Dolmar 64xx/73xx/79xx series, smurfs and solo 665/675/681 thread

[mettee]

I used this to tighten the squish on mine. Reinforced it with some 518. 5$ at Napa for a small roll that will do many saws. View attachment 141779View attachment 141780

I actually have some of that I think....

 

[AlfA01]

Well I started the work on my 7910 cylinder. I'll do the exhaust side next.

The stock squish is .025, what do yall think, will that work without cutting the band or is it better to uniform the band and take that ridge out?

Nice work. When you measured squish was it with or without the base gasket?

Mine were a lot tighter on both saws. I was in the .015 -.017 range IIRC so some squish manipulation was in order get it above .020.

My XD saw is at .021 and the other .022 final squish sans gasket.

 

[huskyboy]

I actually have some of that I think....

Awesome. BTW nice grinding. I hope to be that good someday. For now I’ll stick to simple mods and do my reading up on here lol. I didn’t do anything else to the 7900 internally other than that matching of the base and putting in a 7910 lightweight piston.

 

[mettee]

I dig that way of doing the lowers for sure. That was gonna be my plan as well. And I'm going to stagger the transfers.

 

[huskyboy]

Nice work. When you measured squish was it with or without the base gasket?

Mine were a lot tighter on both saws. I was in the .015 -.017 range IIRC so some squish manipulation was in order get it above .020.

My XD saw is at .021 and the other .022 final squish sans gasket.

I got lucky and it was .028 on all 4 sides with the 7910 piston. The old window piston was .031 I believe. After the thinner gasket I got .020 - .021 on all 4 sides.

 

[mettee]

Nice work. When you measured squish was it with or without the base gasket?

Mine were a lot tighter on both saws. I was in the .015 -.017 range IIRC so some squish manipulation was in order get it above .020.

My XD saw is at .021 and the other .022 final squish sans gasket.

Thats with gasket in place. I was hoping to use a stock gasket. I need to check for freebore again, want to make sure I'm safe.

 

[AlfA01]

I got lucky and it was .028 on all 4 sides with the 7910 piston. The old window piston was .031 I believe. After the thinner gasket I got .020 - .021 on all 4 sides.

Sweet. Nice easy mod right there.

 

[huskyboy]

I discovered by studying the 7910 piston... By eye it looks to flow better than the 7900 windows one, it does not seem to shroud the lowers at bdc and potentially disrupt the flow. I would imagine case compression must be higher too? The saw runs differently with the slab side. Hard to explain, but it feels a touch “freer” and it’s not even broken in yet. Not that it was lacking much before with the windows one...

 

[mettee]

Just knocked out my exhaust port after work. It's like therapy, got rid of all my stress.

I like to grind in rough. Walk away, come back and observe what I did. Then I use a sharpie to mark areas that need fixing. That way I can analyze what needs to be done and not go overboard.

I mark the areas I don't want to grind as well. Something bright like red or pink, stay away from that.

Once I get the exhaust polished up I'll post a pic. Well maybe I'll take one roughed. I have a couple green marks where I need to remove material tomorrow.

I might do a build thread. Lots of details I have learned that are not crystal clear in the other porting threads.

 

[mdavlee]

I discovered by studying the 7910 piston... By eye it looks to flow better than the 7900 windows one, it does not seem to shroud the lowers at bdc and potentially disrupt the flow. I would imagine case compression must be higher too? The saw runs differently with the slab side. Hard to explain, but it feels a touch “freer” and it’s not even broken in yet. Not that it was lacking much before with the windows one...

The solid side doesn’t waste the area with the most force on the flow going out the windows to dead head into the cylinder wall. But a 460 piston seems to work out god in them. It’s up higher in the case so maybe it doesn’t block the lowers but it’s still got windows

 

[huskyboy]

The solid side doesn’t waste the area with the most force on the flow going out the windows to dead head into the cylinder wall. But a 460 piston seems to work out god in them. It’s up higher in the case so maybe it doesn’t block the lowers but it’s still got windows

Very interesting option. Is it lighter than the dolmar piston? The skirts wider?

 

[mdavlee]

I don’t remember the weight. It’s a little wider skirts. The ring ends is the only complaint.

 

[mettee]

Black marks where the top of the port is originally, read not to raise or lower the exhaust.

You can see the black in the port lip, that is the original port

 

[mettee]

Well I started my lower transfers today.

 

[mettee]

I ground on the lip area because they were uneven from side to side, just make them uniform.

Im unsure on the green areas, to remove more material or not.

 

[huskyboy]

I ground on the lip area because they were uneven from side to side, just make them uniform.

Im unsure on the green areas, to remove more material or not.

I wouldn’t remove too much. Randy says it hurts them in torque department if you take too much out.

 

[Lightning Performance]

I'm unsure on the green areas, to remove more material or not.

Welcome, to what next. Shear is what your worried about there. Ever bit takes volume up and primary down.
Two words sum it up best.
Interpreter please....

 

[Wilhelm]

I was at my local Stihl and Husqvarna dealers today.

OEM Stihl rim sprockets, standard spline:
- 3/8" 7 tooth - 0000 642 1223
- 3/8" 8 tooth - 0000 642 1216
- .404" 7 tooth - 0000 642 1206

Oddly they are all listed at identical prices and much lower than I expected.

Husqvarna/Oregon PowerMate rim sprocket:
- 3/8" 8 tooth - 505 30 36-61 , about 1$ cheaper than the Stihl equivalent

I was unable to get Husqvarna part numbers for 3/8" 7 tooth and .404" 7 tooth.

I like the fact that I can get suitable sprockets locally.

What is the consensus regarding quality Stihl vs. Oregon?

 

[mettee]

Welcome, to what next. Shear is what your worried about there. Ever bit takes volume up and primary down.
Two words sum it up best.
Interpreter please....

I tried to create the same effect in the Primary Transfer ports that is happening in the Secondary Transfer ports. The research I did told me not to remove the corners of that side that shrouds the Primary Transfers. I smoothed around the edge, but that's it. So far I have removed less material in that corner than I have seen done.

Hopefully one of the guys with more experience will chime in and help with some advice.

I was going to have Randy or Carl port this for me, but I decided I would like to do it myself, I am glad I did its a lot of fun.

 

[mdavlee]

Put the piston in there at BDC and see what it looks like. You may change your mind where to grind