of the frame? Clutch, or brake?

That's the infamous under-tank front brake master cylinder.  They're prone to leaking and of course require tank removal to see what's going on and maintain.'

Plus they're cable-actuated from the brake lever, adding a certain a-typical ambiguity to an otherwise Germanic approach to engineering.

I'm putting a 'big brake' kit on my R75/6 which allows running a 330mm front rotor, 4-pot Brembo caliper and am converting to a later-year Airhead 14mm bar-mounted master cylinder setup with a single braided line between the MC and caliper.

After riding my F800ST with dual front ABS brakes, my KLR650 with a 320mm Galfer conversion and even my DRZ400S stock brakes, the old Airhead brakes just don't stack up even with a new rotor, new pads, Speigler brake line - still wooden as Pinocchio.

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BTW - with the Siebenrock 'power kit', I'd seriously recommend the upgraded brakes.  I have the same piston/cylinder setup on my R75 and a free flowing Keihan full stainless steel exhaust with open 'silencers' (Jim Cray spec).  Loads of power means you need loads of brakes.

Google R90X Big Brake and you'll find their FB page (don't seem to have any other web presence).  https://www.facebook.com/groups/1114082135373983/ 

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2 hours ago, Tim DTT said:

That's the infamous under-tank front brake master cylinder.  They're prone to leaking and of course require tank removal to see what's going on and maintain.'

Plus they're cable-actuated from the brake lever, adding a certain a-typical ambiguity to an otherwise Germanic approach to engineering.

I'm putting a 'big brake' kit on my R75/6 which allows running a 330mm front rotor, 4-pot Brembo caliper and am converting to a later-year Airhead 14mm bar-mounted master cylinder setup with a single braided line between the MC and caliper.

After riding my F800ST with dual front ABS brakes, my KLR650 with a 320mm Galfer conversion and even my DRZ400S stock brakes, the old Airhead brakes just don't stack up even with a new rotor, new pads, Speigler brake line - still wooden as Pinocchio.

Thanks, I looked at the front in that series of pics, and it looked like a drum brake. After I posted, I scrolled up and found a better pic, and saw the disc... Kinda bizarre!

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3 minutes ago, RichieGoatGruff said:

Thanks, I looked at the front in that series of pics, and it looked like a drum brake. After I posted, I scrolled up and found a better pic, and saw the disc... Kinda bizarre!

It's a pretty weak design.  The MC is prone to leaks as well, stripping the paint off the frame leading to corrosion.  There's a goofy o-ring between the reservoir and MC housing that fails.  The MC body then actually corrodes, ruining the seating surface for the o-ring.

It's also mounted to the frame with a hose clamp - no joke.  No threaded bosses in the frame to bolt to - just a nice BMW stamped hose clamp strapped around the MC housing and frame tube.

Anyhow - for a 45 year old bike, my 1975 works well enough and I've only rebuilt the MC once with a thicker o-ring to eliminate the leak.  BMW also has a warning light with a float switch in the MC to alert you to the fact you're low on brake fluid.  But there's a reason they moved to traditional handle-bar mounted MC's on later years.

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8 hours ago, Tim DTT said:

It's a pretty weak design.  The MC is prone to leaks as well, stripping the paint off the frame leading to corrosion.  There's a goofy o-ring between the reservoir and MC housing that fails.  The MC body then actually corrodes, ruining the seating surface for the o-ring.

It's also mounted to the frame with a hose clamp - no joke.  No threaded bosses in the frame to bolt to - just a nice BMW stamped hose clamp strapped around the MC housing and frame tube.

Anyhow - for a 45 year old bike, my 1975 works well enough and I've only rebuilt the MC once with a thicker o-ring to eliminate the leak.  BMW also has a warning light with a float switch in the MC to alert you to the fact you're low on brake fluid.  But there's a reason they moved to traditional handle-bar mounted MC's on later years.

Yep, rebuilt the MC about 5 years ago. I don’t plan on upgrading the brakes though. They did “just fine” before the engine rebuild and I plan on riding it the same way once it’s running again.

Also, there’s a whole lot that goes into upgrading brakes... new stanchions, wheel, caliper... I don’t want to even think about it.

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Posted (edited)
On 7/20/2020 at 9:18 PM, MarioThePlumber said:

Yep, rebuilt the MC about 5 years ago. I don’t plan on upgrading the brakes though. They did “just fine” before the engine rebuild and I plan on riding it the same way once it’s running again.

Also, there’s a whole lot that goes into upgrading brakes... new stanchions, wheel, caliper... I don’t want to even think about it.

The “R90X Big Brake” upgrade is dead simple, if not cheap.  The adapter kit he sells let’s you mount a 330mm rotor to the BMW front wheel, and mount the Brembo caliper to the stock fork.

Many leave it at that - brake line from the stock MC to the caliper and off you go.

Edited by Tim DTT

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Hopefully I’ve ordered the last parts I’ll need (minus battery). Petcock rebuild kits, updated valve cover studs (BMW increased the length by 5mm sometime in the ‘80s), and battery box mounts ($1.20 ea at McMaster Carr vs $10 ea OEM).

 Fuel line was installed, forks buttoned up, spark wires cut and installed.

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