How Would They Fix This Cylinder?

[Rcannon]

Keep in mind that those oversized pistons are for big bore kits. They are not oversized pistons for the small overbore of a sleeved cylinder.

Also ask them about how the sleeve effects the heat transfer out of the cylinder compared to the stock plating. Then see what kind of BS tale they weave. ;)

MTK, your right. Those big bores may be too big for the sleeve. If so, we are really screwed. There may be no oversized pistons.

 

[motometal]

You're changing the squish band with that dead space. Considering the work that tuners do to set the squish band when porting an engine, I don't think the dead space would have no effect on performance.

You mean, "I don't think the dead space would have ANY effect on performance". :laugh:

 

[mtk]

No, actually I meant that I DO think it would have an effect on performance. The additional squish wouldn't work as well as the correct amount of squish. Since it is something tuners adjust when they port an engine, I'd assume the volume to be important and not something left to chance.

 

[motometal]

I was sort of giving you a hard time there...anyway, I guess it depends what you mean by "squish volume". Maybe we aren't on the same page here...

You are correct that tuners adjust the squish clearance, or actually in some cases "fail to adjust it" but that's a sore subject and I won't air that dirty laundry here. Let's just say it took a bit of "backward motion" for me to get it right and prevent probable contact.

Cutting, say, .020" on the outter diameter of the head would leave a potential gap of .010" x about .035" around the perimeter, this is so minimal that I doubt it would ever have an affect, considering that adjusting the squish clearance (exponentially more area) has "some" affect of course but in my experience is not "night and day". Of course opinions vary on this as well, one of the guys getting big power out of two stroke street bikes right now believes setting it "tight" is overrated, and sets it at about .070". I'm not saying I agree that it's best, but his results are impressive...possibly in spite of this.

I'm sure MSV does matter, "how much" is the question. The other thing to consider is that the piston is only at TDC for a split second.

 

[mtk]

Uh, the entire combustion event takes place in a split second. The piston dwells at TDC for a brief period as well. The specfics of this are a wonderful engineering problem which I don't care to relive at the moment.

Either way, squish is critical for a rapid spread of the flame front within the chamber because the gas in this volume is what gets shot into the center of the chamber as the piston approaches TDC. Yes, it is a small area, but in this game small changes mean things. A few thousandths of an inch, in the right place, is the difference between a long and healthy life for your engine and it dying a quick death.

Also keep in mind that street engines are a different animal because of the sustained high-speed running of the engine. He may need the extra squish to account for con rod stretch at high RPM.

 

[Rhein]

I noticed you had it replated. Good choice. I believe you would have been sorry with a sleeve. My friend sure is.

Thanks, I paid less to replate and weld it anyway. I am happy, just waiting on some gaskets. :cool: :ride:

 

[motometal]

the guy I was referring to builds some street engines, but also many drag engines. Yes, he is concerned about con rod stretch (in my opinion possibly over concerned), although the engines don't run particularly high rpms. 8000-9000 normal redline, although I'm sure 10,000+ on a missed shift could happen. These are generally 250ccs per cylinder.

My main point with mentioning that guy is that folks can theorize all they want about minute changes, and probably be correct to a point, but they you have guys like this that focus on the porting and make the squish clearance almost double "what you are supposed to use" and the motor wins races and does very well on the dyno.

 

[mtk]

"Particularly high revs" is entirely dependent on stroke length; it isn't a universal number.

 

[motometal]

if you want to get detailed, what about reciprocating assembly weight, rod to stroke ratio, and piston speed?

 

[Rhein]

I grinded the flap down a bit and everything seems fine.

 

[motometal]

glad to hear it. sorry for hijacking your thread, whenever mtk posts something I just have to put in a contrary post or two... :) :ride: :blah: