# Stihl FS66 - cheap fuel tank retrofitted



## Sonorous (Aug 10, 2019)

I registered to post this in the hope it might help someone else. The OEM tank (part # 4123 350 0405 I believe) is no longer available and I couldn’t find much info when I searched for alternatives. 

The fuel tank on my dad’s old FS66 was cracked in several places, including along the main seam where the two halves were fuses together. I did a crude ‘plastic weld’ repair (solid 12awg wire in old Weller pistol grip soldering iron) which held for a while but started leaking eventually. 

I took some measurements and it looked a very cheap eBay tank could be retrofitted. The spacing on the new tank was too wide - don’t remember the amount but I figured I could get it on there one way or another! The tank was only ~$5 USD shipped from Hong Kong, including fuel lines, grommet, filter and cap. These are sold as a “40-5” style tank and I suspect any one would work just as well. 

I was planning to fabricate a bracket but realized I could just use a couple Stanley flat plates I had on hand (an L bracket cut in half would work too). For one side I only needed to relieve the corners on the bench grinder to let the bracket rotate without hitting the case or tank.

On the other side I opted to drill a hole and shorten the plate so the tank would sit up as much as possible. This was not a precision job - because both brackets can rotate they can be manipulated to level the tank and provide the correct spacing.

The provided fuel line was slightly too short once I pulled it out enough to reach the carb. I would have replaced it but what I had on hand was impossible to fit in the grommet or loose to the point I worried it would leak. The tank is so much larger I’m not at all worried about getting every last drop of fuel anyways. 

The new tank also has a return line, which isn’t used on the FS66. I just threaded a cap screw in for testing but plan to install a tank vent from an Echo to complete the job. 

To protect the new tank I opted to booger weld some thin wall tube he had on hand into a rough frame. If it was mine I wouldn’t have bothered but I could tell the old tank had a few bumps along the way so it was worth the extra few minutes to give it some longevity. The it would be fairly easy to extend the stock bracket with basic hardware. 

Everything has been working perfectly and the larger tank is not at all in the way during use. For $5, 30-45 minutes and some random hardware it’s an easy fix. 

I used metric hardware because that’s what I had on hand in stainless and 1/4-20 was too big. This could be done with just a drill and flat file but a grinder and vise make it quite a bit easier. 

Hope that helps someone!

























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## jgeorg (Jul 28, 2021)

Sonorous said:


> I registered to post this in the hope it might help someone else. The OEM tank (part # 4123 350 0405 I believe) is no longer available and I couldn’t find much info when I searched for alternatives.
> 
> The fuel tank on my dad’s old FS66 was cracked in several places, including along the main seam where the two halves were fuses together. I did a crude ‘plastic weld’ repair (solid 12awg wire in old Weller pistol grip soldering iron) which held for a while but started leaking eventually.
> 
> ...


This is amazing! Can you send me the website you used. I have the exact model with a leaking gas cap, I’d rather replace the tank and cap rather than just the cap for the kind of price.


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