Building a 290/390

[Adirondackstihl]

no need for any special tools. You just wiggle it in...together with the rings on. no xhit.



see above. Ive done about 10 clams so far and never needed a tool. and Im just about spastic with my manual dexterity.

stone serious. Lube the cyl and piston and don't use a screw driver or anything just wiggle the piston assembly into the cyl.
you'll laugh once its in and say huh ? WTF was all that about. must have been a lucky shot....but it aint.

edit. just remembered there is a slight "taper" that allows the "wiggle" way.

I agree, there is a taper, but not on the bottom of the transfer bridges.
I'll do it my way, you do it your way.
That's a damn good way to break a ring or damage a ring land.

 

[angelo c]

Thanks for that Angelo, I can see this is going to be much different than anything I've done before.

Would putting the cylinder in a vice with the spark plug facing down facilitate the build on these thinks? I'm trying to work this out in my mind before I actually get there.

don't over think this Mike. put the halves together with smaller bolts then slide the assembly in the cradle. once in remove one bolt at a time and replace with the proper length and drive it through the case. its counter intuitive but dirt simple. some times getting the clutch side in and aligned is a challenge but not when assembled. the sealant usually is enough to hold it together.

 

[MustangMike]

I'm sure this will be a learning experience!

 

[Adirondackstihl]

Well......
I coulda finished this thing tonight, but I'm missing the little brake cam spring and a few AV caps.
Gonna have to source those before I go any further.
Then I'll show you the muffler mod I do.

 

[MustangMike]

Jeremy, do you advance the timing at all?

I could not believe how restrictive the muffler is on my 029, surprised the saw could run with it!

 

[Adirondackstihl]

Jeremy, do you advance the timing at all?

I could not believe how restrictive the muffler is on my 029, surprised the saw could run with it!

No I don't Mike.
It's a customer saw.
If it were mine, I'd probably try it

 

[Lightning Performance]

290 fun

Has anyone ever tried to play with the upper portion of those transfers??? The boxy look of them just seems like it does not facilitate a smooth flow of the mix.

I have lifted the transfers 4 degrees. It makes a hell of a difference. I think the radius sucks on the uppers in the back wall. A bit of fill might wake them up. It would help the transition to 90 degrees and stuff the case a bit more. Dropping the intake a few helps with a bigger bar. Ignition time is huge on these things. Add them all up and you have a runner with practically indestructible AV for your ham fisted user.

Oh btw I did build a 390 for a customer a few years back. Threw everything but the kitchen sink at it to see what could be had. The oil pump turned out to be the weak point pulling a 28" full comp 3/8 50 LGX. The pump rework showed that it could hang right with a pro saw in the same CC class. It's a long row to hoe to get there.

Oh Oh btw It has to SCREAM. The stroke is just to short with the BB. Like, barely "Tuned" w/big carb 15000, yikes! Yea, it shakes rattles and rips.

 

[Lightning Performance]

Well......
Then I'll show you the muffler mod I do.

OOOO show us ur muff

 

[Terry Syd]

Ignition timing for this series is all over the place. The manual states because of 'manufacturing tolerances' the acceptable ignition range is between 23.5 and 28.5 degrees. Mine was one of the saws in the low range, I put about 6 degrees more advance into the timing. It really woke it up.

I'm playing with some carb mods now and it's looking like I may be able to pull a couple of degrees out (I made an adjustable coil, elongated the screw holes). If you make an adjustable coil, then you can keep tweaking it until you go too far, then shift the coil back.

The limitation on the intake is the air filter, I had to make my own. To show you how bad the stock filter is, I used my oversized filter three times without cleaning it, then checked the revs with a tach. Then put on a stock filter, clean, never used and did the same test - the revs dropped 75rpm. I didn't bother testing a dirty stock filter.

 

[Adirondackstihl]

More parts arrived today.......

 

[MustangMike]

I have lifted the transfers 4 degrees. It makes a hell of a difference

W/O putting a degree wheel on this thing, about how much distance was that?

 

[Adirondackstihl]

W/O putting a degree wheel on this thing, about how much distance was that?

*f-word that
Just rebuild it

 

[Terry Syd]

Probably around 1 millimeter. - So, how about nipping a millimeter off the edge of the piston next to the transfers? It may also help to turn the flow over the top of the piston on an open port jug. If your worried about dropping the compression a tad, just remove the gaskets from under the spark plug and compression release.

 

[MustangMike]

I was thinking it would be nice to just do a little touch to make the mix go toward the intake side. From the pics, those transfers look flat, and I'm tryin to learn here, not like I'm gonna make my living with this saw.

I want to do it right, but if it screws up, it is not a big deal.

 

[Adirondackstihl]

I was thinking it would be nice to just do a little touch to make the mix go toward the intake side. From the pics, those transfers look flat, and I'm tryin to learn here, not like I'm gonna make my living with this saw.

I want to do it right, but if it screws up, it is not a big deal.

Just trim a few thou off the intake side of the piston skirt for more intake duration......

 

[Terry Syd]

The big problem with open transfers is that the flow moving up along the side of the piston 'lifts' the flow away from the piston crown. I notice on a Farmertech jug that the port closest to the exhaust had a bit of curvature in the roof of the port. The curvature would likely tend to direct the flow downward a bit to help allow the flow to remain flatter across the piston. The transfer port next to the intake remained flat, which because of the open port design would direct the flow upwards a bit. The result of the two port configurations would be a flow design similar to a 372 jug where the back transfer is slightly angled upward and the forward port is flat.

 

[MustangMike]

Probably around 1 millimeter. - So, how about nipping a millimeter off the edge of the piston next to the transfers? It may also help to turn the flow over the top of the piston on an open port jug. If your worried about dropping the compression a tad, just remove the gaskets from under the spark plug and compression release.

Thanks for that. (I typed this earlier but must have neglected to post it).

 

[MustangMike]

Just trim a few thou off the intake side of the piston skirt for more intake duration......

Are we still talking about 1 mm here, and would you "arch" it? It still amazes me that you don't have to worry about throwing these things out of balance with all the RPMs they turn. Also, would you consider widening the port if the piston seems to allow for it? (Intake & Exhaust).

 

[MustangMike]

Damn, I tried to measure 1 mm with my calipers, and I came up with 40/1000. So I went to a conversion chart, and it is 39.37/1000 ... damn, that ain't too bad!

But it is likely a lot more than Jeremy was suggesting, but I will await his response.

This is getting interesting, I like it!

 

[Adirondackstihl]

It's alive!!