Do .010" over pistons exist (did they?)
02-03-2004, 10:23 PM
#1
Melting Slicks
Thread Starter
Do .010" over pistons exist (did they?)
Pulled a head today - after wiping the carbon off the ridge I measured 4.010". The pistons are GM 3795704. I don't think I've ever seen a .010 piston. Is is possible to bore to 4.010 and then use STD pistons?
Thanks,
Brian
Thanks,
Brian
02-03-2004, 11:34 PM
#2
Instructor
Member Since: Sep 2002
Location: Seattle WA
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Re: Do .010" over pistons exist (Allcoupedup)
Hello Allcoupedup,
You might want to get a (telescoping bore ) snap gage or an actual bore diameter gage, and definitely measure farther down in the bore; at least an inch or so from the deck. Meaure poarallel with the crank axis and then perpendicular to it. Compare the two readings while keeping in mind out-of-roundness and wear due to piston thrust. You might be measuring the results of someone's previous ridge reaming effort. You can get 0.010 in over pistons, but they are not as popular [=more $] as 0.020 in or 0.030 in over due to the reduced likelihood of the bores "cleaning up" with such a small overbore. Machinists hate that scenario because they have to go back, re-set up, and re-machine to the next oversize.
Hope this helps.
Dyna
[Modified by Dyna, 5:04 AM 2/4/2004]
You might want to get a (telescoping bore ) snap gage or an actual bore diameter gage, and definitely measure farther down in the bore; at least an inch or so from the deck. Meaure poarallel with the crank axis and then perpendicular to it. Compare the two readings while keeping in mind out-of-roundness and wear due to piston thrust. You might be measuring the results of someone's previous ridge reaming effort. You can get 0.010 in over pistons, but they are not as popular [=more $] as 0.020 in or 0.030 in over due to the reduced likelihood of the bores "cleaning up" with such a small overbore. Machinists hate that scenario because they have to go back, re-set up, and re-machine to the next oversize.
Hope this helps.
Dyna
[Modified by Dyna, 5:04 AM 2/4/2004]
02-04-2004, 08:37 AM
#4
Le Mans Master
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Re: Do .010" over pistons exist (Dyna)
Thanks for the info. I have an .008 (worst cylinder) over 390/427 that I am using for a utility table in the garage. :D
02-04-2004, 09:01 AM
#5
Burning Brakes
Re: Do .010" over pistons exist (Allcoupedup)
The answer to your question is yes. Not only .010 but .020 as well. These were GM only, not available from TRW. I bought .010 and a set of .020 for my 68 Z/28 motor.
I noticed from the pic you are measuring at the top of the bore where the rings do not contact. That should be a fairly true indicator of the bore size before wear sets in. A dial bore gauge will give you the size up and down the bore and show any taper. Unless you have $1500 you want to invest in one of those, your friendly machine shop can help out.
I noticed from the pic you are measuring at the top of the bore where the rings do not contact. That should be a fairly true indicator of the bore size before wear sets in. A dial bore gauge will give you the size up and down the bore and show any taper. Unless you have $1500 you want to invest in one of those, your friendly machine shop can help out.
