Fixing plastic mounts before painting

[BigD_83]

I'm coming up on repainting the 650G, and I have a rather troublesome issue.

One of the rear tail cowling mounts is broken.

Here is a picture of the similar broken mount on a different tail piece. The part circled in red is the forward mount:

On mine I believe I have a little more plastic left, but not much more. Is there a straight forward way to build it back up so it is both strong and good looking?

 

[rustybronco]

It should be made out of ABS. Find some scrap ABS from an automotive bumper cover or similar, mix up some ABS/acetone 'slurry', fixture the scrap ABS to your tail piece and glue them together with the slurry.

 

[spyug]

As Rusty says that is the way to fix it. ABS slurry will bond with the existing plastic as it is the same product. You can make the slurry like a putty by adding chips of ABS to the acetone to thicken it up. Mix it as thick or as thin as seems right for the application. Let it dry thoroughly and work it to make the shape you need.

ABS plastic is readily available from the hardware stores in the plumbing section. Black or white pipe. Either will.do.

If you have a plastics supplier about they will sell sheets in 4'X 8' and will liklely have cutoffs they can supply you with.

Once you get the hang of mixing the paste there is no end to what you can repair or create.

Good luck and show us what you can do.

Cheers,
spyug

 

[BigD_83]

I have tried the ABS paste on another application (seatpan) on a Honda Rebel and had problems with it bonding.

One thing I was considering was making a mold out of the unbroken side and casting the replacement grommet with the ABS slurry, and possibly sinking in a washer to take the stress out of the plastic.

Do you think building the ABS up around a metal washer in would just weaken the plastic by making it too thin? My limited experience suggests the ABS slurry does not bond all that well to metal.

Is there some preparation step that I can/should do to the unbroken piece in order to maximize the strength of bond? Maybe pre-wet it with a little acetone or roughen it up with some coarse-grit sandpaper?

 

[cableguy]

There are lots of YouTube videos on plastic welding with soldering irons as well as torch-heated screwdrivers. The idea is you melt along the crack, creating a valley in the plastic, then adding filler material, usually zip ties.

 

[rustybronco]

Personally I wouldn't try bonding a washer to ABS. I would build up a new tab with ABS, or fabricate a new piece and bond it on. You could also fabricate a metal replacement tab and either bond it or pop rivet it onto where the broken piece was located at one time.

I'm sure you can find something here that would work well at bonding a new piece onto your tail section. http://www.lord.com/products-and-solutions/adhesives/plastic-bonding.xml/81/6

Are you sure that seat pan you tried bonding was made out of ABS?

 

[spyug]

As I mentioned, you can get abs sheet in various thicknesses. You can then fabricate the piece you need to replace and bond it in with the slurry. The secret to the slurry is getting it to the right concistency. Not too runny nor too thick. This is an extension piece I fabricated for the chin fairings on my 82 Kat. They are normally formed in a grill shape but always seem to break off so I just replaced it with this solid piece.

As Rusty says, I don't think bonding a metal washer will work. I think you are better to stay with the ABS and put in an extra thickness as a backing plate as it were.

If it would help , I can send you some small pieces of 3mm sheet. Just PM me with your name and address.

cheers,
Spyug

 

[jpaul]

I wouldn't try to sink a washer into the ABS either. I would think it would weaken the whole assembly as far as vibration resistance goes. I would try putting a washer over the hole, assuming there is clearance to do so. Any epoxy would hold the washer in place to make assembly easier when you go to mount it on the bike. If there is room enough, I would make a rubber washer out of an old inner tube and bond it to the metal washer to go between the washer and the ABS. The ABS will be susceptible to stress fractures from vibration over time. The combination of a metal washer to distribute the forces over a wider area, plus the rubber to dampen some of the vibration should make for a longer lasting assembly.

 

[spyug]

You can see on the remaining tabs that they use a rubber grommet with an inner metal sleeve that the bolt passes through. The grommet gives "flex" to the plastic piece. If you add a washer to it in place of the rubber grommet it will take away this ability to flex and it will crack again im sure.

I would try and replicate the tab in sheet plastic and bond it with the ABS slurry. If done properly it will hold up fine as the slurry melts both the existing and new piece and when cured it all becomes one piece of plastic again.

If it wouldn't be so expensive, I'd have you ship it to me and I'd do it for you.

Good luck,
spyug

 

[BigD_83]

If it wouldn't be so expensive, I'd have you ship it to me and I'd do it for you.

Good luck,
spyug

Now where would the fun be in that? I appreciate the offer, though.

All good advice coming. My biggest concerns with just building it up with ABS slurry is the strength of the piece due to the mating surface of the broken piece being quite small, and sagging of the slurry.

Perhaps Spyug's suggestion of fabbing the mount using a piece of 3mm sheet ABS is the ticket.

Pretty sure I have some replacement bushings somewhere in my pile o' stuff. If not, I believe they are still available from Suzuki. Or, as suggested, a couple of pieces of rubber bonded to a metal washer with Loctite 480 should do it.

I recall seeing a commercially available paste/semi-solid plastic that was workable when "wet", and drillable/sandable when dry, but have not been able to find the product again. However, I do not recall the name of the product (Super-something maybe?). It could be used to build up quite large forms.

 

[SVSooke]

First off be sure it is ABS,not all Suzi plastic is.The lowers on the 85 where not,acetone did nothing but clean the plastic off.Slurry works a charm on ABS for sure and plastic welding is WAY easier than it sounds so look into that if you piece turns out to not be ABS.

 

[BigD_83]

Is plastic welding effective on such small surface areas? I see how it would work well on a side cover, or the chin fairing Spyug showed.

Other than hitting it with acetone (which I am not opposed to doing), do you have any ideas on how to confirm the plastic is ABS?

 

[spyug]

The other stuff I use a lot of for various things is plumber's epoxy putty. A two part putty like play-doh that goes rock hard in 10 to 15 minutes. Fully workable when cured. Available in the DIY stores and now most auto stores. Some brands have aluminum, copper or other materials like fiberglass stands for extra strength. As a bonus, the stuff is impervious to gas. I know as I tested a pebble of it immersed in gas for about 6 months. I use it for filling pinholes in gas tanks and even rebuilt a carb float post once.

You could likely fab something with that quite easily.

Cheers,
spyug

As far as testing acetone would be best but there is always the burn method http://www.boedeker.com/burntest.htm