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Old 27th-September-2012, 04:16 AM   #1
Metica
 
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Piston to bore clearance?

Hi,

I'm buildning a Chevy 350 with 0.040 overbore and Speed Pro hypereutectic pistons.

Last night I measured the Piston to bore clearance. The 0.006 feeler gauge blade fited in the bore around the piston shirt, but the 0.008 blade did not. So the clearance is around .006 to .007 inches. The only data I've got for the Speed Pro pistons is MINIMUM .0010 clearance (the box the pistons came in says so).

Will I end up with piston slap? Is this OK?

Thanks in advance,

Kind regards /Peter
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Last edited by Metica; 27th-September-2012 at 04:22 AM.
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Old 27th-September-2012, 07:20 AM   #2
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Quote:
Originally Posted by Metica View Post
Hi,

I'm buildning a Chevy 350 with 0.040 overbore and Speed Pro hypereutectic pistons.

Last night I measured the Piston to bore clearance. The 0.006 feeler gauge blade fited in the bore around the piston shirt, but the 0.008 blade did not. So the clearance is around .006 to .007 inches. The only data I've got for the Speed Pro pistons is MINIMUM .0010 clearance (the box the pistons came in says so).

Will I end up with piston slap? Is this OK?

Thanks in advance,

Kind regards /Peter
Using a feeler gauge is not going to work when pistons skirts have taper, How do you make sure the piston is square in the cylinders.

Skirt clearance should be built into the piston so you should measure the bore and if plate honed a torque plate should be installed or bolt a head on and measure up from the bottom as that what your pistons are seeing once the heads are bolted on.

Should measure the pistons with a mic and go from there.

Last edited by CNC BLOCKS; 27th-September-2012 at 07:22 AM.
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Old 27th-September-2012, 03:18 PM   #3
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Very interesting information. Thanks.

Talked to the guy at the machine shop today. Who did the job. He said, among a lot of other things (and if I understood him right), that the value I got should be reduced. Just like you say: "How do you make sure the piston is square in the cylinders". With the feeler gauge blade in, that could obviosly not be the case.

A few other q:

1) By mic, you mean micrometer?

2) Should the bore (with plate or head on) and piston both with a micrometer?

3) Sorry for being dumb, but I don't understand the concept "Skirt clearance should be built into the piston"?!

Thanks for your patience... ;-)

Kind regars /Peter
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Old 27th-September-2012, 03:47 PM   #4
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Quote:
Originally Posted by Metica View Post
Very interesting information. Thanks.

Talked to the guy at the machine shop today. Who did the job. He said, among a lot of other things (and if I understood him right), that the value I got should be reduced. Just like you say: "How do you make sure the piston is square in the cylinders". With the feeler gauge blade in, that could obviosly not be the case.

A few other q:

1) By mic, you mean micrometer?

2) Should the bore (with plate or head on) and piston both with a micrometer?

3) Sorry for being dumb, but I don't understand the concept "Skirt clearance should be built into the piston"?!

Thanks for your patience... ;-)

Kind regars /Peter

On question one is yes

Check the bore with a bore gauge and mic the pistons.

First of all find out if you block was plate hone or not ?? If not the ring seal may not be as good.
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Old 27th-September-2012, 04:17 PM   #5
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A torque plate was used during the machine work (the drilling part anyway, do you really need a plate when using the stones for the cross hatch pattern?).

Of course nothing but a bore gauge is used measuring the cylinders... ;-)

Kind regards /Peter
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Old 27th-September-2012, 05:07 PM   #6
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A torque plate was used during the machine work (the drilling part anyway, do you really need a plate when using the stones for the cross hatch pattern?).

Of course nothing but a bore gauge is used measuring the cylinders... ;-)

Kind regards /Peter
The plate needs to be on whenn plate honing and using a good hone is a plus.

Here are some links on plate honing

http://www.camaros.net/forums/showthread.php?t=58964

http://www.chevelles.com/forums/show...ght=blue+print
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Old 27th-September-2012, 07:45 PM   #7
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What Carl is saying about the skirt clearance is that if you buy pistons for a 4" bore and need .005 piston to wall clearance, the piston will measure 3.995". The skirt clearance is built into the piston size. ANd like he said, the plate needs to be used for both boring and honing, otherwise one process will not make the bores straight.
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Old 28th-September-2012, 07:42 AM   #8
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What Carl is saying about the skirt clearance is that if you buy pistons for a 4" bore and need .005 piston to wall clearance, the piston will measure 3.995". The skirt clearance is built into the piston size. ANd like he said, the plate needs to be used for both boring and honing, otherwise one process will not make the bores straight.
I have never used a plate when boring, Guys that have are useing a ceap hone should bore with a plate.

If your using a good hone and leave .005 or more depending on the block to hone out it will come out fine.
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Old 25th-October-2012, 04:47 AM   #9
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Hi again,

I bought myself a micrometer and a dial bore gauge. Win!

What I did then was measuring the pistons (4.03937") and then "zeroed" the dial bore gauge on the very same figure. After that, I stuck down the dial bore gauge in the cylinder and could see (when the dial bore gauge peaked) that the difference from the pistons was around 0.03 to 0.04 mm (0.0011" to 0.0015").

Is that the correct procedure?

Minimum piston to bore clearance according to the piston manufactuer is 0.0010, so I'm good to go on that. What about numbers otherwise? It seems like a good and tight fit to me?!

Kind regards /Peter
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Old 25th-October-2012, 08:40 AM   #10
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Quote:
Originally Posted by Metica View Post
Hi again,

I bought myself a micrometer and a dial bore gauge. Win!

What I did then was measuring the pistons (4.03937") and then "zeroed" the dial bore gauge on the very same figure. After that, I stuck down the dial bore gauge in the cylinder and could see (when the dial bore gauge peaked) that the difference from the pistons was around 0.03 to 0.04 mm (0.0011" to 0.0015").

Is that the correct procedure?

Minimum piston to bore clearance according to the piston manufactuer is 0.0010, so I'm good to go on that. What about numbers otherwise? It seems like a good and tight fit to me?!

Kind regards /Peter
So far all the pistons I have seen the clearance is built into the piston so if you have a .030 over bore the clearance should be fine and a little more clearance does not hurt any thing.

Your on the right track.
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