[Bermuda Blue]

Just got the block back from the machine shop. In preparation for the build-up I thought I would check the machinist's work. Everything looks good with the exception of the piston to cylinder clearance. Below is are the clearance on clyinder #6. This one seems to be the "worst" but the rest are similar.

12-6 o'clock
top middle bottom
0.0022 0.0014 0.0017

3-9 o'clock
top middle bottom
0.0025 0.0018 0.0020

I have never had the luxury of using a dial bore gauge before so I have never been able to measure the clearances for myself. I have always trusted the machinist. I made the measurements by measuring the diameter of the piston with a micrometer and them zeroing the dial bore gauge to the micrometer.

The engine will be a stock rebuild using cast pistons. I thought the machinist was going for 0.0015 clearance but its hard to tell by looking at these numbers.

Are these clearances acceptablable? Is there something wrong with my measurement method? I was under the impresstion that out-of-round and concentricity would be zero. It is unlikely that a torque plate was used. Am I incorrect in concluding that the cylinders were honed poorly or are the results shown above acceptable?

Any input would be appreciated.

[Bermuda Blue]

Just got the block back from the machine shop. In preparation for the build-up I thought I would check the machinist's work. Everything looks good with the exception of the piston to cylinder clearance. Below is are the clearance on clyinder #6. This one seems to be the "worst" but the rest are similar.

12-6 o'clock
top middle bottom
0.0022 0.0014 0.0017

3-9 o'clock
top middle bottom
0.0025 0.0018 0.0020

I have never had the luxury of using a dial bore gauge before so I have never been able to measure the clearances for myself. I have always trusted the machinist. I made the measurements by measuring the diameter of the piston with a micrometer and them zeroing the dial bore gauge to the micrometer.

The engine will be a stock rebuild using cast pistons. I thought the machinist was going for 0.0015 clearance but its hard to tell by looking at these numbers.

Are these clearances acceptablable? Is there something wrong with my measurement method? I was under the impresstion that out-of-round and concentricity would be zero. It is unlikely that a torque plate was used. Am I incorrect in concluding that the cylinders were honed poorly or are the results shown above acceptable?

Any input would be appreciated.

[Lemans1]

Well if your measurements are correct the clearances are way too tight for a basic cast piston rebuild. TRW recommends .004-.006 for their forged pistons. Nicer pistons like Ross recommend .002-.004 clearance. I honestly cant see how they could be that out of round...maybe too much heat in the honing process?? I am sure someone more experienced with that will chime in.

[Black 65 GTO]

When checking piston to cylinder clearance, you should check the piston dimension at the piston manufactures point of measure. This will vary with piston types, material, and manufacture. The measurement is usually taken from ONE POINT of the piston, usually somewhere below the ring package.

Pistons are not designed to be equally round over their entire length. Different areas on the piston expand more than others, so the piston manufacture designs the pistons with a certain amount of "cam" to compensate for thermal expansion. This is why it's important to measure the pistons at the recommended locations.

If a torque plate was used, it would be possible to see the wall dimensions that you are seeing. That is, with no stress from a plate bolted on your block.

All of your measurements are under .001" (.0007"-.0008" are the largest). These numbers would be reduced if a torque plate was used. If you have one of the cylinder heads that you plan on using, mount it on the block, torque to spec and measure the bore again.

Temperature will also play a part in this. Try to measure your dimensions at room temperature or 60-70 degrees.

I would set the dial bore gauge to the specified piston measurement and try again.

Don't be afraid to question your machinist, your the one paying the bill.

[img]http://groups.msn.com/_Secure/0PAAAABsTshS*JL3aL9Lt3DTWpiaZQYuTwADv04vUiCSGPh1UW kUzJcyoBHF!u5vkOCDRCP1bN46o1zkzqk3S2WcjuGbw2xV8/Black-65-2-1.JPG[/img]

[Tom Vaught]

Quote:

"All of your measurements are under .001" (.0007"-.0008" are the largest). These numbers would be reduced if a torque plate was used. If you have one of the cylinder heads that you plan on using, mount it on the block, torque to spec and measure the bore again."

Use a head gasket and torque the head to spec.

If you are wondering how the heck do I read the bores now?

Flip the motor over on the engine stand and take the readings from the bottom! Tom V.

[Black 65 GTO]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Tom Vaught:
Quote:

If you are wondering how the heck do I read the bores now?

Flip the motor over on the engine stand and take the readings from the bottom! Tom V.

http://kurtsplates.homestead.com/files/UR2SLO.jpg <HR></BLOCKQUOTE>

I always wondered why I had trouble getting accurate measurements with the dial bore gauge through the spark plug hole!

[img]http://groups.msn.com/_Secure/0PAAAABsTshS*JL3aL9Lt3DTWpiaZQYuTwADv04vUiCSGPh1UW kUzJcyoBHF!u5vkOCDRCP1bN46o1zkzqk3S2WcjuGbw2xV8/Black-65-2-1.JPG[/img]

[Tom Vaught]

You may laugh but I have actually had people tell me that was impossible to do as the head was on the block.

You can almost get the same visual aid by putting a small 12 volt bulb in the combustion chamber, running the wires through the spark plug hole, putting a piston and single ring in the bore and looking at the roundness of the cylinder from the bottom of the bore with and with-out the head torqued . Tom V.

[khkiley1]

Maybe this is done already but,

I read that Smokey would flip the block over to ensure the cylinder head was situated squarely over the bores.

The IQ and life expectancy of the average American just passed each other going in opposite directions.