The ideal ms260 timing numbers.

[thompsoncustom]

was wondering what everyone's thoughts were on the ideal timing numbers for a ported ms260 work saw.

let's ignore cylinder limitations, for example if u think the best numbers would be 106/120/80 even tho that's not a common achievable numbers just want people's thoughts on what the prefect numbers would be.

 

[bretts]

I wouldn't mind knowing these numbers as well seeing as I build a lot of these saws.

 

[Ketchup]

@drf256 builds a mean one.

 

[drf256]

Try to get your exhaust to 105. Getting there isn’t easy, but you’ve acknowledged that as acceptable.

You pretty much nailed it with your numbers.

 

[thompsoncustom]

Try to get your exhaust to 105. Getting there isn’t easy, but you’ve acknowledged that as acceptable.

You pretty much nailed it with your numbers.

thanks but my question is more theoretical I guess. do you think this saw would preform better with the exhaust at 110.

probably a hard question to answer since it's not normally achievable but is more exhaust always better on this platform?

 

[Ketchup]

Cannot compute: undefined variables.

 

[farminkarman]

thanks but my question is more theoretical I guess. do you think this saw would preform better with the exhaust at 110.

probably a hard question to answer since it's not normally achievable but is more exhaust always better on this platform?

If you could get the exhaust wide enough, you could probably see some gains by going lower than 105. I doubt 110 would be optimal though. Last year I did a husky 350 with a 346xp oe p&c. I got that one to 109 on the exhaust and it ripped…but I was able to get a pretty wide exhaust with that combo, and I ran pretty short blowdown. I have never touched one of these, so I don’t know how much exhaust width you can get. As Doc said, you’re probably looking at 105.

 

[thompsoncustom]

Cannot compute: undefined variables.

Ya kind of an impossible question to answer I suppose. I plan on doing some experimenting with brazing in the exhaust port and I'll aim for 110 on the exhaust and work down to maybe 106 to see what it likes. At 110 blowdown would be very short as I think the transfer are at 120 or 121 if I remember right.

If you could get the exhaust wide enough, you could probably see some gains by going lower than 105. I doubt 110 would be optimal though. Last year I did a husky 350 with a 346xp oe p&c. I got that one to 109 on the exhaust and it ripped…but I was able to get a pretty wide exhaust with that combo, and I ran pretty short blowdown. I have never touched one of these, so I don’t know how much exhaust width you can get. As Doc said, you’re probably looking at 105.

I can't remember how wide in relation to the bore I have it at now but I know it's .050 from the edge of the skirt.

 

[drf256]

In general, you can take 60-65 out of the band in these jugs. Cutting the band and piston dome flat allows one to take the most out of it. You’ll get a compression of around 250-260 with this which will run fine. When you put a longer bar on it, it will lean out at the cut end with all of that compression. You’ll have to tune different for different bar lengths.

Then you have to cut the base to get the squish. The stock bases struggles to be .250 thick, so they get kinda thin. In the .180-.190 range When done.

Taking more than that and you’ll freeport at TDC quite a bit. A little is ok, some of my best runners have had some freeport.

Using a Husky 246 piston works with a bit of work, but the base gets super thin. More of a 2 piece head kinda method.

The exhaust port is gonna be small at 105. Kinda a wide pancake shape. It runs though.

Im not sure on the 110 thing. Unclear if it would run, but the geometry on the 1121 just isn’t there for it. I’ve thought of Belzona epoxy. I don’t think that the high temp aluminum braze would definitely hold up in the ex roof. Tig welding it will cause warpage of the bore-you can try a super tight steel or brass mandrel in it. I’ve warped the bore at the base before doing quick bursts on jugs.

Youll also have to raise your uppers more when you drop it further, so you will lose the nice tight uppers we all want.

Please post you findings if possible. I am interested.

 

[thompsoncustom]

In general, you can take 60-65 out of the band in these jugs. Cutting the band and piston dome flat allows one to take the most out of it. You’ll get a compression of around 250-260 with this which will run fine. When you put a longer bar on it, it will lean out at the cut end with all of that compression. You’ll have to tune different for different bar lengths.

Then you have to cut the base to get the squish. The stock bases struggles to be .250 thick, so they get kinda thin. In the .180-.190 range When done.

Taking more than that and you’ll freeport at TDC quite a bit. A little is ok, some of my best runners have had some freeport.

Using a Husky 246 piston works with a bit of work, but the base gets super thin. More of a 2 piece head kinda method.

The exhaust port is gonna be small at 105. Kinda a wide pancake shape. It runs though.

Im not sure on the 110 thing. Unclear if it would run, but the geometry on the 1121 just isn’t there for it. I’ve thought of Belzona epoxy. I don’t think that the high temp aluminum braze would definitely hold up in the ex roof. Tig welding it will cause warpage of the bore-you can try a super tight steel or brass mandrel in it. I’ve warped the bore at the base before doing quick bursts on jugs.

Youll also have to raise your uppers more when you drop it further, so you will lose the nice tight uppers we all want.

Please post you findings if possible. I am interested.

I don't think the aluminum brazing will have any problems holding up as I brazed in the head on a wild thing that's ported around 70% of the bore and running 170 compression and it's been perfectly fine so far.

I plan on doing the same to my farmertec ms260 jug instead of lowering the jug i'm just gonna braze up in the head and then braze the exhaust port to get it where I want so no problems with the base getting thin at all or freeporting. Figured I'd start outside the normal achievable range like say 110 and work backwards just to see how it performs.

Warpage is my biggest concern as I never checked the wildthing cylinder for it but I will on this one but not a big deal if I wreck it.

I know it's kind of a odd approach compared to the pro's like you but it's what I got.

I do have a question for you Doc; what stainless steel mesh did you make your own ms260 filters out of? I believe it was you I seen that made their own.

 

[drf256]

I buy the AF oem. Still available.

 

[thompsoncustom]

I buy the AF oem. Still available.

Hmm must be someone else I was thinking of then. Not a Fan of the OEM air filter to restrictive in my opinion I'm currently running a aluminum V stack with a 45 degree K&N style filter ms460 carb, bigger intake boot but can't remember which one 038 maybe, I will probably go back to running a OEM style filter and cover once I cut one up and glue some stainless mesh to one just not a big fan of the filter hanging off of a work saw RPM gain was good tho.

 

[drf256]

For all out racing, an HD carb is ok. For the real world they suck. I’d try and 039 carb over an 046 carb. The venturi is simply too big for good throttle response IMHO. You’re using a carb for a saw that’s 60% larger in dispalcement.

I could be wrong, but once you’re in there you may notice an issue with the geometry. The skirt on the 260 is just not that wide. The 44.7 and the 44mm have the same skirt width. The 44.7 is not wider.

At BDC, the piston crown with the stock piston is still way above the exhaust floor, even without a base cut. Again, I could be wrong, as I always cut the base. The 246 piston was the only time a lowered the floor to get more useful area. So you won’t be able to lower the floor for more area, won’t be able to widen the port for more area, and you’re gonna reduce the area of the entire port with the 110 opening.

Hey, noone ever learned anything by not trying. I applaud your efforts. Please post results.

 

[drf256]

This is an exhaust port at 104-105. It’s already short and wide as compared with other models we do. One pic is vs a stocker.

You can see the plating/stock center port because I didn’t raise it.

 

[drf256]

Duane PA 026

This will be a real time build thread, so bear with me fellas. I’ll post as I go, and the saw may not be finished for another month. Duane already has one of my MS260’s, and now he has an excellently built hot lil’ 026 done by CJ Saws. We spoke and he wants something on the wilder side. The...

opeforum.com

 

[thompsoncustom]

At BDC, the piston crown with the stock piston is still way above the exhaust floor, even without a base cut. Again, I could be wrong, as I always cut the base. The 246 piston was the only time a lowered the floor to get more useful area. So you won’t be able to lower the floor for more area, won’t be able to widen the port for more area, and you’re gonna reduce the area of the entire port with the 110 opening.

Hey, noone ever learned anything by not trying. I applaud your efforts. Please post results

The piston being above the floor by a considerable amount is not something I consider been to long since I've been in there. I still plan on playing with it just to see what happens and I'll report back.

 

[thompsoncustom]

At BDC, the piston crown with the stock piston is still way above the exhaust floor, even without a base cut.

well started tearing it down a little today mostly spraying everything off and cleaning it up but I did look at the exhaust at BDC.



looks good so far but remember it's a Chinese saw so you may be right that the piston is higher on a normal 260 also checked compression and it was at 160psi thats with the squish sitting at .018 with no base gasket.

after I braze the chamber I will do all the testing with a base gasket just for ease of install and tear down but will go back to .018 when I'm finished.

 

[drf256]

well started tearing it down a little today mostly spraying everything off and cleaning it up but I did look at the exhaust at BDC.

View attachment 380163

looks good so far but remember it's a Chinese saw so you may be right that the piston is higher on a normal 260 also checked compression and it was at 160psi thats with the squish sitting at .018 with no base gasket.

after I braze the chamber I will do all the testing with a base gasket just for ease of install and tear down but will go back to .018 when I'm finished.

So you can’t gain any port area by lowering the floor or widening it.

 

[thompsoncustom]

So you can’t gain any port area by lowering the floor or widening it.

Ya at this point i'm only going to be shrinking the port which isn't ideal and may not even be needed since I'll be gaining compression by removing area in the head but that's what the testings for. I can't see how the port area would be any different than if you were to lower the jug tho. Actually would probably be better to leave the exhaust roof high if I could still achieve +200 compression with just the head work that would yield more exhaust duration than one lowered to 106 if i'm not mistaken.

And I wouldn't say can't...... It has crossed my mind to try and widen the stock piston by cutting a junk cylinder in half and using it as a form as I braze on the sides of the piston and as nice it would be to get to 70% of the bore I just don't know if I want to go down that road or if it would even hold up. Brazing in the head is a lot different than on the side of the piston going up and down 15,000 times a minute and I just don't mess with these things enough to know what will work without doing it.

 

[Ketchup]

Just random thoughts…

If you can get compression way up there, having a higher exhaust shouldn’t be too bad. But I think @drf256 runs very high compression and still finds 105 to be a good height.

Also the shape of your chamber is important. If you could fill the chamber and then cut it to a smaller bell shape you would probably see more efficient combustion. In theory, you could even fill the plug hole and re-tap into the center of the bell. Like a two piece head.

Are you working with a 44 or 44.7 mm jug? Echo 490 pistons are full circle 44mm. I’ve got one here if you want measurements.

Are you planning to leave the dome on the piston or cut it flat?

You have a bit of luck with the AM jug. What are your current numbers? Looks like the exhaust is higher than 105 but the floor is good news.