Jrod324 Posted November 9, 2013 Report Share Posted November 9, 2013 K guys so i just figured out i cracked a piston my left one (yayyy Quote Link to comment Share on other sites More sharing options...
jbooker82 Posted November 9, 2013 Report Share Posted November 9, 2013 (edited) If it was a fresh top end he probably didn't measure the bore to see if it was out of spec. If the bore is to big the piston slams back and fourth from cylinder wall to cylinder wall as the crank rotates. Just because they are new doesn't mean its right. I would have the cylinders checked out or your probably going to be tearing it apart again. Edited November 9, 2013 by jbooker82 Quote Link to comment Share on other sites More sharing options...
Jrod324 Posted November 9, 2013 Author Report Share Posted November 9, 2013 If it was a fresh top end he probably didn't measure the bore to see if it was out of spec. If the bore is to big the piston slams back and fourth from cylinder wall to cylinder wall as the crank rotates. Just because they are new doesn't mean its right. I would have the cylinders checked out or your probably going to be tearing it apart again. So your saying to go get the cylinders checked out and see what size piston is suppose to fit properly in that bore without that much extra space? Quote Link to comment Share on other sites More sharing options...
Pastrykiller Posted November 10, 2013 Report Share Posted November 10, 2013 Yeahp! Quote Link to comment Share on other sites More sharing options...
KaN Powersports Posted November 10, 2013 Report Share Posted November 10, 2013 That piston is seized all of the way around it. It was either too tight of wall clearance, no oil, or you had a coolant leak. For the intake side to gall like that so soon I'd lay bet's on tight wall clearance. Wiseco has 'tightened' up the tolerances listed on their boxes (pistons that used to be specified for .003 clearance all of the sudden started coming saying .002)-I followed suit and had a few immediate failures-so I started adding .0005-.001 to their specs, depending on bore size, and have been fine since. Quote Link to comment Share on other sites More sharing options...
04_blu_shee Posted November 10, 2013 Report Share Posted November 10, 2013 I have my clearance set at .003 on Wiseco forged pistons. Be sure to warm the motor before you rip it at wide open. Quote Link to comment Share on other sites More sharing options...
sleeper06 Posted November 10, 2013 Report Share Posted November 10, 2013 As stated by kn wiseco recommendation on clearance or any piston for that matter is given for normal use in the case of a banshee these things are always screaming high rpm I always set them up a lil loose Quote Link to comment Share on other sites More sharing options...
KaN Powersports Posted November 10, 2013 Report Share Posted November 10, 2013 I think (speculation) one of the reasons Wiseco changed their recommended clearances was to stay competitive. With a Nikasil/cast piston combo, we started seeing the clearances tighten up to as much as .0005 (a half a thousandth of an inch)! I have mine in my play bike (cast piston in a stock cylinder) at .0015. Forged does expand farther than cast, and the holds it's dimension longer than cast under same temp. Therefore, the initial clearance needs to be compensated for (Main reason for cold seizing-it's pretty loose until warmed up). Cast has earned a bad rep for this reason! It just isn't logical to a seasoned engine builder that when warmed up a 0 tolerance, or in some cases 'interference' fit is acceptable. Then when the cast piston is set to an age old-accepted clearance, the skirts get broken off of them from being too loose in the bore!! Forged pistons are about the worst option imaginable in a sled engine-I have seen them seize with the engine shut off during a soda break! Especially in an aluminum/ plated bore. So, in an attempt to stay on this curve, Wiseco engineers step in and claim the same piston that used to be run at, say, .003 can now be set up at .002. That's where the trouble begins! They haven't changed the piston, just the set-up specs, and it is proving to be not as reliable. Like I stated earlier, I have added a bit of clearance to their 'new' numbers and have had great luck. Pistons machined out of solid billet (CP) do not expand as far as 'power forging', so again, I believe Wiseco is just fudging numbers a bit to stay comparative.. Keep in mind this IS just my personal opinion the matter, but has served me well..... But, as I stated earlier, in the case of the piston above. It looks to me, by one pic to go off of, that the particular piston was too tight in the bore. Quote Link to comment Share on other sites More sharing options...
Jrod324 Posted November 11, 2013 Author Report Share Posted November 11, 2013 I think (speculation) one of the reasons Wiseco changed their recommended clearances was to stay competitive. With a Nikasil/cast piston combo, we started seeing the clearances tighten up to as much as .0005 (a half a thousandth of an inch)! I have mine in my play bike (cast piston in a stock cylinder) at .0015. Forged does expand farther than cast, and the holds it's dimension longer than cast under same temp. Therefore, the initial clearance needs to be compensated for (Main reason for cold seizing-it's pretty loose until warmed up). Cast has earned a bad rep for this reason! It just isn't logical to a seasoned engine builder that when warmed up a 0 tolerance, or in some cases 'interference' fit is acceptable. Then when the cast piston is set to an age old-accepted clearance, the skirts get broken off of them from being too loose in the bore!! Forged pistons are about the worst option imaginable in a sled engine-I have seen them seize with the engine shut off during a soda break! Especially in an aluminum/ plated bore. So, in an attempt to stay on this curve, Wiseco engineers step in and claim the same piston that used to be run at, say, .003 can now be set up at .002. That's where the trouble begins! They haven't changed the piston, just the set-up specs, and it is proving to be not as reliable. Like I stated earlier, I have added a bit of clearance to their 'new' numbers and have had great luck. Pistons machined out of solid billet (CP) do not expand as far as 'power forging', so again, I believe Wiseco is just fudging numbers a bit to stay comparative.. Keep in mind this IS just my personal opinion the matter, but has served me well..... But, as I stated earlier, in the case of the piston above. It looks to me, by one pic to go off of, that the particular piston was too tight in the bore. Question is there a way to see and measure the cylinders or would it be easier to have a mechanic look at it.... And what pistons d you recommend that isnt too crazy on price because i have a decent budget but dont wanna go overboard.... By the way my friend has the same problem as me except his piston actually snapped and was told to open the shee engine to check for the snapped piece should i open mine up as well and see if amy metal grindings from the piston landed in my engine? Quote Link to comment Share on other sites More sharing options...
n2otoofast4u Posted November 11, 2013 Report Share Posted November 11, 2013 You will spend more money than you will ever save being a cheap ass 1 Quote Link to comment Share on other sites More sharing options...
KaN Powersports Posted November 11, 2013 Report Share Posted November 11, 2013 n2otoofast4u has a very valid point. It is an educated situation to know where you are being excessive, and where the extra expense is mandatory. Cast pistons are just fine for stockish engines (what came in it in the first place). If you start down the road of making it 'bigger, badder, faster', your parts selection WILL have to follow suit. To answer your question, on a good piston you measure it's OD about 1/4-1/2 inch up from the bottom on the skirt, and you measure the bore. Subtract the two findings and that's your wall clearance. When you are dealing with a range of .001-.005 you need to be somewhat accurate for this. Difficult to do with vernier calipers but achievable. Measure over and over until you get 'repeatability''. Calipers will be useless in determining if it is an out of round, or tapered bore. A bore gauge is needed for this level of accuracy. Quote Link to comment Share on other sites More sharing options...
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