i originally wanted my cyl-wall clearance to be .0030-.0035. The machine shop went .0040. will that be an issue? (...84.5 mm cp pistons.)not even a noticeable play but should i be concerened?..........i know piston slap will occur but the loosness may cause less friction and faster revs........yay or nay??? let me know i dont wanna have to go 85 mm

 

Make them buy you a new block.

 

damm bro that sucks, what's the name of the machine shop?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vtecdamian &raquo;</TD></TR><TR><TD CLASS="quote">let me know i dont wanna have to go 85 mm</TD></TR></TABLE>

looks like you might have to!

 

i wouldn't worry about the extra clearance. cp pistons require .0040" piston to wall clearance @ .500" above the tip of the piston skirt on domestic applications, i'm not sure about the import application though. we always give the pistons anywhere from .0005" to .0010"+ more clearance then what the manufacture calls for, depending on the engine application we are building. that extra .0005" will help if you plan on running the engine hard

 

Piston clearance is a function of several things. The bore diameter of the engine is one. The larger the diameter of the piston, the more it'll expand, and therefore, the more clearance it'll need...ala a 4" or larger bore domestic piston.
The alloy the piston is made from also affects it's clearance. Pistons made from high-silicon alloys (4032) expand less than pistons manufactured from 2618.
The thickness of the skirt, as well as it's barrel-shape and "cam" ground in to define the skirt's contact area also control piston expansion (and friction).
You might be able to have the shirt's built up with a ceramic low-friction coating and get another half thousandth in piston diameter, but your rings are also going to have huge end-gaps with the clearance at .004".
Consider going to the next size overbore if possible, and tell the machine shop not to do you any "favors" next time.

 

I would suggest you go to the next bore size...

Tell the machine shop that you want them to pay for the difference in price of the pistons and do the next bore and hone for free...it's the least they can do for the extra week of downtime your going to have now waiting for the pistons to come in and returning the old ones..

Your pistons have almost no silicon in them so they will expand, perhaps you could get away with swain coating the sides of the pistons like larry said and getting a little bit back. But I would still be pissed at that machine shop for doing that. What's the name of that machine shop, so I remember to avoid them.

 

He's still have the ring end-gap issue, and of course, the excessive piston rock during warm-up will cause the rings' faces to wear round, making their seal ineffective in no-time.