Modding a Poulan Pro 475

[Four Paws]

Have you evaluated the 7900 or any other models as piston donors?

I don't think 85 is anywhere near too much intake on a cant racing saw.

 

[GoBigBlue1984]

Have you evaluated the 7900 or any other models as piston donors?

I don't think 85 is anywhere near too much intake on a cant racing saw.

I haven't compared to 7900 piston Josh. Do you have one not on a saw to get some measurements?

 

[mdavlee]

50 mm

But similar pistons can be had in 52mm
@mdavlee would know more about em

There'd a 42mm wide skirt 52mm 272 pattern piston. No windows in it but they can be added

 

[mdavlee]

7900 piston isn't any longer skirt than a 460.

 

[Stihlbro]

I have a 52mm wiseco and a 7900 piston, I'll measure up in the morning.

 

[jacob j.]

The crown height on a 7900 piston is quite a bit lower than either a 475 or 272 piston. I built a strong 2077 once with a Stihl 064 piston.

 

[GoBigBlue1984]

The crown height on a 7900 piston is quite a bit lower than either a 475 or 272 piston. I built a strong 2077 once with a Stihl 064 piston.

Skirt wise the 064 is a tad wider than stock correct JJ? Other than that they are pretty similar from what I can recall other than rings and ring ends and of course pin bosses. Crown height was .015 or so difference.
272 skirts allow for wider ports.

JJ does anybody still talk to Tommy Fales or know how to get in touch with him?

 

[GoBigBlue1984]

The crown height on a 7900 piston is quite a bit lower than either a 475 or 272 piston. I built a strong 2077 once with a Stihl 064 piston.

7900 piston would take a mile then to get where it needed to be.

Have you tried a solid piston in a 475/505 before?

 

[mdavlee]

Skirt wise the 064 is a tad wider than stock correct JJ? Other than that they are pretty similar from what I can recall other than rings and ring ends and of course pin bosses. Crown height was .015 or so difference.
272 skirts allow for wider ports.

JJ does anybody still talk to Tommy Fales or know how to get in touch with him?

He's on facebook. 046 requires 2 gaskets and a 16 gauge spacer. 272 needs about .125" spacer on a 7900

 

[Deets066]

7900 piston isn't any longer skirt than a 460.

Yes but a 46 piston has a longer skirt than the 272
And wider

 

[mdavlee]

Yes but a 46 piston has a longer skirt than the 272
And wider

The wiseco does have longer and wider if I remember right.

 

[Deets066]

The wiseco does have longer and wider if I remember right.

I think so too

 

[mdavlee]

I think so too

7900 piston if I remember right

 

[Cut4fun]

Something I found out awhile back. Meteor 064 has wider skirts then the oem 064 piston. Had one in a 372BB.

If you go the 064 route Meteor IMO.

 

[Cut4fun]

Know all about the other 52mm deets. They were shown on my site years ago and in the for sale section.

Per Ed =
52mm fits the 272 which is the base piston I used to build the wide skirt from but will fit the 7900 and the 460 stihl, now remember these pistons are for race not woods port AND you have to have the cylinder bore replated in nikisal cause the ring used from Wiseco is only meant to run on nikisal , if you put this ring in a standard chrome bore it will last a very very short time cause the ring will tear the chrome plating all to hell . You also need to use the light weight 460 wrist pin . Another thing when getting the cylinder replated I run abit more clearance , Box says .0015 , I run .0022 to .0025 clearance plus the clearance given on the box was before the coating on the piston so your under the .0015 in true measurement with coating , .0015 is just to tight for my liking

 

[Cut4fun]

More info from other threads

goblue

Stihl 064, MS 640 Meteor

Height 43mm
Pin 12mm x 33mm x 8mm
Pin hole top to top of Piston 17mm

BB372

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

 

[Cut4fun]

7900 - wiseco52 - 272

 

[Cut4fun]

More info from Ed =
7900 used piston, with ring it weighs 85.4 grams , skirt width of 32mm/ 1.260 inch
middle is the wide skirt wiseco piston, with ring it weighs 79.7 grams and has a skirt width of 1.670 /42,5mm
right piston is a stock 272 piston weight was 82.9 grams with ring , skirt width is 35.83mm/1.414 inch,
so race piston is wider and lighter

 

[Cut4fun]

Mike Eash running Jerry's PP475 77cc alky saw in a 5ci 81cc class. Marcel Vincent built MVP.

1 min into video, big yellow saw.

 

[Cut4fun]

left oem - meteor 52 replacement that isnt right - next to bb also a oem - right bb 372