Author Topic: K75S Belly Pan Repair (Read 11299 times)

The Mighty Gryphon · « **on:** February 21, 2018, 03:25:16 PM »

Had my K75S knocked over a while ago. Knockdown bent some stuff, scratched up the left side fairing and cracked the belly pan where the car that knocked the bike down hit it.

The pan was cracked and the crack opened and closed as the pan was flexed. To stabilize it I needed to add a couple layers of fiberglass to the back to add rigidity to the pan.

First, I scuffed the area to be glassed with 100 grit paper. Then I made two paper templates for the fiberglass and cut out three pieces of fiberglass mat for each patch. Each piece was cut 1/4" smaller at the edge away from the ribs than the next piece.

I mixed up an ounce of polyester resin and laid the glass. Because the patches were pretty much flat I did all three layers in one layup. If there had been any sharp corners or tight curves I would have had to do each layer individually and wait for the resin to begin to set up/gel before adding the next. I started with the smallest patch, going bigger with each successive one. That makes for the smoothest repair.

Since the wife wouldn't allow me to work in the house I had to use a hair dryer for about 15 minutes to get the resin to set up in the 40 degree garage. Tomorrow, after the resin has had overnight to really harden up I'll open up the cracks in the front and fill them in with Bondo.

Chaos · « **Reply #1 on:** February 21, 2018, 03:30:34 PM »

a banana peel should hide that crack nicely

wally.fisher · « **Reply #2 on:** February 21, 2018, 03:47:23 PM »

Quote from: The Mighty Gryphon on February 21, 2018, 03:25:16 PM

Had my K75S knocked over a while ago. Knockdown bent some stuff, scratched up the left side fairing and cracked the belly pan where the car that knocked the bike down hit it.

The pan was cracked and the crack opened and closed as the pan was flexed. To stabilize it I needed to add a couple layers of fiberglass to the back to add rigidity to the pan.

First, I scuffed the area to be glassed with 100 grit paper. Then I made two paper templates for the fiberglass and cut out three pieces of fiberglass mat for each patch. Each piece was cut 1/4" smaller at the edge away from the ribs than the next piece.

I mixed up an ounce of polyester resin and laid the glass. Because the patches were pretty much flat I did all three layers in one layup. If there had been any sharp corners or tight curves I would have had to do each layer individually and wait for the resin to begin to set up/gel before adding the next. I started with the smallest patch, going bigger with each successive one. That makes for the smoothest repair.

Since the wife wouldn't allow me to work in the house I had to use a hair dryer for about 15 minutes to get the resin to set up in the 40 degree garage. Tomorrow, after the resin has had overnight to really harden up I'll open up the cracks in the front and fill them in with Bondo.

Just a hint to prevent further vibration cracking, drill a small hole on the ends of the crack.

Sent from my ONEPLUS A5000 using Tapatalk

The Mighty Gryphon · « **Reply #3 on:** February 22, 2018, 08:17:39 AM »

After curing hard overnight I can open up the cracks on the outside to prepare them for filler. A Dremel tool with a 1/16" ball milling bit gets it done in about 5 minutes. Next is to get some fresh ultra thin CA glue to put in the cracks before filling them in.

This is an important step in the repair because if the cracks aren't opened, they can't be filled, and when the paint is done they will show up worse than before.

The Mighty Gryphon · « **Reply #4 on:** February 22, 2018, 07:34:44 PM »

A bit of bondo to fill in the routed out cracks. Sanded with 100 to knock it down and then 220 wet sanded to feather in the filler to the surroundings.

Next was a couple coats of high build primer surfacer. I use the lightest gray I can find. The lighter the primer is the brighter the final paint job will be. Wet sanded with 320 to smooth it out and feather the edge. Then I look at the surface with a light almost parallel to the surface to show up any defects. The Bondo almost always has tiny voids and shows an edge where it is feathered into the much harder clear coat. The defects are filled with a red spot putty in several super thin coats.

I wait about an hour and wet sand the spot putty with 320 until all that is left is the stuff right in the defects. Two more wet coats of primer surfacer and I gently wet sand the whole part with 600 to remove the primer overspray and smooth the primer.

Check again with the light for defects, none seen. We're ready for paint, probably next Monday when the weather is supposed to be in the low 50's and sunny.

The Mighty Gryphon · « **Reply #5 on:** February 22, 2018, 07:40:48 PM »

In case the moderators want to put this up as a turorial on fairing repair I am deleting all my posts on this thread that don't refer to the repair process ie. chit chat.

lmiklosy · « **Reply #6 on:** February 22, 2018, 07:59:38 PM »

I have to make the same repair to mine so I have two questions. Are you using a sanding block with the 320 to prevent digging in the finish? I planned to paint the inside a dark grey to cover the blemishes like factory overspray and now the fiberglass patch. Do you plan to paint the insides?

Kind Regards.

The Mighty Gryphon · « **Reply #7 on:** February 22, 2018, 11:51:51 PM »

My pan is uncleared Dakar Yellow Base coat inside. I'll do the same when I paint.

Yes, I use sanding blocks. Mostly small chunks of wood with the paper wrapped around them. So far, on this job, I have used a piece of pine 3/4"x1/2"x2" long. On other jobs I've used bigger blocks and pieces of hose ranging from 5/16"o.d. to 2 1/2" o.d.. Depends on the shape of what I'm sanding. Sometimes, though, you just have to use a small piece of paper and your fingertips.

I don't use the 3M blocks. They're too big, and use too much paper. I can usually do all the parts of a bike with 1/2 sheet of 220 and 320 and 2 sheets of 600. If I want to sand the clear for buffing a couple sheets of 2000 and 2500 will do it. A couple scraps of 100 or 180 will knock down the high spots when I do Bondo. I try to wet sand as much as possible with some soap and water and a sort of light touch, makes the paper go almost forever.

richarddacat · « **Reply #8 on:** February 24, 2018, 06:56:29 PM »

Nice job. 🤙

Kinda doing the same to one I bought years back.
Dug it out today and repaired minor cracks with JB Weld. Doing the sanding and repaint from red to white.

I’m missing the bottom brackets and will add a WTB in the flea.

Looks like yours will come out better than new.

Sent from my iPhone using Tapatalk

The Mighty Gryphon · « **Reply #9 on:** March 04, 2018, 12:12:46 PM »

Got it all back together...

richarddacat · « **Reply #10 on:** March 04, 2018, 03:36:35 PM »

Looks great, good work.

Should have mine together this week.

Filmcamera · « **Reply #11 on:** March 04, 2018, 06:07:32 PM »

Great work, great colour, great bike! Colour it dakar yellow and me envy green lol

lmiklosy · « **Reply #12 on:** March 04, 2018, 10:00:12 PM »

Nice Job! I'm doing a Mystic Red three-stage wish me luck. Gulp. FYI here's another Dakar Yellow in San Diego, been posted over a year with recent price drop. https://sandiego.craigslist.org/csd/mcy/d/1994-bmw-k75s-abs/6515430502.html

Cheers.

The Mighty Gryphon · « **Reply #13 on:** March 04, 2018, 11:17:25 PM »

GoOd luck on your paint job. I just did some Pearl Silver tri coat. My first go with that paint system. The tricky part is getting enough of the mid-coat to get the effect without obscuring the base coat. Fortunately I was just doing some repair to a corner of the tank and the battery covers, so I was able to use my airbrush for the base and mid coats.

My K75RT is Mystic Red and I've done a lot of repair on it. If you have problems with doing a tri coat paint job on your bike, you can get a good match in a conventional base/clear paint job. I use paint mixed by a local auto finish shop that is very close to Mystic red but doesn't use a mid coat. It's a minor adjustment to a Ford color made by slightly darkening the red. The Name is Red Fire color code G2. I can't see the difference from the factory paint.

lmiklosy · « **Reply #14 on:** March 05, 2018, 05:50:59 PM »

Thank you Gryphon,
the hints on Mystic Red are very helpful. Here's the paint I used, reading from the can label:

Undercoat (1) and Colorcoat (2)
900+ Series Basecoat
900-170720 OMR
Ford USA (RR)
Ruby Red Met-1
The 'Met-1' is a variant on another lighter shade of this one.

Clearcoat (3)
Nu-EVO Premium Clearcoat 2.1 Low VOC
NE2100

I find the middle coat is the difficult one. The match is good but the shade varies depending on how much middle coat used. Next time I will try the airbrush on the spoiler to lighten-up the shade, I'll post before and after photos.

Cheers!

The Mighty Gryphon · « **Reply #15 on:** March 06, 2018, 01:01:16 AM »

HAve you done a let down card? It will help get the right amount of mid coat.

Only clear half the card so you can match the amount of mid coat to get the final color under the clear.

lmiklosy · « **Reply #16 on:** March 07, 2018, 02:04:44 PM »

Very helpful Gryphon, how did you know I'm painting a car next? Those videos by Eastwood are a goldmine for us beginners, I better watch 'em all first.

Cheers.

lmiklosy · « **Reply #17 on:** March 18, 2018, 03:47:29 PM »

The paint system for the stock metallic finish consists of four paints (see previous discussion), a lacquer grey primer, a metallic undercoat, a colorcoat, a clear-coat with hardener in two steps. Here in seven photos is how I prepared and finished a Mystic Red spoiler from a '93 K75s. Success was not revealed till the very last step: a liberal finish clear-coat. This job requires all the confidence you can muster, so have patience and take time! Good news: the colour matches spot-on. Bad news: the finish still needs a buff-out after the paint has cured (allow a week).

Photos in sequence: 1) Chasing cracks with a Dremel 2) Bondo and Wet or Dry 240 to remove polyurethane clear coat 3) Primer and Wet or Dry 400 4) Metallic undercoat 5) Colorcoat 6) Medium clear-coat as adhesive 7) Liberal finish clear-coat.

Thanks to Gryphon for directions and courage. Good Luck!

The Mighty Gryphon · « **Reply #18 on:** March 18, 2018, 05:10:08 PM »

Nice job! What kind of gun did you use? I'm going to try using a Harbor Freight gun that I reworked to clean out all the bathtub caulk and resealed to stop all the air and paint leaks. Haven't put any paint through it yet but it seems to throw a nice fan with straight reducer.

Looking forward to warmer weather when I can get my parts done. Meantime, I'm putting together a small spray booth to shoot bike parts. I don't want to get 2K clear all over the garage.

maynardjr · « **Reply #19 on:** March 14, 2021, 01:31:05 PM »

I'd like to say thank you to Gryphon for how helpful this thread has been. I cracked my belly pan after knocking my K75S off the center stand in the driveway. It turns out it had been cracked and repaired by a previous owner, who then painted it black instead of the Marrakesh Red. With the help of this thread, it now looks better than when I bought the bike. From somewhere else on Motobrick.com, I found that Jaguar Salsa Red 1964 is a close match for the Marrakesh Red. I used rattle cans of the Salsa Red from automotivetouchup.com.

Before (after stripping the black and routing the crack):

2020-11-21 20.05.27.jpg (62 kB . 768x576 - viewed 810 times)

After:

2021-03-10 19.02.57.jpg (36.97 kB . 768x576 - viewed 805 times)

Back on the bike:

2021-03-12 16.48.28.jpg (123.58 kB . 768x576 - viewed 804 times)

The Mighty Gryphon · « **Reply #20 on:** March 14, 2021, 02:30:44 PM »

Nice job and a nice bike! Glad it worked out well for you.

duckhawk · « **Reply #21 on:** March 14, 2021, 09:36:32 PM »

Thank you for the excellent and very informative guidance on body work repairs. Like you guys, when I do work like this, I try to make the parts stronger than OEM.

stokester · « **Reply #22 on:** March 15, 2021, 07:08:17 PM »

I've used this thread on the repair of my '93 K75S with good success except that I may have to take it somewhere for the final coat of paint.
Does anyone know of a good substitute for the Seiden Blau (338/690 scheme)? I did find a source for Dakar Yellow because that was used on some Bimmers but nothing for the blue.

The Mighty Gryphon · « **Reply #23 on:** March 15, 2021, 07:51:18 PM »

Quote from: stokester on March 15, 2021, 07:08:17 PM

I've used this thread on the repair of my '93 K75S with good success except that I may have to take it somewhere for the final coat of paint.
Does anyone know of a good substitute for the Seiden Blau (338/690 scheme)? I did find a source for Dakar Yellow because that was used on some Bimmers but nothing for the blue.

BMW used BASF paint on the Bricks. The Glasurit paint system has the codes and formulas for our bikes.

These guys are Glasurit dealers according to BASF:

https://refinish.basf.us/where-to-buy/

NATIONAL COATINGS & SUPPLIES #1021
8304 Orcutt Ave
Hampton, VA 23666-0000
(757) 262-0375

stokester · « **Reply #24 on:** March 15, 2021, 08:23:33 PM »

Wow, Hampton. That's just down the road, I'll have to stop in.
Thanks.

News:

Author Topic: K75S Belly Pan Repair (Read 11299 times)