Piston taper = piston slap?
02-24-2005, 04:45 PM
#1
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Piston taper = piston slap? I just measured the diameter of my stock LS1 pistons at various locations.
At the very bottom of the skirt, I measure the piston to be 3.894". This is .005" of piston to bore clearance.
Just below the rings, I measure the diameter to be 3.889 (.005") less. This is .010" of piston to bore clearance.
In the ring area and above the ring area, the pistons are .050" smaller than this meaning they never contact the sides of the cylinders.
Is there normally a taper on stock pistons (skirt area)? or am I seeing wear? If stock pistons don't normally have this taper, the piston slap is clearly responsible for the tapering.
The bores appear largely unaffected. I measure them at 3.898 at the top of the cylinder (where I expect no wear at all) and I measure 3.899 at the bottom.
Has piston taper (at the skirt) come up before?
Comments?
Sam.
At the very bottom of the skirt, I measure the piston to be 3.894". This is .005" of piston to bore clearance.
Just below the rings, I measure the diameter to be 3.889 (.005") less. This is .010" of piston to bore clearance.
In the ring area and above the ring area, the pistons are .050" smaller than this meaning they never contact the sides of the cylinders.
Is there normally a taper on stock pistons (skirt area)? or am I seeing wear? If stock pistons don't normally have this taper, the piston slap is clearly responsible for the tapering.
The bores appear largely unaffected. I measure them at 3.898 at the top of the cylinder (where I expect no wear at all) and I measure 3.899 at the bottom.
Has piston taper (at the skirt) come up before?
Comments?
Sam.
02-24-2005, 07:45 PM
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Most piston clearance is measured 90 to the pin center line so if you measured 4.00 at the pin and then mesured 3.995 at the bottom of the skirt the skirt has colapsed.If you measure 4.00 at the pin and 4.005 at the skirt then you woild end up with .005 piston to wall clearance.In general the amount of taper indecates piston wall clearance.
02-24-2005, 09:23 PM
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Originally Posted by ROGERSPERF.
Most piston clearance is measured 90 to the pin center line so if you measured 4.00 at the pin and then mesured 3.995 at the bottom of the skirt the skirt has colapsed.If you measure 4.00 at the pin and 4.005 at the skirt then you woild end up with .005 piston to wall clearance.In general the amount of taper indecates piston wall clearance.
The diameter is larger at the bottom of the piston. and the piston bore clearance is thus 5 mil.
Thus, the skirt taper is there to compensate for heat differential from the factory.
The question is:
Is it normal to have such a large clearance? 5 mil? Seems pretty high to me. There aren't that many miles on these pistons. Until the piston gets hot, the gap higher is much larger 10 mil.
I thought the gap for stock LS1 pistons was supposed to be about 1.5-2.5 mil. Would this concern you?
Are after market piston better than this? I had a very noisy engine.
Sam.
02-25-2005, 05:48 AM
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Yes sam that is alot of clearance for a hyper piston there are normaly
.0008 to .0015.Thats why there was a recall on the LS1 because of piston nosie when you first start it.It is up to you if you want to run it that way back in the 60 and 70,s it was comen to have .006 to .008 clearance on forged pistons but with today technolgy now you see .004 to .006.So can you run it that way if the noise increses then the skirts are getting knocked in and you may end up cracking one off.In my opion if it was mine no i would have it fixed.
.0008 to .0015.Thats why there was a recall on the LS1 because of piston nosie when you first start it.It is up to you if you want to run it that way back in the 60 and 70,s it was comen to have .006 to .008 clearance on forged pistons but with today technolgy now you see .004 to .006.So can you run it that way if the noise increses then the skirts are getting knocked in and you may end up cracking one off.In my opion if it was mine no i would have it fixed.
