034 tank leaking through screw hole

climbstihl · Dec 29, 2019

I discovered that a friends Stihl 034 AV gas tank is leaking through the bottom handlebar screw on the clutch side of the saw. I noticed it when I took the handle off for cleaning.
Any ideas how this could've happened?
I suppose the only option is to replace the whole tank, is that correct?

Reach · Dec 29, 2019

Saw got dropped, causing a crack inside? I really don’t know how that could have happened, but probably you will have to replace the tank. The only thing I could think of otherwise is to try to patch it, maybe squirt some JB Weld in and thread the screw back in, but I’m not sure I would trust that to be a permanent repair.

climbstihl · Dec 29, 2019

I don’t know the history of the saw, it is a 1985 model. The tank is still original as is most of the saw, it doesn't look like it was ever cleaned either. The tank is made of a hard, non-translucent plastic that seems like it might want to crack more than the tank on my 026 or any other more modern saw I've seen.
Missing two screws for the muffler too.

Jonny · Dec 29, 2019

Wonder if a plastic welding kit would do it. You’d need to find out what kind of plastic the tank is made of, and take some precautions to avoid igniting vapors. Ideally remove the tank and maybe let it dry out or flush it with something not-so-flammable. I don’t think plastic welders make heat like metal welders, but could probably still ignite gasoline.
I got 2 034av I know what you mean, the tank is not see through, it might be PVC but I’m only really guessing and am no expert on these things.
Stihl might be able to tell you exactly what it is, or maybe one of the saw forums.

Also I haven’t heard of anyone doing the plastic weld on saw tanks before, but it might work.

So is it possible the wrong screw was driven in that caused this? One that was too long?

evo · Dec 29, 2019

I have a ms 020 t that had a tank puncture, a larger saw slid into it in the back of the truck and pierced a hole in the fuel tank.. I sanded the area round it, and chipped off the smooshed out bits of plastic. I used some type of JBweld product for fuel tanks and I haven't had a problem with it at all. Bandaid has been there for 5-7 years now, saw is about toast, but still no leaks.

I have HEARD that you can get away with just a wood burning kit, or soldering iron to repair a crack in saw's plastics. No filler, just melt and smush/stir the edges back together. I use to do a little bit of plastic welding many many years ago in a fab shop. We would use basically a wood burner to do a "root" pass in a v groove, then once joined at the root, we would fill the grove with a plastic welder and filler rod if the CORRECT type of plastic. I never got beyond just doing what I was told to do, so never learned all the nuances and types of plastics, chemical resistances etc..

The plastic welder was basically a metal "probe" hot compressed air was the heat source, and you'd add the filler in to a port. The hot air melted the three materials together, and a finger on the probe smushed them all down into place.

evo · Dec 29, 2019

There are many ways it could of happened.. plastics become brittle with UV, chemical exposure, and age.. Simply over tightening the screw can cause enough torque to crack the plastic around the screw threads. Even getting the saw pinched, and prying or tugging it out can cause a crack..

Rob Stafari · Dec 30, 2019

I would certainly attempt to fix it. If I'm reading that right and the fuel is just coming through the screw threads, no big apparent crack or hole. I'd start by emptying the tank, pulling the screw, cleaning said hole out as best as possible with some spray cleaner, squirting some oil/fuel resistant gasket maker(motoseal is readily available at most auto parts stores) in there and running the screw back in.

chiselbit · Dec 30, 2019

If you find a crack I’ve had good results using jb weld and a piece of screen to reinforce it. I’ve used old window screen, spark arrestor screen,,, rough up the plastic with sand paper, clean it and apply thin layer of jb weld, then screen, then more weld.

climbstihl · Dec 31, 2019

Rob Stafari said:
I would certainly attempt to fix it. If I'm reading that right and the fuel is just coming through the screw threads, no big apparent crack or hole. I'd start by emptying the tank, pulling the screw, cleaning said hole out as best as possible with some spray cleaner, squirting some oil/fuel resistant gasket maker(motoseal is readily available at most auto parts stores) in there and running the screw back in.

Yes, it's only coming through the screw hole, in fact, when the screw is in it is completely tight.
I have some silicone gasket maker, is that fuel resistant? I'm not sure I'll be able to get it in way down in there...

Reach · Dec 31, 2019

climbstihl said:
Yes, it's only coming through the screw hole, in fact, when the screw is in it is completely tight.
I have some silicone gasket maker, is that fuel resistant? I'm not sure I'll be able to get it in way down in there...

Some silicone gasket maker is fuel resistant, the label should say if it is or not. You can probably put a bit on the end of the screw and use that to push it in the hole; it won’t take much.

Jonny · Dec 31, 2019

Try putting a generous dab of your gasket stuff on a scrap screw or nail or something, let it dry/cure and then drop it in a capful of gas/mix. See if it breaks down.