Stroking a Dolmar 7900

[Mastermind]

I love all the little nuggets of wisdom that get dropped all over the place at OPE

When I drop stuff it's not usually "wisdom".

 

[Johnmn]

When I drop stuff it's not usually "wisdom".

I lol'd

 

[Fruecrue]

I shimmed the cylinder .100” and measured about .042” squish.
1.5mm or .058” base gasket should net me zero squish.
I can add two standard base gaskets and run it, I can take .020” out of the band and run with the thick gasket, or I can take .020” off the piston crown and run it with the thicker gasket.
What say you?

Eventually all will change and saw will be ported, I’m just eager to see it make some chips.

 

[Mastermind]

I shimmed the cylinder .100” and measured about .042” squish.
1.5mm or .058” base gasket should net me zero squish.
I can add two standard base gaskets and run it, I can take .020” out of the band and run with the thick gasket, or I can take .020” off the piston crown and run it with the thicker gasket.
What say you?

Eventually all will change and saw will be ported, I’m just eager to see it make some chips.

I'd take .020 outta the band and leave the piston as it is.

 

[mettee]

I shimmed the cylinder .100” and measured about .042” squish.
1.5mm or .058” base gasket should net me zero squish.
I can add two standard base gaskets and run it, I can take .020” out of the band and run with the thick gasket, or I can take .020” off the piston crown and run it with the thicker gasket.
What say you?

Eventually all will change and saw will be ported, I’m just eager to see it make some chips.

If you are going to cut the band I say just cut it so you can run a regular non thick gasket. Cut the .078 and run with it unless that will remove too much "bowl" from the combustion chamber. I don't know what is acceptable the veteran guys have a way better idear.

My other concern is that the cylinder is close to the cover and melts it. Being 100 thou higher.

 

[mettee]

When I drop stuff it's not usually "wisdom".

Could be good or bad depending what's being dropped from where.

 

[Intoxsawcated]

Cut the least amount possible to get it running.

Sent from my SM-S327VL using Tapatalk

 

[Deets066]

I’d cut .020 from the chamber to get the comp up a bit. Running a thick gasket isn’t a bad thing. Should check port timing before you make a decision on which way to go

 

[Canadian farm boy]

I'd do the least invasive things possible to get it running. Make a game plan for the porting after you know it works and have a feel for how it runs.
Just my $.02

 

[mdavlee]

If you are going to cut the band I say just cut it so you can run a regular non thick gasket. Cut the .078 and run with it unless that will remove too much "bowl" from the combustion chamber. I don't know what is acceptable the veteran guys have a way better idear.

My other concern is that the cylinder is close to the cover and melts it. Being 100 thou higher.

You cut that much compression will be 250. Plus it will more than likely free port on the exhaust floor.

 

[mettee]

That's true good call, see that's what I mean by veteran guys knowing

 

[mettee]

You cut that much compression will be 250. Plus it will more than likely free port on the exhaust floor.

So if he cuts just the squish band, and not the base won't that put the cylinder exactly where it was to start? The free port space on my piston was about .090 or just under, the stroke is 1mm more or .040, so it makes me think it might work and he can keep port timing.

On the other hand if he uses the thicker base gasket and cuts less squish band, that might put the ports in better position for better numbers.

I'm just spit balling...

 

[mdavlee]

It should be real close. I’d rather be where he’s at with it spaced up than lower them that much more. Be more grinding on exhaust and transfers for what I would like to see.

 

[Fruecrue]

Parts should be delivered today, I’ll be in a tree stand until then.

 

[Sty57]

Yup........ Of my 10 th tree! [emoji12]

Are you logging or making firewood?

How much land do you have or are you cutting for other people?

 

[RI Chevy]

Logging. No
Firewood Yes
Own land. No
Cut for others. Yes

I'm just a hack

 

[Sty57]

Logging. No
Firewood Yes
Own land. No
Cut for others. Yes

I'm just a hack

I just figured you were logging or doing firewood for production.
Because you always say you can only make any money running Stihl's.

 

[RI Chevy]

Because that is all I had and used. Just funnin really. Lol
I do many small jobs. Make spending money. It funds the addiction. stay busy stuff.

 

[Mastermind]

You cut that much compression will be 250. Plus it will more than likely free port on the exhaust floor.

I take .060" out when I do a Solo hybrid. But, I take the exhaust up to 96.....so compression ain't crazy high. Transfers ain't as far off as you would think either. Intake comes in just right because you don't take anything off the base, and the longer stroke makes BDC further down the bore.

But.....I'm not sure if the deck height is the same between the Dolmar, and the Solo. I'm also not sure about the 7900 jug VS the 7910 jug as far as raising the exhaust that much. The 7910 jug has all that "extra" material due to the insert from the muffler into the port.

 

[Fruecrue]

I take .060" out when I do a Solo hybrid. But, I take the exhaust up to 96.....so compression ain't crazy high. Transfers ain't as far off as you would think either. Intake comes in just right because you don't take anything off the base, and the longer stroke makes BDC further down the bore.

But.....I'm not sure if the deck height is the same between the Dolmar, and the Solo. I'm also not sure about the 7900 jug VS the 7910 jug as far as raising the exhaust that much. The 7910 jug has all that "extra" material due to the insert from the muffler into the port.

Solo gasket thickness?