imported_mugen_r

Hey guys, I have a few questions to ask.
I personally have assembled a few engines in the past but non required an overbore. I am going to be rebuilding two fairly high KM Honda engines but I'm just having a few problems understanding the over bore process.


ok, factory bore size on a d16 is 75mm...now from what I understand, there are two main overbore sizes that can be done .025 and .050
So if I were to overbore a 75mm engine by going .025, would that make the bore 75.25mm?

if the bore of the cylinder walls is 75.25mm...what size piston would I need to purchase.
Reason I'm asking is because on the first engine, I want to have the cylinder walls bored out by .025" but the pistons I was sent have 75.5 stamped on top of them.
Was I sent the wrong pistons? or am I all confused and lost?

thanks

imported_2join performance

You just have your measurements a little confused.

The two common boring sizes you refer to are .020" and .040". Thus if you bore .020" on a stock d16, you dont end up with 75.25mm. You need to convert inches to mm, and then add.

.020" = .5mm
.040" = 1mm

So if you want the cylinder walls bored out by .020", then you require the 75.5mm pistons, which you already have.

zeeman

iTrader: (1)

if you are unsure you could always contact the manufacturer and ask....or get out the ole trusty micrometer and check the piston yourself.
But if the pistons you've got are 75.50mm why not just bore it out to 75.50mm?

imported_mugen_r

Thank you! that explained it so good for me...now I fully understand. I was way lost on that aspect as I haven't needed to bore out any cylinder walls and these two engines will be the first for me to have done. Awesome and thank you again



Andrew, I was just lost on the measurements. How I was thinking, I thought I ordered the wrong pistons for the z6 rebuild and I'm starting that in 2 weeks. Just wanted to have this explained as I was pretty certain I was going to be wrong lol.


BTW: I'm not buidling my ls...I sold the car but I will need you to chip a P28 and if possible put a DOHC ZC map on it if possible soon!


Thanks guys

imported_mugen_r

One last question, so using a 75.5mm piston into a 75mm block bored out to .020", What about the piston-to-wall clearance spec or the piston ring specs?

Would that be fairly the same on all pistons that are 75.5mm or does it differ from piston manufacturer to manufacturer?

zeeman

iTrader: (1)

you should get a sheet with the pistons on what ring gap to use.
About the piston-to-wall clearance, its built into the piston basically, like if they need .005" of clearance, they'll make the piston .005" smaller than 75.50mm, this way the machine shop just has to bore the cylinders out to 75.50mm, to save any sort of confusion.
I got you covered for your ecu needs, let me know when you need it done.

imported_mugen_r

See now what I'm worried about...is the z6 engine, the owner picked up the 75.5mm pistons...but from Nippon Racing or NPR.

Pretty much the same piston brands you can pickup off ebay...the OEM replacements I belive.

Now when we got the pistons, I don't recall even seeing a paper/data sheet of any specs that I would need to provide to the machine shop for reference


these are the pistons the owner pretty much bought for the engine

http://cgi.ebay.com/ebaymotors/92-95...spagenameZWDVW

WTi

i would try to provide the piston to the shop boring the cylinders at the time you drop it off for boring. that way you know for sure the bore will be correct. it sounds like you did it the other way around though...

imported_mugen_r

...I didn't do nothing the other way around...nothing was done yet. I'm going to provide them the pistons/rings when the bore is done but I also want to give them the correct specs of the ring gap and whatnot.

zeeman

iTrader: (1)

they will know what to gap the rings to....there are specific standads for ring gap size and it depends on what the engines inteded use is.
A simple search on google will most likely yeild what you are looking for....or you could just have the machine shop gap the rings....if they even needs to be gapped, i know some rings aren't file-fit and don't need to be gapped.