Leaky Clamshell

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TheTone

TheTone

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I'm rebuilding a non-starting MS192TC with 150+ compression and spark. Set the carb aside to check crankcase integrity. Would not hold vacuum and leaked pressure around the seals. I put some Dirko around the outer edge of the seals and later repeated the pressure test to see if anything else showed up. To my surprise, bubbles formed all along both flat mating surfaces of the pan and cylinder. When I got the pan off, the pattern of sealant (looked like red Dirko) covering the sealing area showed no gaps. The bolts had been tight. Is this unusual, or does the sealant just break down over time? I plan to use red Dirko (and new seals) when I reassemble. At the risk of starting a sealant war, should I use something else?
 
Before I started building saws I was doing Pwc and snomobile cases with threebond 1194 I think. Then I started using motoseal and never went back to threebond. I think threebond is a stronger bond but I've had no issues with motoseal. Never used dirko. I know its super important to have both surface clean oil free for any sealant to work properly .
 
Dirko seems to take too long to dry to me.

I had quite a few leak with motoseal on chainsaws & cutoff saws.

I had better luck with threebond 1194, but Yamabond 4 is the best IMO.
It is very good for clamshells and base gasket deletes. Dries fast and tough, plus is pliable like rubber, so can handle expansion and vibration.
It also and sticks great to porous metals, and plastcs, but won't distort from gasoline.
Plus It's not bad to clean off when rebuilding one that's been built with it either.
It's da Yamabomb....
 
I got a batch of non-runners last week....strangely when going threw them a lot if the clamshells were sealed up with a "grey" colored sealant, is yamabond or motoseal grey????


Any way when I pop off all the jugs, there sealant has "bubbles" were it has cured, in the meaty part of the seal(hope that makes sense), anyway I didn't like the looks of it, and judging by these saws, this stuff was leaking.....it also felt very "soft" like gas was weakening it.....it's hard telling what it is though, knowing dealers, it could have been grey elmers glue LMAO!!!

No I personally use dirko, I let it setup over night in warm spot, and never had any issues......I am not saying it's the best, I just like its sealing abilities...oh and the smell is horrible, like silicone caulking x10!!!!
 
Khntr85 said:
I got a batch of non-runners last week....strangely when going threw them a lot if the clamshells were sealed up with a "grey" colored sealant, is yamabond or motoseal grey????


Any way when I pop off all the jugs, there sealant has "bubbles" were it has cured, in the meaty part of the seal(hope that makes sense), anyway I didn't like the looks of it, and judging by these saws, this stuff was leaking.....it also felt very "soft" like gas was weakening it.....it's hard telling what it is though, knowing dealers, it could have been grey elmers glue LMAO!!!

No I personally use dirko, I let it setup over night in warm spot, and never had any issues......I am not saying it's the best, I just like its sealing abilities...oh and the smell is horrible, like silicone caulking x10!!!!
Click to expand...

If those saws were older Stihls, then yep, we've seen that material as OEM sealant. I believe it to be an older version of a Dirko product.

It's rare for the clamshell to leak on older saws just due to normal use. Abused saws with possible impacts or hot/lean conditions can develop problems there. Maybe junk fuel plays a role but the sealant is fuel-resistant and hard to penetrate once torqued. I'd say it's similar to case gasket failures in terms of the numbers.
 
BuckthornBonnie said:
If those saws were older Stihls, then yep, we've seen that material as OEM sealant. I believe it to be an older version of a Dirko product.

It's rare for the clamshell to leak on older saws just due to normal use. Abused saws with possible impacts or hot/lean conditions can develop problems there. Maybe junk fuel plays a role but the sealant is fuel-resistant and hard to penetrate once torqued. I'd say it's similar to case gasket failures in terms of the numbers.
Click to expand...
This was a ms250 any were from 3-10 years old...I have seen/rebuilt quite a few older 029, 025, 018, etc and I have never seen this grey sealant....I just figured it was a dealer that used a different type of sealant..

Did they used to use a gray dirko at the Stihl factories???
 
I have tried most of the sealers above mentioned more than once. They all seem to work fine. I started building dirt bike engines before touching chain saws more than 50 years ago. So was eager to try everything available. A leaking sealer can be devastating for inconvenience and financially. A well maintained saw that does not run into extreme conditions like extreme lean conditions causing excess heat they will not leak for many years. So if the saw is not abused it will for most part be bullet proof. Letting the sealer cure for awhile before closing the halves permanently seems to have some advantages. Thanks
 

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