Topic: Sandcast/K0 airbox repair

[Fasted]

Guys,

Has anyone repaired a Sandcast/K0 airbox?  I am working on my restoration and I need to repair the cracks in my airbox.  What in the world is it made of??

ED

[MrFry]

i'd say get some epoxy on there
i've read about baking soda and superglue?
or there is also plastic repair - body shops use it on bumpers
but really, i think epoxy would do the trick - at least for all the cracks on the inside

[Fasted]

Will the new paint adhere to epoxy?

ED

[Benjamin]

Funny you should ask... because mine is in worse shape than yours...  I don't have a sandcast bike, but it's a 69 and has the same airbox, with some mighty fractures.

I just wrote to the guys at worldmotorcycles.com -- they're a business in San Francisco, apparently, that sells completely restored sandcast 750s (for... um... $29,000 a piece.  ) -- somone got back to me to tell me that the old plastics were styrene, and that he recommended JB Weld.

I haven't tried any repair yet. I was going to do the baking-soda and superglue trick, but I think I'll try the JB weld first. I am planning to do it from the inside, so as not to have to repaint. Please let me know if you find out about a better option...

Good luck!

-Scott

[Fasted]

Thanks Scott.  Anyone know what kind of JB weld to use on Styrene?  I plan on having all of the body parts painted the Factory candy ruby red and I don't want to have to spring for a new paint job 2 years down the road because the repair failed.

ED

[Benjamin]

Hi Ed,
A little searching under styrene repair led me to this site: https://www.urethanesupply.com/aircraftrepair.html

It's essentially an advertisement for the company's products, but you might want to take a look at it as it's really pretty informative. Sounds like the styrene warps easily (it is also, in its vaporous form, a potent carcinogen) so I'm gonna go the adhesive route instead of plastic welding.

Check out also the company's resources for bumper repair, including "cladding" to prime the plastic for a long-lasting paint job. Might be useful for you, since you're painting:
https://www.urethanesupply.com/bcap.html

Please let me know how it all turns out. Pics are always a plus....
-Scott

[rbirkhan]

Ed get out of the chair put the bingo down and get the engine removed.  If its styrene you could probbly use plastic airplane glue as styrene is what they make plastic models out of.   Rub it down with acetone it will melt if its styrene or acrylic.  They also make acrylic glue. I would imagine JB weld or crazy glue would work as well.  As long as its not polyethelene it should be pretty easy to fix.

[736cc]

Those airboxes are hard-plastic and notoriously crack ez on a motorcycle shaking and pounding on the road. They will crack if nstalled on a cold day! The rubber tubes also harden w/ age and cause more problems. In other words, you can fix one crack, but more likely to follow.
Tip: when installing, loosen all 8 intake clamps for extra wiggle-room, soak the upper half in hot water immediately before installing and lube the rubber w/ WD40. Get in front of the motor and pull the airbox on w/ a little wiggling. Tighten the 4 airbox clamps before tightening the 8 intake clamps, then you attach the 2 bolts the frame. If rubber airbox tubes get cold, heat them completely again. Hot air gun also works. Its a delicate operation that requires some force. Too much force and it'll crack.
David Silver Spares sells new repop airboxes that don't crack.

[BobbyR]

I would say the Marine is the JB Weld you would use.

[mlinder]

I haven't tried it, but model glue basically works by melting the plastic together.
Might wanna try it.

[kettlesd]

Ive tried epoxy in the past to fix cracks. I find that the epoxy is soooo rigid and strong that often cracks appear adjacent to the repair. The stuff just has no "give" whatsoever.

[BobbyR]

If the part flexes, a nice coat of silcone glue may help. In my 78 the airbox is a flexable plastic, so they may have found this to be a problem.

[Fasted]

Well I tried Superglue and Acetone and they both seem to bond the cracks together.  The acetone seems to chemically weld the cracks together.  I wet the crack out with a Qtip full of acetone, get it worked into the crack and then hold the pieces together andthey are holding quite well.  Some of the super glued joints popped apart when tested, but the acetone welded seams are staying put.

ED

[Clyde]

I have used Plastex with a lot of success.

http://plastex.home.att.net/

Regardless what you use these are old and will crack again somewhere else

Clyde

[Jim F]

ever thought about laser welding
My company specializes in micro laser and micro tig welding
I have had good luck in wedling tach and speed O housings with the laser system.
also welding busted carburetor float posts.
only thing is if there is rust that is not seen it will show its ugly head when welding
call me if needed at
770-367-7320