Stopping an air leak with heat shrink tubing

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flex_318

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Recently my friend purchased an old motorcycle from the 80s are together we are restoring it back to its former glory. After dismantling the carburetor and cleaning all the gunk out we were able to successfully start it but noticed massive air leaks in the Carburetor boots caused by cracks.

We figured rather than sourcing and spending a small fortune on used Carburetor boots we could seal them without the use of tape. let me know what you guys think.

[video=youtube;HVqjLW_nx2M]https://www.youtube.com/watch?v=HVqjLW_nx2M[/video]
 
if thats the way you want to do it, i would have put RTV silicone over it first then shrunk the heatshrink onto it it.
i can also see a potential air leak when you cut out the holes for the bolts....but its hrad to tell if its smooth or if there is a air gap around the flange.
 
Eaz8 hase a good idea with RTV silicone, I'd go a step further and use a dremel tool to clean out the crack a bit so the silicone has a place to fill then shrink warp or use the plumbers emergency wrap tape for an air tight seal. Its a bandaid approach but a good temp fix.
 
Heatshrink tubing also comes with adhesive inner coatings and shrink ratios of 3:1 and even 4:1. The adhesive coating would eliminate the need for RTV.
 
Blackfin said:
Heatshrink tubing also comes with adhesive inner coatings and shrink ratios of 3:1 and even 4:1. The adhesive coating would eliminate the need for RTV.
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I would think silicone would be more flexible and hold up longer. The adhesive on the coated ones I've used seems very similar to hot glue to me and I wouldn't expect it to hold up to the vibrations of an old motorcycle engine as well as silicone.
 
I said RTV because it's flame retardant. Will hold up much better over time and the Temps that the boot may see.

Cleaning the cracks would also be a good call.
Same concept as when companies have stress welds repaired on cranes or whatever equipment , they grind out the Crack then fill it in.
 
All RTV's and silicones are not created equal so do your homework first. Personally I prefer urethane caulks.

Rednecks swear by JB Weld for fixing anything from bikes to dentures.

Similarly not all heat shrinks are created equal. Some shrinks are double wall and seal fairly well but others are adhesive lined (Think hot melt glue) and bond better. Cutting holes in heat shrink to accommodate fittings could cause it to split. BTW that is a propane torch and I would suggest choking it down to cool and broaden the flame.

If you use the wrong stuff it could make using the right stuff later very difficult. What material is the original part made from and what stresses will it be under when operational again?
 
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What effect will conduction and convection engine heat have on the heat shrink tubing over the longer term?
 
I will keep you guys updated with how it holds up over time. I have used RTV in the passed and although I was happy with the end result I didn't like how messy it made everything.

This provided me a much cleaner look and still served the same purpose. I have subjected the heat shrink to both gasoline as well as carburetor cleaner and it has yet to deteriorate.

The material feels very much like a tough rubber, very similar to a tire inner tube, and still allows for some flex even after it has been heated. Based on past repairs using RTV I have no doubt that it will hold up just as long if not longer.

As I said before, I will keep you updated if anything changes.
 
nobbie48 said:
All RTV's and silicones are not created equal so do your homework first. Personally I prefer urethane caulks.

Rednecks swear by JB Weld for fixing anything from bikes to dentures.

Similarly not all heat shrinks are created equal. Some shrinks are double wall and seal fairly well but others are adhesive lined (Think hot melt glue) and bond better. Cutting holes in heat shrink to accommodate fittings could cause it to split. BTW that is a propane torch and I would suggest choking it down to cool and broaden the flame.

If you use the wrong stuff it could make using the right stuff later very difficult. What material is the original part made from and what stresses will it be under when operational again?
Click to expand...

The original is made from a dense rubber and it will be subjected to the same operational stresses as any carburetor boot. You are correct it is a propane torch, the video was made on the fly and regretted that mistake once I re-watched it. I will monitor for any splits in the hose fitment along with the screw holes.

I had no problems drilling out and rebolting the boots to the engine manifold. I even found the heat shrink material to rest under the bolt, creating somewhat of a washer while also preventing a leak.
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