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I want to check the bore on a 292 that I have. I've got an inside micrometer made by Lufkin. There is a handle that attaches to the micrometer rod making a 'T' out of it. It seems to me there must be a technique for the use of this setup. If the handle is moved too far off center, your measurement is not going to be very accurate. Maybe the idea is to put the handle as close to one end as possible. Any help would be appreciated.
Larry

LGriffin,

You are using it correctly, it takes experience to get a good reading. A steady hand and a good eye are vital. Take a bunch of measurements in the same place and get the feel until you can come up with the same reading several times in a row.

They do make bore gauges with three legs so they will self center and self stabilize. If you know it's a 292 cubic inch, and hasn't been bored, then you will find the bore measurement in a manual or online. A taper gauge would be the proper tool to indicate the health of the bore, but several good readings with your mic can do in a pinch.

A neat trick is to put a piston in upside down and use the skirt to align the inside mic. Good luck.

Stuart

Atomarc, thanks for the excellent reply. My hands aren't all as steady as I would like them to be these days. The upside down piston does sound like the trick. I'm going to be separating the pistons and rods anyway to balance them.

I found a taper gage, didn't know they existed, thanks again. It doesn't look like a precision tool. I may pick it up if the price is right. Part of the story is the 292 lg blk has 10k on a rebuild, and the comression didn't look good. Hopefully it's just from sitting for four years, and the rings are varnished up.

Larry

Larry,

Your reply got me thinking. I called it a taper gauge, when I should have said dial bore gauge. Your comment about the taper gauge not looking too sophisticated threw me. A taper gauge does look low tech...a dial bore gauge looks a little better.

I don't know if it would be worth it to buy one of these for a one time engine job..maybe a friend has one, or just use your inside micrometer. The link shows what I meant the first time!

http://jcsonlinetoolshed.com/product.php/2130/679//0cc93472ca9549f5b3e4486be1659987


Stuart

An inside micrometer only takes a two point measurement. After a little practice and you begin to get a good feel for it, I would measure it, at least 4 different locations to check taper and roundness. Measure it about 1/2 inch down from the top, (write it down), then drop down about half way or more and do it again. Now rotate about 90 degrees and do it again. That is how I would do it. I would also measure over the tips of the inside mike, with a standard micrometer, as a way to verify your readings. If you do not read micrometers very often, it is very easy mis-read and be off by .025.
A dial bore gage is the way to go, that is if you have an accurate way to set it, like a master ring, or setting fixture. That would be the fastest, and more accurate reading.
But if you are patient, and have a good feel, you can get very accurate readings with an inside micrometer.
I have been using measuring instruments everyday on the job for over 25 years.

I think the idea of using the dial bore gauge would be to see the variation, or the taper to a internal bore. It would be placed in a unused area, zeroed, and moved through the bore. This procedure isn't concerned with a specific SIZE, but with VARIATIONS within the cylinder. The internal micrometer would give you the SIZE.

Stuart

Good point J about rotating 90 degrees. I'd forgot about checking for cylinder being out of round. Out of round cylinders really put a kabossh on out jr fuel dragster a couple of seasons ago. Which is to say if a performance engine builder can do it, it would be easy for a rebuild shop. I'll check the pistons for an oversize. Then I'll check above the ring land after cleaning and see if what I've got. Should be plus piston clearance. As I move the piston down the bore with the mic on top the piston. I'll see if I can slip a feeler gage in between the mic and the wall. There shouldn't be much. I've pull the head off some old 292s with standard bore and there was still been cross hatching on the cylinders. This not a race motor, mild performance street motor. I'm looking for varations say double the piston clearance. I'll check two or three cylinders.
Larry