You might call Permatex?

877-376-2839

Most likely the same thing in a different tube. Sure wouldn't worry about it, there's not to much pressure in the crankcase. Steve

True, but even a small air leak will cause all kinds of grief with a 2 cycle.Locktite has a special sealer for that application, I cannot remember the name.

Yes, pressure is an issue in a 2-cycle engine as the piston motion in the crankcase pumps the fule/air mixture into the combustion chamber. What you used may work, but you might ask a local Stihl dealer/shop what they use. For what its worth, the old VW beetle engines had a split alloy crankcase that was sealed with a brownish-red Permatex aircraft sealant that more like a lacquer than anything you see nowadays.

First things first vandyken, your crankcase should not be vented, what you are seeing as a vent is probably the connection for the impulse line. The crankcase must be airtight, both in positive and negative mode, with the exception of what comes in through the intake.

The product that you used may be ok, I`m not familiar with it, Bill was on the right track when he suggested that you call Permatex to find out. The issue is not that the case won`t be adequately sealed but will it remain sealed. Most RTV/silicone based sealants are not gasoline and addditive resistant and over time a leak will develop. The Loctite product for this application is 515.

Since you have already assembled the saw what is the worst thing that can happen if you try it as is? A leak will develop, the engine will run lean, and you could have a lean siezure. If you are very conscious of the fact that a lean condition may develop you could shut the saw down before damage occurs, otherwise you are looking at tearing the saw down to reseal the case halves pre-emptively and even with the horizontally split case on the ms250 you might end up replacing your new crank seals.

This is all just food for thought, you must be the ultimate judge of how much risk and experimemntation you are able to withstand.

I have to get a new cylinder and piston kit for my ms290 because of piston ring freeze up. I know this is a MS250 forum but my question stays with the sealant issue.

The dealer told me I would need to buy a 1 oz tube of Dirko Sealant for about 17 bucks. Use is to seal the cylinder. I asked him wht about RTV Blue. Said his shop only uses Dirko.

So now I just read about Locktite 515 as another possibility. Any consensis opinion about what is the better sealant.
If I have to use the Dirko, is there another place I can get it cheaper than the Stihl dealer.

Your choices are the following:

Locktite 518
Permatex Ultra Copper or Ultra Grey
Yamabond or Hondabond
Dirko HT

preparation of the surfaces is more important then the brand of sealant

How do you prepare the surfaces?

And is loctite 515 not a choice? Because I was under the impression that it was based on past research and what I've read here.