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I was changing the pipe on my bike and i noticed looking up the port that the top edges are so wide that they are into the flat on the sides of the pistons. What will this hurt? Is it pushing the exhaust back around the pistons into the transfers?

runs like a bag of S, right!
I had the same thing, ran a vertex, scuffed it cold, swapped in a proX with just a hone and heard a whisping sound out exhaust port when piston goes down the hole and the compresion and fuel blows out the pipe! I called Prox and told them of it, they said no way, sent them pictures up the exhasut port, showed them the difference in their piston to oem, wiseco, and vertex. dude said he'd never seen it before, I called BS!
now i have a different rep to speak to at La Sleeve, but no compensation.

I've got that setup here, maybee i can take pictures today and post em, you have any port work? mine was polished, but not enlarged

btw, dont run it like that or you'll be changing the case gasket. One good rip of wfo and...

k, this wiseco (left) is better than the old style, prox (middle) and oe honda (right)

at .040 over

ya, some idiot took a picture of the prox intake side, whatever, the windage area arround the pin is the same width on both sides

even the vertex has a dam that blocks the port...
prox (left), vertex (right)

Mine isnt as bad as yours maybe .030" wide gap .250" long? Ive been running it this way for a couple of years now. It has a .040 wiseco piston in it now. I'm sure it is from the porting being extreme.

It seems to run fine just lacking in the power department. aka slow. Thats why im trying a shearer out of frame pipe to see if the motor would come alive. I have a 40.5 pwk on it now with a 150 main @ 2200 elevation and im now wondering if thats why it likes the small jetting.

wow that is small jetting, when I was at Dumont a few weeks ago I was running a 215 main in the Loomis motor and it still wasent blubbering

no doubt the jetting would seem rich, its got no air to burn. Get it sealed up and you'll have WAY more power

Well i guess i will have to send a new cylinder to loomis then cause if a wiseco is the widest piston available the cylinder is junk or i will have to resleeve it.

I have ran that jetting for years even at 30 degrees out side for up to 1/4 mile blasts and never burned up a piston?

the fuel ratio you have jetted for is correct for the air, but deffinately there is way less air than what it should have. A two stroke can do a neat thing by running not lean, but "under fueled" and will deffinately compromise the effectiveness of the pipe by not having adequate pressure to shut the door on the exhaust, likely race gas wont ping, but i cant see how pump fuel wouldnt.

The wiseco needs holes drilled to lube the cyl and keep it cool, the other pistons stil rely on the lube getting to the cyl past the wrist pin.



Even the wiseco i have here that was bought 2 years ago wont close the window like the newer ones.

old and new wiseco, they're both 500 pistons, picture looks odd

the newest version of wiseco doesnt have cutouts. i think someone weighed it and its little bit heavier but i cant remember specifics, the skirt appears to be little thinner also, probly to make up for some the added weight

so I got another jug, an 87. i bored it and fit it to a .75mm piston, had a prox on the shelf.

Tommorrow I'll post pics of both the 87+88 jugs side by side BOTH with prox's in them, and both with the big windage.

Prox has denied its happening.

I sent pictures

They said it was ported wide

i sent more pictures showing stock and measurements

they said im the only one whos ever had this problem

i asked the guy if hes ever walked into a hospital with a broken leg and got that answer, excused myself for beeing an engineer and not a salesman

he hung up

i called again and told him i was only pointing out that someone in charge of things needs to be talking to me instead of a phone monkey

Tommorrw i rain hell on them

its not just that the fuel is blowing thru the ports and out the exhasut, its that less crankcase presure=less air/fuel(power) its that the plug will read rich til its wicked and goes superlean

Roostius_Maximus wrote: they said im the only one whos ever had this problem

You the only one smart enough to see whats happening....

Good Job Hoon!!!!

Good job Adam!

AlisoBob wrote:

Roostius_Maximus wrote: they said im the only one whos ever had this problem

You the only one smart enough to see whats happening....

Good Job Hoon!!!!

i think wisecos may had the same problem many years and im suspecting thats why they had design changes. im not sure what the reason for the latest design change though. the only reason i use wiseco is because i dont like the thought of cracked piston fragmenting, granted it may never happen but it might. if i was roostious i would really consider using the newest version wiseco, theres not cutouts so the desired shape of the port windows is basically unlimited in what you can do. i dont know how wide the stock exhaust window is but i got mine around %95 of the bore and it could easily be widened alot more with the bridge stiill intact, with a wiseco theres no issue but with the cast pistons ive seen there would be problems. if roostious can convince them to change the design thats cool , if not jusdt throw a wiseco in there

I thanked you once before for mentioning this, but I'll thank you again. I've got the old style Wiseco now and it fortunately doesn't compromise the ports. But I was wondering if Wiseco didn't change the piston for these reasons. I was also thinking maybe the new piston wouldn't lower crank case pressures so much? But boy am I glad I don't use Vertex or Pro-X pistons...

My Vertex is fine....

AlisoBob wrote:My Vertex is fine....

you have stock cylinder ...at 100% bore diameter it might not be aight

i bought the newest version wiseco alittle over 1 year ago (no cutouts), and i think slomas had one maybe before me or at the same time but i didnt have high hopes for it. but honestly dudes i think it might be the best design yet after i thought about it

OEM Pistons......

I agree oem is good stuff, its the crap i'm trying to resolve here.
The vertex is almost an exact replica of the honda piston and stil closes the port.
Before finding this problem I'd used vertex, have a vertex in my '00 at 89.50, looks good. The 86 engine has a prox 89.50 that looks good. The 91 engine has a 89.75 i have to check. Nicks 99 has a 89.50 that looks good. My 87 engine failed at 89.50(how i bought it) and at 89.75, my 88 engine failed at 89.75 (first one i noticed it in). and my other jug needs to be sleeved from 91+ so i cant check it

I'm not concerned that it doesnt close the ported cyls, its that it doesnt close the stock ones.
The exhaust port is basically a V, cut the top off it by boring the cyl and the V gets narrower so it should theoretically bring the port back onto the piston.
I havent got a 91mm piston to check in the only cyl larger than 89.75 that i have.

more people need to read this post