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need help after rebuild. no compression. rings stuck on piston

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  #11  
Old 05-26-2012, 04:41 PM
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If the bore looks good besides a few lines. The size of the bore when it came from the shop should be still there and measurable. The piston at this point probably isn't the same size it was when you installed it. So checking actually clearance with that piston will be pointless probably.
But the bore should be close to the nominal size. As the clearance with a wiseco piston comes from it being "undersize" in this case .003" as the box sates for clearance. So if it is a +.50mm(.020"), the bore should measure 72.50mm(2.8543")

most piston cylinder clearance is setup this way. aftermarket cast pistons seem to differ from this at times. The few factory yamaha four-stroke pistons I have done bore jobs for have had the clearance in the bore, with the piston on size.
 
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Old 05-28-2012, 04:08 PM
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so should i order another wiseco or get a cast piston. i doubt the machine shop will try to help me out at all.
 
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Old 05-28-2012, 05:08 PM
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Just have the piston measured if there are no score marks or seizure marks on it. Take the cylinder and piston back to whoever bored it out in the first place to have them double check their work. The rings stuck for a reason! Either the cylinder bore is too tight, not enough oil around the piston rings in the first place, rings upside down, something wrong you may have missed on the bottom end,etc. You might just be able to hone the cylinder slightly if it isn't scored bad (as you said it wasn't) and only have to get a new set of rings and gaskets if you can salvage the piston. Most machine shops can at least give you a reason what may have happened even if they can't or won't guarantee just a bore job (most won't on a partial engine repair) Better than having any of us on the forum just speculating what may have happened or what needs to be done!! OPT
 
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Old 05-30-2012, 08:44 AM
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so i took it back to the machine shop and he said everything looks good. said i installed the rings upside down. i showed him the note in the box that said there is no up or down to the rings. he said doesnt matter what the note says, the rings are up side down. said there is no damage to piston or cylinder flip the rings over and reassemble
 
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Old 05-30-2012, 10:11 AM
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The rings should have an "N" or an "R" and the oversize lightly printed on the end and this side goes up. Sometimes hard to see! Haven't seen any Wiseco piston that the rings weren't marked! The rings are beveled(chamfered) so the rings will scrape and seal against the cylinder wall. You're not the first or last person to do this! Your choice on whether to try reuse or just get a new set of rings,but you will need a new base and head gasket any way! OPT
 
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