Bottom End Question
01-24-2004, 07:02 PM
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Bottom End Question I dont mean to be a pain but im learning. Now, do you guys get piston slap fixed cuz it causes problems or cuz its annoying? What can i do to take care of the piston slap? From what i herd i have to redo the bottom end. the car is under warrenty but i really dont want a dealer touching my car. I dont know one dealer up here where your car will come back in better working condition then you brought it. Also, if you guys know of any good shops in the nj area that can do performance installs and tuning, please let me know.
Last edited by PG45; 01-25-2004 at 10:46 AM.
01-27-2004, 10:41 PM
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Staging Lane
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Piston Slap Fix Hi,
Piston slap is the piston rocking over from the minor thrust side to the major thrust side at combustion. It is worse when the car is cold because the piston-to-wall clearance is greater so the piston can rock over further from side to side. The fix is a tighter piston-to-wall clearance and that takes a different piston or coating the current piston. Either way you’re taking the piston out.
To find which piston is slapping, pull plug wires one at a time and you will hear the noise go down when you hit a loose cylinder because the combustion pressures are not pushing the piston over to the major side.
If the clearance is close, you can try to find a bigger piston or coat the existing piston. Chevy buys a new set of pistons and uses only the biggest one of the set to tighten up the offending bore on some warranty jobs. That’s not very cost effective for us. You can mod your existing piston by coating the skirts. Talk to a coating company about the options. You can find coatings from a few 10ths to several thousands of an inch but I think you talking ~0.0005” on the skirts. Chevy runs the late coated pistons as close as ~0.0000” clearance when the coating is new! That ought to be tight enough! With this option, on a low miles engine, you can reuse the existing rings if you re-install them in the same position that they where taken out, and you don’t touch the cylinder walls. If your engine is an oil burner, use the late replacement Chevy rings that have a much-increased oil ring tension. Chevy uses a ball hone, in this case, to condition the cylinder walls.
If the cylinder is out of spec, you can have it honed oversize using the .010” over Chevy piston, but the block is coming out of the car. (Some of the Mercedes dealers use a service to hone in the car.) I am not sure if the weight of the 10-over piston is the same as a standard bore, so check the weight of the piston. Chevy does not match-balance the stock pistons, they are produced close enough for the General.
The third alternate is to just go for aftermarket pistons. Finding a local shop that knows the difference between a SBC and an LS1/6 can be a challenge.
To do this job yourself, you will need a shop manual for specs and guidance, a dial bore gage to measure the bores, a 3-to-4” micrometer to measure the pistons plus all the tools to tear the engine apart. This is not a weekend project.
Good luck,
Steve
Piston slap is the piston rocking over from the minor thrust side to the major thrust side at combustion. It is worse when the car is cold because the piston-to-wall clearance is greater so the piston can rock over further from side to side. The fix is a tighter piston-to-wall clearance and that takes a different piston or coating the current piston. Either way you’re taking the piston out.
To find which piston is slapping, pull plug wires one at a time and you will hear the noise go down when you hit a loose cylinder because the combustion pressures are not pushing the piston over to the major side.
If the clearance is close, you can try to find a bigger piston or coat the existing piston. Chevy buys a new set of pistons and uses only the biggest one of the set to tighten up the offending bore on some warranty jobs. That’s not very cost effective for us. You can mod your existing piston by coating the skirts. Talk to a coating company about the options. You can find coatings from a few 10ths to several thousands of an inch but I think you talking ~0.0005” on the skirts. Chevy runs the late coated pistons as close as ~0.0000” clearance when the coating is new! That ought to be tight enough! With this option, on a low miles engine, you can reuse the existing rings if you re-install them in the same position that they where taken out, and you don’t touch the cylinder walls. If your engine is an oil burner, use the late replacement Chevy rings that have a much-increased oil ring tension. Chevy uses a ball hone, in this case, to condition the cylinder walls.
If the cylinder is out of spec, you can have it honed oversize using the .010” over Chevy piston, but the block is coming out of the car. (Some of the Mercedes dealers use a service to hone in the car.) I am not sure if the weight of the 10-over piston is the same as a standard bore, so check the weight of the piston. Chevy does not match-balance the stock pistons, they are produced close enough for the General.
The third alternate is to just go for aftermarket pistons. Finding a local shop that knows the difference between a SBC and an LS1/6 can be a challenge.
To do this job yourself, you will need a shop manual for specs and guidance, a dial bore gage to measure the bores, a 3-to-4” micrometer to measure the pistons plus all the tools to tear the engine apart. This is not a weekend project.
Good luck,
Steve