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Still the Same!
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1,781 Posts
Discussion Starter #1 (Edited)
Hey Randy, and everybody else...

For Christmas, I got a set of Mikes that range from 0-5" The 0-1 is electronic and so is the 4-5. Rest are digital.

Along with those, I got bore gauges. .7"-1.5" and 2"-6".

Today, I decided to dig these out and start playing with them. I got a handle on how they work and all of that. Set them to be zeroed at the bore dia you wished for.

MY question is how does one check a cylinder bore? Also, what is acceptable for a bore job and what is not.

I walked all over the cylinder and got a difference of 8 tenths.... eg: smallest reading was -.0016 and largest was -.0008. This is a really used cylinder. Has the heat marks, kind of yellowish brown, and can still barely make out the cross hatching. I did NOT measure a piston for my readings, I just winged it on the bore size. 3.937 for a S&S 106 kit that had been bored +10 by S&S on warranty. Bore ranged from 3.9354" to 3.9362"

The heat marks and the skuffing really didn't change the measurements. I am wondering this: if I send cylinders out to be bored and honed, upon their return..... what is an acceptable deviation? Also, does one 'map' the cylinder in specific spots, etc? What 'grid' is used to do this? (NOT THESE CYLINDERS).

trying to learn the PROPER method to do this stuff.

Also, how does one measure a piston? Where is the best spot to check at? Some have coatings, some do not.

Thanks!!!:beer::beer:
 

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569 Posts
Most cylinders are tapered to some extent. Walk a bore gage back and forth looking for the highest reading. Check 1.5 below the top, in the middle, and 2.0 up from the bottom.

Please listen to what NHRS has to say:

http://www.nrhsperformance.com/tech_cylinderstraightness.shtml



You will need to mount your cylinders in torque plates to get an accurate measurement. They are not cheap.

http://www.bhjproducts.com/bhj_content/products/honingplates/hp_hd.php

http://www.delkron-mfg.com/products/products.asp?pg=CmpntsToolsTorquePlates
 

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Gearhead
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1,114 Posts
Best thing to do is contact the piston manufacturer and ask them were to take the measurement. Had a set of Mahle pistons for a ultima motor I was rebuilding. Took them to Dave mackie for fitments in the cylinders. Dave asked were to measure them from I said
just pick the narrowest spot and he refused to do the work until I contacted the piston manufacturer as to were to measure from...needless to say that was a PIA to do. Turned out to be .700 down from the oil ring land on the skirt. Good ol anal Dave.
 

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Premium Member
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2,566 Posts
Hey Randy, and everybody else...

For Christmas, I got a set of Mikes that range from 0-5" The 0-1 is electronic and so is the 4-5. Rest are digital.

Along with those, I got bore gauges. .7"-1.5" and 2"-6".

Today, I decided to dig these out and start playing with them. I got a handle on how they work and all of that. Set them to be zeroed at the bore dia you wished for.

MY question is how does one check a cylinder bore? Also, what is acceptable for a bore job and what is not.

I walked all over the cylinder and got a difference of 8 tenths.... eg: smallest reading was -.0016 and largest was -.0008. This is a really used cylinder. Has the heat marks, kind of yellowish brown, and can still barely make out the cross hatching. I did NOT measure a piston for my readings, I just winged it on the bore size. 3.937 for a S&S 106 kit that had been bored +10 by S&S on warranty. Bore ranged from 3.9354" to 3.9362"

The heat marks and the skuffing really didn't change the measurements. I am wondering this: if I send cylinders out to be bored and honed, upon their return..... what is an acceptable deviation? Also, does one 'map' the cylinder in specific spots, etc? What 'grid' is used to do this? (NOT THESE CYLINDERS).

trying to learn the PROPER method to do this stuff.

Also, how does one measure a piston? Where is the best spot to check at? Some have coatings, some do not.

Thanks!!!:beer::beer:
NHRS has pretty good info, all of the pistons that we use have instructions on where and how to measure pistons, this varies.
We generally allow .0005" deviation on checked stuff, .0002" on the cylinders that we hone. We have checked factory new kits that are already out to their service wear limit spec., some of the aftermarket cylinders were zero clearance on the spigot and out of round .002".
 

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OUCH! That hurt
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696 Posts
Best thing to do is contact the piston manufacturer and ask them were to take the measurement. Had a set of Mahle pistons for a ultima motor I was rebuilding. Took them to Dave mackie for fitments in the cylinders. Dave asked were to measure them from I said
just pick the narrowest spot and he refused to do the work until I contacted the piston manufacturer as to were to measure from...needless to say that was a PIA to do. Turned out to be .700 down from the oil ring land on the skirt. Good ol anal Dave.
That's because all pistons are not designed the same. As they heat up they change shape. Measuring in the wrong spot will cause them to be fit incorrectly.

The MOCO want's you to measure the cylinder across the bolt holes measuring in at least 3 different spots - top, middle & bottom. If your cylinder is perfectly round you can put the gauge anywhere in the cylinder & it would read the same. Measuring with torque plates will give you a different reading than without but if your cylinder measures within .001 without the plates I would say it was in good shape.
 

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Measure the piston at its gage point. The piston mfg. should give this location. Zero bore gage to this measurement then check bore. This reading will be your clearance. Parts must be clean and at room temp. I like to take 4 readings, A= 90 deg from wrist pin at 1" from top, B= 90 deg from wrist pin at 2" from bottom (right about where the ring travel stops), C= in line with wrist pin at 1" from top and D= in line with wrist pin at 2" from bottom. Any difference in measurement from A and B or C and D is taper. Any difference in A and C or B and D is out of round. I dont know where the sad face cqame from!
 
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