After a tear down of my B18B , I noticed that my pistons have a decent size gap between the cylinders and the piston? The pistons are aftermarket SRP and the block is STD bore. My question is, do these expand and heat up to compensate? I measured the bore of the cylinder and the piston and they are fairly close. I left the numbers at my shop, but I will update. Just wondering how tight your aftermarket pistons fit. Not sure if these were the right ones, or the cylinders where honed too much. There was 5k on the motor. Motor has 9.1:1 comp and was turboed. It just appeared that most of the compression was taken on the rings..

Any input would be great, thanks.


Modified by x2gold at 6:15 PM 5/16/2006

 

The clearance is measured near the bottom of the skirt.The top of the piston is a lot smaller than the skirt if that is what your looking at.

 

to add to that a forged piston will expand more when heated up than a cast piston due to the amount of silicon in the piston also forged pistons have higer thermal expansion rates. also theLOWER THE SILICON CONTENT THE more piston-towall clearance you need. like a cast honda piston will need only .0004 to.0014'' clearance when a forged piston will need .0025 to .0030 ( these vary from company to company)

 

good, these are some answers I want to hear.. I was getting nevous as the pistons practially fell out with little pressure. All my big blocks I did, they were super tight but these were stock/ oem pistons... this was my first time with forged/ import. I'll check the clearances from teh skirt on the bottom, ..I hope they are tighter. Also, what do you use to check these clearances? A feeler gauge does not bend too well( esp in a round cylinder). Thanks again guys.

 

well, here are the specs, still a little confused. Bore measures 81mm, piston skirt (.6 in from bottom measures 81 mm. Top of the piston above the first ring and the top of the piston measures 80 mm? Is this how they are built? Does the piston expand this much?

 

bump, need some help...things just don't seem right. It's as if there would be too much pressure on the rings.

 

anyone with aftermarket pistons... bump for some help

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by x2gold &raquo;</TD></TR><TR><TD CLASS="quote">well, here are the specs, still a little confused. Bore measures 81mm, piston skirt (.6 in from bottom measures 81 mm. Top of the piston above the first ring and the top of the piston measures 80 mm? Is this how they are built? Does the piston expand this much?</TD></TR></TABLE>

Yes.That's the way they're made.