displacement limit

[2stroke]

I plan to bring an old Kawasaki twin cylinder rotary valve two stroke to Maxton and want to get a ruling on a displacement question.  In stock form, this engine has a 53mm bore and a 56mm stroke (a volume of 247CCs).  This engine was last produced in '71 and the supply of consumable parts is fast drying up, but  I have found a couple of cylinders, one is .5mm overbore, the other is a very loose .75mm overbore (probably really needs 1mm overbore piston).  I have no problem using cylinders of different displacement as I really want to run this bike and want to be perfectly legal.  What can I run and still fit into the 250cc class?   Thanks for your help.

[Seldom Seen Slim]

Well, if no one else will -- I'll tackle this one.  In the '08 ECTA rulebook, page 72, rule 7.B.13 "engine Size" it is stated that "To permit minor reconditioning of worn cylinder blocks in classes other than Production, it is permitted to increase cylinder bore diameter .020 in. (.508mm) beyond that which provides maximum displacement for the class."  It goes on with discussion of discounting the extra amount for purposes of record certification.

So -- You see that you can get away with a .5mm overbore without any difficulty.  As for the larger cylinder -- I'd say that you would need to determine what the displacement would be in you used the .5 on one and the .75 (or whatever) on the other -- and if the resulting displacement is precisely 250 or below -- it's okay.  If it's 250.01 or above -- nope, you'd be in the next higher displacement class.

I think, that is.  If you don't already have a rulebook -- by all means get one and read the pertinent language so you can make your own determination of the issue.

Regards,

Jon

[2stroke]

Thanks for your help.  I do have a rule book, but I kind of found the .020 overbore confusing.  I will start another search for legal stuff.  Anybody know of a good source for old Kawasaki parts?

[Stan Back]

Why don't you enter as a 350cc and quit worrying about it?

Stan Back

[2stroke]

That might be a good idea except that Scott Guthrie has the 350 records pretty well covered, the engine is only 335cc when it is a "big bore", and I really want to explore what can be done with the "little brother".

[wfojohn]

Hi 2stroke,
Maybe bore the smaller one to cleanup and have a sleeve installed into the bigger one to bring it back to stock thus keeping you legal. Possibly best to sleeve them and go to stock bore on both, it is usually easier to find standard bore pistons at the dealer than oversize ones. I did not notice if you said what class, are you looking at production, modified or altered? Where are you located? if you are close to Lawrenceburg, TN stop in and say hi, I always have time for bench racing (too damn old for anything else).
John Ritter
www.vintageporting.com

[Sumner]

That might be a good idea except that Scott Guthrie has the 350 records pretty well covered, the engine is only 335cc when it is a "big bore", and I really want to explore what can be done with the "little brother".

I'd look at it from the stand point of use what you have and see how fast you can run and if you can get close to or above the existing record, if there is one, then get the parts to get you into the class.  You don't need to be "legal" to run, only to set a record.

Sum

[Stan Back]

That's what I was getting at!

[Sumner]

That's what I was getting at!

Who do you thing I got the idea from  ,

Sum

[Beairsto Racing]

2 strokes are cool! Are you running an A1 Samurai or are you fortunate enough to own an A1R? Could you post some pictures. Thanks.
-Scott

[2stroke]

The bike is in process of being built, but it consists of (most of) an A1 Samurai engine, in a Honda CB160 chassis (much modified), a fake fuel tank ("borrowed" from a Suzuki T-125 Stinger), with the real tank being under the seat.  The swing arm is from a Suzuki Titan, the front end is from Suzuki T200 Invader, and the real wheel is off some Yamaha dirt bike.  The idea is to replicate (sort of) a home brewed drag bike from the sixties.  I had planned to play at the drag strip, but Maxton sounds like MUCH more fun and a little machine won't be out of place there.  I'd love to have a real A1R, but A1 parts are tough enough to find.  I hope to make the September meet.   2Stroke