measuring bore in impound

[hawkwind]

I was concerned by 2 issues for running bubs ...... measuring the bore in impound,if a record was set .....and a  capacity overlimit issue  seems I have 2 strikes .......my bike was built under the older SCTA rules  which allowed a cylinder overbore of 20thou/.5mm over the 1000cc limit  which I took advantage of ...the stock size bore 74mm and stroke of 58mm = 997.8cc  after a .5mm rebore of each cylinder  its now 1011.3cc. So if the AMA rules require  all cylinders to be measured and a max of 1000cc no rebore allowance im sunk. Each piston was custom made for size and CR as well as head gaskets and the head and block are o'ringed. My budget wont allow changes any time soon ,Ill give it a miss untill such times as I can meet the rules.
Thanks everyone who responded and keep the shiny side up

 PS.Question an option would be to run in FIM  Whats their policy on cc limits is there any allowance if one is just over the limit? as is the case with SCTA?

Cheers Gary

[nrhs sales]

It is the inspectors option on whether they want to check all the cylinders or not. You have to be prepared that they will.

[55chevr]

I have had one cylinder measured and I have had both cylinders measured.  It appears to be the inspectors option and so be it.

[Freud]

It seems to me that if one cyl is over sized both of them will be.

From what I saw of the FIM years ago they have no allowance for oversize within the class.

FREUD

[fastman614]

Having once been involved in motorcycle racing and, later on, inspection, the old rule about a .0.5mm overbore turned into a can of worms and was dropped. I believe it was pretty much only an SCTA rule anyway.

You had, in the motorcycle classes, an aggregate total of allowable oversize of 1cc...... In the car classes, you had a theoretical aggregate total of allowable oversize of 1 cubic inch (16.387cc)..... DON'T CONFUSE THE TWO OF THEM!....
NOW, for any car guys reading this thread, in practical application (and Stainless may remember this), in some of the car classes, the cubic inch breaks did not exactly corelate to an exact equivlent cubic centimeter size - specifically the 750cc - 45 cu. in. class ..... 45 cu. in. equals about 737.5cc - so you actually have less than .3 of a cubic inch of "grace" in that class.

One other option for testing swept volume is the use of a burrette, which, after the valve gear is deactivated, can be pumped into a cylinder with an adaptor into the spark plug hole.....once the air is expunged from the cylinder and the piston is taken to bottom dead center, a slow turn over of the engine will pump the oil back into the burrette and establish the swept volume of the cylinder being checked. The amount, when multiplied by the amount of cylinders, establishes the "as inspected" displacement of the engine it is accurate to about 1cc (or less per cylinder - and usually shows the displacement as being on the smaller side of "as measured and calculated")..... SCTA uses this option on motorcycles and smaller displacement car engines if the owner of the vehicle is okay with this procedeure.... it can be a time saver and, if you have expensive head gaskets and o-rings etc, it can save both time and money on a teardown... You do have to run the engine a bit after with a slightly hotter plug so as to burn the residual oil out of the cylinder as well....

It may be worthwhile to ask if this is also an acceptable method.

[Stainless1]

Yep, scared the crap out of us in impound when we ran the zx-7.... motor measured over with oil, took the head off, measured 45.7 inches in the 45 inch class... 749cc... luckily it was a car motor and the next class started at 46 cu... too close
the class breaks can be fun, but no overbore allowance in cars either....
always thought the overbore was legal cheating....

[donpearsall]

I don't see how the burette method can be accurate at all. There will be some leakage of oil past the pistons and rings even with the best of sealed cylinders.  And the longer you take to do the measurement, the more volume will be lost.

How can the cylinders be sealed enough to get an accurate measurement?

Don

[Seldom Seen Slim]

Freud said:  "It seems to me that if one cyl is over sized both of them will be."

I remember Scott Guthrie talking about his Yamaha 2-stroke multi-cylinder bikes.  To get to various classes he DID run different size cylinders/pistons some of the times.  Sure, it was a tad unbalanced, but it ran well enough to get him records.  He mentioned that one time he was in impound and the official measured one cylinder - and was about to do the multiplication to get total displacement.  Scott told the guy to measure the other cylinders - and the official was quite surprised to learn that indeed, the cylinders were NOT the same.

[fastman614]

I don't see how the burette method can be accurate at all. There will be some leakage of oil past the pistons and rings even with the best of sealed cylinders.  And the longer you take to do the measurement, the more volume will be lost.

How can the cylinders be sealed enough to get an accurate measurement?

Don

Don.... It is a little difficult to explain but being that I am the co-owner of one of the burrette's that was used in the past, I have shown a few people..... showing is easier than telling.

The actual check of the swept volume takes only a few seconds of the actual inspection time..... due to the fact that, after the entrapped air has been purged from the cylinder, the engine is slowly turned so that the cylinder being checked is at bottom dead center.... the engine is then slowly turned over until that cylinder is then at top dead center..... and surprise surprise, when the graduations on the burrette are read, the engine displacement is calculated, the size is confirmed and it is so close to actual size that it is and has always been good and accurate enough for even World Records.... and one other little thing about using a burrette or "burrette-like" instrument for checking displacement..... NASCAR, NHRA and the SCTA, amongst other organizations, use an "air pump" type of size checker....air has about 1/5000th the amount of viscosity as oil and not enough air slips past the rings for it to be an issue.... Having said that, while using the burrette with oil, over the years, we HAVE diagnosed holed pistons for more than one competitor.... at which point, we ask that they check other cuylinders to see if they have compression and then we will subsequently check another "good" cylinder or, at the competitor's option, the head gets removed to directly measure the bore and stroke.

BTW, Stainless.... that was me who made you pull that 750cc cylinder head off.... and, if I recall correctly, you also showed us the fact that the cylinders were a bit "barrel-shaped" from ring wear - which was the real contributing factor to that engine pumping over-sized....

[fastman614]

Freud said:  "It seems to me that if one cyl is over sized both of them will be."

I remember Scott Guthrie talking about his Yamaha 2-stroke multi-cylinder bikes.  To get to various classes he DID run different size cylinders/pistons some of the times.  Sure, it was a tad unbalanced, but it ran well enough to get him records.  He mentioned that one time he was in impound and the official measured one cylinder - and was about to do the multiplication to get total displacement.  Scott told the guy to measure the other cylinders - and the official was quite surprised to learn that indeed, the cylinders were NOT the same.

Scott was using a TZ250 on one half and a TZ350 on the other half of a TZ750 engine ....for running the 650cc classes..... I recall checking his bores and strokes in his pit area and sealing his engine prior to him running.... It sure saved impound/record certification time....

[fastman614]

Don.... one other thing.... you ARE allowed to refuse the use of a burrette to have your engine checked AND to pull your own cylinder head and have the bore and stroke measurements checked..... if you feel that another competitor, who has set a record and had his engine checked with a burrette is not legal, you ARE allowed to protest.... (it costs money to do so though..... and, in recent memory, nobody has done so due to how close the burrette method of measurement has actually proven to be)

[donpearsall]

Thanks for the reply Fastman. I only run at BUB now, and I don't think the techs have the burette equipment. But I will do ANYTHING rather than take the heads off my bikes. That would virtually be a whole days work, then the bike would not be able to run again for the rest of the meet. Way too complex to put back together on the salt.

Don

[Jon]

Don.... It is a little difficult to explain but being that I am the co-owner of one of the burrette's that was used in the past, I have shown a few people..... showing is easier than telling.

Did you buy it or make it Fastmam?

Would you have any pictures?

Thanks
jon

[Stainless1]

Fastman, yes it was a junkyard piece we were throwing N20 at if I remember correctly... needed to know how to get it apart anyway....just scared us when it measured over.  Yep that class is really close to the limit.

[fastman614]

Don.... It is a little difficult to explain but being that I am the co-owner of one of the burrette's that was used in the past, I have shown a few people..... showing is easier than telling.

Did you buy it or make it Fastmam?

Would you have any pictures?

Thanks
jon

Jon, It was a surplus piece of laboratory equipment that came from, IIRC, The University of Utah.... (not important in and of itself though).... It is a glass unit that is one liter in capacity and the valve spigot (what you would attach a hose to) was broken off..... the valve itself also leaked....A friend of ours was  able to "weld" glass.... we had him put a large diameter (3/4") valve on to it. The reason being is that with a smaller diameter (they are usually 1/4"), the oil will squirt out of the top of the burrette like a geyser erupting.... with 9 times the area to the 3/4" diameter, the oil does not develop the velocity to erupt (unless some cranks the engine over with the starter or something, that is - ask me how I know that one)....Also, a good quality plastic one will work well too.... I recall from chemistry classes in high school that the teacher favored taller ans smaller in diameter as the separation between each 5 cc graduation was separated widely enough to "ACCURATELY guess" one or two cc above or below each 5 cc graduation mark. The real trick with a "store bought" plastic one is the installation of a large diameter tube with bulkhead nuts and O-rings in the bottom after removing the standard sized small valve and spigot.

Don,,,, I think that the present SCTA/BNI bike inspectors have one or two of them.....Do any of them come up to BUB and help? Also, ask BUB's chief of inspection about whether they have one, whether they accept that as a legiimate method of measuring the swept volume and, if they accept it but don't have on, whether if you brought your own, would they accept it as a a true method of checking the displacement of your bike....Back in the sixties and seventies, when the AMA certified all motorcycle records set at the SCTA/BNI National event (Speedweek), Earl Flanders was the AMA steward in charge of this...... He used this method....After the AMA was no longer involved, we (my brother and I) used our burrette for doing this.....Having said the first parts of the above now, and, if they WILL accept it, you may find yourself "pressed into service" as a cubic displacement inspector.....