361 muffler Mod

[arborworks1]

By eliminating the base gasket, I am raising compression. What kind of problems, if any will the increased heat cause? And what kind of power increase can I expect.

 

[SkwerI]

The EPA mufflers on a stock saw cause much more heat buildup than eliminating the base gasket. If you want to save your saw from excess heat and shortened life then mod the muffler FIRST.

The people here who run stock saws off the shelf for years with stock mufflers damage their saws much more than people who modify their saws. EPA compliant does NOT equal longest life or best performance. In fact they are rarely compatible. If you want longer saw life and better performance then remove the EPA restrictions from the saw.

 

[arborworks1]

I was messing with my 260 today, The 250 looked to damn hard to take apart just for a polish. Anyway, the base gasket ripped when I pulled off the jug, I am thinking about leaving it off and seeing what I can get out of it.

 

[High Scale]

The muffler on the 361 looks like a real pita to split, was there any problems with refolding the seam?

 

[woodworkingboy]

I was messing with my 260 today, The 250 looked to damn hard to take apart just for a polish. Anyway, the base gasket ripped when I pulled off the jug, I am thinking about leaving it off and seeing what I can get out of it.

If you eliminate the base gasket, you will need to use a liquid gasket type sealant in it's place, one that stands up to gasoline, heat, and pressure, or at least make yourself up a thinner gasket with paper or metal. You also need to check the clearance at the top of the piston with the combustion chamber, at top dead center in the piston's stroke. Around .020" is the general clearance recommended for a working saw to be safe. If you get too close, the heat becomes a negative factor, can melt the piston crown. If the piston touches the top of the cylinder, likely bye bye saw. Expansion occurs with heat, that's why the clearance is necessary.

In addition, when lowering the jug, you have to make sure that the intake port is still covered by the bottom of the piston skirt at 180 degrees after top dead center, that is the lowest point in the piston's stroke.

It's not difficult to check any of these things.

By eliminating the gasket, you'll definitely up compression, but how much depends on the piston clearance. You'll end up with more torque likely, but for best advantage, the cylinder ports need to be worked on and raised and widened as well. Just lowering the cylinder changes the timing of the engine, the point in the piston's stroke where the ports open and close. Raising the ports at least back up to stock timing, is an accepted way to get good safe power improvement with a working saw. Race saws generally push the envelope more.

Hope that gives an idea of some of the basic processes involved.

Jay

 

[Al Smith]

As a general rule a Stihl base gasket is around 19-20 thou thick .By eliminating same and using some type sealant you are likley to drop the cylinder by 17-18 thou once you squash the sealant ,maybe a tad less .

You shouldn't run into problems on the intake .The exhaust and transfer will operate a tad late though which could raise the torgue perhaps by a tad bit but could knock a few r's off the top speed .There shouldn't be any problems with piston to cylinder top clearance nor should you experiance any heat related problems .

Easy enough to do and if it doesn't work out ,put the gasket back in .All this would be rather moot though if the muffler didn't get some attention .Remember ,if it can't get out ,it can't get in .

 

[woodworkingboy]

I agree with you Al, he'll probably be alright with the piston clearance after eliminating the gasket, maybe just where he wants to be....but I have had a saw or two drop down to within .015" clearance without the gasket. I think on the safe side to check for sure.

 

[Al Smith]

I also agree it would be a good idea to check .

I sometimes forget that most or actually all of my limited enhancements have been done on older saws where there was normally 45 or so thou clearance in stock form . The newer ones could in fact be less so better play it on the safe side .

 

[High Scale]

I decided not to crack open the muffler, not without a spare anyway, I did drill and open up the baffling and I noticed that the exhaust port and the muffler opening did not match, a swift go with the flat file and the muffler is back on the saw, it has a more throaty sound now, yet to try it in wood.

 

[sotc]

i pulled the jug off my 260 a week ago and havent had a chance to work it since. i was going to attack it with files but sounds like i better run to sears and get a dremel, im sure my die grinder is to aggressive

 

[squisher]

Any pics of the process would be apreciated Willie. Ya know step by step with detailed explanations.

 

[arborworks1]

I'm going to take my saw back apart and polish the exhaust port. I'll get some pictures of the process. Should go alittle smoother, now that I have some wrench time already on it. I opened up the exhaust port slightly and jusy sanded it clean. I think polishing it to a mirror finish will more a tad more air. Any thoughts! Plus in my rush to get it back together I forgot some rtv sealant.

 

[darkstar]

Some recent mods ive seen were far less complicated and didnt even require removing the exahaust.
The guy just drilled two holes in it.
That was on a 372 and his 394 .
I was like uhhh man i think there is a better way he said naw its just a wast of time this works almost as good.

 

[sotc]

Any pics of the process would be apreciated Willie. Ya know step by step with detailed explanations.

sure, as long as i get some critisizem along the way about whats right and whats wrong. and if it gets into a war i get to say SHUT UP!!
first question is how do you all get your saws so clean before dismantling? i ran my compressor for a half hour straight before pulling the jug off and its still dirty where the jug mates to the cylinder

 

[SkwerI]

Willie, the air nozzle is just about the most effective cleaning tool. But keep a rag handy to wipe off any missed crud before snapping the picture.

 

[sotc]

ha! i thought so!

 

[sotc]

i just went to sears and bought a dremel. came home to try out the bits i got works good but i decided to stop till i got my camera in the shop

 

[woodworkingboy]

Make sure when opening the ports that you don't go wider than what the piston crown will cover....best to leave about 3/32". The shape of the top of the port is important, too flat can snag the ring and do damage to it. Chamfer the inside of the port edges well. Take a good look at the edges when stock, the stock saw will have the edges chamfered.

 

[arborworks1]

I realized that and shaved them back and sanded it real smooth. I already had a small scratch on my piston. I buffed it smooth as best I could. How would I go about adjust the squish if its to close?

 

[SkwerI]

Either use a thicker base gasket or else shave the piston. Al posted some pictures a while back of how he shaved the piston on that 038 he built, after he shaved the jug too far.