Wrist pin surface finish.

Smokem said:
Along the lines of...
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On that note, I just got my pistons back from having the reliefs cut and being coated. Reliefs are the correct diameter(hope their fixture put them in the right place) of 1.45. I asked for .030 deep and on the first two i checked they range from .0255 to .0325. I would assume that in automotive terms that is "right on the gnat's arse".
 

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RonA said:
On that note, I just got my pistons back from having the reliefs cut and being coated. Reliefs are the correct diameter(hope their fixture put them in the right place) of 1.45. I asked for .030 deep and on the first two i checked they range from .0255 to .0325. I would assume that in automotive terms that is "right on the gnat's arse".
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hope you figured in a extra .0045 cause you might end up losing some ceramic coating.
 
Joesixpack said:
Sandpaper will hold oil good too, can still sand with it though!
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ever heard of wet sanding....LOL
RonA said:
I'll let Wade explain it. I bought them from him for my p-pumped 6.7 daily driver.
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The pins you bought were custom order and much lighter than stock, yet even stronger by like 35% or along those lines. The finish is exactly how they were out of the shop that made them for me, the same exact finish that all of schieds and enterprise engines has put in there builds. No issue's. i first was thinking along the same line as you when i first started to get these made for me, few years ago. But time has tested and the truth is out they accually wear better than a polish surface due to holding more oil, while a polish finish will accually shed oil... To micro polish them would have been another $100 each pin and as i recall you declined that option, due to the cost and the fact that others including myself were useing them AS-IS with great luck.

Some of the most powerful engines in the country use these pins, trust me Ron you are fine with what you have. If it makes you feel better and you do however want a micro polish finish let me know.
 
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DIESEL_POWER said:
ever heard of wet sanding....LOL

The pins you bought were custom order and much lighter than stock, yet even stronger by like 35% or along those lines. The finish is exactly how they were out of the shop that made them for me, the same exact finish that all of schieds and enterprise engines has put in there builds. No issue's. i first was thinking along the same line as you when i first started to get these made for me, few years ago. But time has tested and the truth is out they accually wear better than a polish surface due to holding more oil, while a polish finish will accually shed oil... To micro polish them would have been another $100 each pin and as i recall you declined that option, due to the cost and the fact that others including myself were useing them AS-IS with great luck.

Some of the most powerful engines in the country use these pins, trust me Ron you are fine with what you have. If it makes you feel better and you do however want a micro polish finish let me know.
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:umno: :badidea:famous last words.
 
Joesixpack said:
http://www.bmeltd.com/Wristpin.htm All look pretty polished to me.


$1200 for polished pins, that at Ron's RPM will be near to impossible to measure on the dyno. Thats some expensive hp.
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"Yeah, but dem dere Bee Emm E's ain't goin' in no deezul." LOL


All kidding aside, one thing that's always surprised me, you pull a high mileage aluminum piston out of a motor and the entire body is lathe turned with a finish that's very unimpressive....yet not a sign of wear anywhere on it.
 
nwpadmax said:
All kidding aside, one thing that's always surprised me, you pull a high mileage aluminum piston out of a motor and the entire body is lathe turned with a finish that's very unimpressive....yet not a sign of wear anywhere on it.
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I thought of the same thing, however the forces between the wrist pin and piston (or rod) are much greater than the forces between the piston and the cylinder walls.

If it works and has been proven, that's what matters. I'm just unedumacated...
 
If you polish these, they will go undersize. I don't recall being given the option when i ordered them, but after as many piston sets as I've bought, I'm not going to have any trouble finding a set of wrist pins i can lighten.LOL
 
RonA said:
If you polish these, they will go undersize. I don't recall being given the option when i ordered them, but after as many piston sets as I've bought, I'm not going to have any trouble finding a set of wrist pins i can lighten.LOL
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Dont lighten the stockers, you'll be back on here telling us how you should have listened...

BTW clearance in the wrist pin should be between 1 thou and 1.3 thou in a perfect world....little more is fine, but what would i know....
 
GOT-Torque said:
I thought of the same thing, however the forces between the wrist pin and piston (or rod) are much greater than the forces between the piston and the cylinder walls.

If it works and has been proven, that's what matters. I'm just unedumacated...
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if im not mistaken the rod might only move 1/16" back and forth at the wrist pin because of the rods length. ive seen some awful rough stuff that lasted forever.
 
I've talked to a couple of people that have lightened their stockers and had no problems. Actually, I haven't heard of anyone having a wrist pin failure. I also find it interesting that a lathe turned set of pins is $650 and then a premium set that has been ground is $750 but rough is better for holding oil.
 
RonA said:
I've talked to a couple of people that have lightened their stockers and had no problems. Actually, I haven't heard of anyone having a wrist pin failure. I also find it interesting that a lathe turned set of pins is $650 and then a premium set that has been ground is $750 but rough is better for holding oil.
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Ron, give Rip a call about lightening the stockers. He can give you some info on how to do it, without making them weaker then stock. Though I would guess you already have that info...

6.7 specs:

Pin diameter
Min - 1.5747
Max - 1.5749
Bore diameter
Min - 1.5750
Max - 1.5753

Connecting rod bore diameter w/bushing
Min - 1.5764
Max - 1.5765

Connecting rod side clearance
Min - 0.004
Max - 0.013


These are stock specs. With the billet rods, make sure you get the specs from the rod manufactor for the connecting rods. They often get shipped tight, so that the installer can pin fit them on installation.

Paul
 
Good morning Paul.
I talked to Rip once before and actually did some cutting on a couple of pins. I'll give him a call.
Thank you for the specs and the heads up on the bushings in the rods.

RonA
 
GOT-Torque said:
I thought of the same thing, however the forces between the wrist pin and piston (or rod) are much greater than the forces between the piston and the cylinder walls.
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Yes, of course, just was using that as an example of where something works fine that initially I would have had the opposite gut feel.

And to state it more clearly, the forces per unit area are higher on the wrist pin (and in lots of other places)

Maybe the lathe turned wrist pins work fine in competition engines because you're also probably using a very high viscosity oil (50 wt?) that you would never run in a DD, and the oil is doing exactly what it needs to.

A while back there was some media coverage of a technique where you hone the cylinders very smoothly and then use a cnc laser to etch tiny "dashes" into the walls for oil retention. IIRC it was Daimler who was working with it.

Surface finish effects are quite interesting...
 
RonA said:
On that note, I just got my pistons back from having the reliefs cut and being coated. Reliefs are the correct diameter(hope their fixture put them in the right place) of 1.45. I asked for .030 deep and on the first two i checked they range from .0255 to .0325. I would assume that in automotive terms that is "right on the gnat's arse".
Click to expand...

How hard is it to hold a tolerance better than that? I would think you could have done better yourself Ron.

And I wouldn't take Wade's "trust me" for anything.

JMHO,
Chris
 
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