Venolia piston to wall clearance 2.2/2.5

[going4speed]

that sounds like madness to me. you always want to size each piston to each bore.

[Shadow]

This may come as a Shock, but it's not going to be very often that machine work is Perfect. (and I'm talking about the Better machine shops out there)

So, you measure pistons and bore 4 holes. Those 4 holes are very rarely going to be Exactly the same. So you measure the finished holes and match the best fitting piston to each hole. (we are talking .001" or less)

If you're dealing with a sub standard machine shop, you could be talking .001" or more

I don't remember my machinist ever mention Venolia's being and further out of tolerance than any other popular forged pistons.

[acannell]

This may come as a Shock, but it's not going to be very often that machine work is Perfect. (and I'm talking about the Better machine shops out there)

So, you measure pistons and bore 4 holes. Those 4 holes are very rarely going to be Exactly the same. So you measure the finished holes and match the best fitting piston to each hole. (we are talking .0001" or less)

If you're dealing with a sub standard machine shop, you could be talking .0001" or more

I don't remember my machinist ever mention Venolia's being and further out of tolerance than any other popular forged pistons.

Yes this makes the most sense..except the 0.0001" part, I think you mean 0.001".

I don't know how most machine shops are typically boring cylinders, but getting 4 holes to within 0.001" of each other, and to a specific target diameter, over 6", is something that really requires a slower process than something that uses a cutter, more like grinding or honing. So I would think they are probably boring it to within a couple thou then honing it the rest of the way, so they can creep up on the target diameter. Its possible that they are using a cutter, but since they are going to hone it anyway, I would think honing would be the final sizing and surface finish operation rolled into one, you would get alot more control that way. Or there is probably some kind of Sunnen specially designed cylinder boring machine that somehow gets things done in one pass, who knows. Im sure there is a spectrum of equipment at machine shops from a $1k bridgeport to a $20k specialized machine, and probably just as many "techniques".

And then if you take your pistons and match them to the bores as close as you can, as Shadow describes, you can probably get a little closer, assuming the piston diameters and the resulting bore diameters (and your measurements) can be optimized to each other.

One thing I have learned after getting into machining is that there is no magic force field that you walk through when you take your engine parts into a machine shop, guaranteeing it all comes out great and "fixed". Pretty much the opposite of that. They will do whatever they feel like doing, including sizing you up to see if you are even capable of telling if they screwed up. If you dont know what you are doing and they smell that, they will most likely "take over" and just do things the way they think will work, which is probably better than what you are thinking anyway unless you actually know whats going on. And if they get the feeling you are going to inspect their work with a microscope, they will probably just tell you to go elsewhere.

I dont see why Venolias would have any more variance in manufacturing tolerance than any other piston. Talk to 10 machinists and you'll get 30 opinions about whats what.

[ajakeski]

I've used the same machine shop for over 20 years. Never had any issues.
They hone each cylinder to the final size required.

[Shadow]

Yes this makes the most sense..except the 0.0001" part, I think you mean 0.001".

I don't know how most machine shops are typically boring cylinders, but getting 4 holes to within 0.001" of each other, and to a specific target diameter, over 6", is something that really requires a slower process than something that uses a cutter, more like grinding or honing. So I would think they are probably boring it to within a couple thou then honing it the rest of the way, so they can creep up on the target diameter. Its possible that they are using a cutter, but since they are going to hone it anyway, I would think honing would be the final sizing and surface finish operation rolled into one, you would get alot more control that way. Or there is probably some kind of Sunnen specially designed cylinder boring machine that somehow gets things done in one pass, who knows. Im sure there is a spectrum of equipment at machine shops from a $1k bridgeport to a $20k specialized machine, and probably just as many "techniques".

And then if you take your pistons and match them to the bores as close as you can, as Shadow describes, you can probably get a little closer, assuming the piston diameters and the resulting bore diameters (and your measurements) can be optimized to each other.

One thing I have learned after getting into machining is that there is no magic force field that you walk through when you take your engine parts into a machine shop, guaranteeing it all comes out great and "fixed". Pretty much the opposite of that. They will do whatever they feel like doing, including sizing you up to see if you are even capable of telling if they screwed up. If you dont know what you are doing and they smell that, they will most likely "take over" and just do things the way they think will work, which is probably better than what you are thinking anyway unless you actually know whats going on. And if they get the feeling you are going to inspect their work with a microscope, they will probably just tell you to go elsewhere.

I dont see why Venolias would have any more variance in manufacturing tolerance than any other piston. Talk to 10 machinists and you'll get 30 opinions about whats what.

Well said Bro! And yeah, .001"! lol

Also, you are correct that they bore, then finish hone to spec.

[Warren Stramer]

If your favorite machine shop cannot get the finished bore size honed to within a couple of tenths (.0001) straight and round, Then you are not dealing with a machinist, but a blacksmith. You will need to find a better machine shop.

[acannell]

If your favorite machine shop cannot get the finished bore size honed to within a couple of tenths (.0001) straight and round, Then you are not dealing with a machinist, but a blacksmith. You will need to find a better machine shop.

Anything involving 100 millionths of an inch that does not involve a XX setting ring gauge, a calibrated bore gauge that measures in tenths, and a temperature stabilized room to measure in, is called "faith".

If that thing goes on to be bolted to something different than what it was machined to 100 millionths of an inch with whether that be a honing plate or nothing, raised in temperature 200F with hot spots galore and variable material thicknesses and attachments, and subject to 3000 psi pulses, now its called "dreaming".

[Warren Stramer]

Seriously, All my precision measuring tools and any professional engine builders tools measure and read in tenths of thousandths. to the nearest .0001
If you cannot measure critical parts to this tolerance get a different hobby.

[acannell]

Seriously, All my precision measuring tools and any professional engine builders tools measure and read in tenths of thousandths. to the nearest .0001
If you cannot measure critical parts to this tolerance get a different hobby.

Just because it reads in tenths does not mean your measurements are accurate to tenths. Pretty much any precision instrument has a way to be calibrated to a standard, and usually comes with a standard. What you get with an instrument that reads in tenths is repeatability and incremental accuracy, not absolute accuracy. The standard is where the absolute accuracy comes from and the calibration is how you transfer that accuracy to your instrument. Even my cheapo chinese ID micrometer came with 0.20000" @ 20C standard. Thats why there are XX ring setting gauges with precisions in single digit millionths of inches, specified at a specific temperature, its how you calibrate bore gauges and other ID measurement devices.

Steel expands 6 uin / in / F. So a 3.4" object changes size by .00002" every F. 5F and there goes 0.0001" in your measurement. Aluminum is twice that. Your instruments are also made out of metal and their error changes according to temperature (especially a dial bore gauge with several inches of reach).

A simple scenario where pistons are measured in a temperature controlled environment like a house, and a block is measured somewhere colder like a garage, and now you have some serious differences that could get up to 0.001". Add to that whatever error you have simply because youve never calibrated your instruments to a standard, and maybe you've been doing lots of measurements so the mic has started changing temperature since you calibrated it (assuming you calibrated it at all).

Its not difficult to make proper measurements. You just get into trouble when you ignore everything and think that they will just happen on their own. Do everything at a stabilized temperature. Calibrate your instrument to a standard that is more accurate than what you want to measure, and do it right before your measurement. Dont hold onto instruments any longer than needed. Use the right kind of instrument to measure what you are measuring. I've measured pistons with calipers and micrometers but its really not the right way to do it. They are tapered, you cant do it properly by hand if you truly want your measurement to be accurate to 100 millionths of an inch. But that accuracy isnt really required anyway.

If a shop isnt doing this then their measurements arent accurate to tenths.

[Warren Stramer]

Just because it reads in tenths does not mean your measurements are accurate to tenths. Pretty much any precision instrument has a way to be calibrated to a standard, and usually comes with a standard. What you get with an instrument that reads in tenths is repeatability and incremental accuracy, not absolute accuracy. The standard is where the absolute accuracy comes from and the calibration is how you transfer that accuracy to your instrument. Even my cheapo chinese ID micrometer came with 0.20000" @ 20C standard. Thats why there are XX ring setting gauges with precisions in single digit millionths of inches, specified at a specific temperature, its how you calibrate bore gauges and other ID measurement devices.

Steel expands 6 uin / in / F. So a 3.4" object changes size by .00002" every F. 5F and there goes 0.0001" in your measurement. Aluminum is twice that. Your instruments are also made out of metal and their error changes according to temperature (especially a dial bore gauge with several inches of reach).

A simple scenario where pistons are measured in a temperature controlled environment like a house, and a block is measured somewhere colder like a garage, and now you have some serious differences that could get up to 0.001". Add to that whatever error you have simply because youve never calibrated your instruments to a standard, and maybe you've been doing lots of measurements so the mic has started changing temperature since you calibrated it (assuming you calibrated it at all).

Its not difficult to make proper measurements. You just get into trouble when you ignore everything and think that they will just happen on their own. Do everything at a stabilized temperature. Calibrate your instrument to a standard that is more accurate than what you want to measure, and do it right before your measurement. Dont hold onto instruments any longer than needed. Use the right kind of instrument to measure what you are measuring. I've measured pistons with calipers and micrometers but its really not the right way to do it. They are tapered, you cant do it properly by hand if you truly want your measurement to be accurate to 100 millionths of an inch. But that accuracy isnt really required anyway.

If a shop isnt doing this then their measurements arent accurate to tenths.

I agree with everything you just wrote.....My point is, GOOD shops ARE doing this!!

[acannell]

Also, as described above, measurements to 0.0001" of things that are a few inches in size are only meaningful if the temperature is specified along with the measurement. Other wise just change the temperature 5F and now 3.4000" measures 3.4001"