044 Can I repair this tank crack with epoxy?

[mike.scopp]

Thanks to lurking in this forum and reading so many informative threads I decided to tackle the rebuild of this 044.
I bought it fi for 200 when I got a job bucking for a tree removal service, it ran little sporadically. Eventually it wouldn’t start anymore. I saved and got a 400c and now I’m tearing this down and doing my first ever rebuild. My interest in combustion engines was began 6 months ago when that saw wouldn’t run, so a steep learning curve.
I discovered this crack disassembling today. There was no fuel leaking but I could get it to start pouring fuel into the carb but that was it. This crack may have been leaking air in? All the rubber bits were intact. I wonder if I could get away with epoxying that crack?

 

[pioneerguy600]

If it doesn`t leak fuel it won`t leak air into any part of the saw that would matter to the engine running,it could be filled in with epoxy but not really necessary for the saw to run proper.

 

[HansFranz]

I don't know whether the crack was the cause of your engine trouble, but epoxy should adhere just fine, so long as you degrease the saw real well. I would use brake cleaner, then scuff up the paint around the crack with sandpaper to give the epoxy some "tooth" to adhere to, then degrease again, then apply the epoxy, then cover the crack with some kind of thin fabric or even coffee filter paper (to hold a layer of epoxy in place), then "wet out" the fabric or paper with epoxy by "poking it" with the bristles of an acid brush until it turns transparent with the resin.

If it's exposed to sunlight, you will need to paint over the epoxy after it hardens to shield it from UV. (You should sand it before painting it and then wipe it with a rag with water to "deblush" the epoxy, or else your paint may not adhere to the epoxy composite.) Good luck.

 

[buzz sawyer]

I've had problems getting standard epoxy to adhere well to plastic. They make a version specifically for plastic repair and that has worked well for me.

 

[Squareground3691]

Q Bond Repair Kit Small Quick Bonding Adhesive 2 Pack https://a.co/d/7LX4lOz
This stuff works well,

 

[HansFranz]

I've had problems getting standard epoxy to adhere well to plastic.

I was thinking the crack was in metal, but if it's plastic, yeah, ignore what I said earlier. Some plastics (like polyethylene) are technically waxes, and most epoxies/paints will not adhere to them without special treatment:

https://theepoxyexperts.com/flame-treatment-plastic-substrates-adhesive-bonding/
https://www.epoxyworks.com/index.php/flame-treating-plastics/

 

[Oletrapper]

If it doesn`t leak fuel it won`t leak air into any part of the saw that would matter to the engine running,it could be filled in with epoxy but not really necessary for the saw to run proper.

I totally agree with pioneer. I would try pressurizing the tank to see if it is what I call a through crack or stress crack. Might just be on the surface and not all the way through. I feel certain that if it were all the way through, you would be leaking fuel. jmho OT

 

[user 122190]

I don't know whether the crack was the cause of your engine trouble, but epoxy should adhere just fine, so long as you degrease the saw real well. I would use brake cleaner, then scuff up the paint around the crack with sandpaper to give the epoxy some "tooth" to adhere to, then degrease again, then apply the epoxy, then cover the crack with some kind of thin fabric or even coffee filter paper (to hold a layer of epoxy in place), then "wet out" the fabric or paper with epoxy by "poking it" with the bristles of an acid brush until it turns transparent with the resin.

If it's exposed to sunlight, you will need to paint over the epoxy after it hardens to shield it from UV. (You should sand it before painting it and then wipe it with a rag with water to "deblush" the epoxy, or else your paint may not adhere to the epoxy composite.) Good luck.

When I use to build and fly remote control gliders we added a fiberglass filler to epoxy. Epoxy alone would be brittle in some cases and the fiberglass would give it the additional strength to stand up to the stresses of flying in strong winds.

I'd consider cutting and grinding fine steel wool to add to the epoxy. Might be overkill but can't hurt.

 

[irhunter]

My somewhat contrary opinion.

You are making a living running saw. Right?

The 044 will be a back-up to the MS400. Right?

You're just learning to fix saws. Right?

I'd suggest, doing it right, and sourcing an un-cracked tank. New crank seals, rubber lines, piston rings. You'll learn a lot, and have a back-up saw which will be 100%.

Sell the cracked tank for 10 bucks to some homeowner who just broke off their rear handle when they fell off a ladder while running the saw.

Roy

 

[HansFranz]

I'd consider cutting and grinding fine steel wool to add to the epoxy. Might be overkill but can't hurt.

Yep, pretty much any fiber (fiberglass, carbon fiber, cotton, polyester, paper, etc etc etc) will work to reinforce the epoxy and give it something to "soak into" to create a composite with sufficient thickness. There are very few fiber types that won't work, mainly those made from things like polyethylene and other similar plastics that (as mentioned above) are technically waxes in their molecular structure, causing adhesion problems. Certain types of fiberglass that are intended to work with polyester resin also cause problems because of something they're coated with ... I forget. (If you can't get the fiberglass cloth to "wet out" and become transparent with the epoxy resin, this is probably why.)

 

[Chevboy0167]

As said above, a bit of air in the tank then use soapy water to see if the crack indeed does leak. If yes, replace with new or good used..

If no leaks, I have had good luck with JB Weld Plastic bonder or something similar for PA6 plastics.

https://www.jbweld.com/product/plastic-bonder-syringe
https://www.jbweld.com/product/seamweld-syringe

 

[buzz sawyer]

As said above, a bit of air in the tank then use soapy water to see if the crack indeed does leak. If yes, replace with new or good used..

If no leaks, I have had good luck with JB Weld Plastic bonder or something similar for PA6 plastics.

https://www.jbweld.com/product/plastic-bonder-syringe
https://www.jbweld.com/product/seamweld-syringe

That's what I used, good stuff.

 

[Chevboy0167]

Well, may not be the best after all. Most of what I find states to use a 2 stage polyurethane for bonding on PA6 plastics. Hmmmm...

 

[dboyd351]

According to the reviews and the manufacturer's response to one of the reviews, the JB weld product does not work well on polyethylene or polypropylene.

I have had luck repairing a hole/crack in the sprayer tank of a Stihl backpack sprayer by fiberglassing after sanding it, but I don't know what type of plastic that tank was made of or if the gas tank is the same plastic.

 

[The Stig]

Structural piece. Won’t last get another one

 

[teacherman]

I wonder if one of those heat welders for plastic might reconfigure the cracks and cause them to no longer be weak spots. As this is a structural piece, as The Stig points out, it seems that use of the saw will stress those cracks and cause eventual widening and failure at that place. I believe the saw tank/handles are nylon, at least that's what Lakeside said back in the day. He was able to effect strong repairs using a plastic welder, which might be more effective now than after the crack is all the way through.