Sealants VS Fuel

[Vintage Engine Repairs]

A friend dropped off a machine that wasn’t running. He had used dirko on a carby gasket which blocked the impulse. Here is a picture of how different sealants react to fuel after a few hours.

The only one that really stands up to fuel is Motoseal (left which I had to use my nail and pick at it to remove it) the others are ThreeBond 1104, Yamabond 4 and dirko all are affected. ThreeBond dissolves, Yamabond and dirko swell and crinkle.


i’ve mentioned before that used correctly they’re fine, but be very careful if you use them as a dressing for gaskets both due to blocking holes or swelling into the intake.

A quick repair in this case, but thought I’d share a pic here. The only dressing compound I use for gaskets is either hylomar or aviation form a gasket. Both of which don’t react to fuel. You could use Motoseal but you’ll rip it on disassembly.

 

[lehman live edge slab]

I tried motoseal on the halves of an 075 tank because i didn’t think i had a gasket and figured it would work to seal the seam. Next day the full tank a mix was on the garage floor so even it seems to dissolve after 10-12 hours. I did let it cure all day before filling with gas.

 

[Vintage Engine Repairs]

I tried motoseal on the halves of an 075 tank because i didn’t think i had a gasket and figured it would work to seal the seam. Next day the full tank a mix was on the garage floor so even it seems to dissolve after 10-12 hours. I did let it cure all day before filling with gas.

Na, I wouldn’t use it there, i wouldn’t use it in anything that stays in constant fuel submersion, eventually it will fail. It’s just fuel resistant rather than fuel proof, but in this short test fuel didn’t affect it. In 12 hours I’d expect it would be soft.

Very few sealants are truly fuel proof. “Seal all” is one of a few that may be an alternative to look into?

Best to make a gasket

I have come across a few air leaks where sealant was used instead of a gasket. Just the other day I had to do a full tear down on an fs85 because Stihl used dirko on the cases and it failed a pressure test. It’ll last a while, but not as long as a gasket does. For a comercial unit it did surprise me.

Edit: Seal-All

 

[lehman live edge slab]

Na, I wouldn’t use it there, i wouldn’t use it in anything that stays in constant fuel submersion, eventually it will fail. It’s just fuel resistant rather than fuel proof, but in this short test fuel didn’t affect it. In 12 hours I’d expect it would be soft.

Very few sealants are truly fuel proof. “Seal all” is one of a few that may be an alternative to look into?

Best to make a gasket

I have come across a few air leaks where sealant was used instead of a gasket. Just the other day I had to do a full tear down on an fs85 because Stihl used dirko on the cases and it failed a pressure test. It’ll last a while, but not as long as a gasket does. For a comercial unit it did surprise me.

Edit: Seal-All

Was an experiment and it failed, was going to tap a gasket out of material I had but then i remembered I bought a pile of gaskets from an old Stihl shop and there was a few in there didn’t even need to make or buy one

 

[Vintage Engine Repairs]

Was an experiment and it failed, was going to tap a gasket out of material I had but then i remembered I bought a pile of gaskets from an old Stihl shop and there was a few in there didn’t even need to make or buy one

Do you still have the 075? What a tank! I had an 076 super and it was fantastic in the hard woods.

 

[lehman live edge slab]

Do you still have the 075? What a tank! I had an 076 super and it was fantastic in the hard woods.

I still have the 075 also have a 076 super that needs to be cleaned and reassembled. First generation 045 numbers cast into top no plate. And few other old Stihls that need some love when I get time like an 07 and 040. Sold my 090 just before Christmas because I didn’t run much other than some milling and it vibrated too much.

 

[timg]

Motoseal is a great gas resistant sealant when used as directed. It's only issue is it has poor gap filling characteristics. Not insinuating that was your issue Chris. But it is what I've learned from using it.

 

[lehman live edge slab]

Motoseal is a great gas resistant sealant when used as directed. It's only issue is it has poor gap filling characteristics. Not insinuating that was your issue Chris. But it is what I've learned from using it.

I know it’s a great sealant and it’s possible the gap may have been to large because I don’t know what that is but was in direct contact and most sealers in direct contact usually give up. Gap wasn’t much I’m betting 3-5 thousandths at wide points maybe the narrow points were the issue too and it squeezed all the sealant out in the areas with screws leaving basically metal to metal. Not sure

 

[bwalker]

Loctite 510. Excellent strength and gasoline resistance. Also expensive.

 

[lehman live edge slab]

Loctite 510. Excellent strength and gasoline resistance. Also expensive.

Motoseal has been great when used where intended so I’m good with it and available locally. Also I’ve pretty much gone to the orange loctite on lots of stuff vs blue with occasional purple on real small screws.

 

[Motorka]

By time ger hard and not sealing. My experience. Now on dirko an Hylomar M.

 

[hacskaroly]

I tried motoseal on the halves of an 075 tank because i didn’t think i had a gasket and figured it would work to seal the seam. Next day the full tank a mix was on the garage floor so even it seems to dissolve after 10-12 hours. I did let it cure all day before filling with gas.

I worked on an 075 tank that was leaking, turns out someone repaired it, took out the gasket and then poured something into the tank to seal it. It didn't work, the stuff peeled up and the fuel got around it. It was a pain to get it all out. Ended up using a gasket and Permetex Aviation Form-A-Gasket and it is now rock solid!!

 

[lehman live edge slab]

I worked on an 075 tank that was leaking, turns out someone repaired it, took out the gasket and then poured something into the tank to seal it. It didn't work, the stuff peeled up and the fuel got around it. It was a pain to get it all out. Ended up using a gasket and Permetex Aviation Form-A-Gasket and it is now rock solid!!

Probably that pour in kit they make for rusted atv/ motorcycle tanks.

 

[hacskaroly]

Probably that pour in kit they make for rusted atv/ motorcycle tanks.

Could be, didn't work very well and was a pain to clean out...lol