HELP! Did fuel dissolve my Threebond gasket?

[Huskyvarnya Saws]

I rebuilt this Husqvarna 350 around 4 years ago using Threebond 1184 as a sealer. It has been a very reliable saw up until recently, when it developed a vacuum leak on the rear right corner of the bearing cap. When I disassembled the saw to reseal it, I noticed that there was almost no threebond left between the bottom clamshell and the bearing cap, as well as the top of the bearing cap and the cylinder.

I know that I used a good bit more than what is left on the mating surfaces, if anything I thought maybe I was using too much at the time. Has anyone else experienced this? I have rebuilt a hand full of saws using the same sealant so its a bit concerning. Any insight would be appreciated. Thanks!

 

[Huskyvarnya Saws]

I forgot to snap a pic of the paper base gasket, but there was almost no trace of threebond left on it either.

 

[cuinrearview]

In my opinion, nothing in your pics suggests that there was ever "a lot" of sealant. Did you take a before pic?

I'm not up on 1184, but I believe some of these sealants are anaerobic, so if there is oxygen present they won't set up and can disappear as time goes on. The Hylomar seems to be different than the others in my experience.

 

[Huskyvarnya Saws]

In my opinion, nothing in your pics suggests that there was ever "a lot" of sealant. Did you take a before pic?

I'm not up on 1184, but I believe some of these sealants are anaerobic, so if there is oxygen present they won't set up and can disappear as time goes on. The Hylomar seems to be different than the others in my experience.

I can see how one may come to that conclusion based on the pictures, but I know for a fact there was. There is still plenty of excess sealant left on the bearing cap screw threads. I would wager there is more sealant left in the screw holes/threads than on the entire mating surface.
I have always applied a thin layer over the entire mating surface with a q-tip, that has never changed. You would never believe that by looking at the pics though, I get it. Unfortunately, I don't have any assembly pics. This saw was built a few years back.

Have you used the Hylomar stuff that you speak of with good results? I appreciate the input.

 

[EFSM]

I have used Right Stuff sealant by Permatex quite a few times and have never had a problem. I smear only enough to cover the mating surfaces, because I'm OCD about having extra sealant obstruct the transfer flow. After torquing the cylinder down a bead of sealant 1/16" or less will be left around the base. Lots of extra sealant doesn't prove much in my opinion, but with your situation it probably won't hurt anything.

Anerobic sealant may work for some people, but it failed on the one and only saw I used it on.

 

[cuinrearview]

1/16" of sealant squeezed out would be a shît ton, imho.

I have used Hylomar. I didn't care for the way it never seemed to set up. It was useful for porting practice, when you may have a saw apart a half dozen or more times.

I always end up going back to the tube of Yamabond, which looks a lot like the 1184 in the pics. It could even be the same stuff. Did you true the flat surface on the bearing cup? They are notoriously "un-flat".

 

[EFSM]

bead of sealant 1/16" or less

1/16" of sealant squeezed out would be a shît ton, imho.

I should have stressed the OR LESS. I like to have just enough to make it look like a little black sewing thread around the base.

Did you true the flat surface on the bearing cup? They are notoriously "un-flat"

^^^This!

 

[Stump Shot]

^^^This!

+1

 

[Huskyvarnya Saws]

1/16" of sealant squeezed out would be a shît ton, imho.

I have used Hylomar. I didn't care for the way it never seemed to set up. It was useful for porting practice, when you may have a saw apart a half dozen or more times.

I always end up going back to the tube of Yamabond, which looks a lot like the 1184 in the pics. It could even be the same stuff. Did you true the flat surface on the bearing cup? They are notoriously "un-flat".

Yes sir, I did "true" the surface of the bearing cap before assembly. If anything, I used too much sealant when assembling this saw. It was my first full rebuild. The saw was very reliable with no issues at all for 4-5 years, until recently when it was suddenly out of tune, and wouldn't hold one. Thats when I discovered the leak through a pressure test.

This ordeal has me second guessing all of my rebuilds now. I have only ever used threebond 1184 from the start, and this was my first saw, so I can't help but wonder if the others are a ticking time bomb with the same issue. Makes me want to pull the cylinder on one of my other saws to see what it looks like.

 

[Huskyvarnya Saws]

If you look closely, you can still see the bead of threebond that was left after torquing down the cylinder. There is hardly any left on the paper gasket, or mating surface though. It peels right off with no effort.

 

[Moparmyway]

A “skin” layer is all that’s needed if both surfaces are true. Remember, the manufacturers have tolerances, and any sealant used is designed to work with these tolerances, so a thin skin layer left is perfect and will do the job.

Dissovling sealant is another thing

 

[EFSM]

I can see sealant dissolving if the crankcase was flooded with gas due to a leaking carb or primer bulb, but under normal circumstances the fuel in the crankcase is almost entirely vapor.

 

[Moparmyway]

There’s still a cloud of fuel entering the crankcase, atomizing as it moves up into the transferrs. In the transferrs is where it’s entirely vaporized, but that crankcase is usually wet with enough raw fuel to look foggy

 

[EFSM]

that crankcase is usually wet with enough raw fuel to look foggy

Fuel or oil? The oil shouldn't atomize since it is not volatile.

 

[Moparmyway]

Fuel or oil? The oil shouldn't atomize since it is not volatile.

Both

It takes time to change state, even with the pressure difference, the fuel DRIES out as it travels through the crankcase, eventually all vapor as it enters the cylinder. The oil falls out of suspension with the liquid fuel drops as they atomize, leaving the oil in the crankcase.

 

[lehman live edge slab]

I know none of the ones I’ve tried will survive raw mix gas in full contact. I tried to seal the two halves of an 075 tank once and it held gas for about 6 hours

 

[Ketchup]

I’ve used several tubes of 1184 now. I have rarely had an issue with it but I’ve seen a few base gasket deletes that looked bad. I think if the surfaces have true, tight tolerances the sealant will last quite a long time. If the surface contact is irregular or the parts have movement, 4 years is about the best you can hope for.

Holymar Blue is a little harder to work with but some people swear by it.

 

[EFSM]

if the surfaces have true, tight tolerances the sealant will last quite a long time

Amen! this isn't Great Stuff.

 

[EFSM]

It takes time to change state, even with the pressure difference, the fuel DRIES out as it travels through the crankcase, eventually all vapor as it enters the cylinder. The oil falls out of suspension with the liquid fuel drops as they atomize, leaving the oil in the crankcase.

You're right. I don't think there should be enough liquid fuel in the crankcase to damage sealant, though.

 

[Moparmyway]

You're right. I don't think there should be enough liquid fuel in the crankcase to damage sealant, though.

More like very tiny droplets, atomizing as they go ……. the crankshaft/connecting rod area are pretty much operating in a fuel/oil fog