<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tony1 &raquo;</TD></TR><TR><TD CLASS="quote">Coated pistons and clearances are fine if done the right way. Call the manufacturer of the coating being used and find out how the clearances should be set. It's not magic. If Wiseco says to set the clearances at .0025 over the coated piston o.d., then do it. The manufacturer will know how to set it up properly and will tell you. If they don't know, then you bought the wrong ****. lol Wiseco is who you should be talking to, not HT. </TD></TR></TABLE>

As I said before, I wanted to run a looser clearance because I am running a stock sleeve GSR motor plus its overbored a bit. Overboring will weaken the sleeves, even just a little. I'm trying to make EVERYTHING with this build go perfect. The recommeneded clearance would be fine under normal circumstances. My main concern at the start of the thread was the fact that this coating would NOT endure any engine use at all... period. Rubs off on my finger. The coating you see on a type-r piston does not rub off on your finger...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MatrixGSR &raquo;</TD></TR><TR><TD CLASS="quote">

As I said before, I wanted to run a looser clearance because I am running a stock sleeve GSR motor plus its overbored a bit. Overboring will weaken the sleeves, even just a little. I'm trying to make EVERYTHING with this build go perfect. The recommeneded clearance would be fine under normal circumstances. My main concern at the start of the thread was the fact that this coating would NOT endure any engine use at all... period. Rubs off on my finger. The coating you see on a type-r piston does not rub off on your finger...</TD></TR></TABLE>

I am assuming you are running different rings then the ones supplied because that should throw your ring gap off, correct?

 

I wish I had seen this last week when I dropped my block/pistons off. The place apparently does some work for King, so hopefully they know what's up. I guess I'll have to ask anyways.

 

I have a feeling this is why Wiseco recommends a bit tighter clearance than most other mfgs. While Wiseco specs .0025" piston to wall clearance, most of the other brands are atleast .0030". If the visible portion of this coating wears off then in reality we are looking at about .0030-.0035" p/w clearance.. right up there with everyone else.. correct? I'm running Wiseco in my build.. no problems as of yet. Everything was bored to Wiseco spec.

 

Exactly, if you set it up to wiseco's specs, they've accounted for the coating on their pistons. If you want to go .001 bigger than their specs, then go .001 bigger than their specs.

 

And is there anyone who knows the exact thickness of the coating that Wiseco uses? Just curious. Perhaps a measurement before and after?

 

I bet wiseco knows...

 

Hi there, Wiseco considers the coating used on shelf stocking parts to be a "break in" coating. It's there to help on initial start up and prevent problems associated with washing down the cylinder (injector/tuning problem). It's .0005" thick, so the recommended clearance was moved back to .0025" from .003" to get a net .003" "metal to metal". Because Wiseco's are Diamond turned for better skirt shape definition, there is a fine series of ridges going down the skirt and you'll find that the coating remains in the deep parts. Also, because Wiseco uses the stronger 2618 almost exclusively...they last longer (even with the basic coating) compared to other 2618 pistons because the silicon content is lower than 4032. The piston conforms to the bore better than uncoated.

If a customer is targeting over 600whp and a pin upgrade or otherwise is being considered, Wiseco also offers an upgrade coating on custom pistons (only) called Zylan. Much harder, does show a noticable improvement in horsepower in Wiseco's testing, and is usually a bit thicker at .0007-.0008". Because the pistons are done as custom, Wiseco and the engine builder decide on all the different factors to determine net clearance. If a guy needs .0045 "metal to metal" in 550whp+ "straight to the track at 30lbs" applications, Wiseco will build the pistons and coatings to net that number.

Do not feel the need to take the coatings off to get an accurate piston to wall clearance, you're doing more harm than good. If you do want "an extra thou.", just measure it to the outside of the coating and don't try to compare it to other aftermarket pistons because the forging design and skirt tapers aren't applicable to theirs or vice-versa. Expansion characteristcs are differnt because of that.

-Brian Nutter

 

 

Never the less, I still wanted a more slack clearance to allow extreme amounts of heat and stock sleeves. Even though there are much less things to worry about, this motor is strictly race and rarely street driven. Again, I appreciate all the responses and I feel a lot better.