Small Diameter Wrist Pin Life

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Warp Speed
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Re: Small Diameter Wrist Pin Life

Post by Warp Speed »

The smaller the clearance between the rod and piston pin tower, the more support the pin has. One of the natural advantages of a piston guided design. With a rod guided strategy, you want the clearance to still be a minimum, without binding rod movement.
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Re: Small Diameter Wrist Pin Life

Post by ptuomov »

Warp Speed wrote: Mon Nov 25, 2019 8:26 pm The smaller the clearance between the rod and piston pin tower, the more support the pin has. One of the natural advantages of a piston guided design. With a rod guided strategy, you want the clearance to still be a minimum, without binding rod movement.
Makes sense. Any splash oiling considerations, though?
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Re: Small Diameter Wrist Pin Life

Post by modok »

I don't think oiling the pin bushing is much of a concern period, a far as it's basic dimensions.
if the bushings outlasting the engine already, they may not even want bother to drill oil holes.
I mean....it's true right?
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Re: Small Diameter Wrist Pin Life

Post by Warp Speed »

ptuomov wrote: Mon Nov 25, 2019 8:49 pm
Warp Speed wrote: Mon Nov 25, 2019 8:26 pm The smaller the clearance between the rod and piston pin tower, the more support the pin has. One of the natural advantages of a piston guided design. With a rod guided strategy, you want the clearance to still be a minimum, without binding rod movement.
Makes sense. Any splash oiling considerations, though?
Not typically. I have ran this type of setup, although with piston oilers, without any presurized oiling from from either rod or piston, at over 20" of crankcase depression.
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Re: Small Diameter Wrist Pin Life

Post by ptuomov »

Warp Speed wrote: Tue Nov 26, 2019 5:16 am The smaller the clearance between the rod and piston pin tower, the more support the pin has. One of the natural advantages of a piston guided design. With a rod guided strategy, you want the clearance to still be a minimum, without binding rod movement.
...
I have ran this type of setup, although with piston oilers, without any presurized oiling from from either rod or piston, at over 20" of crankcase depression.
That's good to know as I am looking at these Mahle Subaru pistons and they have very little pin to boss overlap and better have a rod that's snug there between the bosses.
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Re: Small Diameter Wrist Pin Life

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Warp Speed wrote: Mon Nov 25, 2019 8:26 pm The smaller the clearance between the rod and piston pin tower, the more support the pin has. One of the natural advantages of a piston guided design. With a rod guided strategy, you want the clearance to still be a minimum, without binding rod movement.
The new pistons I have measure 1.220" between the pin bosses. The last set of aluminum rods measured 1.050" wide. Thinking of ordering the next set with a dimension of 1.180" which would give me 0.040" total clearance and support the pin a bit more. Pins are DLC coated 0.787" x 2.225" x 0.185".
Any concerns with this plan?
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Re: Small Diameter Wrist Pin Life

Post by Warp Speed »

donclark wrote: Wed Dec 04, 2019 5:37 pm
Warp Speed wrote: Mon Nov 25, 2019 8:26 pm The smaller the clearance between the rod and piston pin tower, the more support the pin has. One of the natural advantages of a piston guided design. With a rod guided strategy, you want the clearance to still be a minimum, without binding rod movement.
The new pistons I have measure 1.220" between the pin bosses. The last set of aluminum rods measured 1.050" wide. Thinking of ordering the next set with a dimension of 1.180" which would give me 0.040" total clearance and support the pin a bit more. Pins are DLC coated 0.787" x 2.225" x 0.185".
Any concerns with this plan?
As long as you have some clearance, the extra support will help. Although, with that pin diameter, I would rather see a thickness of .200ish. Do you know what material the pin is?
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Re: Small Diameter Wrist Pin Life

Post by donclark »

Warp Speed wrote: Thu Dec 05, 2019 5:14 am
donclark wrote: Wed Dec 04, 2019 5:37 pm
Warp Speed wrote: Mon Nov 25, 2019 8:26 pm The smaller the clearance between the rod and piston pin tower, the more support the pin has. One of the natural advantages of a piston guided design. With a rod guided strategy, you want the clearance to still be a minimum, without binding rod movement.
The new pistons I have measure 1.220" between the pin bosses. The last set of aluminum rods measured 1.050" wide. Thinking of ordering the next set with a dimension of 1.180" which would give me 0.040" total clearance and support the pin a bit more. Pins are DLC coated 0.787" x 2.225" x 0.185".
Any concerns with this plan?
As long as you have some clearance, the extra support will help. Although, with that pin diameter, I would rather see a thickness of .200ish. Do you know what material the pin is?
They are H13. They are tapered but reach full wall thickness at the point beyond the piston tower.
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Re: Small Diameter Wrist Pin Life

Post by Warp Speed »

donclark wrote: Thu Dec 05, 2019 7:45 am
Warp Speed wrote: Thu Dec 05, 2019 5:14 am
donclark wrote: Wed Dec 04, 2019 5:37 pm

The new pistons I have measure 1.220" between the pin bosses. The last set of aluminum rods measured 1.050" wide. Thinking of ordering the next set with a dimension of 1.180" which would give me 0.040" total clearance and support the pin a bit more. Pins are DLC coated 0.787" x 2.225" x 0.185".
Any concerns with this plan?
As long as you have some clearance, the extra support will help. Although, with that pin diameter, I would rather see a thickness of .200ish. Do you know what material the pin is?
They are H13. They are tapered but reach full wall thickness at the point beyond the piston tower.
What's the intended usage?
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Re: Small Diameter Wrist Pin Life

Post by blackford »

machstang70 wrote: Mon Mar 17, 2014 6:29 pm I was thinking the same and just wanted to get some more opinions. I am using a Speed Pro piston so a shorter pin is not an option. I was thinking of going to a .927" pin, but that little change may not be worth the trouble.

Mike
With the same wall thickness of .132, the pin will be about 5% stiffer.
65 Mustang FB, 331 custom built with 289 H beam rods and 383W piston, 282S cam, Ported Maxx 180s, T5z, 9" 3.89 gears. ~460HP@6500

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Re: Small Diameter Wrist Pin Life

Post by donclark »

Warp Speed wrote: Thu Dec 05, 2019 9:55 am
donclark wrote: Thu Dec 05, 2019 7:45 am
Warp Speed wrote: Thu Dec 05, 2019 5:14 am

As long as you have some clearance, the extra support will help. Although, with that pin diameter, I would rather see a thickness of .200ish. Do you know what material the pin is?
They are H13. They are tapered but reach full wall thickness at the point beyond the piston tower.
What's the intended usage?
N/A drag race, 9400 rpm, bore size is 4.180
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Re: Small Diameter Wrist Pin Life

Post by Warp Speed »

donclark wrote: Thu Dec 05, 2019 3:29 pm
Warp Speed wrote: Thu Dec 05, 2019 9:55 am
donclark wrote: Thu Dec 05, 2019 7:45 am

They are H13. They are tapered but reach full wall thickness at the point beyond the piston tower.
What's the intended usage?
N/A drag race, 9400 rpm, bore size is 4.180
I'd say that's pushing it a little. The pins we ran it that size range were a minumum .200 straight wall.
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Re: Small Diameter Wrist Pin Life

Post by trmnatr »

Warp Speed wrote: Mon Oct 08, 2012 1:17 pm
axegrinder wrote:
Adger Smith wrote:Now let's talk materials. C-350, C-300, M2, H-13 H-11, 9310, ect. That is where the real strength is and what the material does in compression and flex. A well know T/F team buys a lot of M2 pins so we used them in an A/F dragster engine I helped build. It's best asset is it is crack resistant. From what I understand a lot of the P/S teams use C-300 or C-350 material. The material and coating is what cost you on pins. I've found it is well worth the expense, esp in blown or NOS applications. I've seen too many shelf stock piston pins fail when the power levels go way up.
C-350: 8.08 grams/cc
9310: 7.80grams/cc
Titanium: 4.65grams/cc

Looks like the Pro Stock guys are going in the opposite direction of lite weight materials.
A wrist pin is not one of the areas to save weight in. Hence the direction you mentioned!
I don’t skimp on weight or wall thickness & Trend has many materials to choose from. I’ve had good luck from Ross heavy wall (.150”) standard .927” pins
www.autotransdesign.com www.gzmotorsports.com
www.cranecams.com www.prosystemsracing.com
www.hardblok.com
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