Dolmar 6100 and 7910 muffler mod questions

[SOS Ridgerider]

Guys, I have both of these saws with the mufflers off, ready to do some mods, and I have some questions. Both of these mufflers have the SLR piece sticking out and into the exhaust port.
The exhaust ports on both of the saws have this edge that the SLR piece butts up against.
I'm sure that removing the guts in the mufflers and opening them up a little extra will help quite a bit. I've done a 421, a couple of 5105's and a 6421 before, but they don't look like this.

My question is this: Should I be looking at grinding this edge off? Does it make much of a difference? I'm mechanically inclined and have all the tools needed, but I've never done any grinding on the cylinders on my saws.

7910 exhaust port


6100 exhaust port


7910 muffler on the left, 6100 on the right.

 

[CoreyB]

Subbing! I thought I read that the piece is removed when making the 6100 hotter. I bet @Mastermind or @Miller Mod Saws could she'd some light.
I don't understand that piece on the 6100 because it doesn't have the slr in the muffler just a bird cage. Other than making it easier to line up.

 

[David Young]

Subbing! I thought I read that the piece is removed when making the 6100 hotter. I bet @Mastermind or @Miller Mod Saws could she'd some light.
I don't understand that piece on the 6100 because it doesn't have the slr in the muffler just a bird cage. Other than making it easier to line up.

Any chance the steel insert is to help keep the exhaust heat out of the jug being the steel is likely to transfer heat

 

[Mastermind]

The exhaust port is very narrow on both of those saws. I would suggest gutting the mufflers, and then pulling the jugs and widening the exhaust ports on both. Then you can smooth the edges of that step while it's apart.

 

[mdavlee]

Be careful doing that. You can raise and lower the exhaust port when you do.

 

[Cut4fun]

Poulan uses something like that inside the cylinder, but not attached to muffler. They call it Exhaust Port Insulator

Part #52

 

[SOS Ridgerider]

The exhaust port is very narrow on both of those saws. I would suggest gutting the mufflers, and then pulling the jugs and widening the exhaust ports on both. Then you can smooth the edges of that step while it's apart.

Be careful doing that. You can raise and lower the exhaust port when you do.

I don't want to mess with lowering or raising the exhaust. That's above my pay grade. At least for now. But, if I'm careful and just bevel the edge of that step out to match the rest of the port, and widen the port towards the muffler I should be good?
Is there a certain width to shoot for at the muffler end? I didn't look at the gasket to see if I could match the port to it, for a quick template. I'll have to take a look in the morning.
I might have to do the mufflers for now, and do the grinding when I have more time. I want both of these saws to be up and running for the CT GTG on Saturday. Can't have only Stihls and Huskys there. Lol.

 

[mdavlee]

I've never had the slr muffler to compare. The old style muffler doesn't leave much meat around the inlet if you open it to match a 7910 cylinder.

 

[Adirondackstihl]

 

[SOS Ridgerider]

View attachment 39380

Very cool! I might have to copy that...

 

[SOS Ridgerider]

What is the best source for the mesh screen?

 

[Backtroller]

A few guys sell sheets on eBay. I've bought 1/8 stainless steel mess for a few bucks. Cuts nicely with a dremel cut off wheel.

 

[SOS Ridgerider]

A few guys sell sheets on eBay. I've bought 1/8 stainless steel mess for a few bucks. Cuts nicely with a dremel cut off wheel.

Great! Thanks.

 

[Miller Mod Saws]

Subbing! I thought I read that the piece is removed when making the 6100 hotter. I bet @Mastermind or @Miller Mod Saws could she'd some light.
I don't understand that piece on the 6100 because it doesn't have the slr in the muffler just a bird cage. Other than making it easier to line up.

I agree with what Randy said. I will have to look at my notes but I wanna say port width is like 50% on both. When you widen them the steps on the sides will disappear or very close. And I always leave a couple mm on the floor step untouched where it goes into the cylinder. But blend the corner nicer. When you port both of these models. When you cut the base and squish you will cut a lot of the ledge out of the top as well lol.

 

[Miller Mod Saws]

Stock

 

[Miller Mod Saws]

And here's 68% width with a non agressive exhaust port.

 

[SOS Ridgerider]

And here's 68% width with a non agressive exhaust port. View attachment 39411

That's great information! All the info is very much appreciated!! Once the winter really kicks in up here, I'll look more into it. I'd feel comfortable with starting with widening the exhaust and beveling that step down. Cutting the base and squish is for big boys only. Lol.
Here's a stupid question: Does the very edge of the port get a slight bevel into the cylinder?

 

[Adirondackstihl]

Here's a stupid question: Does the very edge of the port get a slight bevel into the cylinder?

Yes
That's what keeps the ring(s) from snagging the port

 

[SOS Ridgerider]

Yes
That's what keeps the ring(s) from snagging the port

That's what I thought, but better to ask the experts first. Thanks!!

 

[Adirondackstihl]

Try to use a diamond burr if possible