Plastic repair

Charlie Tackett · Posted: Tue Oct 02, 2001 4:30 am Post subject: Plastic repair

Ok, this isn't exactly kating related, but sinc ekarts do at times utilize plastic bodywork, thought maybe someone might have some advice to offer.

The lower cowling on my old crotchrocket has cracked and split in two. New ones are $$$$. What's the best way to try and repair this....and strengthen it at the same time.

John Denman · Posted: Tue Oct 02, 2001 5:02 am Post subject: Plastic repair

Plastic welding on thermoplastic compounds is an art we learned many years ago in fixing the fenders of our Honda Pilots. It took some practice, but we managed to get some good results.

It takes a good heat gun sometimes 2. Don't use anything with a flame since the carbon in the exhaust will fuse with the plastic.

If its white plastic, your in luck. You can use white Hefty trash bags as the "welding rod". Otherwise you may need some OEM scrap pieces to get the same color. We found some red poly flags that were very close to the red fenders on the Honda and there was little color difference after being welded on.

You will need some hardwood spoons to use as a form. The need to be polished with no grain ridges. We had some made fro maple that worked well. Take a cloth and rub some peanut oil on them. It prevents the plastic from sticking too much.

From there its just an art that takes a few hours to master. The working temps are about 250 to soften and 375 to melt so it can burn skin. Caveat emptor. I did it without gloves.

There are some kits for this at bodywork stores, but I never tried them. I think the stuff used on cars is more a mix of thermoplastic and phenolic (thermoset) filler.

If I see you with your hands wrapped up in Vegas, I will know why.

Erik Frank · Posted: Tue Oct 02, 2001 5:54 am Post subject: Plastic repair

Some thermoplastics can be melt-welded with MEK solvent. The results will be strong and functional, but probably not very aesthically pleasing. No heat input required, however.

Karting related comment: You can probably do this on blow molded CIK style sidepods with success. (also good for attaching vanes, fins, etc.)

Same Caveat emptor comment made above applies...except this time its for the fumes! whew!

Also, if you're looking for old fairings at a good price, might I suggest Ebay?

What kind of bike?

-erik

(edit: added word "probably"....)

[ October 02, 2001: Message edited by: Erik Frank ]

Scott McFadden · Joined: 20 Jul 2001 Posts: 125

You could try West System epoxy and a fine weave fibre mat. You'll be trying to achieve a mechanical bond as much as adhesion but this stuff is very strong and easy to work with. you can add microballoons or other fillers and sand the surface for painting. The laminate you create will likely be stronger than the original part.

Saro Marcarian · Posted: Tue Oct 02, 2001 9:41 am Post subject: Plastic repair

Charlie-

Just come out to the LA Area. Lots of Plastic Surgeons in Beverly Hills...

-Saro

Andy Szyszkowski · Joined: 01 Aug 2001 Posts: 149

"Just come out to the LA Area. Lots of Plastic Surgeons in Beverly Hills..."

But they specilize in silicone, Saro!

"Some thermoplastics can be melt-welded with MEK solvent. The results will be strong and functional, but probably not very aesthically pleasing. No heat input required, however."

Usually, the non-fiberglass pods are made from rotationally molded Polyethylene (or perhaps polypropylene). You cannot solvent bond this polymer, nor will any type of resin that is used with a fibre reinforcement effectively adhere to it. Your only real option is a heated gas welder, or John Denman's clever little method.

Andy

Erik Frank · Posted: Tue Oct 02, 2001 11:40 am Post subject: Plastic repair

Andy,

Thanks for the clarification.

I could have sworn that you could do that with polyethylene, or polypropylene...if not, which ones can? Polystyrene?

I revised my earlier statement in the post above, so as not to further confuse anyone.

Gas welder on plastic sounds like an invitation for trouble...sounds very tricky! I think I'd rather TIG weld on an aluminum can!

-erik

Greg Maxwell · Posted: Tue Oct 02, 2001 1:12 pm Post subject: Plastic repair

Charlie, I own a plastic welder. Its from Urethane Supply Co. part #5500HT their number is 1-800-633-3047. While I have never used it for go-kart or motorcycle plastic, I'm sure it would work great. It is sold to repair plastic bumpers on cars. It comes with many different types of "welding" rods (Polyurethane, Xenoy, TPO, TEO, TPE,& Ploycarbonate) It even comes with an instructional video! They also have a websitewww.urethanesupply.com Hope this helps, Greg

Andy Szyszkowski · Joined: 01 Aug 2001 Posts: 149

quote:
Originally posted by Erik Frank:
Andy,

Thanks for the clarification.

I could have sworn that you could do that with polyethylene, or polypropylene...if not, which ones can? Polystyrene?

I revised my earlier statement in the post above, so as not to further confuse anyone.

Gas welder on plastic sounds like an invitation for trouble...sounds very tricky! I think I'd rather TIG weld on an aluminum can!

-erik

Erik,

What I meant by "heat gas welder" was not an oxy/acetylene torch. It is actually a plastic welder such as Greg Maxwell describes.

Polystyrene and ABS polymers can be readily solvent-bonded using MEK. You can grind-up some ABS, and mix it with the MEK to your own "glue."

So how did you end-up with enough "empty" beer cans to get good at TIG welding them?

Andy

Rob Linders · Joined: 18 Jul 2001 Posts: 725

Charlie,

If you are interested in a Professional job, I used a place that repaired cracked plastic on a RG500 Suzuki Gamma I used to own. These bikes were not brought into the states, they are 4 cylinder 2 strokes, so parts are sometimes difficult to find. Anyways, they specialize in sportbikes and can repaint them to match original colors. I also had my Dad's 87 GSXR 1100 repainted in all factory colors through this shop and they did a good job. If you are interested I can get the number, since I can't even remember the name of the place at this point. However, I'm pretty sure I can make a few calls and get you a number. As I recall the prices are pretty reasonable since the shop has to compete with someone just buying new plastic.

Rob

Bob Vehring · Posted: Wed Oct 03, 2001 5:05 am Post subject: Plastic repair

Charlie, I have a plastic welder and have all the different rods in stock ( I own a body shop for a day job)welding works good on about 75% of the plastics out there, also allot of epoxy fillers made now to finish of the job. If your coming to Gingerman this weekend I'll bring the welder, (its small) and well do it there Bob

Charlie Tackett · Posted: Wed Oct 03, 2001 6:51 am Post subject: Plastic repair

Well, that's the best method of repair yet, Bob!....Let someone else do it!!!

WIll bring 'em around. DOes that thing work well when its in the 30's and raining, Bob?

I have no idea what kind of "plastic these things are. The bike didn't have any lowers on it when I got it. Its a '90 Honda VTR250...my 65mpg commuting to work bike. Searched all the online salvage yards I could find to even come up with this set of lowers. Bike was only imported here from '88-'90. Not potent enough for the American market, I guess, but is still sold and is popul;ar thruout the rest of the world.

I do like some of the suggestions...especially the Hefty one from John!! Also where do you find this MEK solvent? Might "weld" on some fins or something to Ted's sidepods...just to see how long it takes for someone to complain or copy them. (hehehehe)

Saro....belong to an HMO. INstead of a Beverly Hills Plastic surgeon, they'd probably send them to some Revell model builder in Hickory Hollow Idaho!!

John Denman · Posted: Wed Oct 03, 2001 9:56 am Post subject: Plastic repair

quote:
Originally posted by Charlie Tackett:
Does that thing work well when its in the 30's and raining, Bob?

Searched all the online salvage yards I could find to even come up with this set of lowers.

Brrrr. Now that the summer heat is done in Texas I am beginning to appreciate the weather here again.

Have you tried Bent Bikes in Toronto? I don't know if they are online, but they seemed to have an extensive collection of bikes in the range you are looking for. Its been a few years since I dealt with them, but they were great to buy from.

Chuck Bunnell · Posted: Thu Oct 04, 2001 7:42 am Post subject: Plastic repair

For any of you that want to use MEK, (methyl ethyl ketone), it's potentially some pretty nasty stuff and should be handled with extreme care. Here's a link to its MSDS, (Material Safety Data Sheet), http://www.state.nj.us/health/eoh/rtkweb/1258.pdf I would go with the plastic welder myself especially since that type of plastic doesn't even like tape or paint much. You can buy MEK from any fiberglass supplier where it's used as a thinning agent or from most industrial suppliers where it's used as a degreaser.

[ October 04, 2001: Message edited by: Chuck Bunnell ]

Erik Frank · Posted: Thu Oct 04, 2001 8:38 pm Post subject: Plastic repair

Chuck,

Thanks for the MSDS link.

MEK in this discussion of plastic welding is now a moot point, because evidently it can't be used to effectively solvent bond polyurethane.

From Andy:

quote
Quote:

So how did you end-up with enough "empty" beer cans to get good at TIG welding them?

Four years of college; and now graduate school!

-erik

[ October 04, 2001: Message edited by: Erik Frank ]