Author Topic: Radiator shroud/radiator trim mounting tab fix  (Read 7718 times)

Offline Motorhobo

  • +25 years of K75
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Radiator shroud/radiator trim mounting tab fix
« on: March 18, 2025, 03:34:11 PM »
The tab that goes into the mounting grommet broke off. Wondering if anyone has had any luck epoxying or gluing it back on there. JB Weld isn't too good on plastic but they do make this PlasticWeld stuff...
UPDATE: See below for the fix

The pics show the broken piece and what it's supposed to look like on the trim section.

https://www.jbweld.com/product/plasticweld-epoxy-putty
1994/1995 K75 ABS Frankenbike: original engine 136k miles, frame from Gary Weaver (RIP), 173k miles -- Current Odometer: 198k miles
1994 K75 since 2013, 82,000 mi (19k mine) w/California Sidecar Friendship II Sidecar & Black Lab 'Miss B' - RIP

Past: 1974 Honda 550/4 (first bike), 1994 K75 (sold), 1995 K75 ABS (parts bike), Sidecar Dog & Best Bud 'Bo' - RIP

Offline natalena

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Re: Front trim tab broke off - is it JB weldable?
« Reply #1 on: March 18, 2025, 04:10:17 PM »
Have had great results with standard epoxy.  Acetone cleaning, scuff, acetone again, and then epoxy. Did the side panel spring retainers, and they're still holding.  Good luck,  Cheers
  • MST
  • 1987 K75s #0919, '05 Sportster 1200C, '21 ARGO 8x8, '24 KLR650
"Hard to beat a 10x beaver, 'specially if you're gonna work it."

Offline Motorhobo

  • +25 years of K75
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Re: Front trim tab broke off - is it JB weldable?
« Reply #2 on: March 18, 2025, 04:27:15 PM »
Thanks - when you say 'standard epoxy' I think two-part liquid resin epoxy like West Systems. That's a lot of mess I don't want to deal with and it seems too thin for this application. What brand of epoxy did you use? Was it putty, or liquid, or spreadable paste? There are many different kinds of epoxy, JBWeld being one of easy-squeezy out of the tube kinds. I'm trying to avoid unnecessary trial-and-error here...
1994/1995 K75 ABS Frankenbike: original engine 136k miles, frame from Gary Weaver (RIP), 173k miles -- Current Odometer: 198k miles
1994 K75 since 2013, 82,000 mi (19k mine) w/California Sidecar Friendship II Sidecar & Black Lab 'Miss B' - RIP

Past: 1974 Honda 550/4 (first bike), 1994 K75 (sold), 1995 K75 ABS (parts bike), Sidecar Dog & Best Bud 'Bo' - RIP

Offline natalena

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Re: Front trim tab broke off - is it JB weldable?
« Reply #3 on: March 18, 2025, 11:57:40 PM »
I'm thinking of the JB Weld Plastic Bond, which is technically a urethane, but is still a 2 part mix. About 8-9 bucks for a 2oz mix syringe. I've also used JB Weld Steel on BMW plastics with good results. West is the go-to for fiberglass and wood working. Cheers
*West Systems over penetrating epoxy on wood/wood/tungsten bond, and wood 316SS bond, over/under speargun.
  • MST
  • 1987 K75s #0919, '05 Sportster 1200C, '21 ARGO 8x8, '24 KLR650
"Hard to beat a 10x beaver, 'specially if you're gonna work it."

Offline Motorhobo

  • +25 years of K75
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Re: Front trim tab broke off - is it JB weldable?
« Reply #4 on: March 20, 2025, 12:42:55 AM »
Thanks, I'll go get me some of that JB Weld plastic stuff   112350
1994/1995 K75 ABS Frankenbike: original engine 136k miles, frame from Gary Weaver (RIP), 173k miles -- Current Odometer: 198k miles
1994 K75 since 2013, 82,000 mi (19k mine) w/California Sidecar Friendship II Sidecar & Black Lab 'Miss B' - RIP

Past: 1974 Honda 550/4 (first bike), 1994 K75 (sold), 1995 K75 ABS (parts bike), Sidecar Dog & Best Bud 'Bo' - RIP

Offline Motorhobo

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Re: Front trim tab broke off - is it JB weldable?
« Reply #5 on: April 04, 2025, 03:31:18 PM »
The JB Plastic Weld didn't hold, because the feet on the broken piece don't provide enough purchase, see the pic. So I'm going to create and 3D print a plastic block that will fill in the empty space between the feet. Then I'll glue that inside the empty space, then glue the assembly to the inside of the radiator shroud where it fits into the tank grommet.

Question is, how hot is it going to get in there? I want to use PETG which has a melting point of 176-185F or 80-85C. Anyone think that's going to be a problem?

1994/1995 K75 ABS Frankenbike: original engine 136k miles, frame from Gary Weaver (RIP), 173k miles -- Current Odometer: 198k miles
1994 K75 since 2013, 82,000 mi (19k mine) w/California Sidecar Friendship II Sidecar & Black Lab 'Miss B' - RIP

Past: 1974 Honda 550/4 (first bike), 1994 K75 (sold), 1995 K75 ABS (parts bike), Sidecar Dog & Best Bud 'Bo' - RIP

Offline The Mighty Gryphon

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Re: Front trim tab broke off - is it JB weldable?
« Reply #6 on: April 04, 2025, 06:11:04 PM »
How important are the cosmetics?  IMO the only reliable repair is mechanical. 

I would drill through the trim panel into the center of the stud and run a #4 sheet metal screw through the panel into the stud to provide the strength to take the pull necessary to pull the stud out of the grommet on the tank.  Put a washer under the head of the screw to help prevent it pulling through the panel. 

I think the part is molded in ABS.  I'm pretty sure the glue sold at the hardware store for ABS plumbing can be used to hold the parts in place while you do the drilling.  I think you can get a thickened gap filling adhesive that can add a little extra area to the bond by using it to make fillets.
  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

Offline sooprvylyn

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Re: Front trim tab broke off - is it JB weldable?
« Reply #7 on: April 04, 2025, 06:20:07 PM »
When my k75c rad shroud broke in this exact location after a crash I reaffixed it thusly:

1. Roughed up the inside of the shroud at teh mounting point pretty aggressively with a dremel and cutoff wheel. Had to be a little careful not to go all teh way through, but wanted some really good surface to bond to. Probably an area about 1.5" diameter. Made sure I had a lot of deep grooves and some undercuts all over the area.

2. roughed up the tab a bit similarly, cut some good notches randomly in several directions into the base w the cutoff wheel.

3. Used fiberglass reinforced filler(the catalyzed stuff you buy in a small tub) to reattach the tab, and sort of encompassed the lower half of the tab with the stuff.  I covered the entire roughed area with the filler as well.

Held well for a couple years after that, and even through a 2nd crash at speed hitting that same side of the bike.  I was always pretty careful disengaging the pin after that repair, just in case. You can sorta reach around to the back of the tab when its in the rubber grommet and push from the back instead of pulling on the shroud.
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Offline gard

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Re: Front trim tab broke off - is it JB weldable?
« Reply #8 on: April 12, 2025, 03:28:36 PM »
I repaired my side panels with a plastic welder, it is basically a solder iron with controllable temperature. The kit comes with filler rod. Easy enough to build new parts and add extra reinforcement if needed. A lot of body shops use them now. I have used my fair share of epoxy, self tapping screws, wire and tywraps but think the plastic welding is better in some cases.
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Offline Motorhobo

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Re: Radiator shroud/radiator trim mounting tab fix
« Reply #9 on: April 21, 2025, 03:26:40 AM »
This is what I did to attach the broken radiator shroud mounting tab. Pretty much the same as what sooprvylyn said, except I used fiberglass matte and epoxy. I put it on yesterday and tested it by removing it and installing it a few times. It looks super solid, lot more so than the original.

The problem with this OEM piece is that it's basically a hollow part with two feet that are molded to the back of the shroud. Those two feet are weak where they meet the shroud and break off, and being +25 years old doesn't help.

So the solution is to fill in that hollow part with epoxy putty give it a solid base to attach the shroud, and then add a fiberglass matte floor to the shroud. When you saturate the matte with liquid epoxy and press the part in place, the part sinks in to the matte. You can then add some epoxy around the base of the part to give it some extra bonding surface. I added some fiberglass cloth around two sides of the base, too, just for good measure. 

Materials:


* Two part epoxy putty, I used the West Marine stuff because a neighbor had some lying around.
* Two part JB Weld plastic epoxy, about $10
* Small square of fiberglass matte, about 1/2 inch larger than the base of the part.
* Two small pieces of fiberglass cloth for the corners where the base of the part meet the shroud surface.

Instructions:

1) Mix a small amout of epoxy putty.
2) Mix a very small amount of the JB weld plastic epoxy and add a thin coat to the inside surface of the hollow part.
3) Fill in the hollow section of the part with the putty and wait for it to set. This took about 1 hour for the West Marine stuff.
4) Sand the putty down so it's on the same plane as the two feet of the part. This will give you a solid base to glue to the shroud surface. Sand off any excess at the sides. You want to part to look the same as the original part, except with the hollow section filled in with putty.
5) Mark the position where the part will attach.
6) Lay out a square of fiberglass matte where the part will attach. The matte should be about 10mm larger than the base of the part.
7) Saturate the matte with JB weld epoxy.
8) Press the part in place.
9) Lay down two very small rectangles of fiberglass cloth on the left and right side of the part and press them into the corners where the base of the part meets the fiberglass matte.
9) Saturate the cloth and the outside corners where the base meets the fiberglass matte.
10) Press firmly into place and clamp.
11) Wait for it to cure. The JB weld stuff should cure quickly but I left it overnight.
12) Clean it up with a dremel with a sanding drum to get rid of any cloth or matte strand sticking up anywhere.
13) Install and ride.

This is what it looks like before I cleaned it up with the dremel.

BTW the K75 I bought from Gary Weaver (RIP) in 2013 had the drill-though-the-outside-of-the-shroud fix. It looks crap and I think the above fix might even be stronger. This is a better alternative, IMO.
1994/1995 K75 ABS Frankenbike: original engine 136k miles, frame from Gary Weaver (RIP), 173k miles -- Current Odometer: 198k miles
1994 K75 since 2013, 82,000 mi (19k mine) w/California Sidecar Friendship II Sidecar & Black Lab 'Miss B' - RIP

Past: 1974 Honda 550/4 (first bike), 1994 K75 (sold), 1995 K75 ABS (parts bike), Sidecar Dog & Best Bud 'Bo' - RIP

Offline natalena

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Re: Radiator shroud/radiator trim mounting tab fix
« Reply #10 on: April 21, 2025, 09:36:51 AM »
Looks like a robust fix, well done.
BMW engineers must have been chasing grams, as there's many tabs that are made with feet, like an I-beam on end, when a solid fixture foundation would be superior.

Many times working on the brick, look up at the sky and scream "KHAAAAAAAANNNNNNN!" in frustration.
  • MST
  • 1987 K75s #0919, '05 Sportster 1200C, '21 ARGO 8x8, '24 KLR650
"Hard to beat a 10x beaver, 'specially if you're gonna work it."

Offline The Mighty Gryphon

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Re: Radiator shroud/radiator trim mounting tab fix
« Reply #11 on: April 21, 2025, 02:22:47 PM »
Those parts are injection molded.  Molded plastic shrinks as it cools.  The engineers had to design the part that way to avoid having a sunken pit form on the visible surface of the part.  The design of the part is limited by the ability of the machine to get the plastic into where it needs to go, avoiding the sink in the surface, and the ability to get the finished out of the mold.

I have greatly reduced the force needed to remove parts held with those buttons by filing down the diameter of the button that is pushed into the grommet.  Take a little off, give it a try, take a little more.  Continue until you don't have to pull the bike over to get the part to release.  A little Petroleum Jelly on the pin helps a bit as well.
  • In my garage in Marilla, NY
  • '91K100RS White/Blue
Current:
'91 K100RS16V "Moby Brick Too"

Past:
'94 K75RT "Ilsa, She Wolf of the SS"
'92 K100RS16V "Moby Brick" (RIP, deceased in a vehicular assault)
'94 K75S Special Edition Dakar Yellow "Cheetos"
'89 K100RS Special Edition "Special Ed"

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