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Discussion Starter · #1 ·
Figured that I should post the exact question since I'd hate to misread other posts and guess what to do. Lol. Better safe than sorry.

I've got a rough bored block at .040" over (bigger). I have a new set of Mahle .040 over pistons with rings installed.

Based upon the piston info in the picture, I would assume that the finished hone diameter should be 104.013mm (4.095").

Does anyone have the clearance between cylinder and piston diameter range for a .040" over bore?

Last question, should the clearance be larger on the #7 & #8 cylinders?

thank you everyone for your time. I appreciate it.
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It doesn't matter if over sized or not where clearance is concerned...

If the pistons haven't been coated by a professional performance coating shop you should use factory or piston manufacturing specs.. If the pistons have a printed break in coating on them there will be a small spot on the skirts that doesn't have the coating, that spot is where they should be measured, not on top of the break in coating..

Question, where did you purchase these pistons ? Reason I ask is according to Mahle's web site and when talking to them, ALL there pistons are made in the USA... the pic you posted says China, and says " suitable for GM " this is not something I have seen with real US made Mahle pistons, I happon to have a new in the box set here I will double check .. maybe I'm wrong...

Anyway, clearances 1-6 = .003" , 7-8 = .004"

Could you post a pic of the box they cam in ???
 

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Discussion Starter · #4 ·
It doesn't matter if over sized or not where clearance is concerned...

If the pistons haven't been coated by a professional performance coating shop you should use factory or piston manufacturing specs.. If the pistons have a printed break in coating on them there will be a small spot on the skirts that doesn't have the coating, that spot is where they should be measured, not on top of the break in coating..

Question, where did you purchase these pistons ? Reason I ask is according to Mahle's web site and when talking to them, ALL there pistons are made in the USA... the pic you posted says China, and says " suitable for GM " this is not something I have seen with real US made Mahle pistons, I happon to have a new in the box set here I will double check .. maybe I'm wrong...

Anyway, clearances 1-6 = .003" , 7-8 = .004"

Could you post a pic of the box they cam in ???
Thank you so much for the detailed info.

Yes I did notice the China label and was surprised as well. The pistons were drop shipped directly from Mahle. The order was placed through AGKits... and was excellent.

The inner box was all branded and the pistons look exceptional. Packaging etc was all top shelf. The skirts are not coated but the piston tops are and the swirl areas are roughened. Interesting for sure. Everything is at the machinists but I can post pics another day.

I included pictures of the outside shipping box label.

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Not suprising they are made in China. Mahle has about 40 manufacturing plants in China. Including Mahle Aftermarket. They are world wide company. They have plants all over the world. Not just USA.
One of the few USA engine part makers left is Sealed Power.. But even the last engine kit I got from them (Ford 302) had some stuff made in Mexico. But at least it was all North American.:)
 
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Figured that I should post the exact question since I'd hate to misread other posts and guess what to do. Lol. Better safe than sorry.

I've got a rough bored block at .040" over (bigger). I have a new set of Mahle .040 over pistons with rings installed.

Based upon the piston info in the picture, I would assume that the finished hone diameter should be 104.013mm (4.095").

Does anyone have the clearance between cylinder and piston diameter range for a .040" over bore?

Last question, should the clearance be larger on the #7 & #8 cylinders?

thank you everyone for your time. I appreciate it.
View attachment 639172
Nice to see that you found another block.Good job👍
 
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Discussion Starter · #9 ·
Nice to see that you found another block.Good job👍
Thanks so much. Yes I found a 94' 599 non-squirt casting from a local scrap yard. Lucky find.

Btw I now have two oil pumps (94 STD volume and 97 high volume). I'm planning to use the std volume but wondered if the longer vanes in the 97 is better... And could swap the oil pressure bypass if that would be an issue. Any thoughts? Thank you
 
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Stick with the standard volume pump because if you use the high volume pump on a non squirter block you can suck the sump dry(that’s what I read a few years ago)unless you install a oil pan with a deeper capacity and that would have to be custom made along with the oil pump pickup tube.High volume pumps are only suited for 506 blocks.
 
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Discussion Starter · #11 ·
Stick with the standard volume pump because if you use the high volume pump on a non squirter block you can suck the sump dry(that’s what I read a few years ago)unless you install a oil pan with a deeper capacity and that would have to be custom made along with the oil pump pickup tube.High volume pumps are only suited for 506 blocks.
Makes sense. Thank you
 
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Discussion Starter · #13 ·
Here's an update... Wanted to get opinions.
The top of the Mahle piston had the diameter inscribed on it of 103.881 and the sticker on the box of pistons had "BORE 104.013" which is 0.132mm (0.00519") of clearance. The machinist said that Mahle typically specs the dimensions like this.

I'm leaning towards going with Mahle recommendation as above. Any concerns? I was planning to have 0.0040" for #1-#6 and 0.0045" for #7&#8 anyway... So this larger clearance may be based on the particular material having a larger coefficient of expansion perhaps, etc.

Splitting hairs but figured I'd ask the diesel fam in case I'm overlooking. Lol

Thank you for your time
 

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Did you have those pistons measured by a machinist and then have the block bored and finish honed based on those measurements?The rear cylinders are said to run hotter so the machinist can finish hone those rear cylinders a little longer to give you the additional clearance.

You can’t go wrong with the Mahle recommendation for clearance but always ensure the machinist measures whatever pistons you give him and then he’ll know how much material to remove during the boring process.

I know of one horror story where a machinist accidentally bored out a 6.2 to .040 when it should have been .030 and he did this with no piston set present.
 
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Discussion Starter · #15 ·
Did you have those pistons measured by a machinist and then have the block bored and finish honed based on those measurements?The rear cylinders are said to run hotter so the machinist can finish hone those rear cylinders a little longer to give you the additional clearance.

You can’t go wrong with the Mahle recommendation for clearance but always ensure the machinist measures whatever pistons you give him and then he’ll know how much material to remove during the boring process.

I know of one horror story where a machinist accidentally bored out a 6.2 to .040 when it should have been .030 and he did this with no piston set present.
Thank you for the info. He's got the pistons in hand and measured to confirm. Originally I was going to run the #7,8 slightly larger but will keep everything to the Mahle single bore number since it's .005 over with all. My guess is that Mahle specs one number instead of two to make it easier to explain etc.
 
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Thank you for the info. He's got the pistons in hand and measured to confirm. Originally I was going to run the #7,8 slightly larger but will keep everything to the Mahle single bore number since it's .005 over with all. My guess is that Mahle specs one number instead of two to make it easier to explain etc.
Anytime.Your more than welcome 👍
 

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Just curious, an opinion from the pros. ."004 clearance on all pistons, "except" the last 2, recommended .0045"
Seriously? half a thou difference will be felt on a street motor? I'll bet that half a thou goes away the 1st 1K miles, and no-one would be the wiser.
One other question. Are all these aftermarket pistons now "Hyperutectic"? I'm don't know if I've even seen forgings offered anymore.
Good luck on your rebuild. Hope to see some pics at assy. (y)
 
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Just curious, an opinion from the pros. ."004 clearance on all pistons, "except" the last 2, recommended .0045"
Seriously? half a thou difference will be felt on a street motor? I'll bet that half a thou goes away the 1st 1K miles, and no-one would be the wiser.
One other question. Are all these aftermarket pistons now "Hyperutectic"? I'm don't know if I've even seen forgings offered anymore.
Good luck on your rebuild. Hope to see some pics at assy. (y)
I heard the silvolite brand is one to stay away from but that’s only what I’ve read.I usually stick with genuine GM or Mahle.Yes your right about the clearance on the rear cylinders.That certainly will change as the miles get put upon it.
 
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