Author Topic: Dolmar 7900 piston choices  (Read 7002 times)

0 Members and 0 Guests are viewing this topic.

Offline Cut4fun

  • Administrator
  • Nitro Hotsaw
  • *******
  • Posts: 4121
  • Karma: 171
  • OHIO REDNECK
Re: Dolmar 7900 piston choices
« Reply #70 on: May 11, 2014, 11:37:16 am »
Bump for good read on EHP 52mm wiseco pistons
REDNECK Saw Repair

Offline KilliansRedLeo

  • Nitro Hotsaw
  • *******
  • Posts: 2361
  • Karma: 80
  • Location: Rochester, NY
    • RoCHusqvarna
Re: Dolmar 7900 piston choices
« Reply #71 on: June 13, 2014, 02:37:13 pm »
In an earlier post in this thread someone said
Quote
For an 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.

Since I had an older red top 7900 on my bench for a rebuild, I thought I would test that, I used a stock 7900 jug a 272 & 038 magnum pistons. I cut out a spacer out of 0.305 material, thinking 0.305 should get me the required space for an 038 Magnum piston since the CH of the 038 is 22.5mm and the 272 is 24mm or about 0.059055 taller than the 038 Magnum. So if you take the spacer 0.305 add to it 0.059 you come up with 0.364 as how much room you would have. Subtract the 0.174 from the 0.364 leaves you with 0.019 no base gasket needed......COOL, thought I!


Wrongo! The 038 Magnum piston runs smack into the head with 0 squish, so that blows that number all to hell. Be back in a bit with the 272 numbers.

OK, with the degree wheel on the saw the 272 piston hits the top of the cylinder about 2.5 degrees before the 038 hit which stands to reason because the 272 piston is 1.5mm taller than the 038 Magnum e.g. 0.018-0.019 = 1.

So my feeling is that the quoted set of numbers must be for a pop-up.
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

Thomas Jefferson
1743-1826

Offline Cut4fun .

  • Administrator
  • Nitro Hotsaw
  • *******
  • Posts: 22134
  • Karma: 552
  • OHIO REDNECK Saw Repair Getter Done
    • Redneck Chainsaw Repair
Re: Dolmar 7900 piston choices
« Reply #72 on: August 30, 2015, 01:21:23 pm »


@jacob j.  Think the pics and info specs start on page 2 by EHP on wide skirt 52mm wiseco made pistons.



REDNECK Saw Repair Getter Done

 

Related Topics

  Subject / Started by Replies Last post
201 Replies
3806 Views
Last post October 17, 2014, 11:42:53 am
by EHP
1 Replies
1174 Views
Last post March 10, 2012, 07:00:24 am
by MCW
29 Replies
3607 Views
Last post July 29, 2012, 08:03:35 pm
by Cut4fun .
0 Replies
312 Views
Last post March 10, 2013, 07:58:03 pm
by Cut4fun .
8 Replies
498 Views
Last post July 30, 2013, 09:20:17 am
by farmboy
28 Replies
2304 Views
Last post April 09, 2016, 02:02:55 pm
by computeruser
6 Replies
952 Views
Last post June 30, 2017, 05:39:15 pm
by Philbert
2 Replies
369 Views
Last post June 19, 2014, 03:32:20 pm
by farmboy
6 Replies
144 Views
Last post June 14, 2014, 02:48:05 pm
by KilliansRedLeo
0 Replies
13 Views
Last post November 28, 2020, 08:10:57 am
by Cut4fun .