View Single Post
      08-20-2012, 04:37 PM   #61
bruce.augenstein@comcast.
Lieutenant Colonel
21
Rep
1,907
Posts

 
Drives: Legacy GT - 13.704@99.39
Join Date: Jul 2007
Location: Manheim, PA

iTrader: (0)

Quote:
Originally Posted by swamp2 View Post
...Things built by machine are in general more accurate, more consistent and these issues contribute greatly to overall quality. One also should not confuse the machining and grinding accuracies and tolerances of individual components with the assembly of parts manufactured using these processes.

In modern automotive engine machining and grinding tolerances can be measures in microns or even smaller. Higher quality engines will have improved tolerances. Modern statistical process control and 6 sigma manufacturing techniques along with 100% in process part inspection compensate very well for items like tool wear, heat, etc. These are nearly non-issues. Of course higher accuracy and smaller tolerances still cost more money to manufacture and higher end engine components will have better controls in place for this compared to those going into cheap engines. But then again the cheap engines of today have components more consistent and accurate than higher end engines of just a decade or two ago.
Agree with most of this, assuming when you say "microns", you mean a whole bunch of them. Tolerances smaller than a micron in the automotive world? Forget it. You're dreaming.

Quote:
Originally Posted by swamp2 View Post
Now again we must not confuse component accuracy with assembly quality. They are not all that related. Volume of production is the almost the sole factor that will determine how much of an engine is hand built (hand assembled to be clear since ALL parts are CNC machined). For low volumes the investment in very expensive and accurate robotics for assembly simply does not provide a return on investment. Just hire the skilled labor and even in small numbers they can meet the production requirements.
My point exactly about not confusing component accuracy with assembly quality. In fact, that's THE point.

Here's a list of tolerances I found on the 'net for an S52 engine:

S52 3.2L Piston Rings: (all in millimeters mm.)
1st groove - plain compression ring
end clearance 0.25 - 0.40
end float 0.03 - 0.065
2nd groove - tapper face ring
end clearance 0.2 - 0.4
end float 0.02 - 0.055
3rd groove - oil ring (scraper w/hose-spring)
end clearance 0.25 - 0.50
end float 0.020 - 0.055

Piston:
diameter
Std. 86.365 (+/-) 0.009 mm
1st oversize 86.565 (+/-) 0.009 mm
Piston running clearance 0.026 - 0.058 mm
Max wear clearance piston/cylinder (engine operated) 0.113 mm

Rods:
Diameter big end 48.000 - 48.016 mm
Pin bushing inside dia. 22 (+0.010/+0.005) mm
Max deviation weight (per engine) without bearing (+/-) 4g

Cylinder Bore: (in millimeters mm.)
Bore 86.400 (+0.014)
Intermediate bore dimensions a)
a) new or recon work 86.450 (+0.014)
Grinding dimension 86.600 (+0.14)
Permitted roundness deviation of cylinder bore a) 0.005
Permitted conicity of cylinder bore a) 0.01
Permitted total wear clearance between piston and cylinder engine run in 0.113


Apparently BMW is being coy about publishing current M3 numbers, but these'll do.

Just casually perusing these items (and forgetting my snickering in regard to your sub-micron statement), can you see how cylinder to cylinder variation is way more than an antiquated notion? Can you also see how hand fitting pistons at the top end of the tolerance to cylinders at the top end of the tolerance can make sense, and make a difference?

Quote:
Originally Posted by swamp2 View Post
Just about everything a human can do with his/her hands a robot and computer can do better. Now that being said it also requires a very ingenious machine designer and engineers to design the assembly machines In this endeavor as in any the consistency, speed and flexibility of these machines can vary widely. You pretty much will get what you pay for. The thing is that this field of manufacturing engineering is extremely mature.

I believe our misbeliefs about this human vs. machine thing come from some expired and romantic view of human superiority over machines. 40 or so years ago this may have still had some validity but today it just doesn't. Surely there still are (not much in the automotive world though) bad/crude assembly machinery and robots that can be outperformed by a carefully trained, managed and monitored group of humans. This just is not the norm at all...
I am not aware of BMW (or anyone else) using an automated process to custom fit individual pistons to individual cylinders. Are you? Seriously, if you know of such an automated process, I'd like to know about it too.

Quote:
Originally Posted by swamp2 View Post
I completely agree that MB's claims about this engine are a huge stretch of any reasonable definition of "hand built" and in doing so they are simply continuing to promote a curmudgeonly/antiquated view of the superiority of robots and computers for the vast majority of high volume manufacturing.
Do you actually know how far either AMG or the M group go in the hand-building process? If so, tell us. If not, then I hope you now know how hand building can make a difference even in these modern times.

Now for my final point, in spite of some of the information I've provided, I am assuming that you will cling to your belief that today's automated tolerances have made any advantage of hand-building moot.

If that's the case, then why would anybody do that unless volumes were very low.

Don't say marketing please. You think marketing dictates build techniques at MB? Don't be silly.

If not marketing or finance, then why?

Bruce

Last edited by bruce.augenstein@comcast.; 08-20-2012 at 05:30 PM.