Decompression Scallop "Shadowing"

[AlisoBob]

Iggy.... FYI...... you posted a photo of your piston, where you called regular old blowby staining from the scallops.



This is my scallop staining.... its much more defined.

[britincali]

Pfft.... scallops...... get rid of em..

[M.F.D.B.]

Pfft.... scallops...... get rid of em..

Yup yup, scallops are for short, sissy, 140 pounders...

[AlisoBob]

Yup yup, scallops are for short, sissy, 140 pounders...

I cant start my bike without them.....

[M.F.D.B.]

HAHAHA, yeah suuuuuuure...

[iggys-amsoil]

Those look pretty wide compared to my 89.50 slug.

I think there won't be much left at 89.75.

[M.F.D.B.]

I had my jug bored to 90mm the first time. They were gone...just like I wanted..

[AlisoBob]

I try to keep my bore as small as possible. Stable cylinderwalls stay round and less blowby = more power.

I will gladly trade displacement for ring seal!

[M.F.D.B.]

I try to keep my bore as small as possible. Stable cylinderwalls stay round and less blowby = more power.

Agreed, this is why I have decided to resleeve rather then buy a new jug...

[hagendog]

So what are these Scallop staining things you guys are talking about. In the pic I see how do you say blow by i guess. Is that the Scalloping? My 250 piston had marks like that and a very good mechanic told me to take the old piston and hold it next to the new one and mark those spots and then file them down. My 250 had 5 spots on it that I filed, 1 for the exhaust bridge and the other 4 were almost in the same spot on all 4 sides. The filing does no damage since its running on the rings, right. Anyways after about a year on that one it looked better than any of the others a had laying around. I wish I could remember this guys name, he was the man for PJ1's race team and also built the first Works pipes back in the day for Leichen and those guys. I think it was like 81 or so. Bob your knowledge is quite vast and I like to read so keep it coming please. What kind of info you got on wet nitrous systems for the 2 stroke.

[AlisoBob]

Bob your knowledge is quite vast and I like to read so keep it coming please. What kind of info you got on wet nitrous systems for the 2 stroke.

I dont know if anyone has ever done it, but I would stick a fogger nozzle right into the crankcase, and force as much N20 in as she would take.

Reeds probably would never open.....

That sucker would make some power!

[AlisoBob]

So what are these Scallop staining things you guys are talking about.

In a stock, late model 500 jug, there are "Decompression Scallops" ground into the jug to allow some of the cylinder pressure to bypass the rings while you kick start it. Once running, there isnt a whole lot of time for the gases to bypass, and the effect goes away.

The jugs with the scallops color the piston as seen in the photo.... Some folks confuse it with blowby, some others confuse blowby with the staining.

The staining is very precise, and defined.

Blowby looks like a big mess.

[M.F.D.B.]

So what are these Scallop staining things you guys are talking about.

Blowby looks like a big mess.

So THATS why Brits bike is so nasty...HAHA

Dude, direct case injection on NOS, thats something I have wanted to try for a long time, got a loaner motor??