Porting my 361

[Lakeside53]

Be careful Brad.. next you'll have a lathe, a mill, and have way more money in tooling than all your saws forever... LOLOL


As for you piston.. Make something to hold it in your drill press, spin it fast and just touch emery paper on a ridgid holder (wooden stick) to the outer 1/3 of the top (no need to take off the entire top. Measure as you go...

then go buy a lathe

 

[blsnelling]

Excellent idea. However, in this case I wanted to polish the top of the piston anyway and that alone removed about .004". Believe it or not I don't even have a drill press. I have a lot of hand tools and do a lot of different work, but no drill press. I finally bought a MIG welder last year. I used it to weld a hole shut in the 460 muffler. When removing the inner baffle, one of the spot welds pulled out.

 

[Cut4fun]

I decided to do the 361 first. the 260 is already ported, but I need to go in and do the piston like the others. I'll recheck the shape of the exhaust port while I'm at it.

You know this is all your fault. "Hey Brad, when are you going to do your 361?":hmm3grin2orange:opcorn:

Brad in timed cuts, what gains were made with the 460? before doing the piston and after what was gained time wise in the cut?

 

[blsnelling]

I'd have to go back to Bills and cut that 15" log again. I don't have anything to cut here My time before was 6.4x If I recall correctly.

 

[Sawdustmaker]

Dude, we got to have some video of this thing:chainsawguy:

 

[Andyshine77]

What are you doing up this crazy time of night? I can't seem to quit working on this thing.

I get to work nights in the winter, I love every minute of it.

 

[blsnelling]

Here's the last pics before it goes back together. I'm just hoping the squish is right and I don't have to sand and repolish the piston top.

A couple scratches, but polished.

 

[blsnelling]

My squish came out at .014", so I've got to take another .004" off the piston and repolish. After being up until 4 AM this morning working on it, I'm too tired to mess with it tonight. I'll get it tomorrow evening.

 

[Andyshine77]

Brad do you hone the cylinder after you're done porting it?

 

[blsnelling]

No I don't. Those are factory hone marks. This is a relatively new P&C with excellent compression, so I don't want to mess with a good thing.

 

[blsnelling]

I'm consideing going ahead and using a gasket of some type. What material have I heard mention than can be used and is .003"? Was it brown paper grocery bag? That way I could use a gasket with a light coating of grease and skip the Dirko.

 

[Crofter]

There is some quality vellum writing paper that is probably near 3 or 4 thou. You will find a variety thickness of brown paper that should get you there. Our aluminum beverage cans are around 6 thou. There is no heat there and only 5 or 8 psi pressure so the main thing is have something with enough body that it will not continue to yield over time and slack away your torque and change your squish. It is always good idea to retorque and recheck squish after running esp. if you are running dicey tight clearance.

 

[blsnelling]

After all this talk and indecision, I just went ahead and sanded the piston top some more. I've got it all back together and running. Squish came out at .017", right where I wanted it. I pulled a compression check after getting it fully warmed up and tuning the carb. It's still warm so compression will be higher yet when cooled off. It was at 165, so will likely be >170 cold. It was 168 when cold before I started. I thought I'd see more gain than that with the squish coming down from .025 to .017. Maybe I did more to the exhaust height than I though. I'm fine with 170 though. It's a work saw. It definately makes more RPMs now. It's still trying to 4-stroke at 14,700. I didn't go any higher. I left it a 14,600, ran it WOT for a couple seconds and shut the throttle off while WOT. The plug is still nice and brown. I'll leave it there and fine tune it in the woods. I think she'll haul Oh, I pulled the muffler back off too and the piston still looks like new. Another saw has been Snellerized and has become a BS361. Now I just need to get my hands on a 084.

 

[5shot]

And where's the video?

 

[blsnelling]

It's only run enough to tune the carb. Plus it's dark and there's no wood at the house here to cut. I'll try to get a video this weekend when I try it out.

 

[blsnelling]

I checked the compression cold and it's exactly 170 psi. That's only 2 psi more than I started with, so I must have raised the exhaust more than I though. I know, I should start using a degree wheel. 170 should be fine for a work saw though. This morning it popped with two pulls and started on the third. I hope to get to cut with it tomorrow.

 

[Majictree]

Hi ya'all..
I'm new to this site did a Google search for stihl 361 and found this.

All I can saw is wow, my Father and I have been tuning 2 stroke carts for two generations now hear in NC...
I have to say this form of porting is astounding I don't under stand how it can work..... No way of knowing how this motor is timed what so ever.
Have you never heard of a degree wheel???
I would be willing to bet a stock saw will run with this mess I sure hope you don't do work for others...

 

[5shot]

Not exactly trying to make friends with your first post....

 

[Jacob J.]

Brad- did you do any kind of sanding or honing to the cylinder before putting it back together? I saw you say that you probably weren't, however you could get a little more PSI if you were to do a little finger work in there with some emery cloth and liquid wrench, that way the rings have some fresh scratches to seat back into...

 

[blsnelling]

I did nothing to the cylinder walls. This P&C has very little time on it. The tiny little ridges on the rings are all still there. Compression was excellent before opening it up. The work I did should not affect ring sealing at all. The rings are in the same position riding on the same surface as they did before. I figure, why mess with it?