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Old 10-15-2010, 10:52 PM   #1
GuamKid
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Default To hone or not to hone?

First off excuse the newbness, I'm sorry and the only teachers I have are the wonderful members of Nasioc!

I've picked up a set of standard sized CP pistons(92mm) as a direct replacement for an EJ205, now I've been told that when dropping in pistons its a MUST to hone the block to avoid scuffing ect.. ect.. Now on the other hand I have people saying that if the piston is a standard sized piston and the block DOESN'T have any scuffing, warping, scratches, I should just go ahead and install the pistons since CP pistons come gapped to .0030 already.

Who's right?
Teach away!
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Old 10-15-2010, 11:06 PM   #2
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I don't claim that I'm an expert on this topic, but I'm currently rebuilding my EJ257 and planning on dropping in forged standard size pistons. The block is certainly going to be rehoned for the new pistons. I would rather be safe than sorry and hone the block for the new pistons rather than taking the risk.
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Old 10-15-2010, 11:26 PM   #3
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yeah and thats probobly best, but in my case my local machine shop says that if they were to hone the block my PWC would be somewhere around .0050 since CP's come .0030 from factory already, hence the problem.
I'm not sure if this really matters but I'm re-using a block that had a bent valve on it.
(no damage visibly to the PW, finding out if its warped on Monday)
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Old 10-15-2010, 11:33 PM   #4
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Buying pistons without first knowing the measured condition of the bore is not the best idea...

For new pistons you need new cross-hatching on the cylinders in most cases. This depends on the ring material as well. I do not know what kind of material CP uses but this information should be readily avialable.

First things first though; you need to measure the bores for roundness and straightness to determine if you can even use a drop-in piston...

Since every bore is going to be different the pistons will not have the clearance that's printed on the box or the spec sheet. You have to MEASURE after first determining the condition of the bore.

Honing is not a measure to avoid "scuffing" honing is a measure to seat the rings properly and achieve good seal. A correct cross hatch on the cylinders is going to both hold an oil film and provide enough abrasive action during the break-in to seat the rings. If the cylinder does not have the correct finish the pistons won't "scuff" however the rings may not ever be able to seat properly...

.030 is big to my way of thinking. If the pistons are coated .0020-.0025 is good clearance to allow some wearing of the coating and makes for a quieter less oil thirsty motor.

You should get in touch with a machinist/builder before going further.


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Old 10-16-2010, 12:39 AM   #5
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Newb here
Is crosshatching a process that can be done by my local machinist?

Last edited by GuamKid; 10-16-2010 at 01:19 AM.
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Old 10-16-2010, 07:10 AM   #6
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Cross hatching is the finish put on the cylinder by the honing process. Correct cross hatching is ~45 degrees (although it's not absolutely critical for a boxer motor) and finish will depend on the piston rings. Some rings need a rougher finish while other ring materials such as plasma-moly need fine finishes.

More information about honing requirements specific to CP pistons is found on their site here:

http://www.cp-carrillo.com/Tech/Pist...4/Default.aspx

I don't know the capabilities of your local machinist so I can't say what he can do or not...
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Old 10-16-2010, 02:35 PM   #7
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Would it be necessary to hone the block at all if the block was to spec?
I checked each cylinder and I can clearly see the crosshatching, the block is still to be measured on Monday regardless and I know the cylinders will most likely not be to spec, but i'm an optomist!
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Old 10-16-2010, 03:42 PM   #8
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Quote:
Originally Posted by GuamKid View Post
First off excuse the newbness, I'm sorry and the only teachers I have are the wonderful members of Nasioc!

I've picked up a set of standard sized CP pistons(92mm) as a direct replacement for an EJ205, now I've been told that when dropping in pistons its a MUST to hone the block to avoid scuffing ect.. ect.. Now on the other hand I have people saying that if the piston is a standard sized piston and the block DOESN'T have any scuffing, warping, scratches, I should just go ahead and install the pistons since CP pistons come gapped to .0030 already.

Who's right?
Teach away!
Whether you buy off the shelf or custom pistons they don't come gapped to anything already. You order them in a nominal bore size and they will be close within a tolerance. You make the bore fit the piston to achieve the desired piston to wall clearance. Even with a brand new block and brand new drop in pistons the P/W clearance may have to be tweaked by boring and/or honing.

As you've said before your machine shop said you P/W clearance would be .005 already you should probably look into selling those pistons and buying .01" bigger the boring to achieve the correct P/W clearance.
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Old 10-16-2010, 03:53 PM   #9
kellygnsd
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Quote:
Originally Posted by GuamKid View Post
Would it be necessary to hone the block at all if the block was to spec?
I checked each cylinder and I can clearly see the crosshatching, the block is still to be measured on Monday regardless and I know the cylinders will most likely not be to spec, but i'm an optomist!
Crosshatch can still be visible on an engine with 200K+ miles on it but I wouldn't count on the actual surface finish to be rough enough at that point to properly seat a set of rings. If you really want to know if you surface is right measure the surface roughness with a profilometer and compare that with the finish your piston manufacturer recommended for their rings(probably have to call them for this info) and then hone to achieve the right finish...

Or you can just get the right sized pistons, bore and hone to clearance and know its right.

I prefer the latter. You can always sell you current pistons on here.
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