Author Topic: 6400 Dolmar  (Read 1234 times)

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Offline mdavlee .

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Re: 6400 Dolmar
« Reply #10 on: February 05, 2014, 07:53:02 am »
Interesting seeing the reversion. How much blow down is that cylinder running.

Offline KilliansRedLeo

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Re: 6400 Dolmar
« Reply #11 on: February 05, 2014, 10:16:40 am »
Just guessing here but the piston on the right appears to be the 359, correct? Is the stock piston windowed?
I am interested in your performance results as I am replacing a windowed piston with a slab sided one in a closed port Husqvarna cylinder and I have a NOS 6400 saw I want to try some stuff on. Also, please post the measurements on both pistons, overall height, compression height pin center to top and pin top to top on the two pistons, if you would be so kind.
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

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Offline KilliansRedLeo

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Re: 6400 Dolmar
« Reply #12 on: February 05, 2014, 10:55:22 am »
Also looks that there may be another piston option from Meteor that has a 21mm compression height rather than the 20mm on the 359, it is windowed but full circle type rather that open skirt. Go here and have a look:

http://www.meteorpiston.com/Lists/Gardening/Join.aspx?List=831329fb%2Dc6b1%2D403e%2Dab58%2D966a2b8b6758&ID=1068&Source=http%3A%2F%2Fwww%2Emeteorpiston%2Ecom%2FLists%2FGardening%2FCatalog%2Easpx


Stihl model 08/TS-350 47mm may give a couple more possibilities, it appears to be slab sided but with a domed top. However it is taller by 6mm because of the domed top and has a compression height of 27mm, may be a very tight squeeze!
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

Thomas Jefferson
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Offline aclarke

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Re: 6400 Dolmar
« Reply #13 on: February 05, 2014, 01:06:40 pm »
Putting a new crank in the Saw. I'll Pat the before after number tonight.

The 359 piston seems to be within a mm both ways so it should be an easy fit

On this application I think a slab sided piston will work just as well. 359 piston is heavier, May remove a little weight.   Adam

Offline KilliansRedLeo

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Re: 6400 Dolmar
« Reply #14 on: February 05, 2014, 06:45:42 pm »
So Adam, do you think that using a slab sided piston in a open port saw will better control the flow reversal you are seeing? Just wondering about your thought process behind the non-windowed piston.
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

Thomas Jefferson
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Offline aclarke

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Re: 6400 Dolmar
« Reply #15 on: February 05, 2014, 11:28:55 pm »
Perhaps, although the blowdown is likely the real issue. I put the New crank and bearings in the case and buttoned it up tonight so I'll be able to see what the original and altered timing number are.

I find it interesting that dolmar went to the slab piston in the 7900. Not that I don't think it works well but, however, the original piston was designed with asymmetric windows in the piston which were done for a reason and took a lot of thought and engineering. I'm very curious why they dropped that piston for the slab side?? Can the slab side be lighter? Hard to believe, but perhaps they opted for a lighter piston when the crank issues came up?

On a side note, the New crank I pressed into the bearings/crank halves had a lot more interference fit than any previous 7900 I've worked on. Almost Stihl tight!!! Lol

Offline KilliansRedLeo

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Re: 6400 Dolmar
« Reply #16 on: February 06, 2014, 05:34:12 am »
So, is the new crank stroked or stock?
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

Thomas Jefferson
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Offline mdavlee .

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Re: 6400 Dolmar
« Reply #17 on: February 06, 2014, 07:01:31 am »
I think the slab sided is lighter. I know Randy got more power with the slab sided with the same port timing. I'm thinking it keeps velocity up better for transfer flow.

Offline farmboy

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Re: 6400 Dolmar
« Reply #18 on: February 06, 2014, 09:16:43 am »
Slab pistons 5100 and 7900 are a lot lighter.  Don't remember how much tho.  I can get wt's on 7900 if needed.  IIRC i wrote the wt on the box.  I used windowed piston in my Solo 665/681 conversion because I went too wide on the ring end side.  The windowed piston pin is in the middle.  The slab pistons are in the box.  I need to send em and have the pins relocated.  I did measure skirt width the slab pistons are a little wider.  Interesting the Solo 665 cylinder is quad port like the 7900 where the 6400 is open.
Shep

Offline aclarke

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Re: 6400 Dolmar
« Reply #19 on: February 06, 2014, 09:26:02 am »
Interesting.  Wonder if the slab sided piston was a fix to reduce crank failures?

 

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