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Staggered main bearing sizes vintage GM

General engine tech -- Drag Racing to Circle Track

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Truckedup
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Re: Staggered main bearing sizes vintage GM

Post by Truckedup » Thu Jan 28, 2016 8:55 am

1953 235 engine Powerglide was the first with full pressure "modern" oiling. By 54 all the 235's and the new 261 had full pressure oiling and the shimmed mains were gone late 1954...
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire

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Re: Staggered manin bearing sizes vintage GM

Post by Kevin Johnson » Thu Jan 28, 2016 11:25 am

Dan Timberlake wrote:...

I think typical basic models of first mode crankshaft torsional vibration show, when a heavy flywheel is attached to the "rear" end of a crank, that end is a "node" acting as an anchor, and the motion there is near zero. The full +/- 0.5 degree twist-untwist happens at the "anti-node" snout/damper end . In that case the extra torsional damping that //may// be provided by the 4% larger diameter journal is at the wrong end. But, back in 1937 Chevy applied a torsional damper right at the anti-node, the most effective place for it to be.
http://chevy.oldcarmanualproject.com/ch ... o/3729.htm
The higher surface speed and stiffness of the rearward bearing journals tend to work to reduce eccentricities of movement but at a cost of increased friction. The more forward journals, being less stiff and at lower (and torsionally varying) surface speeds would oscillate more eccentrically in the bore thereby generating a "conflict" or damping due to circumferential pressure differentials of greater magnitude within the fluid film. This is consistent with the forward placement of the dedicated torsional damper.

http://www.epi-eng.com/piston_engine_te ... arings.htm

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Re: Staggered main bearing sizes vintage GM

Post by PackardV8 » Fri Jan 29, 2016 12:09 pm

PackardV8 wrote:Many stovebolt owners ask to have them line bored all to the same diameter as the later 6-cyls and used those bearings.
My apologies for not clarifying the above. The '57 and earlier stovebolts have eccentrically shaped main bores which require the use of shims to size the bearing clearance. As above, it's possible to remove the shims, nip the caps and bore the bearing bores round to use '58-'62 bearings.
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Re: Staggered main bearing sizes vintage GM

Post by modok » Fri Jan 29, 2016 8:11 pm

Basically, yes. It's actually simpler than that. The shims can be eliminated. the shims were .004", with the .004 shims in there, it should be round and on-size. If you want to removed the shims probably won't need to cut the caps at all, jsut bore it.
But due to people messing with them sometimes it's a real puzzle, if they have been repaired by farmer brown, who, having already pulled all the shims decides to file the caps to tighten it up, unevenly, at an angle, and then he ruins one and grabs one from another block..... Also the lockwashers destroy the surface of the caps with repeated loosening and tightening.

There are more than two kinds of bearings, but the modern book only lists two. I have some catalogs from the 70's that show the other variants, I believe the thrust width is different. WW2 era engines were made in several plants geared up for the war effort, and they apparently used slightly different bearings and sizes all at the same time.

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Re: Staggered main bearing sizes vintage GM

Post by Kevin Johnson » Wed Nov 13, 2019 12:53 pm

modok wrote:
Tue Jan 26, 2016 11:10 pm
...
i assume they did it for the same reason they do with cam bearings bores. Why did chevy do it? I'd guess it would be a way to speed up production with whatever method they were using to bore the main housings, but I'm not sure, I don't know how they did it. Before my time. But It may have been something more like a giant reamer rather than line boring with single point tools. ...

This thread popped up in the forum; search engines are better now and the problems that the 240Z experienced with early production straight six engines inspired me to search again: viewtopic.php?f=15&t=49273&p=835091#p835091

The key is to use "stepped" main bearings or shaft as a search parameter rather than staggered.

https://books.google.com/books?id=iP4iA ... ll&f=false

Image

So modok is correct.

I am assuming that the engineers also recognized that the stepped mains increased the torsional rigidity of the "shaft" in the same manner as transmission gear shafts.

There is a large literature and many patents on using oil films as dampers with shafts but attributing this to the 1920s-1930s automotive industry is indeed too much of a stretch. Perhaps Sir Frank Whittle thought about it.
https://patents.google.com/patent/US3473853A/en wrote:
Vibration damping device

In operation radial vibrations of the shaft 6 cause radial movement of the bearing. Due to the flexibility of the arms 20 and 21, relative radial movement takes place between the land 24 and the inner surface of the sleeve 17.
The film of oil in the gap between the land 24 and the sleeve 17 therefore changes in thickness and the thickness of the gap is so arranged that on relative approaching and receding movement between the land and the inner surface of the sleeve 17 a hydrodynamic squeeze film of oil is formed in said gap.
The hydrodynamic squeeze film of oil is effective in damping the radial vibrations of the shaft 6.

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Re: Staggered main bearing sizes vintage GM

Post by Dan Timberlake » Sat Nov 16, 2019 2:21 pm

I think "squeeze film" damping typically refers to radial damping.
Radial damping can be especially useful when lateral shaft vibration "modes" are the concern.
Turbines and such, with multiple stages of close running compressor wheels and seals, and few bearings are concerned about lateral vibrations.
https://encrypted-tbn0.gstatic.com/imag ... ePwUPK4j&s
https://www.cascademvs.com/wp-content/u ... 28x353.jpg

It doesn't take much lateral displacement/whipping to wreck close fitting seals and stationary compressore etc parts.

https://assets.new.siemens.com/siemens/ ... core-5.jpg

https://assets.new.siemens.com/siemens/ ... core-4.jpg

==========.

I think the vibration issues with long automotive crankshafts are typically torsional.
I'm guessing the torsional damping provided by the oil shearing during crank torsional oscillations in the main bearings is insufficient to be very useful for torsional crank resonance.
Main bearing #1 at the crank snout would be the best candidate for heroic torsional damping measures, like making it's diameter as big as the innards of a Fluiddamper or a conventional rubber-in-shear damper so 1 or 2 degrees of rapid twisting and untwisting causes significant relative motion.

Kind similar to why Koni shocks work better bolted to one "stationary" and one oscillating suspension component, than in boxes in the trunk.

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Re: Staggered main bearing sizes vintage GM

Post by SchmidtMotorWorks » Sat Nov 16, 2019 2:36 pm

Seems like a very deep rabbit hole for engines making what power density? Maybe 0.25HP/CI?

The simplification of line boring aspect seems reasonable.
http://www.schmidtmotorworks.com Prototypes, Tooling, Molds.

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Re: Staggered main bearing sizes vintage GM

Post by Kevin Johnson » Sat Nov 16, 2019 2:56 pm

Dan Timberlake wrote:
Sat Nov 16, 2019 2:21 pm
I think "squeeze film" damping typically refers to radial damping.
...
Yes, typically. However I saw that there is also a large literature on the shifting of journals due to torsionally induced bending of the crankshaft. If you can reject the torsional energy by heat generation in the oil film that also acts as a damping mechanism.

MadBill made a comment in another thread about the oil temp in straight six engines at critical rpm rising by 20 degrees and was taken to task. The bearing oil film temp rise EASILY exceeds that.

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Re: Staggered main bearing sizes vintage GM

Post by exhaustgases » Sat Nov 16, 2019 4:03 pm

Kevin Johnson wrote:
Wed Nov 13, 2019 12:53 pm
modok wrote:
Tue Jan 26, 2016 11:10 pm
...
i assume they did it for the same reason they do with cam bearings bores. Why did chevy do it? I'd guess it would be a way to speed up production with whatever method they were using to bore the main housings, but I'm not sure, I don't know how they did it. Before my time. But It may have been something more like a giant reamer rather than line boring with single point tools. ...

This thread popped up in the forum; search engines are better now and the problems that the 240Z experienced with early production straight six engines inspired me to search again: viewtopic.php?f=15&t=49273&p=835091#p835091

The key is to use "stepped" main bearings or shaft as a search parameter rather than staggered.

https://books.google.com/books?id=iP4iA ... ll&f=false

Image

So modok is correct.

I am assuming that the engineers also recognized that the stepped mains increased the torsional rigidity of the "shaft" in the same manner as transmission gear shafts.

There is a large literature and many patents on using oil films as dampers with shafts but attributing this to the 1920s-1930s automotive industry is indeed too much of a stretch. Perhaps Sir Frank Whittle thought about it.
https://patents.google.com/patent/US3473853A/en wrote:
Vibration damping device

In operation radial vibrations of the shaft 6 cause radial movement of the bearing. Due to the flexibility of the arms 20 and 21, relative radial movement takes place between the land 24 and the inner surface of the sleeve 17.
The film of oil in the gap between the land 24 and the sleeve 17 therefore changes in thickness and the thickness of the gap is so arranged that on relative approaching and receding movement between the land and the inner surface of the sleeve 17 a hydrodynamic squeeze film of oil is formed in said gap.
The hydrodynamic squeeze film of oil is effective in damping the radial vibrations of the shaft 6.
Before I read modok's and this post, I was going to post that they would do this for production machining in the day. And actually the use of different size bores would drastically increase cutter life on the production line. Instead of cutting 4 holes in the one block with the same cutter, they would be cutting one hole in 4 blocks.

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Re: Staggered main bearing sizes vintage GM

Post by Kevin Johnson » Sat Nov 16, 2019 8:21 pm

Kevin Johnson wrote:
Sat Nov 16, 2019 2:56 pm
Dan Timberlake wrote:
Sat Nov 16, 2019 2:21 pm
I think "squeeze film" damping typically refers to radial damping.
...
Yes, typically. However I saw that there is also a large literature on the shifting of journals due to torsionally induced bending of the crankshaft. If you can reject the torsional energy by heat generation in the oil film that also acts as a damping mechanism.

MadBill made a comment in another thread about the oil temp in straight six engines at critical rpm rising by 20 degrees and was taken to task. The bearing oil film temp rise EASILY exceeds that.


If you watch the simulation carefully you can see a coupling between the first and second modes of vibration and the third mode, i.e. torsional vibration. This will lead to axial squeeze film damping in the bearings rather than simple radial.


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Re: Staggered main bearing sizes vintage GM

Post by Kevin Johnson » Sun Dec 01, 2019 12:32 pm

No speculation needed; empirically demonstrated by a damper manufacturer testing real engines. My emphasis:
https://www.speed-talk.com/forum/viewtopic.php?t=22589#p248840 wrote: Re: Harmonics V's Oil Viscosity.

Postby bill@bhj » Mon Jul 26, 2010 11:29 pm

I can only partly answer the question -
While testing OEM crank dampers on an inline 6, (292 Chevy) we used to make a quick sweep across the rpm range to spot the general pattern of where the torsion peaks were, then go back and go very slowly across the rpm band where the worst peaks were to get a more exact reading of where those peaks were. We wanted the frequency of those peaks for fine tuning the damper. Inline's are not alone here, I just use it as an example - They usually had several nice peaks to contend with.
If we would set the engine directly on a high peak, (say .6° p-p) we would see that peak slowly rise (~20-30%) and see a corresponding rise in the oil temperature ( say 20-30°) Since the engine owner didn't want to pursue this any longer than necessary, we never sat there to see how high either value would go.
All it proved was that the torsion was enough to make each of the bearings into a small viscous damper which would absorb some energy at the expense of heating the oil in the bearings and consequently in the pan.
This was only an issue if one were going to have the engine run right at one of the torsion peaks when these peaks might be only 100 - 200 rpm wide at the worst amplitudes.
For an engine that was up and down the rpm range and just running quickly back and forth through the peaks, it was a non-issue. NOW, for a big speedway situation where the rpm may be in a narrow rpm band for a big % of the lap, you sure wouldn't want the engine to be sitting right on a significant torsion peak. For the NASCAR size V8's this is typically in the high 6000 - low 7000 rpm neighbor hood and is usually the 2.5 order peak. In that situation, oil heating in the bearings could get significant and the oil viscosity would be going down with rising temp.
So - The torsion peaks can be influenced by the oil viscosity - and vice / versa.
Also, the high rpm track motors can certainly benefit from careful sizing and tuning of the damper to keep from having the engine dwelling on a torsion peak. All those dampers aren't the same and not enough people are measuring their effect.
In other Engineering tips threads it was pointed out that the stepped construction would improve torsional rigidity as is the case with transmission gear shafts.

I tend to think that engineers in the past were every bit as intelligent as their modern day counterparts and could steer designs whilst using alternate justifications to accountants. Bearing beams are good for NVH; see Nissan's patents -- well known to '50s hotrodders for bolstering flexible blocks.

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