Just curious bc right after the dyno numbers that i put down, in my sig.. We took the block apart bc it was burning 2 quarts every 3 days and the PTW clearances were 5 thousandths at the bottom and over 10 thousandths at the top of the piston. max clearance should be 5 thousandths i think. How much power could be lost bc of this?

 

Too much. Bore it out or sleeve it and buy new pistons and rings.

 

wow.
what kind of pistons do you have in there?forged?

 

They where forged JE 12.5:1 84mm bore and yea i had to resleeve it and increase the bore again. Im surprised the motor even ran somewhat quietly with that big of clearance issues in the first place. But can any significant power be lost from this?

 

Huh? I thought you were expressing PTWC as a means to determine the straightness of a cylinder. My bad if that's the case.

Btw, some pistons are measured 90 degrees from the pin hole but it's up to the piston manufacturer to determine how you actually measure a piston. Many pistons are cam ground, meaning they're slightly oval in shape. I wouldn't use top ring land to cylinder wall clearance as a means to determine piston wear. Some top lands are intentionally machined slightly smaller anyway.

Forged pistons grow the most, far more than cast and especially glass pistons, so they require much greater clearances.

 

well, power thats scaping through the rings is lost power; so im mean...
thats a shitload of ptwc. shouldnt your clearance be around 3 thou.

 

yea clearance should be round 4 or so, least i can hope for some better numbers next round at the dyno

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 1BadCvC &raquo;</TD></TR><TR><TD CLASS="quote">yea clearance should be round 4 or so, least i can hope for some better numbers next round at the dyno </TD></TR></TABLE>

are you spraying? if not then i would go the smallest ptwc that the piston allows for. im not sure what JE calls for.

 

How exactly can you cone the top of the cylinder but keep the bottom without tolererance? Piston slap? sideloading forces?

 

usually when you run lots of tolerance the cyl. will oval shape.

 

Ah, oval. I had a picture of a perfectly round circle gaining diameter in my head.

An oval or out of round bore makes more sense.

 

that much wall clearance is costing you a ton of cylinder pressure.

..honing without a deckplate and hot hone fluid circulating will mean the block distorts when head is torqued and its hot.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mike_belben@yahoo.com &raquo;</TD></TR><TR><TD CLASS="quote">
..honing without a deckplate and hot hone fluid circulating will mean the block distorts when head is torqued and its hot. </TD></TR></TABLE>

most hondas are open deck design...

 

Agreed. That would be true on a closed deck sbc where the head literally bolts onto the cylinder walls. Much less true on other closed deck designs where the bolts grab along the block's inner and outer walls (traditional Pontiac V8, etc.). It's irrelevant on open decks where the head bolts to the block's inner and outer (front and rear, left and right?) walls.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hybrid2nr &raquo;</TD></TR><TR><TD CLASS="quote">... It's irrelevant on open decks where the head bolts to the block's inner and outer (front and rear, left and right?) walls. </TD></TR></TABLE>

irrelevant is a strong word. i agree unnavoidable for closed cast iron decks and maybe something you can get away with on open decks, but still considerable for any engine if the hone is intended to be taper free to the tenthousandths place.. which should be a goal if nothing else. a high end honejob is done with a deckplate regardless. for skipping such a simple, easy, inexpensive step, i dont consider a shop who doesnt use honing plates to be high end or particularly specialized.

rereading the post and considering a whopping .005" taper, i will change my answer to:

"incompetent hone operator"