#129403, "Pistons/bore size" Jan-22-10 09:27 PM by 97AllMtr
If I have a set of .020 over pistons that are in a block, and I want to use a different set of .020 pistons, (so they are the same bore) am I safe to just "swap" them, or would I need to take them to the machine shop? As long as the rings are gapped correctly, I am okay right? I know if I want to be 100% positive, go to the machine shop, but more than likely I would be okay. Right?
#129405, "RE: Pistons/bore size" In response to Reply # 0
The chances that the new set of 0.020 over pistons are exactly the same diameter as the old ones is not likely. Machine shops bore the cylinders with the actual piston diameter and the piston to cylinder wall clearance in mind.
If your new pistons are of a different material/brand as the old, manufacturers generally have their own recommended clearances to use.
Rings and pistons are not 100% interchangeable. Meaning your new pistons will work with only certain rings. 1.0 mm? 1.2 mm? Compression rings are of different sizes.
Additionally rings are something I would avoid reusing. They are not that expensive anyway. If you are trying to do a budget rebuild and not have the cylinders rehoned and reuse the old rings you are wasting your time and money. This is not a place to skimp on money.
See what I am getting at? It is your money and time, but I would not install new pistons without block prep and the reuse of old rings, etc.
#129406, "RE: Pistons/bore size" In response to Reply # 1
I hear you. The pistons that were originally in the motor were JE 8.8:1 .020 pistons. The new ones are JE 8.8:1 .020 pistons as well lol. Don't ask, not my motor or money. New rings will be used. You think it would be okay to not rebore/hone?
#129407, "RE: Pistons/bore size" In response to Reply # 2
Depends on useage.
If your going N/A use to Boosted use then no your not ok.
If its simply a replacement due to oh say a detonated piston then you would need to mic the piston size, measure the bore and determine the clearance you will be left with.
A manufacturer can make a series of pistons at a given size.....eventually the molds wear out and a new series of pistonis designed and it might not have the same skirt size. Coatings ect also vary. Only way to know for sure is to actually measure.
Same goes for piston weight. If the piston you have is lighter or heavier then it must be balenced to the crank. Most machine shops DO NOT balence a crank to the piston, they combine both and avergae the two together. This is done for a reason and i dont think anyone really wants to know why at this point.
#129408, "RE: Pistons/bore size" In response to Reply # 3
Thanks guys, pretty much confirmed what I was thinking. I think at this point he's going to be using the other set of JE's due to his lack of money. But, I get to say I told him so now.
#129409, "RE: Pistons/bore size" In response to Reply # 3
Originally posted by Star Turbo Talon Most machine shops DO NOT balence a crank to the piston, they combine both and avergae the two together. This is done for a reason and i dont think anyone really wants to know why at this point. Terry
I'd like to know, but I'm geeky like that.
Erik P. Official 2GNT thread Hijacker Some say that he's driven over more Covenant than he's shot, and that his grenades aren't where you'd expect them to be... All we know is, He's not The Stig... But he is The Stig's Spartan cousin!
#129468, "RE: Pistons/bore size" In response to Reply # 5
Mic it. Bore diameter isn't the only measurement you need to take. Also check for taper and out of roundness. If everything's within spec then lightly refinish the bores using a ball or brush hone.
#129847, "RE: Pistons/bore size" In response to Reply # 6 Mar-02-10 04:30 AM by 97AllMtr
So we were going to just take the block down to the machine shop with the new pistons, the crank is still in the block. Can they measure everything and do whatever they need to do if the pistons are a different size if the crank is still in the shortblock? I only ask this because we really don't want to have to take the oil pump off and sprocket etc.
#129848, "RE: Pistons/bore size" In response to Reply # 7
More of a pain in the ass and heavy to move it with the crank installed. They can take measurements but if any work needs to be done to the block they are going to want it apart.
#129849, "RE: Pistons/bore size" In response to Reply # 3
Originally posted by Star Turbo Talon h. A manufacturer can make a series of pistons at a given size.....eventually the MOLDS wear out
As I understand JE and most aftermarket forged pistons are not made by mold... I belive they are CNC out of a solid piece of material... Check out JE's page they have a video of the machines making the pistons, and if this is so then I highly doubt that the pistons size will vary between series unless the design itself was changed. Not mentioning the few times those pistons have to me measured to pass ispection before they get shipped out.....IMO
I do agree that he needs to check his block for out of roundness, etc.. but as far as piston bore size they should be the same.
Status- Need to do break-in...
Try not to challenge me, I'd rather tie up than lose. Either way you NEVER WIN.... - Me..
#129870, "RE: Pistons/bore size" In response to Reply # 9
yeah i agree, forged pistons are machined and SHOULD be reasonably close to the same size as the old ones. if there isnt very many miles on the block you might be alright to just drop in the new pistons, but i wouldnt. while its all apart it is a good idea to just do it right so you dont have to redo it all 1000 miles down the road. shouldnt be too much work though, may need to rehone the bores...also check the piston to wrist pin oil clearance. good luck
#129876, "RE: Pistons/bore size" In response to Reply # 9
Originally posted by Cyexmaster
Originally posted by Star Turbo Talon h. A manufacturer can make a series of pistons at a given size.....eventually the MOLDS wear out
As I understand JE and most aftermarket forged pistons are not made by mold... I belive they are CNC out of a solid piece of material... Check out JE's page they have a video of the machines making the pistons, and if this is so then I highly doubt that the pistons size will vary between series unless the design itself was changed. Not mentioning the few times those pistons have to me measured to pass ispection before they get shipped out.....IMO I do agree that he needs to check his block for out of roundness, etc.. but as far as piston bore size they should be the same.
Makes total sense, terry said "molds" and my mind locked on that, lol. So, they are JE 8.8:1 .020 over brand new pistons. The block has only 2,000 miles on it, do you really think it needs to be rehoned? As of right now, the crank, flexplate, oil pump, crank sprocket, and udp (inner detatchable part) are all still installed. If I absolutely need to, I will disassemble all of it, but I just don't have enough experience to make that judgement call. Based off of all that info, am I safe to put the new pistons in since they are basically replacing the exact same pistons (brand, bore, and compression)? Thanks for the help guys.
Search
Printer-friendly copy
3 Users in Chat
good luck