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Author Topic: Dolmar 7900 piston choices  (Read 15658 times)

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Dolmar 7900 piston choices
« on: May 07, 2011, 09:18:00 am »
Have any of you guys tried putting a stihl 064 meteor or stihl 038 mag piston with pop up in 7900?  Just curious, been seeing 7900 and 7901 with small spacers under base and pop up pistons in them.
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Re: Dolmar 7900 piston choices
« Reply #1 on: May 07, 2011, 09:45:47 am »
or maybe even a Wiseco 52mm piston with 1mm rings or stihl ms460.
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Re: Dolmar 7900 piston choices
« Reply #2 on: May 07, 2011, 01:15:35 pm »
what would be the advantage? compression?

What was your initial feeling , buying a used saw with shims under a wrong piston?

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Re: Dolmar 7900 piston choices
« Reply #3 on: May 07, 2011, 03:52:55 pm »
Never owned one and never will. I have only seen them Jeff. They were strong as get out torque wise.

 Look on youtube and you will see more of them being built here and in Calif.  ;)



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Re: Dolmar 7900 piston choices
« Reply #4 on: May 09, 2011, 02:26:05 pm »
Guess I better clarify this. I owned a 7900 - 7901 in 07-08 that had a stock oem dolmar piston and off center pop up with finger ports DN Dave Neiger had put in.   I was talking about the new stuff people are putting out there with non dolmar pistons.

For me now days Jeff I dont even want pop ups since I cant make one quickly to replace in a firewood saw.
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Re: Dolmar 7900 piston choices
« Reply #5 on: May 10, 2011, 04:43:21 pm »
I looked at a lot of pistons, including the ones you mentioned.  None of those made the list I kept for one reason or another.  Foran OEM 7900 jug, I came up with a 272 piston which should require about a .174" spacer under the cylinder.  If a 13mm wrist pin could be used, a 281 could be used with only a .095" spacer.

For the 7900BB, I only found the 288 piston, which has a 13mm wrist pin and would require a .095" spacer.

I don't recall if my calculations took into account for a popup or not.  The main thing I was looking for was increased skirt width.  I've not tried any of these combinations yet though.
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Re: Dolmar 7900 piston choices
« Reply #6 on: May 11, 2011, 07:38:38 am »
Quote from: Chainsawrepair on May 09, 2011, 02:26:05 pm
Guess I better clarify this. I owned a 7900 - 7901 in 07-08 that had a stock oem dolmar piston and off center pop up with finger ports DN Dave Neiger had put in.   I was talking about the new stuff people are putting out there with non dolmar pistons.

For me now days Jeff I dont even want pop ups since I cant make one quickly to replace in a firewood saw.
If it's a work saw why would anybody even consider one, unless the builder is close by or your a machinist.

Now here's a something to ponder, how much better "flow" or how much more of a port is exposed so you can go lower or higher to get "gains" or how much "better" is 200lb compression vs. 160 or 180.

Percent wise I'm talking.

If you had a saw that cut 10 seconds in a given stick, what time would be the final time with all those "upgrades"?
 
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Re: Dolmar 7900 piston choices
« Reply #7 on: November 28, 2011, 07:33:23 pm »
I just noticed this topic.
I've got a Makita 6401 that I'm putting a OEM 79cc top end on and will be porting.
And I'll be playing around with a couple different pistons, seeing which one works best
I've got a 272, 281, 046, and 064 pistions I'm just going to see dimensions if any will work.
Since the skirts are so narrow on the OEM Dolmar piston.
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Re: Dolmar 7900 piston choices
« Reply #8 on: November 28, 2011, 10:55:31 pm »
The current 7900 OEM piston has no windows
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Re: Dolmar 7900 piston choices
« Reply #9 on: November 29, 2011, 08:01:44 am »
New 510-5100-5105 piston doesn't have windows either.  Looks just like the "upgraded" 7900 piston.  The area around the pin boss is too thin to put windows in.
Shep
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