Motorcycle oversize bore question?

[Carl Johansson]

OK -  I read about this in either the rule book or here in the forum -  but now I can't find it -  and all of a sudden it is important -  asw the purchase of a motorcycle to use as a platform hangs in the balance!

So I know the bike I'm looking at is actually 346 CC.  I know each overbore (.01) results in an increase of 3cc

So 1st overbore would be 349 -  so far so good

But what about second overbore (0.02)  that would put me at 352cc.

I know the bike (due to looking at reciepts) was bored to first overbore -  but another reciept from a later year is not clear -  it may or may not have been rebored to .02 -  i just don't know!

seems to me there is some provision for overbore -  I'm not looking to up power or size -  just cleaning up the engine.

Anyone know -  Hey Slim -  you ought to be able to answer me -  since you are just sitting around bragging your nuts -  and bolts through the snow!

Carl Johansson

[Seldom Seen Slim]

Why you picking on lil' ol' me?  Worse still, we don't have snow -- Jon Amo's got it all in Denver.

7.B.13  Engine size:  Displacement must be greater than the maximum allowable for the next lower class.  To permit minor reconditioning of worn cylinder blocks, in classes other than Production, it is permitted to increase cylinder bore diameter .020 inch (.508mm) beyond that which provides maximum displacement for the class.  In all cases, the resulting displacement must be exceeded to qualify for the next higher class.  The .020 inch (.508mm) will be discounted for record certification and will be noted on the certification card and in the logbook."  2006 rulebook, page 95.

So first of all, make sure that if you're at 349 it's with STOCK stroke.  What's the STOCK bore?  Make sure you've got some definitive guarantee that the inspector can read (factory specs in the owner's book, maybe) so you and he know what the stock bore was, and what it is now.  Then you can feel safe with the .020/.508 overbore.

In other words, the displacement may be over the 350 limit -- but only if you increase it with the boring bar, not a stroker crank.

I think....

[aswracing]

So first of all, make sure that if you're at 349 it's with STOCK stroke.  What's the STOCK bore?  Make sure you've got some definitive guarantee that the inspector can read (factory specs in the owner's book, maybe) so you and he know what the stock bore was, and what it is now.  Then you can feel safe with the .020/.508 overbore.

In other words, the displacement may be over the 350 limit -- but only if you increase it with the boring bar, not a stroker crank.

I think....

Jon, I don't read it that way at all.

The rule, as written, doesn't specify a reference starting point for the bore, and it doesn't mention stroke at all. Nothing about "stock" in the rule at all.

And "stock" becomes nebulous in the modified & altered classes anyway. Especially in larger displacements, there was never any model made that has the same displacement as the class, so all of these motors are customs. For example, myself, running in 1650cc using a Harley. Well, no Harley was ever made that big (until just recently). My motor has a larger than stock bore AND stroke than ever came in the chassis in which it's fitted.

And of course, in "A" classes, the chassis may be home made. The whole concept of what's "Stock" becomes meaningless.

The way I read the rule, your motor can be over the class limit by .020 of bore size and you're still OK. In other words, if your motor is too big, but it'd be legal if your bores were .020 smaller, you're golden. That seems like the only reasonable interpretation of the rule.

Am I wrong?

[Seldom Seen Slim]

I think I see what you mean, and maybe I went at answering Carl a little bit wrong.  Ooops.  I was thinking that his motor, starting with 346 and not being allowed to go over 350 (except for that .020 overbore) didn't leave much room for interpretation.  As I re-read I think I see that 350 cc plus .020" of bore is okay.  It doesn't talk about stroke at all, does it?  So does that imply you could take a 346 motor, stroke it to 350, then overbore it another .020"?

I gotta stop all this thinking.  I think it's thinking -- maybe it's just cavitation.  See you tomorrow, folks.

[narider]

Am I wrong?

Yeah Jon... is he wrong?  Or can you figure that out without snow on the ground?

IMO(useless at SCTA by the way), is that(taken literally) it does not pertain to Harleys(or those motors utilizing removable cylinders), as it refers to cylinder BLOCKS(and not replaceable cylinders) in line #2 of Article 7.B.13.

And in all references, refers to bore only and never an increase in stroke, which would at all times require proof of stroke when originally assembled as well as in impound if over the limit(production or otherwise).
I wasn't there, but I can guess of at least a few motors that caused the when and why(spirit of the rule) for this to be enacted(2 of which would contradict the cylinder "BLOCK" part of the rule).

With sleeving so readily available and cost effective today I would think it should be removed from the book... then again ECTA removed and put it back with just enough timing to allow me to waste alot of time and money in a new piston design and size between the two decisions(water under the bridge and it was a great learning experience).

Back to my opinion(and what would happen at ECTA if this is questioned), if you have proof of original bore size(oe or otherwise) and you are going .020"(or less) over"bore"... then you are legal - that simple.
Todd

[aswracing]

narider, I have personally taken advantage of this allowance, on Harleys, on motors with non-original bore & stroke, and I've had records certified with the overbore allowance. So I'm sure it's not interpreted the way you describe.

[DahMurf]

narider, I have personally taken advantage of this allowance, on Harleys, on motors with non-original bore & stroke, and I've had records certified with the overbore allowance. So I'm sure it's not interpreted the way you describe.

Good to know, thanks for posting. Sometimes it's hard to tell when you read the rules exactly what was meant, what the intent was and how it will be interpreted. It's good to know exactly what has worked with others.
Deb

[jimmy six]

All whats above makes me glad I race a car. not a bike.....Carl if you put a M/C engine in a car, all this stuff is moot. It's cubes/cc only. Good luck

[landracing]

To understand the rule better you might want to ask the history of the rule and why it came about.

I think it was Dale Martin that implemented the rule, for a vintage class, (which i think was a dale martin rule too), where cylinders were not available or scarce, the overbore rule was to allow minor reconditioning of these cylinders. And was intedended for motors that were at the or very close to size limit of class. expample a 998cc motor in the 1000cc class.

I asked I think it was in 2002, about taking a 599cc motor and taking advantage of the .020 overbore rule and going beyond the 650cc class limit. I was struck down, saying it was not in SPIRIT of the rule.

So again another motorcycle rule that is interpreted many ways, and as written could be taken different ways. I dont like IN SPIRIT OF THE RULES. Because the spirit of the rule depends on who is tech'ing your bike.

Scott Guthrie and Jack Dolan can maybe add more onto this also.

Kinda like a tech inspector writing in your log book he didnt like your Ace hardware safety wire on axel nuts (which was largest diameter that would fit thru axel nut), and wrote in log book it needed to be changed to stainless steel safety wire for next event. The rule book says safety wire...

Maybe I need to build a roadster... Rules are pretty much set in stone... No overbore rule either... Car Rule #1, Dont follow motorcycle....

Jon

[landracing]

Am I wrong?

With sleeving so readily available and cost effective today I would think it should be removed from the book... Todd

I disagree with this. It is more cost effective to purchase a new-used block off of ebay and lightly hone the cylinders then it is to go thru swapping sleeves and re-decking the block. Put it on and go...

Jon

[Nortonist 592]

Oh to have the motorcycle rules set in stone.  The motorcycles rules are changed more often than my socks. 

[DahMurf]

I asked I think it was in 2002, about taking a 599cc motor and taking advantage of the .020 overbore rule and going beyond the 650cc class limit. I was struck down, saying it was not in SPIRIT of the rule.

So again another motorcycle rule that is interpreted many ways, and as written could be taken different ways. I dont like IN SPIRIT OF THE RULES. Because the spirit of the rule depends on who is tech'ing your bike.

We've heard the same thing about the spirit of the rule, but it seems Aaron may have a different story? 
Deb

[DahMurf]

Oh to have the motorcycle rules set in stone.  The motorcycles rules are changed more often than my socks. 

I hear that! Between the rules & the 200 minimums it really makes you wonder what's going on.
It's not like motorcycles are "new"! 

[Carl Johansson]

All whats above makes me glad I race a car. not a bike.....Carl if you put a M/C engine in a car, all this stuff is moot. It's cubes/cc only. Good luck

Ya know -  I wonder what class I could be in if I took this motor and fabbed a car around it -  this is a hot little motor -  maybe they have like a shriners car class -  where you take the parade car and dink with it till it becomes lethal!  that sounds like a challenge to me!

Carl " I can see the carnage now" Johansson

[Loose Goose-Terry#1]

  Put it on a Go-Kart and really have some fun with the rules!!