I just got my block back from my machinist--decked, bored to 75.5 (up from 75 d16a6) and a hone. I am using SRP 4.3cc dome pistons (4032)--For this bore size SRP calls for a piston to wall from 0.0022" to 0.0028"--I chose 0.0025". Now I specified this number to my machinist on 2 or 3 seperated occasions and also gave him a copy of the piston info sheet SRP sends with its pistons. I decided to measure the pistons and bore to make sure I have adequate clearance. I have a set of micrometers but I don't have a dial bore gauge--I do have snap gauges though. So when I measured the difference between the bore size and the piston diameter (btw I made sure to measure specifically where SRP says to which is 1/2" up from the bottom of the skirt) and even taking the "widest" measurements I am getting a clearance of 0.0018"--I took a number of measurements because snap gauges are hard to measure with properly--but all my measurements gave me a piston to cyl. wall clearance of 0.0015-0.0018. Could these numbers be off due to the fact I am using snap gauges? I really don't want to waste any more time on this, he took almost a month to do the machine work and didn't even do finish work like beveling the top of the cylinders. Its pretty upsetting because even to get him to do it over it would probably take another week (he now has a second job and does the machine work on the side) I am tempted to find a reputable shop and have them measure and re-hone if necessary. He also told me that the pistons are at zero deck (because I specified I wanted zero deck) and they are clearly at least 0.010" in the hole. I just want to know from people with experience if I can trust these readings I got, considering I used snap gauges to get them.

 

what's a snap gauge?

 

A snap gauge looks like a T. On either side is a spring loaded plunger--you compress the plunger, place it into say a cylinder, let it spring open, try to make sure its even and that you are measuring the largest diameter and twist the **** on top which locks it in that postion. At that point you take it out and take a standard (outside) micrometer and measure from one end of the t to the other--its sort of convoluted and sometimes its not very accurate.

 

Not accurate enough. I have a set but rarely ever use them, not for any critical measurements. In fact, i made a thread on here about setting main bearing clearances, i used a dial bore gauge, but for ***** and giggles i gave the telescoping gauges a shot, and they were horrible. The results would vary on the same housing bore by way too much from one check to the next for me to be comfortable with them.

 

Put your piston in the bore and hold it down just the 1/2 inch. Then see if a .002 feeler guage will go between. Then a .0025, and .003 that is the easies if you do not have inside mikes or dial bore guage. You can also set up the snap-bore guage in the mikes and try the feeler guage. You need to use snap-bore guages alot to get a feel.

 

No, I have neither inside mics or a dial bore gauge. I will try the feeler gauge with the piston. thanks.

 

Snap gauges can be as accurate as your mic.s with some experience.I feel they are within .0005" if your getting repeatable readings.Your doing the right thing by doing it several times to get repeatable measurements.There are times that snap gauges are the most practical way to measure things.Make sure your mics are calibrated with a standard.Two peoples "feel" on mics can easily very a couple of tenths.It's very easy to be off a half thou just from temperature.If your checking the block out in the garage that is 65* and the block was done in a shop that was 80* the measurements can change.Even taking the mics from your basement that's 75* and bringing them out to the garage that's 60* your measurements will change until everything balances out temperature wise.
If I was in you situation I would acurately check all four piston deck heights and bore clearences.If your .0005" below the min wall clearance I would have it honed a touch more.If your deck heights are .010" down I would have the block decked at the same time.

 

thanks for the info. Well the deck not being as low as I originally asked for is actually a blessing in disguise--I think I would prefer the 12.1-12.2 instead of the 12.5 I would get at zero deck--this way I can take full advantage without having to compromise my tune on the gas I am using which will be Cam2 100 octane unleaded. The bore situation is different--I am trying to get in touch with my machinist to see what happened and to see if there is a problem and what he can do about it. I have always heard about getting a "feel" for snap gauges will give you pretty accurate measurements.