piston resizing

Mike Pearson · 11-06-2015, 09:49 AM

have some good JE super stock pistons that I would like to resize for a smaller bore size. I broke the crankshaft in my engine and it ruined the block. I need a new block but don't want to bore it out to the max on the first go around. Can this be done

Mike Taylor 3601 · 11-06-2015, 10:54 AM

Possibly, depends on how much you are talking about,most likely ring lands would also have to be made deeper also,unless rings could be back cut enough,but they may already be as thin radially now as can be.
Might talk to Eric @ Rebco,he does piston mods,not sure about diameter though.
Mike Taylor 3601

Mike Pearson · 11-06-2015, 01:15 PM

They are for a 4.075 bore now. I would like to go down to 4.065 if possible. That would be .005 off the radius.

Rick Leininger Jr. · 11-06-2015, 09:07 PM

Show a pic of the bottom of the piston, and measure how thick the strap is below the wrist pin hole, it may be possible.

Dan Timberlake · 11-08-2015, 08:01 PM

Quote:

Originally Posted by Mike Pearson

They are for a 4.075 bore now. I would like to go down to 4.065 if possible. That would be .005 off the radius.

Piston skirts are usually not cylindrical. Some times they are some combination of tapered, cam ground, barrel shaped.
I wonder if JE can resize them.
https://www.jepistons.com/Catalogs/Automotive/NHRA.aspx

As others said, the ring grooves may need deepening. I don't think that can be done without the ring seal suffering,

Adger Smith · 11-09-2015, 02:40 AM

Call Frank Parks. He has started doing pistons for the Nostalgia Dragster crowd. He might be able to give you some advice or even do what you want.
His Son Scott is very talented and can do just about anything with a CNC.

Mike Pearson · 11-09-2015, 10:09 AM

Quote:

Originally Posted by Adger Smith

Call Frank Parks. He has started doing pistons for the Nostalgia Dragster crowd. He might be able to give you some advice or even do what you want.
His Son Scott is very talented and can do just about anything with a CNC.

Thanks Adger. Can you send me a Pm with his contact info or text to 813-433-4742

RonP · 11-09-2015, 02:00 PM

Hi,
Normally, OEM piston skirts are tapered horizontally and vertically.
The top land is also tapered from the chamber down to the top ring groove.
All the land diameters are specially sized too.
Ring grooves should be adjusted appropriately as well.

Trying to resize the piston will be difficult with the center boss removed.

Resizing a piston without a properly tapered shape would be a concern for scuffing,...especially for high rpm, high load applications.

Thanks, Ron

Rick Leininger Jr. · 11-10-2015, 08:09 AM

Most piston skirt shapes on racing pistons that make good power are a near straight profile in the Z axis, with a non-linear radial profile leading to the oil ring groove and a smaller yet non-linear radial profile at skirt bottom, all the while also cutting a variable elliptical shape. The CNC lathe that accomplishes this is about a 1/2 million dollar investment, so not something that can be done on the usual shop equipment.

Trying to recut the ring grooves deeper, yet maintaining the same ring groove width will ruin them, best option is to back cut any rings as necessary if possible.

If there isn't enough cross section remaining in the bottom of the piston to re-machine a locating register to hold the piston with while machining, then all of this discussion is moot. That's why I asked for a picture and measurement previously, I likely designed your pistons in the first place.

Mike Pearson · 11-10-2015, 09:05 AM

Quote:

Originally Posted by Rick Leininger Jr.

Most piston skirt shapes on racing pistons that make good power are a near straight profile in the Z axis, with a non-linear radial profile leading to the oil ring groove and a smaller yet non-linear radial profile at skirt bottom, all the while also cutting a variable elliptical shape. The CNC lathe that accomplishes this is about a 1/2 million dollar investment, so not something that can be done on the usual shop equipment.

Trying to recut the ring grooves deeper, yet maintaining the same ring groove width will ruin them, best option is to back cut any rings as necessary if possible.

If there isn't enough cross section remaining in the bottom of the piston to re-machine a locating register to hold the piston with while machining, then all of this discussion is moot. That's why I asked for a picture and measurement previously, I likely designed your pistons in the first place.

Thanks for the reply Rick. Can you send me an e mail address to send some pics to you. PM me or e mail me at ssia2485@yahoo.com with your contact info. Thanks again for your reply's

11-06-2015, 09:49 AM	#1
Mike Pearson VIP Member Join Date: Mar 2007 Posts: 2,446 Likes: 614 Liked 1,919 Times in 576 Posts	piston resizing have some good JE super stock pistons that I would like to resize for a smaller bore size. I broke the crankshaft in my engine and it ruined the block. I need a new block but don't want to bore it out to the max on the first go around. Can this be done __________________ Mike Pearson 2485 SS

11-06-2015, 10:54 AM	#2
Mike Taylor 3601 VIP Member Join Date: Oct 2008 Location: Somerset,Ky Posts: 1,371 Likes: 352 Liked 304 Times in 102 Posts	Re: piston resizing Possibly, depends on how much you are talking about,most likely ring lands would also have to be made deeper also,unless rings could be back cut enough,but they may already be as thin radially now as can be. Might talk to Eric @ Rebco,he does piston mods,not sure about diameter though. Mike Taylor 3601

11-06-2015, 01:15 PM	#3
Mike Pearson VIP Member Join Date: Mar 2007 Posts: 2,446 Likes: 614 Liked 1,919 Times in 576 Posts	Re: piston resizing They are for a 4.075 bore now. I would like to go down to 4.065 if possible. That would be .005 off the radius. __________________ Mike Pearson 2485 SS

11-06-2015, 09:07 PM	#4
Rick Leininger Jr. Member Join Date: Jun 2007 Posts: 162 Likes: 0 Liked 0 Times in 0 Posts	Re: piston resizing Show a pic of the bottom of the piston, and measure how thick the strap is below the wrist pin hole, it may be possible.

11-09-2015, 02:40 AM	#6
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: piston resizing Call Frank Parks. He has started doing pistons for the Nostalgia Dragster crowd. He might be able to give you some advice or even do what you want. His Son Scott is very talented and can do just about anything with a CNC. __________________ Adger Smith (Former SS)

11-09-2015, 02:00 PM	#8
RonP Junior Member Join Date: Mar 2003 Location: Detroit,MI Posts: 81 Likes: 28 Liked 29 Times in 14 Posts	Re: piston resizing Hi, Normally, OEM piston skirts are tapered horizontally and vertically. The top land is also tapered from the chamber down to the top ring groove. All the land diameters are specially sized too. Ring grooves should be adjusted appropriately as well. Trying to resize the piston will be difficult with the center boss removed. Resizing a piston without a properly tapered shape would be a concern for scuffing,...especially for high rpm, high load applications. Thanks, Ron

11-10-2015, 08:09 AM	#9
Rick Leininger Jr. Member Join Date: Jun 2007 Posts: 162 Likes: 0 Liked 0 Times in 0 Posts	Re: piston resizing Most piston skirt shapes on racing pistons that make good power are a near straight profile in the Z axis, with a non-linear radial profile leading to the oil ring groove and a smaller yet non-linear radial profile at skirt bottom, all the while also cutting a variable elliptical shape. The CNC lathe that accomplishes this is about a 1/2 million dollar investment, so not something that can be done on the usual shop equipment. Trying to recut the ring grooves deeper, yet maintaining the same ring groove width will ruin them, best option is to back cut any rings as necessary if possible. If there isn't enough cross section remaining in the bottom of the piston to re-machine a locating register to hold the piston with while machining, then all of this discussion is moot. That's why I asked for a picture and measurement previously, I likely designed your pistons in the first place.