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

[huskihl]

Thanks for the reply. I was thinking the slab side would help direct the air/fuel mixture better towards the lowers.

Is there a difference in weight? I don't feel like spending 100.00 plus for a piston to get some specs. Haha.

As long as there is a path that’s not restrictive to get the charge into the lowers it doesn’t matter. The slabs are wider (further apart) on the windowed piston. Not enough room between the slab and wall to get quite enough charge into the lowers. The non windowed slabs are angled more to the center to increase that gap.

If the bearing pockets were lower like on a 372, there would be enough room for the charge to enter from the bottom. But on a 7900 there’s only about 1/8” below the deck so they need some help from the side

 

[Powerstroke Cowboy]

As long as there is a path that’s not restrictive to get the charge into the lowers it doesn’t matter. The slabs are wider (further apart) on the windowed piston. Not enough room between the slab and wall to get quite enough charge into the lowers. The non windowed slabs are angled more to the center to increase that gap.

If the bearing pockets were lower like on a 372, there would be enough room for the charge to enter from the bottom. But on a 7900 there’s only about 1/8” below the deck so they need some help from the side

Thank you for the explanation and help. It's much appreciated.

The new piston is quite a bit lighter. But the ring pin is in a spot that makes it land very close to the upper transfer. Gotta be careful when porting that hole because of it.

Okay, sounds good. It even looks lighter just from pictures I have seen. But looks are subjective. Thank you for the information. Its much appreciated.


Thinking out load here. (Don't yall laugh to hard, but if you do, remeber laughter good for you!!) The lighter piston should help performance and longevity. But if there benefits to the windowed piston helping feed the transfers due to not much space. What if a guy windowed the newer piston? Would that get you the best of the new and old design into one piston? Plus, make it even lighter in the process?

 

[huskihl]

Thank you for the explanation and help. It's much appreciated.

Okay, sounds good. It even looks lighter just from pictures I have seen. But looks are subjective. Thank you for the information. Its much appreciated.


Thinking out load here. (Don't yall laugh to hard, but if you do, remeber laughter good for you!!) The lighter piston should help performance and longevity. But if there benefits to the windowed piston helping feed the transfers due to not much space. What if a guy windowed the newer piston? Would that get you the best of the new and old design into one piston? Plus, make it even lighter in the process?

If I had them both to choose from, I’d go with lighter and wider skirts

 

[Powerstroke Cowboy]

If I had them both to choose from, I’d go with lighter and wider skirts

Thank you.

 

[Mastermind]

Thank you for the explanation and help. It's much appreciated.

Okay, sounds good. It even looks lighter just from pictures I have seen. But looks are subjective. Thank you for the information. Its much appreciated.


Thinking out load here. (Don't yall laugh to hard, but if you do, remeber laughter good for you!!) The lighter piston should help performance and longevity. But if there benefits to the windowed piston helping feed the transfers due to not much space. What if a guy windowed the newer piston? Would that get you the best of the new and old design into one piston? Plus, make it even lighter in the process?

I'm not keen on adding windows to any piston. I've pulled a couple of saws apart over the years with that done and both had cracks in the piston.

 

[Powerstroke Cowboy]

I'm not keen on adding windows to any piston. I've pulled a couple of saws apart over the years with that done and both had cracks in the piston.

Thanks for the information. I will keep that in mind.

 

[davidwyby]

@Kiwioilboiler Pirate Ship

 

[Stefaan]

Wanted to weigh some 7900 pistons i have laying around. I also put in a aftermarket big bore 52mm 372xp piston.

I was surprised how light the aftermarket 7900 pistons were compared to the original Mahle one, especially after i ground on the original one in the past (it was straight gassed and scored pretty bad, so i ground a little on it just to get the feel on grinding pistons)

Weights.
Mahle: 79g
Dolpima: 77g
White box china: 72g
372xp 52mm: 91g

I also noticed that the two aftermarket ones have this little nub under the wrist pin support that could be removed without doing any harm I believe. Making them even lighter.

 

[Wilhelm]

What do You do (in a pinch!!!) when You max out both Your PS-6400 (73xx/79xx) chain adjuster & bar slot?


Utilize a 8 pin sprocket.


But don't forget to remove the rubber chip deflector, unless You already boogered it up on a prior occasion.
Mine was pristine, it ain't no more.


This is NOT a solution!
It is merely a temporary fix to get the job at hand done.
A stretched out chain no longer complies to its specified pitch resulting in a rough running chain and causing increased stresses to the PH!

Dolmar PS-6400 FTW!!!

 

[Shane¹]

What do You do (in a pinch!!!) when You max out both Your PS-6400 (73xx/79xx) chain adjuster & bar slot?



Box the saw up and ship it off to someone with a new chain for it. Where do I put my address lol

 

[Wilhelm]

I haz a chainz or thirty-ish!



But I only have one Stihl Rapid Duro 3!

I guess it is time to try the new cheaper not-Stihl Carbide tipped chain I purchased a while ago.

Anyways, You don't want this PS-6400!
One owner, ran on pump gas, no issues to fix - You'd be bored by this saw.

 

[Powerstroke Cowboy]

I haz a chainz or thirty-ish!

View attachment 374899

But I only have one Stihl Rapid Duro 3!

I guess it is time to try the new cheaper not-Stihl Carbide tipped chain I purchased a while ago.

Anyways, You don't want this PS-6400!
One owner, ran on pump gas, no issues to fix - You'd be bored by this saw.

I dought I would d be bored by it, I'd have fun modding it!!

 

[Wilhelm]

I dought I would d be bored by it, I'd have fun modding it!!

And THAT is why You ain't getting mine, she is perfect factory stock!

 

[Wilhelm]

Fallen back to third page?!
That ain't right.

Bumpity!!!

 

[Kiwioilboiler]

Soooo, despite reading that lots of well respected saw men think that HD filters are a step backwards, I bought and fitted one because I like a high top saw.
Howeverrrrr, my cylinder cover is a smooth glossy plastic, but the HD is a matte textured plastic. Just doesn't look right to me.
Did I order the wrong one?
View attachment 372422View attachment 372423

So it turns out that good friend @markds2 and i only had to swap the HD air filter tops off our own saws to sort this shemozzle, which only required a couple of boxes inter-island.
Popped it on today with some flippy caps.
If y'all could just remind me where I've hidden the momentary switch I bought I'd be forever grateful.

 

[jcf86mod]

So it turns out that good friend @markds2 and i only had to swap the HD air filter tops off our own saws to sort this shemozzle, which only required a couple of boxes inter-island.
Popped it on today with some flippy caps.
If y'all could just remind me where I've hidden the momentary switch I bought I'd be forever grateful.
View attachment 380425

Looks great @Kiwioilboiler, flippy caps a nice touch. Have you put the toggle kill switch in as well? Nice simple mod. As for that bloke called @markds2 , yea he's not bad, in fact damm helpful and pretty handy to know!

 

[huskihl]

Looks great @Kiwioilboiler, flippy caps a nice touch. Have you put the toggle kill switch in as well? Nice simple mod. As for that bloke called @markds2 , yea he's not bad, in fact damm helpful and pretty handy to know!

He just talks funny

 

[jcf86mod]

He just talks funny

Like Ally yum yum

 

[huskihl]

Like Ally yum yum

Exactly

 

[Hulsty]

Been awhile since i've used my 7901 in anger, camping over the weekend and there was a big (4' barrel) gum tree dead over the track, nice dead branch at waist height, bought a smile to my face quickly slicing up the below. Other campers nearby were using battery saws or small/blunt sounding saws and battling away.