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That's exactly what I assumed. Thanks for the answer.
I have been toying with the idea of going with this S12 kit...http://rogersmotorcycleparts.com/cb160.htm...but I think the complications of fitting those pistons and getting it to run properly are plentiful.
Could your average machine shop bore out my block for those pistons?
An average machine shop may not be able to go that small. You'll need an average motorcycle machine shop.
Quote from: MCRider on October 28, 2009, 09:42:16 amAn average machine shop may not be able to go that small. You'll need an average motorcycle machine shop.When I Googled "CB160 big bore kit" I read this on the first result:"This high compression kit requires careful installation by a qualified race mechanic. Pistons will need to be clay checked and possibly modified to fit your specific engine configuration."I have no idea what "clay checked" means. It's also worth noting that it might not be the same big bore kit.
High compression and big bore are two different things, though often you get both with a big bore kit. Clay checking is what they used to do (and still do?) to check that the higher dome of the high compression piston doesn't hit the valve. Assemble the motor with a layer of clay on the piston tops, turn it over, disassemble and see if the valves left an imprint in the clay.YOu wouldn't need to do it with a 836 kit on a 750 for example as they are all made to fit. Now if you put a high lift cam in with the 836 kit, you'd be wise to do something to be assured they wouldn't hit. Or take the word of someone with the same set up or of your vendor.
Quote from: MCRider on October 28, 2009, 10:46:44 amHigh compression and big bore are two different things, though often you get both with a big bore kit. Clay checking is what they used to do (and still do?) to check that the higher dome of the high compression piston doesn't hit the valve. Assemble the motor with a layer of clay on the piston tops, turn it over, disassemble and see if the valves left an imprint in the clay.YOu wouldn't need to do it with a 836 kit on a 750 for example as they are all made to fit. Now if you put a high lift cam in with the 836 kit, you'd be wise to do something to be assured they wouldn't hit. Or take the word of someone with the same set up or of your vendor.INTERESTING. So, in other words, a big bore kit won't necessarily have the higher dome?
That's right, case by case. You cna have a big bore kit with a relatively flat dome or big dome, just depends on whose making it and what the intended use is. AS mentioned before, you'll get some bump in compression ratio from a flat dome big bore kit just due to the fact you've got a larger volume of mixture in the cylinder squeezing into the same size dome in the head. So a 10.25 to 1 big bore kit may not have much of a dome on the piston at all, while a 12 to 1 would. Still if you don't have a very secure source of info that you trust, you would need to clay check or the modern equivalent, to be sure.
Quote from: MCRider on October 28, 2009, 11:14:43 amThat's right, case by case. You cna have a big bore kit with a relatively flat dome or big dome, just depends on whose making it and what the intended use is. AS mentioned before, you'll get some bump in compression ratio from a flat dome big bore kit just due to the fact you've got a larger volume of mixture in the cylinder squeezing into the same size dome in the head. So a 10.25 to 1 big bore kit may not have much of a dome on the piston at all, while a 12 to 1 would. Still if you don't have a very secure source of info that you trust, you would need to clay check or the modern equivalent, to be sure.Awesome, thanks. So, if someone were to say this..."Try to avoid the Hap Jones big bore kit for the 160, it lowers the compression to 8:1 for some reason. I haven't look at the HJ pistons, but they probably have a low crown."...it would almost have to be user-error as a big bore kit could never lower the compression if installed properly?
No.A big bore kit could have dished pistons, or weird, wrong wrist-pin to deck height, etc. This would lower compression.Bore is the diameter of the cylinder. Has nothing to do with height, shape, or anything BUT diameter of the piston.
In a CB160 that needs new pistons and has never been bored, is there much of a horsepower gain between a S1 .25mm and S3 .75mm overbore?Thanks!Adam
