Author Topic: Dolmar 7900 piston choices  (Read 6980 times)

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Offline 660magnum

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Re: Dolmar 7900 piston choices
« Reply #40 on: May 08, 2012, 11:51:32 pm »
The Wiseco pistons are different enough that you can tell what they are.
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Offline EHP

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Re: Dolmar 7900 piston choices
« Reply #41 on: May 09, 2012, 09:12:16 am »
you can tell if its got a 272 piston quite easy , first the saw will have a spacer under the jug as the pin hole is lower on the 272 piston and as far as there being a wiseco wide skirt piston out there I would say no cause they had to make the mold to build mine . may have been a narrow skirt piston but not a wide skirt and I had a hell of a time getting them to build the piston the way I wanted as they kept wanting to narrow the skirt on the bottom and I told them that that would not work
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Offline EHP

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Re: Dolmar 7900 piston choices
« Reply #42 on: August 15, 2012, 04:59:51 pm »
anybody got a picture of the new 7900 piston , I just want to see if its any wider on the skirt than the old 7900 piston

Offline Cut4fun .

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Re: Dolmar 7900 piston choices
« Reply #43 on: August 15, 2012, 05:40:05 pm »
All I have read is the skirts were pretty much the same. Just the new piston was half a ounce lighter.

Last pic is new 7900 p compared to 6400 p.


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Offline EHP

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Re: Dolmar 7900 piston choices
« Reply #44 on: August 15, 2012, 06:15:57 pm »
Ok I thought someone told me they were full skirt but that for sure is not the case  ;D

Offline farmboy

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Re: Dolmar 7900 piston choices
« Reply #45 on: August 16, 2012, 09:09:10 am »
The new piston is about 2mm wider.
Shep

Offline Cut4fun .

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Re: Dolmar 7900 piston choices
« Reply #46 on: August 16, 2012, 02:19:19 pm »
The new piston is about 2mm wider.
Shep

Good news on 5100 piston it's about 2mm wider.
Shep

The 7900 is 2mm wider too or are you talking about the 5100 piston?

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Offline EHP

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Re: Dolmar 7900 piston choices
« Reply #47 on: August 16, 2012, 05:56:48 pm »
every little bit helps on a 7900 , they cannot make the skirt to wide unless they change either the crankcase or pin location in the piston , a wider skirt hits before ever getting to BDC

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Re: Dolmar 7900 piston choices
« Reply #48 on: August 16, 2012, 06:50:23 pm »
What is the old 7900 skirts and new lighter replacement 7900 skirt widths?  Top of pin hole to crown height?

Found your spec info Ed. 


7900  piston with ring it weighs 85.4 grams , skirt width of 32mm/ 1.260 inch

52mm wide skirt wiseco piston, with ring it weighs 79.7 grams and has a skirt width of 1.670 /42.5mm

stock 272 piston weight was 82.9 grams with ring , skirt width is 35.83mm/1.414 inch,


Just trying to compare to a 52mm mahle piston I pulled out of another saw.



272 comparing too.

Height 40.5mm
Pin 12mm x 33mm x 8mm
Pin hole top to top of Piston 18mm


BB7900 specs
 
Height 40mm
Pin 12mm x 7mm x 32mm
Pin hole top to top of Piston 13.25mm
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Offline EHP

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Re: Dolmar 7900 piston choices
« Reply #49 on: August 16, 2012, 09:31:10 pm »
the 272 piston pin is set lower in the piston than a 7900 piston so this raises the piston once its on the rod , that is why you put a spacer under the cylinder  but also because the bottom of the piston skirt sits higher on a 272 piston than a 7900 the piston can have alot wider skirt cause it will clear the top of the crankcase when the piston is at BDC

 

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