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Author Topic: Dolmar 7900 piston choices  (Read 3703 times)

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Online 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
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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
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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
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Offline Cut4fun_

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Re: Dolmar 7900 piston choices
« Reply #46 on: August 16, 2012, 02:19:19 pm »
Quote from: farmboy on August 16, 2012, 09:09:10 am
The new piston is about 2mm wider.
Shep

Quote from: farmboy on August 16, 2012, 09:09:10 am
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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Offline Cut4fun_

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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. 

Quote from: EHP on August 16, 2012, 05:56:48 pm

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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Offline Cut4fun_

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Re: Dolmar 7900 piston choices
« Reply #50 on: August 16, 2012, 10:02:21 pm »
The 52mm oem open windowed I have here I know is around 16.75mm top of pin hole to crown and 12mm pin. I will have to get the rest tomorrow if I get time.

Oh I aint looking for a piston for a dolmar either.  Pretty much staying away from them now days.
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Offline Cut4fun

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Re: Dolmar 7900 piston choices
« Reply #51 on: August 17, 2012, 01:18:55 pm »
Man if I measured this OEM 52mm piston right (my digital calibers was giving me fits).  It is a very nice stock piston  ;D.

Correction made on ext and int today with new battery

top of pin hole to crown 16.75mm
ext int skirt 35.20mm 35.15
height 42.65mm
pin 12mm




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Offline 604f_1

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Re: Dolmar 7900 piston choices
« Reply #52 on: August 17, 2012, 07:41:31 pm »
PP475 piston ?
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Offline Cut4fun_

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Re: Dolmar 7900 piston choices
« Reply #53 on: August 17, 2012, 10:41:51 pm »
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Re: Dolmar 7900 piston choices
« Reply #54 on: August 18, 2012, 07:16:46 pm »
CORRECTION:

New battery put in and checked skirts again. The first measurement is WRONG they are NOT 40mm they are only 35.20 ext and 35.15 int. Sorry, but like I said the digital calibers were acting up first time.
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Re: Dolmar 7900 piston choices
« Reply #55 on: August 19, 2012, 04:52:22 pm »
Anyone know the skirt width on the meteor 064 piston?  I know the meteor was wider then the oem piston. Used to have a BB372 with a meteor 064 piston in it.

    Stihl 064, MS 640 Meteor
   
    Height 43mm   
    Pin 12mm x 33mm x 8mm
    Pin hole top to top of Piston 17mm
   
BB372

Bore 52mm
Height 42.5mm
Piston Pin 12mm x 8mm x 36mm
Pin to top of Piston 16.75mm


2 different makers of 046 pistons


Stihl 046, MS 460
Replaces Part Number 1128 030 2009
Bore 51.96mm
Height 39.25mm
Head Type Flat
Piston Pin 12mm x 35mm x 7mm
Ring 52mm x 1.2mm (Caber F-Cast GH.F)
Compression/Pin Top to top of Piston 15.5mm
Compression/Pin Center to top of Piston 21.5mm

Stihl 046, MS 460
Replaces Part Number 1128 030 2009
Bore 52mm
Height 39.25mm
Head Type Flat
Piston Pin 12mm x 7mm x 35mm
Rings 52mm x 1.2mm Ductile Split Groove
Circlips 12mm
Compression/Pin to top of Piston 15.5mm
Compression/Pin Center to top of Piston 21.5mm






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