Formulas for Good Runners Without Porting

Yeow, Kevin I like the color and what looks to be a Meteor piston! How much did you have to take off the pin boss? On a 372, I have to take off about 0.006 each side. I machine it off but the setup is a PITA! IIRC a member on CR used a raker file to take it off.

Missing fins look to be a good place for a picture of Tim Allen and Al, LOL!

 

Dont recall Tim. Just trial and error fitting for me. Used the generic foredom.

The broken fins recoil, I have a redneck fix and pics posted on that fix too. Start to finish.

 

OH I followed along on the 505 build thread. However I thought this was a different saw because the color looked more Poulan green to me than the saw in the thread! You break down and buy a new camera or steal the wife's?

 

Still the cheap camera and same pics. The green on 505 looks just oem poulan green on a 5200 etc. Just pics never look right.

 

Tim I do have another one I am going to build done up in a bright orange with black covers and tank. I just cant get in the mood to do another when I have done every cc range in those series of saws already. 65cc 71cc 77cc 83cc

 

Is that the 'Harley Saw'?

 

Another old pic to see how the green shows on this site. Has more of that yellow look on this one. Trust me it is lime green. Wish I had that pic from poulan gtg beside the 5200. Looked same.

 

Yep just lost interest.

 

Just thought I would share some insights about porting/piston swaps.

Using an alternative to the OEM piston is a quite common practice when porting a saw. There are situations when the port changes necessary to make a good worksaw into a great worksaw go beyond the physical dimensions of the OEM piston.

An example might be that you need to widen the exhaust port 'n' amount, however the skirt width of the exhaust side of the OEM piston is too narrow to allow you to do that, so you substitute a piston of the same configuration with a skirt width which supports your desired port change. Same would apply to using a piston of differing over all height or a difference of piston pin location.

Using a piston with a shorter over all height is sometimes used when the cylinder itself will not allow you to drop the floor of the intake port.

Porting a two-stroke engine is not a matter of just grabbing your Foredom tool and grinding away. It involves a whole bunch of math, precise measurements and mapping of the stock engine timing, component selection and most importantly a PLAN on what changes may produce the desired results. The work you do must be precise as well, good enough will not get it, small differences in the accuracy of your work may turn a good worksaw into a dog not a great worksaw!

However even after you do all the above there is still garuntee that your plan will actually produce the desired results.

 

I never use a non stock piston anymore. I've tried nearly every combination you can imagine, but never do I see a increase from swapping pistons that surpasses what I can get with the OE piston.

One of the worse things you can do is use a windowed piston in a 372. It kills case compression, and torque suffers.

On the 7900.......the best piston is the newest version of OEM piston. The weight and shape have both been improved over the earlier windowed version. Case pressure is increased and a stronger saw results.

Port width is a small part of performance, unless you are building a race saw.

 

Agreed. Probably also explains why the BBKs on 7900s don't seem to work as well as the stock top end. CCV on the Dolmars is small to begin with.

 

Hey........I got a email from FHC.

I'd love to be more active here.....

 

I think the admins fixed e-Mail alerts just a bit ago. See if you get another e-mail with this post.

 

Can you hear me now ? LOL !

 

Good to see you over here Randy!

 

Working great guys.....

Hope y'all don't mind me hanging around.

 

I don't think you being around is any sort of problem. Perhaps we will all learn something or get good recipies for pie or red clover honey from Fuzz since he has sworn off saws to BUY MORE BEES!!!!

 

I keep bees too.

 

Well given that you also keep bees, Fuzz will go nuts!

Dexter, perhaps we will be needing an 'Official Bee Keepers thread'!