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Bad Rat 414 10-06-2005 11:21 AM

How do you use a cylnder bore gauge?
I Bought a "Central" brand bore guage. It's marked off in 0.0005 incriments. It has a - side and a + side on the guage. I usually leave this kind of thing to the machine shop, but I want to learn. What is the proper way to use this and what mesurements and tolerances am I looking for in the bore?

Jeff L88 10-06-2005 10:41 PM

How to use a cylander bore gauge 101
OK, you bought this new fancy tool and you want to put it to good use, right?Measure each piston individually to their respective bore perpendicular to the ring bore with your micrometer, you do have a good set of these right? Good. Each piston manufacturer, and each type; cast, hyperutectic, and forged has a specified location where to measure,and how much piston to cylinder wall clearance you should have, however if you cant find it, measure at the widest location. When you mic the piston and feel comfortable with the "feeler gauge "method, lock the micrometer. Now take the dial bore gauge and "rock" it in the mic you have locked to come up with the shortest distance. This is your piston diameter. Zero your gauge with the dial and put the gauge back in the mic to double check your reading. Now put your dial bore gauge in the appropriate cylinder that the piston will live in and rock it again to find the shortest distance. The + side will tell you how much clearance there is between the piston and the cylinder wall, if you have negative clearance -, I suggest you go back to your machinist, this time with a baseball bat! You should be OK. Good luck!!

Bad Rat 414 10-07-2005 05:54 AM

That was great, thanks.

Fast Orange 10-07-2005 05:55 PM

Besides checking piston clearance,you can use a bore guage to check cylinders for out of round and taper from bottom to top.These checks help you determine if a used block is reusable.For example,with a 400 SBC that has siamezed cylinder walls,excessive out of round may indicate a block with a core shift problem.


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