I am tired of the machine shops telling me about clearance and measurements etc, so I decided and borrowed a Fowler micrometer with a set of telescoping gauges. FYI, took measurements multiple times, and with another micrometer to confirm the first readings.

Here are the numbers:

Cylinder #4

83.89mm hirizontal from center of cylinder wall
83.89mm vertical from center of cylinder wall

83.95 horizontal top of cylinder wall
83.95 vertical of cylinder wall

Piston 4 measurements83.85mm

Clearance suppose to be .28mm for boosted application with Supertech.

How does the clearance piston to wall deal works?

i took more measurments, but all these high tech calculations got me fried, lol, just a long workind day and am tired, will post tomorrow.

 

Make sure you are using those telescoping gauges correctly. Squeeze them together diagonally, then rotate them until it gets easy again, hopefully this is at the narrowest (level) point in the bore. However, because the gauge was tight in the bore, you need to measure the gauge with your micrometer set just as tight. Normally if you're measuring a shaft, you shouldn't be treating the micrometer as a c-clamp, this is one of the incredibly few times you should. Readings can alter .003-.004" in queen's english, or .1-.07mm.

 

I don't think any of your measurements are correct. Supertechs come in 83.5mm and 84mm. The 83.5mm slugs we build motors with measure in at 3.287x", which is anywhere from 83.49mm to 83.51mm. I sincerely doubt you have an 83.8mm Supertech piston.

Curly, I don't think you're using telescoping gauges right. You should never rotate the gauge - you center it on the bore diameter, snug it up, then sweep through the bore in one motion. Once you get the hang of it, you should be able to produce readings well within .0005". On main bearing clearances, if I'm not getting within .0002", something's wrong.

Our micrometers have a small secondary **** with a ratchet so the same amount of pressure is applied on every measurement - when you're dealing with ten-thousandths of an inch, no other method is even remotely accurate.

 

I was a certified inspector in a machine shop. I may not be describing the method correctly, but I assure you I know how to use them. Your description sounds like what I was trying to say.

The ratchet ***** are a point of argument among machinists, and especially the certifiers that came around and recertified our inspection equipment every six months. That **** isn't adjustable to any sort to any sort of accuracy. If a mic hasn't been abused, it's probably fine. But most machinists would rather trust their own "feel".

Where I worked we weren't allowed to use the ratchet when signing off on a first part inspection. Then again they wanted us using three point bore mics too.

I digress though, and refer to your vast experience when it comes to the supertechs.

 

I work nearby an airport facility, and have access to highly precise measuring gauges, and friends who are certified avionics mechanics. Will bring the pistons to them, and will post the results.

One of the reasons to open the thread is I want to understand how this overbore, piston clearance thing work. From what I can pick up the pistons are precisely 84mm, and the stock BP block is 83mm.

Is it always consistent? the 83mm stock bore...

Do the machinist measures the stock block and just add +1 to the boring machine? and then add a little more for piston clearance, so in reality is lets say 84.27mm overbore?1

I have many questions, but one to talk them one at a time so as to not cluster the thread with too many different topics at one time.

Do appreciate the replies.

 

I'm a calibrator for the USAF working in physical dimensional standards...have cald a fair number of mics, plenty down into the ±50 micro inch accuracy.

Ratchets are definitely not set to any specific torque but I haven't come across any (other than very abused/grimy ones) where the ratchet has a high enough breaking torque that it would compromise the measurement. Usually, you can crank it as much as you want as long as you use the ratchet. Micrometers that are ±.001" accuracy are pretty much **** so it doesn't matter anyways. ±.0001" mics from Starrett, Mitutoyo, and S-T almost always have repeatable measurements no matter how much you crank the ratchet provided you are square to the measuring surface. Usually any difference is in faulty technique, especially once the size gets above the 4-5" mics. Ratchet or other torque limiting devices are awesome on big mics. Otherwise light brushing with your finger will do the trick.

I do regularly see mics that have shifted a count or two off over 12 to 24 months of use without ever using a zero setting standard. Most of the time it's less than that. They are pretty solid instruments and about the only time we ever toss them is when the anvil and spindle faces aren't flat anymore. If they're carbide tipped, they'll last forever.

We had a customer that purchased over $20K of three anvil bore mics (digital, nice handles, etc) and ring gage setting standards for them that turned out to be complete ****, both the mics and gages. LOL

 

Yeah, it wasn't a "don't use the ratchet" comment, just an interesting factoid about the "controversy" around them.

If you're truly ---- about them, you'll clean everything with alcohol wipes before use. I was mostly doing over pin measurements on gears, the pins were a topic of conversation, as they were usually covered in oil and chips, because idiots used magnets with them.

Bores always pissed me off. Arguments would go on forever, as to whether or not they were being measured correctly, all because they didn't know how to use the CMM sitting up in the inspection office. Once I did, it shut a lot of them up. It's interesting what a 100 point measurement can show you.

 

You sure you want a .0110 piston/bore clearance?

Sav.. what clearance do you run on supertechs? Just out of curiosity?

 

Really, really consistent. Factory tolerance is 3.2659"-3.2667" (82.953-82.975mm) for an OE-sized piston - that's a range of less than .001". Block tolerance is 3.2678"-3.2684" (83.000-83.019mm). Factory wall clearance is .0011"-.0025" (.025-.066mm).

Gotcha. The "diagonal" part is what confused the hell out of me. Good to know that I'm using my own tools correctly

Different for every motor. N/A street motors will get .0025". Light boost (<300whp) is .0030. Heavy track use or very high horsepower (aka black car) is .0035".

 

That is 0,0711424". Now where did you get that info?

 

lol, I missed that one. Supertech specs a minimum wall clearance of .00236".

 

Good to know. Pretty on par with my motor then. IIRC it's .003.

 

We don't quite have one of those but I can imagine how it made them quiet down. Talk about orders of accuracy. We have a roundness machine that'll plot out the roundness at a couple of points in or outside of a gage/bore and our universal measuring machine (not quite a supermic, has probes that move on an air bearing track, uses laser for measurement) is accurate down to about ±3 microinches, slightly better if we have the right gage blocks to set it with. But even then it's usually just a few points we'll check on a ring gage.

The one unfortunate part of what I do is that I'll know how to cal and check a tool/gage/fixture but I'll oftentimes not know what exactly it's used for. I still see different types of mics from time to time that make me go wtf. But it's always nice to know that I can bring parts in and get a measurement that's way more accurate than I'll ever need.

(Sorry for the threadjack mazpr)