Author Topic: Converting Solo 665 to a 681  (Read 174 times)

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Offline KilliansRedLeo

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Converting Solo 665 to a 681
« on: October 16, 2014, 01:03:47 pm »
OK guys, time for some advice. Dolmar changed the piston configuration for the 7900 from windowed to slab sided. Most think that the change made for better performance out of the 7900.
 
DexterDay and I were discussing using the new Dolmar 7900 piston in this project instead of the Solo windowed piston that comes in the Mahle OEM Solo 681 P/C kit.

Dexter is going to covert one of his 665s to a 681 using a new OEM Solo P/C kit. I measured the two pistons and the deminsions of the pistons are the same except the weight, the slab sided Dolmar is a little lighter than the windowed Solo.
 
I read somewhere that a couple of builders favored this route on the Dolmar 7900 but I have no specific knowledge or opinion on how the piston would perform in a stock 681 saw. Any thoughts?  ???
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

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Offline aclarke

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Re: Converting Solo 665 to a 681
« Reply #1 on: October 16, 2014, 04:10:26 pm »
Tim, i'd go lighter in the reciprocating mass, I.e piston, rod, etc. I can't See any advantage to a heavier piston . Slab side is 15 grams or so lighter. Maybe use a stihl double butted pin (tapered internally) Adding mass to the rotating flywheel could be a hindrance or help. It's gonna take power to accelerate the heavier mass so in cases like a hot start saw race where you can spin up the mass prior to hitting the wood where the stored energy could be utilized. Real world use it would be a wash IMHO

Offline KilliansRedLeo

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Re: Converting Solo 665 to a 681
« Reply #2 on: October 18, 2014, 12:24:04 pm »
Thanks Adam, any Idea which Stihl wrist pin?
"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: Converting Solo 665 to a 681
« Reply #3 on: October 18, 2014, 08:03:51 pm »
I'll check in a few and get back. ..

Offline farmboy

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Re: Converting Solo 665 to a 681
« Reply #4 on: October 18, 2014, 10:10:52 pm »
I wanted to use the slab piston in my 665/681.  Cut the wrong side on intake port had to use AM windowed piston ring pin in center.  Plan on sending slab piston out to relocate pin to the center.  Don't know why Dolmar put the ring locating pin on the side on the slab piston.  IIRC the slab piston skirt is about 2mm wider than windowed piston.
Shep

 

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