Porting the dolmar 421...

[Red97]

Damn Pat, I agree with you again. I see a trend here.

Can't wait to see what Joe does here. I personally can't see it beating the echo 490. After all, there's no replacement for displacement. If both are properly ported, as Joe will do, the 8cc's has to give the echo the edge.

I tend to agree, but I'm gonna try an get as much from this little dolmar as it will give me. Without sacrificing longevity...

When I get done with the 5105 I'm moving on to these. So subbed as your gonna make my job a bit easier. Lol. Thank you!

Feel free to join it, never been in a dolmar. Curious to see what is inside...

 

[Backtroller]

One cool thing that I noticed when I took the muffler apart is that there is a thick and heavy brace inside of the muffler that holds the muffler body to the cylinder that I've never seen before.

 

[Red97]

Ok, just some comparisons...

This is my dad's 241c less than 6 tanks through it. 14" bar picco semi chisel. I would say that adds probably 1-2 second to the cut time vs if it had full chisel.

All of the saws are lined up by the lower handle bolts.

The dolmar and echo both balence well with the 18" gb bar. The 241 really needs a 16"+ to balence out.

The echo feels like the smaller saw, as seen by the handle placement. Shortest distance from handle to trigger.

Dolmar and stihl have the better av with the echo just being ok.

 

[drf256]

WOW.

So a 42cc saw that's the size and weight of a 50.

Looking forward to your craftsmanship, but I don't get what the OEM was thinking.

 

[Red97]

Now for this dolmar....


Looks pretty good overall. As said above seems to handle just fine with the 18" lo pro setup.

Air filter setup seems to do a really good job keeping the junk out.



Stock comp.



Silly coil... you supposed to be mounted to the case...
Not sure if I like that setup.


Typical dolmar piston rather short and narrow skirts... but super light.

Super excited to see 6 transfer while checking port timing...

Only to find out they are open still think it can be made to run a bit better.

Intake side.

Ex port

Intake. Pretty healthy burrs leftover from the factory beveling.

 

[Red97]

Stock numbers with base gasket.
Intake, 73
Exhaust, 113
Transfers, 131
Squish .023
Base gasket .020

Think I'm going to cut the base .020-25 (.040 max edge of freeport)
Set exhaust at 108 with 17/18 blowdown. Open intake and exhaust a touch while reshaping. Set squish .018-20

Open up the muffler baffle to let it breathe a bit better.

Think that is about all this saw gives us, every one I have talked to raves about how well it works stock.

I'm thinking a decent bump in compression, along with some port shaping will liven this saw all that the carb and coil will allow...

Thoughts???

 

[CoreyB]

WOW.

So a 42cc saw that's the size and weight of a 50.

Looking forward to your craftsmanship, but I don't get what the OEM was thinking.

Well it is the smallest lightest 50cc saw. How do other 42ish size saw compair?

 

[Red97]

So some things about the "build quality" of this saw.

in MY OPINION.

Pro,
Same size fastener used throughout. T27 torx
Solid cored base gasket, for easy removal

Con,
No intake boot clamp/spring nothing just a snug fitting rubber boot.
Coil mounted directly to the cylinder, just a couple hard plastic insulators.
The jug quality was slightly less than I expected, rough ports/bevels casting on the outside looked good, no major flaws, plating was ok, I've seen better and worse.

Everybody has preferences, not my place to make that call. Other than the things I mentioned it is on par with every other saw I have been into.

 

[Backtroller]

I'm surprised the compression is so low. At least raising the compression should add something.

Those burrs are awful. I guess that is why this is a $320-350 saw. The cylinders on my 6421 and 7910 were beautiful. I would have expected more. I'm glad you are going into it.

Do you think that it would be possible or necessary to add some sort of a clamp to the boot?

 

[RIDE-RED 350r]

Subbed.... Despite the OP design, this little saw still intrigues the hell outta me

 

[Red97]

I'm surprised the compression is so low. At least raising the compression should add something.

Those burrs are awful. I guess that is why this is a $320-350 saw. The cylinders on my 6421 and 7910 were beautiful. I would have expected more. I'm glad you are going into it.

Do you think that it would be possible or necessary to add some sort of a clamp to the boot?

Well the saw dosent have much run time on it. So I would imagine it in the 160's when fully broke in stock.

I'm hoping to get it up around 200psi.

As for the burrs, eventually something slides past quality control. I doubt that is common with the other dolmars.

I plan on adding a dab of sealant to the boot before I re install.

I'm still hoping for decent gains out of it. I was really surprised to see the open transfers.

 

[Backtroller]

Of course my saw had to be assembled on a Friday by a dude who was hung over

 

[fordf150]

Open up the muffler baffle to let it breathe a bit better.



Thoughts???

I will get some pics of my muffler but just using the embossed area and cutting the gills out is all i normally do but i have played around quite a bit and there is a very slight gain by going bigger. cutting out the entire embossed area around the gills and reforming the deflector to give an even larger opening but from my experience it wasnt enough of a gain to justify the extra noise. i bet ported you will need that extra area though.

this is my normal mm.

 

[exSW]

Those burrs are awful. I guess that is why this is a $320-350 saw. The cylinders on my 6421 and 7910 were beautiful. I would have expected more. I'm glad you are going into it.

Yes. I think hitting the price point with a pro built saw explains a lot. Spur drum,crappy stock bar, over the top cat . But the package is still built better than anything else. None of the naysayers have much if any time on this saw.

 

[drf256]

6 transfers looks great.

 

[Red97]

WOW.

So a 42cc saw that's the size and weight of a 50.

Looking forward to your craftsmanship, but I don't get what the OEM was thinking.

2 40cc and a 50. All of them are close to the same physical size, and "feel" about the same weight.

I will get some pics of my muffler but just using the embossed area and cutting the gills out is all i normally do but i have played around quite a bit and there is a very slight gain by going bigger. cutting out the entire embossed area around the gills and reforming the deflector to give an even larger opening but from my experience it wasnt enough of a gain to justify the extra noise. i bet ported you will need that extra area though.

this is my normal mm.

View attachment 19078

That was kind of what I was thinking. Thank you for the pics.

6 transfers looks great.

They are tiny... lol. Wish they were closed too. At least I can see the way they transition into the bore.

 

[drf256]

Looking at this little jug makes me think about a lot of things.

I'm gonna put posts separately to try to keep things straight here.

So you have .023 squish WITH gasket. Are you planning on running one Red13.5?

I see why it runs so well. They left little on the table.

So you take 20 off the base, leaves you with -17 sans gasket. Take 37 out of the band. Am I following here?

 

[drf256]

Exhaust height.

You've got a limited coil again Joe.

I'm not sure if raising the roof is gonna do that much. The reason this little sucker pulls so well may be that exhaust height. I think I'd raise it back to 113 and leave it there. If the compression is too high, I guess you can raise it.

That flywheel is a work of art joe. As this is a small displacement saw with a rather large overall size, I bet compression around 230 would be a nice compromise.

 

[Miller Mod Saws]

Stock numbers with base gasket.
Intake, 73
Exhaust, 113
Transfers, 131
Squish .023
Base gasket .020

Think I'm going to cut the base .020-25 (.040 max edge of freeport)
Set exhaust at 108 with 17/18 blowdown. Open intake and exhaust a touch while reshaping. Set squish .018-20

Open up the muffler baffle to let it breathe a bit better.

Think that is about all this saw gives us, every one I have talked to raves about how well it works stock.

I'm thinking a decent bump in compression, along with some port shaping will liven this saw all that the carb and coil will allow...

Thoughts???

Is this gonna be a one shot try or you gonna tear it down a few times? I only ask as I may add a couple degrees to the blowdown for initial testing! Looks good so far my man. I'm watching and liking!

 

[drf256]

Transfers.

Do the entry angles differ from exhaust/mid/intake roofs?

You should have LESS case pressure from lowering the intake floor. You'd need a higher (physically) than stock upper to compensate. But you also are removing the muffler cat and venting exhaust better. That would make me want a lower transfer opening.

I'd personally go with openings of 129/130/131-opening the exhaust first, then the mid, then the intake. I'd open the exhaust one more squarely to the chamber and increase the angle upwards as you get to the intake one.

Depending on just how crazy you wanna go, you could fill the exhaust transfer with JB weld and make it thinner in width. Kinda make it into an exhaust finger.

You have a lot of relative cross sectional transfer area there Joe.

I'm just thinking out loud. I love the puzzle of porting theory.

I don't see a lot left on the table here. They probably created a saw on the edge of max performance.