Hey guys, i'm just doing a piston/rod build on my b16. It was completely stock when i pulled it, and the sleeves look great, there is still crosshatch visible. I want to just hone it and slap in some srp's, but i was curious what my piston to wall clearance will be. The stock pistons looked like they had like one thousanths, and i know about 4 thousanths is pretty optimal for turbo. I really don't want to bore because i would like to keep as much meat on the sleeves. TIA

 

you wont know til you get your pistons and measure them.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boostedcivicsir &raquo;</TD></TR><TR><TD CLASS="quote">you wont know til you get your pistons and measure them. </TD></TR></TABLE>

Correct. Also, you'll be taking off very little material with setting the proper clearances so do it right the first time or have fun doing it again later down the road.

 

is piston wall MEASURED or CALCULATED or BOTH?

if its calculated, how is it calculated?

 

By subtracting the piston diameter from the cylinder diameter... 4 thousandths is too much, you will have slap if you have that much clearance.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nonvtecD &raquo;</TD></TR><TR><TD CLASS="quote">By subtracting the piston diameter from the cylinder diameter... 4 thousandths is too much, you will have slap if you have that much clearance.</TD></TR></TABLE>

so if i got a 81.5mm bore, and i measure piston #1 and it comes out as 81.496mm, thats my piston to wall? (.004)

then does that mean the ACTUAL bore diameter for cylinder #1 will be 81.508mm?

how i got that was by taking the piston to wall clearance X 2 to cover the full diameter of the piston....are my concepts and calculations correct so far?

so im assuming that u measure the bore of the block and the diameter of the pistons BEFORE having it bored?

 

no, your wall would theoretically be 81.5mm. you're thinking of radius, which has to be multiplied by two.

edit: yes you measure first so you can bore the cylinder to the correct size for each piston.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kyden &raquo;</TD></TR><TR><TD CLASS="quote">no, your wall would theoretically be 81.5mm. you're thinking of radius, which has to be multiplied by two.

edit: yes you measure first so you can bore the cylinder to the correct size for each piston. </TD></TR></TABLE>

so can you give me a detailed description with the #'s i used in my previous post?

thanks!

 

youre calculations are correct but like they said 4 thousanths is a little to much

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 94civicgsr &raquo;</TD></TR><TR><TD CLASS="quote">youre calculations are correct but like they said 4 thousanths is a little to much</TD></TR></TABLE>

right, but i was just using those calcs as an example......

anybody else?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kyden &raquo;</TD></TR><TR><TD CLASS="quote">no, your wall would theoretically be 81.5mm. you're thinking of radius, which has to be multiplied by two.

edit: yes you measure first so you can bore the cylinder to the correct size for each piston. </TD></TR></TABLE>

if its THEORETICALLY 81.5mm then what would it PRECISELY be? 81.508mm??? (according to my calculations)

 

its whatever reading you get from measuring it. if you want a .0035 gap, then take whatever measurement you get from your piston, and add .0035 to it.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AaronJ &raquo;</TD></TR><TR><TD CLASS="quote"> I really don't want to bore because i would like to keep as much meat on the sleeves.</TD></TR></TABLE>Ok first off you cannot have the cyl's bored and stay at the stock piston size.A boring bar can only be accurate upto a few thousandths,and then you still have to hone the bore for crosshatch so that means oversizes pistons with any boring.
The standard amount of material left after boring is .005 and the rest is honed to size.If you don't have enough p/w clearance then you will need to hone the needed amount out.
In most cases the piston company will have the pistons sized to fit the bore with their desired amount of p/w clearance and you don't have to worry about it unless you have an application they aren't used to having their pistons run in.
Today's cnc machines are very accurate unlike the old days when they were cut on manual machines and the operator had to control the tolerances.Usually the problem isn't not enough it's too much clearance.
But this is not to say you shouldn't check them.We can all make mistakes even piston companies.

You measure piston to wall by measuring the cyl's bore and then measuring the piston at the manufacturer's desired location per the instructions and subtract the two.It's just like any other clearance measurement-mains rods,etc.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Fkned &raquo;</TD></TR><TR><TD CLASS="quote">
You measure piston to wall by measuring the cyl's bore and then measuring the piston at the manufacturer's desired location per the instructions and subtract the two.It's just like any other clearance measurement-mains rods,etc.</TD></TR></TABLE>

After you subtract the piston diameter, from the bore diameter, and come up with .xxxx, what do you do with that answer? Do you have to add it into the bore diameter? Im not an engine builder by any means, hence the reason im asking the questions. Is piston to wall clearance not measured by sticking .XXXX feel gauge between the piston and the cylinder wall?

 

Holy thread hijack! i'm glad someone is getting some info. And mr meangreenmachine...your making it 9x harder than it needs to be. Measure the cylinder bore, you will get a number. Measure your piston at the location of where the piston manufacturer suggest, take that bore number, and subract it by the piston number...thats your clearance. After you subract the piston diameter from the bore diameter, and come up with .xxxx THAT IS YOUR CLEARANCE, that number.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AaronJ &raquo;</TD></TR><TR><TD CLASS="quote">Holy thread hijack! i'm glad someone is getting some info. And mr meangreenmachine...your making it 9x harder than it needs to be. Measure the cylinder bore, you will get a number. Measure your piston at the location of where the piston manufacturer suggest, take that bore number, and subract it by the piston number...thats your clearance. After you subract the piston diameter from the bore diameter, and come up with .xxxx THAT IS YOUR CLEARANCE, that number.</TD></TR></TABLE>

Im not an engine builder by any means and im trying to get as many resources as I can before tackling my first engine build after the piston to wall clearance has been figured and calculated, from there, do I proceed to have the machine shop bore the block out to the diameter that I want for each piston?

EX:
1. Measurement of cylinder bore =81.5mm
2. measurement of piston = 81.499
3. measurment of cyl bore - measurement of piston ( 81.5 -81.499) = .001 &lt;&lt;&lt;this # is the piston to wall clearance

then that piston to wall clearance # gets added to the piston measurement to get the # you should be reading when u measure your bore with a dial bore gauge after the block has been bored? yes? no?


Modified by MeanGreenMachine at 8:41 AM 2/7/2008

 

You want your cylinder bore to be about .004" or .0035" bigger than your piston when its all said and done. Its basically what you said, but you said it much more difficult and confusing. Take the measurement of your pistons, add .0035" or .004" and that is how big the bore needs to be.

If you are having this done at a machine shop, which i assume you are, just drop off the pistons and the block, ans say "i want .004" clearance" and they will get it done, plain and simple.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AaronJ &raquo;</TD></TR><TR><TD CLASS="quote">You want your cylinder bore to be about .004" or .0035" bigger than your piston when its all said and done. Its basically what you said, but you said it much more difficult and confusing. Take the measurement of your pistons, add .0035" or .004" and that is how big the bore needs to be.

If you are having this done at a machine shop, which i assume you are, just drop off the pistons and the block, ans say "i want .004" clearance" and they will get it done, plain and simple.</TD></TR></TABLE>




THANKS!

 

i know cp has the ptwc built in..so you get a 83.0 mm piston bore and hone to 83.00 not sure about other brands... i have done several rebuilds using the same stock pistons over again and just nock the glaze off with a dingle berry hone and re ring the motor and they have allways been strong and no sealing or smoking issues...

 

You guys need to remember to convert your units. When a piston asks for .0035 clearance it is .0035 of an inch and not of a millimeter!

So...
81mm = 3.189in
3.189in or whatever your bore size is minus the piston diameter in inches will give you the piston to wall clearance. If its too small you will need to bore it out some.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by champLSinteg &raquo;</TD></TR><TR><TD CLASS="quote">You guys need to remember to convert your units. When a piston asks for .0035 clearance it is .0035 of an inch and not of a millimeter!</TD></TR></TABLE>

true.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by champLSinteg &raquo;</TD></TR><TR><TD CLASS="quote">You guys need to remember to convert your units. When a piston asks for .0035 clearance it is .0035 of an inch and not of a millimeter!

So...
81mm = 3.189in
3.189in or whatever your bore size is minus the piston diameter in inches will give you the piston to wall clearance. If its too small you will need to bore it out some.</TD></TR></TABLE>

Yep, i'm not sure who would be dumb enough to think you would need .004 of a millimeter though, if they do...they really shouldn't be assembling a motor

 

I'm no engine builder either but i'm pretty sure piston to wall clearance is relative to the application. Meaning if you are trying to make a ton of power, you will need more ptw clearance because of piston expansion. I'm sure it depends on the pistons as well, but for some applications I don't think .004 is too large.

 

Anybody who thinks .004" is too big probably hasn't done much high hp stuff.

Take a look at the GM build book and see what they're running their race motors at...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tony1 &raquo;</TD></TR><TR><TD CLASS="quote">Anybody who thinks .004" is too big probably hasn't done much high hp stuff.

Take a look at the GM build book and see what they're running their race motors at...</TD></TR></TABLE>

But their builds don't generally have anything smaller than 100mm pistons, nor do they do much endurance racing...

I recall some guys mentioning running &gt;.005 for weekend street/race Hondas and being fine. The main thing to be concerned about is that the cylinders are true (wall parallel-ness). You could have perfect clearacne at the top, but have ovaled walls in the middle. Its easiest just to spend $50 to have a machine shop look it over & hone it exactly to your pistons.