2013 rule for overbore of MC motors

[Koncretekid]

Sometimes I'm a little dense, and this is one of them.  I haven't competed at SCTA events yet, but this new addition to the 2013 rules has me baffled:
7.D CLASSIFICATION of DISPLACEMENTS, FRAMES, ENGINES, and ENGINE TYPES:
7.D.3 Engine Displacement Classes:
Displacement shall 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 in. (.508 mm) beyond that which provides maximum displacement for the class only if the OEM bore diameter is within .020 in. (.508 mm) of the maximum class displacement.

If the OEM bore diameter is within .020" of the maximum class displacement, then boring by .020" isn't going to increase the displacement beyond the maximum class limit, unless one has already increased the stroke to the limit.  Am I missing something?  And does this mean I can't bore my motor beyond .020" in classes other than production?

Tom

Edit!  I think I got it!  If the OEM bore is within .020" (less than), then an overbore of .020" would make it over the limit, and now this is permitted.  I.E., my B50 (my roadracer) is 498cc from the factory (84mm x 90mm), but I've bored it .5mm (.020"), and now it is 504.5cc.  This is now legal by the new rules to run in the 500cc class.  Is this right?

[dw230]

Best reply here is to check section 16 for the m/c tech guys and ask them the question.

DW

[RansomT]

This is what I think the rule change is getting at:

Before this, based on interpretation of the rule, you could have any bike bored to above the cc class limit by .508mm per cylinder even though the starting point (OEM) was way smaller, claiming reconditioning.  e.g. a Gen 1. 1299cc Busa could be bored to something like 1360 cc and still run in the 1350cc class.  Under the new rule, you are absolutely limited to 1350cc.  But the rule still allows for "reconditioning" above the cc limit only when needed.  e.g. a BMW S1000rr because it is right at 1000cc OEM could be a 1006 cc and still be legal in 1000cc class because of reconditioning.

[Stainless1]

KK, I think you are correct.  I think where the rule is going is you can have one reconditioning .020 over if the stock bore was already close to the max in class, but you may not take a .050 overbore that is .020 past your class limit.  I think this is a good revision.

[wfojohn]

2 thoughts on this. 1st, rule didn't seem broken but got fixed, happens sometimes and usually just me not seeing the need. 2nd, if for example of the 1299cc Busa, could it be stroked to 1349cc and then bored? I was just wondering, I don't have any involvement in a Busa nor are any of my bikes affected by this, their engine size is close to class size and will legally be slightly over with allowable .020" bore. John

[Stainless1]

Lets look at a gsxr 1000, 73x59 987.7cc stock
old rule you could bore to 73.95 for a 1013.6cc displacement... 73.45 to get 999.9 and then .5 more
new rule 73.5 for 1001.3cc
So you have a basic 160 Hp motor, you get 4 more hp worth of displacement with the old rule... and 2 Hp with the new rule, keeping you closer to the class displacement.
If you think this is nitpicking... maybe it is, but most of us will use the rules to our maximum advantage.

I doubt you will be able to use the reconditioning rule to gain size after you add stroke to get bigger than class size in the future... but you never know which way the wind is blowing next to the MC inspectors trailer.

[hawkwind]

Ok so if I for example have a kawasaki of 998cc stock bore and used the 20 thou overbore reconditioning allowance this would be ok if it went over the 1000cc limit ?  but not if i first rebore to the 1000cc limit  then do the 20 thou overbore. ?  second what if I in the past took the block to 1000cc then did the 20 thou rebore when this was legal ... does this now become illegal when claiming a record?

Mute point now really as Noonan just bumped up the A/BF 1000 to 229mph and my old school 1000 has 2 chances of reaching that  none and buckleys.

cheers gary

[Stainless1]

Ok so if I for example have a kawasaki of 998cc stock bore and used the 20 thou overbore reconditioning allowance this would be ok if it went over the 1000cc limit ?  but not if i first rebore to the 1000cc limit  then do the 20 thou overbore. ?  second what if I in the past took the block to 1000cc then did the 20 thou rebore when this was legal ... does this now become illegal when claiming a record?

Mute point now really as Noonan just bumped up the A/BF 1000 to 229mph and my old school 1000 has 2 chances of reaching that  none and buckleys.

cheers gary

Gary, that is the way I read it... in the past you could have bored to 1000, then overbored .020, not any more.  The rule is to allow you to overbore for reconditioning, not get additional cubes. 

As for the record... do what John did, turn up the boost and tuck in tight