Hey, i just picked up a set of RS machines P73 pistons. They were supposed to be the 81.4mm overbore, but luckily I decided to wait for them to show up and mic them before getting the block bored. Anyway, when I actually measure them with a micrometer, they come out as a little under 81.99 if i carefully measure on a bare metal spot on the very edge of the skirt, which should be fine for an 82mm bore. However, if i measure them on the coated area, they are exactly 82.00mm, which is not ok.

So basically I am wondering if anyone has any input on what the correct bore size should be. Is the coating soft and slippery enough that the engine wont sieze once it warms up with that little clearance, or should I have the block bored to a little bit over 82mm?

 

You will bring the pistons to the machine shop with the block. They will determine how much to bore it by the size of the pistons.

 

Of course I am going to bring the pistons to the machine shop with the block. that still doesnt answer my question. The machine shop may not know what to do about the coating on the piston, so I was hoping to hear from someone on here who had some experience with this. Also, I would just like to know the answer.

 

anybody?

 

There is no special way to bore or install for those pistons. The machine shop should set the piston to wall clearance to factory specs. .001-.0015 will work fine. The coating is very thin and is meant to reduce friction, there is no issue with engine seizing or clearance changes.

 

You didnt read well enough before you bought. They are .040 INCH oversize not .4mm oversize. 0.40" is ~1mm = 82mm pistons.
Take the pistons with you to the machine shop when you have your motor bored and they will sort it out for you. If the RS pistons are anythign like Wiseco coated pistons they should have come with a spec sheet with a bore size.

 

Safety recomends .035mm/.0013 on their pistons.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Hardt &raquo;</TD></TR><TR><TD CLASS="quote">Safety recomends .035mm/.0013 on their pistons.</TD></TR></TABLE>

there you go

 

i ran the 82mm CTR's in my block but i had them bore the block accordingly

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by CRiXZc &raquo;</TD></TR><TR><TD CLASS="quote">You didnt read well enough before you bought. They are .040 INCH oversize not .4mm oversize. 0.40" is ~1mm = 82mm pistons.
Take the pistons with you to the machine shop when you have your motor bored and they will sort it out for you. If the RS pistons are anythign like Wiseco coated pistons they should have come with a spec sheet with a bore size.</TD></TR></TABLE>

Well, maybe you are right, but they were advertized as .40 over, so i kind of assumed they meant mm, since that would be about 10mm oversized.

They probably did mean .040, though, so you are probably right. It is hard to imagine what is going through a company's head when they decide to sell 81mm pistons .040" oversize. Pick a measurement system and stick with it, damnit!!