I've seen .0008" recommended and i'd agree that would probably be what i asked for if i overbore to remove the scratch in cylinder 2. But the manual says the service limits are 2.4055" and 2.3957" for the cylinder and piston respectively, which i fit within. I believe i have the original standard pistons (see pictures), i'm assuming those are cast and not forged?
I'm not gonna say my measurements are exact as i'm using fairly cheap equipment so the actual measurement could be +/- a few thousandths but the wall to wall clearance should at least be fairly accurate as i was using the same micrometers for all measurements. I did repeat measurements and they all came out within a few tenths of each other if not the same. Also, its currently 40 f in my garage so the pistons and potentially the cylinders could be measuring slightly smaller than there normal value at a more reasonable temperature of 70 f or so.
Good job..
You’re on the right track..
I like to zero the taper indicator in the bottom inch of the cylinder opposite the piston’s major and minor thrust sides.
Yes that means it’s in line and parallel to the where the piston pin would be traveling. This should be the original bore diameter from Honda because no rings or piston shirts have traveled here.
Still in the bottom 1 inch of the cylinder bore, then I rotate the indicator 90* so it measuring between the major and minor thrust sides. Where the piston shirts have/may have worn the bottom of the cylinder bore. Record the indicator reading and compare to your zero sideways reading. If there is any difference this is how much the bottom of the cylinder is worn egg shaped.
While still in the bottom 1 inch of the bore slowly and still measuring the minor and major side of the cylinder wall, slowly draw the taper gauge steady up the cylinder to the top ring groove while monitoring the total movement of the indicator. From the bottom to top indicator readings is total taper, record reading. Subtract top ring groove indicated reading from sideway zero set up. This is total wear from original bore. Turn indicator 90* to measure for egg shape at top of bore. If any difference record. If you can repeat the measurements your set up is valid.
With the taper gauge still zeroed from the sideways bottom 1 inch cylinder bores zero, find and measure the piston’s shirt’s largest diameter perpendicular to the pin and lock the outside micrometer’s lock mechanism. Place the still zeroed taper indicator between the outside micrometer’s pads. This is your piston to cylinder wall clearance at the bottom of the cylinder.
Rezero taper indicator at the top ring groove or largest area indicated by your taper gauge. Then place the taper gauge between the pads of your still locked outside micrometer. This is your piston to cylinder wall clearance at the top of the cylinder..
This is the same or similar procedure used by many because it eliminates most inconsistencies and stacking of errors..
Egg shape cylinder’s adds its own compromises to this also but usually it all gets looser as you go up in the used cylinders.
Thats where using forged piston may allow you another option if your clearances are getting close to the replacement size.. The forged pistons generally need quite a bit more piston to cylinder wall clearance new. As compared to 0.0008 cast minimum clearance. Your forged piston manufacturer will recommend the preferred clearance for the intended usage. Racing, street, blown, etc.. but even with iron sleeves and an aluminum block forged pistons will require quite a bit more clearance depending on their alloy.. how much it could be 0.001- 0.002 thousands more. Basically making a worn out cylinder new size for a forged piston application…
For example a stock mid 70’s 350 4inch cast SB Chevy piston could be fitted as tight as 0.0008 to as loose as 0.0018.
But the factory gm 4 inch TRW forged T slot piston required at least 0.0035 minimum and you had to break them in properly so they would heat cycle season (shrink) before any sustained wide open throttle operation.. And a high performance TRW drilled oil holes returns (no T slot drains) piston required 0.0045 minimum and up to 0.007 depending on boost and or nitrous.. so what I’m implying is forged pistons generally can/may allow you to use a junk block (for cast pistons) as a new block for forged pistons.
