87 K75 Complete Rebuild

[frankenwing]

New to this site. Been building some different bikes for a while. This one's my first BMW. So I'm pretty excited about it. I picked this one up a few weeks ago for $650. It's in pretty rough shape, but I was able to ride it and test it at least. Motor sounds and runs strong.

I'm doing this build in 2 phases. The first phase is to get some necessary work out of the way. Since the purpose of buying this bike is simply because my wife and I don't have a bike that we can ride on together. All our other bikes are single seater customs of mine. And we have a bike trip planned soon.

2nd phase will consist of the finer details. Like making a new 2-up seat designed specifically for this frame. Then maybe some minimal frame modification at the far back. Wire up new gauges and dashboard (from what I've read, thats a bit of a mission for these bikes). The rest is uncertain, it really just comes down to how i see my vision moving forward once I get there.

So a list of things to be done:
• Fix and update wiring issues. Couldn't believe the botch up job that was done to "fix" broken things on this.
• Clean / Rebuild injectors and throttle body.
• Clean out and paint motor block. Polish up some metal bits. Remove paint off of some things and polish.
• Polish/paint valve and cam covers.
• Powder coat wheels and frame to a faded goldish color.
• Paint tank white.
• Repaint remaining body parts black.
• Maybe reshape front fender a little bit

Here's the bike as I bought it and brought it home:

[frankenwing]

After taking the bike apart, finally got to see how much crap there was to clean off. Some areas had up to an inch of caked on mud/grease!

[frankenwing]

Before and after of basic cleaning on the throttle body

[frankenwing]

Painted the motor block / valve cover / swing arm etc black

[frankenwing]

After cleaning out the throttle body and injectors, i started to put some stuff back together. Cleaned out the airboxes and a fresh coat of paint to cover up some faded plastic.

Stripped the paint off of the fuel rail, shifter, brake pedal and a number of other things.

[Shiny]

Do you have any pictures of the masking you did on the block/transmission? Any worry about separating pieces/covers when you need to disassemble in the future?

And good lord, did you use a pressure washer or 20 rolls of paper towels to get all that grease off? That's incredible.

[frankenwing]

I started with oven cleaner to get rid of the majority of it as quick as possible. That stuff is gold. Just dont ever let it sit TOO long. I also bought one of these things: https://www.shop.brushhero.com This is absolutely one of my favorite toys for cleaning bikes.

No pics of masking. I did however remove all the panels that can be removed easily from the motor and painted separately. Then just covered and masked any open areas of the motor. Simple enough job.

[Shiny]

Now I really want a Brush Hero. Even the dog, they say...

For masking the block without the valve, crank, and timing cover, just painters tape and like newspaper or something?

[frankenwing]

Yup, thats all I used.

[kennybobby]

Are you going to paint the crank cover too?

Why remove the black coating from the fuel rail--black radiates heat better than anything and you want your fuel cool...?

That was the worst greasy motor top that i've ever seen--how could it get that bad.

[frankenwing]

I've painted the inside grooves of the crank cover. The rest of it I'm polishing. Still workin on that.

As for the temp on the fuel rack, that's not something I thought of. But after thinking about it, wouldn't it be hotter with black still on it? I'm no scientist or anything. Just assuming that it would absorb more heat if it was black, right? With the cleared metal its going to reflect light. But maybe I've got that backwards?

[Shiny]

Unpainted metal will have a higher thermal conductivity, thus transferring heat more easily. Black paint would absorb more heat from light. It doesn't matter in the least.

[frankenwing]

Interesting. Definitely nothing I factored in. I'm thinking since the fuel will pass through there fairly quickly anyways, it should be fine and not have any affect. But if it does it's easily reversible.

[Shiny]

Yeah I don't think the temperature of the fuel changes much after it leaves the tank and gets to the injector. I've heard of fuel boiling in the tank, but not too much you can do about that.

[kennybobby]

Black absorbs energy better than any other color, and it radiates in the infra-red region (aka heat energy).

my k75 fuel tanks have a sheet of insulation glued to the bottom to reflect engine heat away from the tank.

The action of the fuel pump puts heat into the fuel, it gets recirculated constantly thru the fuel rail and back to the tank.

We paint electric motor housings black and they run 10-20 degrees cooler than if left unpainted aluminum.

But don't take my word for it, do your own research if you care or think it matters.

i think painting the engine and trans black was a good idea, for looks and thermally.

[frankenwing]

Finally an update to show for. The frame and wheels have been with my powder coat guy for a few weeks (been taking forever) and I'm finally picking them up today. I've fixed the wiring issues and repaired the botched up jobs. So now it's just time to start putting it back together. Will be ready to paint the tank and panels soon.

[Vespa no more]

Re: Black paint on fuel rail

On an RT, the fuel rail is covered in foam. As a result heat conductivity would be next to nil - either heat loss or heat gain.

Really don't think it is a concern. Furthermore, your bike may end up naked (no foam), so heat loss will occur if anything.

While you have it apart, you might update the radiator fan to a Spal 6.5" puller fan (approx $50 and up) - my current project. Coupled with the insulation blanket on the underside of the fuel tank, heat issues should not be a concern.

Regards

Guy

[frankenwing]

Thanks for the tip on the fan. I do hear a lot about peoples' fans seizing up. I currently have a manual switch hooked up for it as well.

Got the frame and rear wheel mounted now, absolutely loving the gold finish.

[herseyb]

Whoa, that black and gold! It's totally baller, as I would have said as a teenager.

  I kind of hope you're down in New Orleans.

[frankenwing]

It was a bold move for me, I've always stuck with black frames. I just had a vision for this one and i saw the gold frame and wheels working really well. The tank will be a white / pearl, and remaining body parts will be black.

[jakgieger]

  can't wait to see the finished product...

[TrueAce]

Great attention to detail! You are going to have an awesome bike!

[frankenwing]

Inching along

[TrueAce]

BEAUTY! :clap:

[Markus77]

Looks amazing so far! Looking forward to seeing how it progresses:)