Modding the Dolmar 7900
- Thread starter parrisw
- Start date
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Mastermind
Work Saw Specialist
272 piston is the one you want.....
GBD
ArboristSite Operative
Don`t you have to space up the cylinder quite a bit with that one?
parrisw
Tree Freak
That's what I'm using.
Mastermind
Work Saw Specialist
tdi-rick
Addicted to ArboristSite
Hmm, I thought the pin-crown height was too much on that one too.
There you go.
There you go.
Mastermind
Work Saw Specialist
tree monkey
Addicted to ArboristSite
i've done alot of piston swap moters, don't always work out as planed
putting in a taller piston is kinda like long stroking the moter, it changes more then you think
putting in a taller piston is kinda like long stroking the moter, it changes more then you think
I put a husky 395 piston in a bb 660 jug. Ya just gotta want to.
Try putting a 395 piston in a 390
GBD
ArboristSite Operative
I put a husky 395 piston in a bb 660 jug. Ya just gotta want to.
Yeah, I`m going to try that one, but I would have preferred it to be a little lower.
tree monkey
Addicted to ArboristSite
GBD
ArboristSite Operative
The bigbore kit needs a 56mm.
tree monkey
Addicted to ArboristSite
Mastermind
Work Saw Specialist
GBD
ArboristSite Operative
Yes, thats for sure, but the 7900 shouldnt be the worst candidate. Crankcase compression will suffer, but the 7900 has loads of it. The exhaust is fixed only to the cylinder. It has rubber inlet, and the upper AV-mount should be able to cope with it. :msp_thumbup:
parrisw
Tree Freak
Got the 272 piston, looks like I need to make up .173" to get the proper squish. Could just make a spacer, skirts are quite a bit shorter as well, so I don't know how much more intake that will give it.
Mastermind
Work Saw Specialist
Take some out of the squish band and some off the top of the piston. Use the spacer to set your intake timing.
parrisw
Tree Freak
Ya, problem is, I've already machined the squish .050" and machined the bottom of the cylinder. So that said I've started making a spacer, almost done. I don't know how much more is safe to take out of the chamber, I don't want compression to be way outa hand, stock they are over 170.
parrisw
Tree Freak
Here is the start of the spacer, should be able to finish sometime today, then I can check timing and squish.
Machining the sides, and getting square.
Machining thickness.
Layout of holes and inside.
Finished outside dimensions and thickness.
Machining the sides, and getting square.
Machining thickness.
Layout of holes and inside.
Finished outside dimensions and thickness.
parrisw
Tree Freak
Got the spacer finished up. I'm done cutting on metal for today, I enjoy this stuff, but hours of it at a time get to me. After porting the ex and int on the 372 then making this spacer, I'm tired, took longer then you'd think to make this spacer. Next time it'll be easier, wont need a spacer if ya don't machine the bottom of the cylinder.
Worked out real well. Intake timing is now at 161* duration. Exhaust is only at 145* duration, I think that can come up a little.:msp_smile: Squish is only at .0175-.018. Going to take a few though off the top of the piston. Plus the skirts are way wider on this piston. Should make a runner!!
Worked out real well. Intake timing is now at 161* duration. Exhaust is only at 145* duration, I think that can come up a little.:msp_smile: Squish is only at .0175-.018. Going to take a few though off the top of the piston. Plus the skirts are way wider on this piston. Should make a runner!!
