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Piston Pin Reaming
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Powerflite
Posted 2017-04-07 9:51 AM (#537541)
Subject: Piston Pin Reaming



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So I want to put 440 H-beam rods with my 392 pistons. It seems that these pistons were setup to use 440 rods to begin with, yet they still use the 392 .984" piston pin. I can get some rods with .990 pin holes, but not .984. Would it be OK to ream the pistons to .990 instead of yanking out all the new rod bushings and putting new ones back in? Seems like it would be cheaper to do it this way.
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57chizler
Posted 2017-04-07 1:06 PM (#537559 - in reply to #537541)
Subject: RE: Piston Pin Reaming



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Rather than ream the pistons, I would hone them. Enlarging the pin bore .006" shouldn't have a negative effect.

What king of pin locks, Tru-Arc or spiral-locs.
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Powerflite
Posted 2017-04-07 4:38 PM (#537572 - in reply to #537559)
Subject: RE: Piston Pin Reaming



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Right now they have reverse snap rings in them.
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57chizler
Posted 2017-04-08 3:13 PM (#537633 - in reply to #537572)
Subject: RE: Piston Pin Reaming



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Internal Tru-Arc retaining rings have enough surface area so as not to be sensitive to bore diameter. You'll be OK.



(TruArc Internal.jpg)



Attachments
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Attachments TruArc Internal.jpg (50KB - 41 downloads)
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Powerflite
Posted 2017-04-08 10:05 PM (#537654 - in reply to #537541)
Subject: Re: Piston Pin Reaming



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Yeah, that's what I have. Thanks for the help.
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Powerflite
Posted 2017-04-14 1:14 PM (#538112 - in reply to #537654)
Subject: Re: Piston Pin Reaming



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I need to use 440 rods with these pistons to get the proper height. The big end is too wide for the 392 so I have to machine down the thickness, along with the bearings. I assume it would be easiest to machine the bearings and rods at the same time, but is it possible to use 392 bearings with a 440 rod instead?
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wayfarer
Posted 2017-04-14 8:32 PM (#538129 - in reply to #537541)
Subject: Re: Piston Pin Reaming



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Given that the 440 rod is .200 shorter than the 392 rod I have to ask what piston are you dealing with?

Rather than make a one-off bearing why not open the journal the 0.04" or so that is needed...assuming that the crank is out. This allows for making the side clearance what you want based on the rods in hand. Or just use the more expensive 392 bearing.
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Powerflite
Posted 2017-12-06 3:28 PM (#553815 - in reply to #537541)
Subject: RE: Piston Pin Reaming



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Location: So. California
Here is a picture of my pistons on the right. A 10:1 392 piston is on the left. These pistons are a lot taller than normal. I measured them to be a whopping .255" ± .01" higher from the top ring land to top ring land. When I had the rods machined, the machinists highly recommended to leave the pistons alone so I ended up changing the bushings on the rods to match the pins. It turns out that I had 2 pistons that were made in a separate batch so they weren't very well balanced.... but they are now.

Edited by Powerflite 2017-12-06 3:33 PM




(392Hemi-440Rod.jpg)



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Attachments 392Hemi-440Rod.jpg (173KB - 3 downloads)
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Powerflite
Posted 2017-12-06 6:22 PM (#553822 - in reply to #537541)
Subject: Re: Piston Pin Reaming



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I read that you should never install the snap ring with the opening to the sides of the piston because it is weaker in that position and can result in snap ring failure. Is that true? There doesn't seem to be any side force possible from the rod to the piston so how could having the opening on the side have any effect? Having it on top or bottom doesn't seem any better in that regard. What am I missing?
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58coupe
Posted 2017-12-07 11:01 AM (#553850 - in reply to #537541)
Subject: Re: Piston Pin Reaming



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Never heard that one about position of the retaining ring but there is some side load, that is why some Mopar engines (and others) were built with offset pins to negate that.
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