Author Topic: motorcycle overbore rule????  (Read 4557 times)

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Offline FADED

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motorcycle overbore rule????
« on: June 15, 2015, 04:10:25 PM »
How exaclty is this measured, I run the 175cc calss and our current specs would be 176.4cc with a 1 overbore. Would this move us up a class or would it still be considered a 175cc??

Offline John Noonan

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Re: motorcycle overbore rule????
« Reply #1 on: June 15, 2015, 06:09:10 PM »
If you are not a flathead or a vintage looks like you are in the next size class..did you read the 2015 SCTA book?


J


Offline Nortonist 592

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Re: motorcycle overbore rule????
« Reply #2 on: June 16, 2015, 01:16:19 AM »
Page 129 2015 rule book.  All classes except production are allowed .020" overbore.  Vintage is allowed .050" overbore.  My guess is you are good to go.
Get off the stove Grandad.  You're too old to be riding the range.

Offline rouse

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Re: motorcycle overbore rule????
« Reply #3 on: June 16, 2015, 08:30:32 AM »
"1" if in "mm" would be .039", so how much over the class limit did that make the bore, and how close was the original bore to the class limit.

The way I read the rule is if the original bore was so close that you would go over your class limit to freshen up the engine, then up to .02" would be allowed. However, if the engine could have been bored from stock size without going over, then you are SOL if you go oversize.

I am not effected by this rule so I'm just curious as to the final call on your bike. One thing for sure, you need to contact the folks that will make the final call.

Rouse
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Offline Seldom Seen Slim

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Re: motorcycle overbore rule????
« Reply #4 on: June 16, 2015, 09:12:49 AM »
Johnnie Rouse said:  "...you need to contact the folks that will make the final call."

Always the best route.  And make a hard copy of what you learn and include it in your logbook for when you're at tech and the inspector takes issue with your interpretation of said rule.
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Offline rouse

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Re: motorcycle overbore rule????
« Reply #5 on: June 16, 2015, 09:50:07 AM »
SSS said even better than I did. Get it in writing and log it in.

Rouse
Johnnie Rouse
Bike 4680 P-PP2000 SCTA record 153.325    A-PF3000 182.920
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Offline dw230

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Re: motorcycle overbore rule????
« Reply #6 on: June 16, 2015, 12:18:37 PM »
Oh happy day! You guys are learning that section 126 is your friend.  :cheers:

DW
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Offline Nortonist 592

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Re: motorcycle overbore rule????
« Reply #7 on: June 16, 2015, 01:23:18 PM »
The .020" overbore is based on the max. class limit.  In Lance's case his class limit is 175cc.  175cc + .020".   As Tom Evans said to me many years ago.  "Read the damn rulebook!!"
Get off the stove Grandad.  You're too old to be riding the range.

Offline FADED

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Re: motorcycle overbore rule????
« Reply #8 on: June 16, 2015, 02:07:46 PM »
If you are not a flathead or a vintage looks like you are in the next size class..did you read the 2015 SCTA book?

J



NOPE TO MANY BIG WORDS

Offline Nortonist 592

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Re: motorcycle overbore rule????
« Reply #9 on: June 16, 2015, 09:18:04 PM »
If you are not a flathead or a vintage looks like you are in the next size class..did you read the 2015 SCTA book?

J



NOPE TO MANY BIG WORDS

You really should learn those big words Lance.  Lots of freebies in the rulebook if you read it right.
Get off the stove Grandad.  You're too old to be riding the range.

Offline FADED

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Re: motorcycle overbore rule????
« Reply #10 on: June 16, 2015, 10:22:30 PM »
Thanks for the help guys, here is what we figured out.
The stock/factory bore was  66.25 =171.1 cc
with a 66.75 over bore it would be  174.75cc (acceptable?)
our bore at a 67mm = 176.3cc   (not acceptable?)

Offline Nortonist 592

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Re: motorcycle overbore rule????
« Reply #11 on: June 17, 2015, 01:33:54 AM »
FWIW  Reading page 129 it says its permissible to overbore by .020" (.508mm) beyond the maximum class limit if the original bore was within .508mm of the maximum class displacement.  The way I read it is you OEM bore is 66.25mm.  Throw in a .508mm bore and that comes to 66.758mm.   which would give you 174.75 cc.  Under the 175 cc limit.  So to me you are good.  The 67mm bore I'm sure about.  I'd talk to Tom or Matt and get it in officialspeak.
Get off the stove Grandad.  You're too old to be riding the range.