Cylinder bore how to measure

[dcooke007]

Measuring an 03 Wombat cylinder and took some pictures to demonstrate process and tools used. More sophisticated tools are available but basic quality micrometer and telescoping bore gages can get the job done.

This is the kind of job that you need three hands. Micrometer holders / stands are available but in this case vise and padded jaws. Still looking for a good deal on a micrometer holder.

Note radius on ends of telescoping gage.

Most people think the proper way to use a telescoping gage is to attempt to center, square up the gage and then tighten the locking nut. There is better way. Place the gage in the bore at an angle and tighten the locking not firmly. Pivot one end of the gage up while maintaining the opposite end in the same location. The gage will telescope in, center in the bore and give an accurate reading. Practice and proper technique is required. When done properly repeatable measurements will be the results.

CENTER telescoping gage and measure with micrometer. Again practice makes perfect. A light touch is required on the micrometer to prevent the telescoping gage from.......well telescoping in if too much pressure is applied with the micrometer.

Proper measurement of a Hodaka piston is performed 90 degrees to the piston pin and at the largest diameter. Largest diameter is just slightly above the bottom of the piston skirt.

Cylinder bore measurements are taken in several locations to determine out of round and taper. In this case cylinder bore is .0075 to .008 inch larger than the radom piston I chose. Piston to bore clearance is excessive. Cylinder bore has very little taper or out of round.

Temperature extremes are to be avoided when making precise measurements. You would be surprised how much an aluminum piston shrinks at 30 degrees compared to 70.
Danny

[Bullfrog]

Excellent post! (Let the quibbling begin ). Up near the top I think it would better to say "snug up" the tightening knob on the bore gauge. ( Rather than "tighten the locking nut".) The bore gage has to be snugged up enough that it won't spring "out" on its own when removed from the bore, but not so tight that it requires excessive force to move it thru the arc which self-centers on the exact bore diameter. Precision measurements require a bit of "touch" or "feel" - and a bit of practice. Since I don't do precision measuring every day or even every month these days, I like to take a specific measurement multiple times and throw out the extremes to zero in on the most accurate dimension.
Ed

[matt glascock]

Great discussion fellas. Wonderful to enjoy a discussion between two guys who engineered and wrenched on their own race bikes.

[viclioce]

Where is a good place to buy these gauges and what is the “Typical” price for them? I’d like to purchase a set! Danny? Victor

[bobwhitman]

Danny
If you agree, I’d like to use this in the Resonator, attributing it to you. While I can lift it from the chat group, it works better if you could email me .jpg copies of the photos and the text separately. Gregg and I can then fit it more easily into the newsletter.
Bob Whitman 541-954-0101
[email protected]

[dcooke007]

Victor,
I like the basic 436 Starrett version micrometer with carbide faces and 10th scale. Micrometers measure in 1 inch lengths and the one used for the 125 bore is a 2 to 3 inch. I think you would need a 1 to 2 inch version for the 100 bore. I bought all my micrometers on ebay. Micrometers are either heavily used or used very little. I look for mics that have seen very little use and pay no more than 2/3rds the retail price....sometimes much less. Some very good deals can be found. I also have standards for all my mic's to verify they are adjusted properly and standards can be used to practice your measuring technique. Quality varies and some very cheaply made micrometers are out there and should be avoided.
The telescoping gages I purchased many years ago from Snap-on. They do not make their own and I think they are General brand and not very expensive on ebay new.

Danny

[dcooke007]

Hey Bob,
I deleted the pictures I took shortly after posting this info. You are free to use the pictures here and the info listed for the Resonator.

Danny

[bobwhitman]

Thanks Danny, I’ll do it that way.
Bob