Anyone ever had any success repairing cracks in plastic gas tanks?

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9/15/2017 8:05 AM
Edited Date/Time: 9/15/2017 8:39 AM

Found these cracks, one of which has a very slow leak. This is a WR500 tank, which is no longer available and very hard to find. Anyone ever had luck fixing something like this? Being so close to the brass inserts, and the fact that the tank mounts attach at this point may complicate things... Photo

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9/16/2017 2:29 PM
Edited Date/Time: 9/16/2017 2:34 PM

I've had luck with a soldiering iron ,to kinda fill melt and open the cracks , then used Permatex plastic tank repair epoxy. There is alot of plastic gas tank epoxy's out in Google land.,, Should post in Tech help.

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9/17/2017 6:25 AM

i have a decent wr tank

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9/17/2017 7:12 AM

pete24 wrote:

i have a decent wr tank

Sent you a PM.

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9/17/2017 7:14 AM

Pat_Boyd wrote:

I've had luck with a soldiering iron ,to kinda fill melt and open the cracks , then used Permatex plastic tank repair epoxy. There is alot of plastic gas tank epoxy's out in Google land.,, Should post in Tech help.

That sounds like a good plan of attack. Thanks for the info.

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9/18/2017 4:13 PM

pete24 wrote:

i have a decent wr tank

Moto Mofo wrote:

Sent you a PM.

i got your message i just have to locate the tank and ill get pics be another day or so

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9/18/2017 6:53 PM

pete24 wrote:

i got your message i just have to locate the tank and ill get pics be another day or so

Thank you, sir!

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9/18/2017 8:31 PM

I fixed a tank on an '85 CR once by grinding an inverted vee into the crack and taped the backside through the filler neck. I then cut up bits from an old fender of matching color and placed them in a ladle, heated it with a torch and after melted, poured it into the vee. Time consuming and tedious but a last resort for a high schooler on a shoestring budget.

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9/20/2017 8:17 AM

Is the blind nut spinning in the tank? I have had a few older tanks crack when the blind nut spun and never found the solution to save them and keep nut from spinning inside

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9/21/2017 12:57 PM

I made a plastic welding rig out of a nozzle for my heat gun.
Photo

Ordered 1/4" HDPE rod from McMaster-Carr and welded up a few tanks. Here's the KX80 tank I had to re-work to get the XR100 motor to fit.

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Most tanks are an HDPE mix of some secret proportion, but straight HDPE will bond very well. I would "V" out that tank and cracks and weld in that nut so it doesn't spin.

Good luck!

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9/21/2017 9:52 PM

Thanks Tdub13! Fixing tanks in my experience and research has a high failure rate. To get anything to really bond to tank plastic is a slippery slope to conquer. With that heat gun setup does the tank surface get molten at the same time the HDPE rod does as you run it along? Or whats your process?

I can see how the v notch is important, if you simply run a soldering iron over the crack, you are only making a 1mm or less "patch". The vibration will open that thin layer in no time.

IMO Yamaha tanks are the most notorious for cracking, going back many years!

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9/22/2017 2:08 AM

classic solid soap working perfect

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18 Yamaha YZ450F
94 Honda CR 500
90 Honda CR 500
81 Yamaha SR 500
68 BSA Thunderbolt
69 Triumph Tiger 100

9/22/2017 6:55 AM

You're right notme. The only thing that will permanently bond to HDPE is HDPE. There are products that come close, but plastic welding is the best because it "co-polymerizes".
I usually use the tip of that welding nozzle to create the "V" by "plowing" it into whatever I'm welding. Then I'm pushing the HDPE rod through the nozzle and filling the gap. While in process, the white HDPE rod will turn clear and you should be able to tell when the tank material is hot enough to bond. Takes practice, but it's a cool process. Try it on a junk panel or fender first!

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9/22/2017 1:57 PM

Tdub13 wrote:

You're right notme. The only thing that will permanently bond to HDPE is HDPE. There are products that come close, but plastic welding is the best because it "co-polymerizes".
I usually use the tip of that welding nozzle to create the "V" by "plowing" it into whatever I'm welding. Then I'm pushing the HDPE rod through the nozzle and filling the gap. While in process, the white HDPE rod will turn clear and you should be able to tell when the tank material is hot enough to bond. Takes practice, but it's a cool process. Try it on a junk panel or fender first!

Thanks for sharing this. Any leaks with the gas tank? What do you do to mitigate the chance of a fire or explosion?

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9/22/2017 3:40 PM

Arent there liquid liners that might work for this job? Its a small leak so going inside and sealing it up seems to make the most sense to me. I have never tried them, but thats where I'd start. If it works, it also wont ruin the outside appearance of the tank.

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9/22/2017 3:43 PM

It can leak if you don't do a good job welding. However , if you get good penetration and no voids, it should last longer than your interest in the bike! Just like welding anything.
I got a little more gas smell during welding, but a dry tank can't be of danger, except for catching the plastic on fire itself. If that happens, you're doing it wrong...way wrong!
Look up my YZ125 race build also. I repaired a .22 slug hole in that tank the same way. No leaks after many races and abuse..

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9/22/2017 4:45 PM

I find it odd I'm the only one that wants to know how your YZ was shot with a .22 Tdub

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9/23/2017 7:30 AM

I wish I had a story for the .22 slug buried in the tank. Bike was purchased in the back woods of New Hampshire. That may be the best explanation in itself. cool

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9/23/2017 8:12 AM
Edited Date/Time: 9/23/2017 8:13 AM

Let me help you out...you were racing against a bitter rival that didn’t appreciate you slamming the door on him in turn one after he got the hole shot in the 125 main event at the the 1980 Super Bowl of motocross in LA. After 20 grueling laps, you launched off the final jump taking the checkered flag. As you took your victory lap the trusty YZ ran out of gas. No worries, you just one the biggest race of your life. As you dismounted, you dropped the YZ into the dirt and the remaining race gas poured out of a small hole from the side of the mud splattered gas tank.

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9/26/2017 10:18 AM

laughing
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