Connecting rod math.

[Shaner]

Awe c'mon, I'm still waiting for my questions to be answered from a couple pages back.

This whole thing can be answered easily I think. Record the thickness of a new bearing and then install it. After, remove it and re-measure. Wouldnt that work?

I was recently looking at an auction for a set of bearings. The outside was 2.938, the thickness was .094. If the crank is 2.749...it doesn't leave much for the oil clearance...or am I doing the math wrong?

I already explained why the clearance will actually be larger, on page one.
As far as the thickness....
Exerting any force on any material results in SOME change of dimension. temporary pr permanent.

And as i also said before, if you want to look for that, for increased thickness, look at the weakest point of the bearing. Generally oil holes or at the parting.

Was that the comment about interference fit? Hole is actually larger?

So if I am using a highly sophisticated, telescoping, doohickey, snap gauge, chingus tool or an inside sliding yard stick caliper micrometer...that measured the inside hole...how can I gain size?

If one is supposed to measure with these tools how do you gain size? Confused.

[Shaner]

I recall discussing this in the past, so, I searched
Related topic:
viewtopic.php?f=1&t=53428
and, in a mostly unrelated thread

The point is to get the right bearing crush, so where you want to be depends on the bearings.
In the past using Clevite bearings being in the middle to high end of the housing specification they listed was often good, because they usually kept the crush fit on the high end (even says so in the catalog) but that was then.....now is now.
If in doubt figure it out.

If you run too much interference fit, you start seeing the bearings folding inward near the parting lines right to begin with, and you also might THINK you have more clearance than you actually do, if you measure the bearings in the housings, because some of that is going to relax as it actually runs. You can only compress the bearings so much before they smoosh, and they may not smoosh in a healthy way or immediately, so, like many specifications, it has a happy zone and you want to stay in it.

Thank you!

[modok]

Correct.
Stuffing a thing in a hole, that's bigger than the hole, either the thing shrunk and/or the hole is larger.
Basic, but very true.

When your thing IS actually in the hole, you can't really see what's goin on.
You might imagine it either way, depending on fetishes, ect.

[Shaner]

Well it just doesnt make sense...

If a journal is 2.7493 and you need .0026 but the inside hole of the bearing is 2.7490...there's not really any room.

As a noob how is one supposed to order bearings and get it correct if there's not much to go on?

[modok]

Lets look at it with another perspective for clarity

IF the ID measured.... exactly the same as the housing size minus2X bearing thickness...... then it has NO, ZERO interference fit.
And that is bad.
And WHEN you find that to be true, you will hopefully know that's goin on, and fix it.

[Dave Koehler]

Do you have the original bearings for this project? Do some measuring.

[Shaner]

Lets look at it with another perspective for clarity

IF the ID measured.... exactly the same as the housing size minus2X bearing thickness...... then it has NO, ZERO interference fit.
And that is bad.
And WHEN you find that to be true, you will hopefully know that's goin on, and fix it.

I'm dumb.

[modok]

No, you aren't.
I had a 40 year veteran crank grinder guy, ask me what it means when the bearing id measured different 45 at degrees, and I said I didn't know, and I didn't figure it out for another 8 years.

[Kevin Johnson]

I apologize for deviating off into advanced engine tech but I think it is important. When I went to technical school they expected you to know the science and mathematics (at least conceptually) of the trade you were practicing. Ferris State had an engineering program and also trained automotive technicians. I know many of the students I met went straight to work for the Big Three at the time.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Thank heaven there is no need to appeal to Harry Potter when Newtonian physics and Occams razor provides a reasonable explanation.

Deflect all you want Kevin and refer to all your professors but my post stands.
It says NOTHING about the bearing shell becoming thicker.

I will try again using online educational materials and a symposium paper presented specifically on the topic of bearing crush.

First, there is a difference between elastic deformation and plastic deformation. I think you have the idea of plastic deformation in mind.

Elastic/Plastic Deformation

When a sufficient load is applied to a metal or other structural material, it will cause the material to change shape. This change in shape is called deformation. A temporary shape change that is self-reversing after the force is removed, so that the object returns to its original shape, is called elastic deformation. In other words, elastic deformation is a change in shape of a material at low stress that is recoverable after the stress is removed. This type of deformation involves stretching of the bonds, but the atoms do not slip past each other.

When the stress is sufficient to permanently deform the metal, it is called plastic deformation.

The paper I am citing below uses the term "deformation" five times. It also specifically uses the terms "elastic deformation" and "plastic deformation." I cite papers assuming that the reader will actually read the paper. The paper is full-text without a paywall.

http://web.posfemec.org/posmec/14/TRB/TRB1446.pdf

The picture below shows the radial displacement with and without bore relief. Radial displacement is another way to present the varying thickness of the bearing shell.

Bore relief.jpg

The picture below illustrates radial displacement with and without the assumption of a perfectly rigid housing/bore:

Distribution of radial displacement due to the bearing crush.jpg

I think the paper is fairly self explanatory and certainly has many references if you want to explore the topic. If you are not used to reading academic papers you just need to take your time. There are many college level online educational references available free-of-charge.

[engineguyBill]

Note that the information from King Bearings refers to the ID of the housing bore being within the recommended tolerances. If the bore is not within these tolerances, then there may be some deformation of the thin area of the bearing shell, adjacent to the parting line when the caps are torqued into place.

Thus it is up to the engine builder to verify that the housing bores are within specifications in order for the bearings to survive.

[modok]

Subaru LOCKED right up
Oh yeah, I verify the housing bore was right at the TOP side of KING's own specification, before throwing them out and getting clevite, which worked fine.
Not to say I have any ax to grind with king any more than with subaru, but people make mistakes.

Where it gets REALLY weird is aluminum blocks, and worst of all mag blocks. You need a LOT more interference fit then.

[Kevin Johnson]

Subaru LOCKED right up
Oh yeah, I verify the housing bore was right at the TOP side of KING's own specification, before throwing them out and getting clevite, which worked fine.
Not to say I have any ax to grind with king any more than with subaru, but people make mistakes.

Where it gets REALLY weird is aluminum blocks, and worst of all mag blocks. You need a LOT more interference fit then.

The modulus of elasticity or elastic modulus of a common Mg alloy at a standard temperature of approximately 20 degrees C is only in the neighborhood of 45 GPa. A typical value for an aluminum alloy is in the neighborhood of 69 GPa; cast iron ~93 GPa.

[modok]

Well yes, that's why we don't use it for bolts.

try thermal expansion coefficient

[Kevin Johnson]

Note that the information from King Bearings refers to the ID of the housing bore being within the recommended tolerances. If the bore is not within these tolerances, then there may be some deformation of the thin area of the bearing shell, adjacent to the parting line when the caps are torqued into place.

Thus it is up to the engine builder to verify that the housing bores are within specifications in order for the bearings to survive.

The paper by the head of the engineering consulting agency that King Bearings uses cites the symposium study that I recently provided a link to. That symposium reference clearly states that (my emphasis):

When the bearing is bolted together, the crush area touches first. As tightening progress, the crush
area is forced beneath the bore parting edges, thus opening (bending outward) the insert and creating a
tight insert to bore contact through radial pressure Fig. 2b. The tightening of the bolts also results in a
inward displacement close to the split line, Fig. 3a, thus reducing the clearance between the journal and
the bearing in these regions

Thus the deformation of the thin(ned) area of the bearing shell normally occurs even when the housing bore is within recommended tolerances. If the bore was outside the spec the deformation could be lesser or greater depending on the side of departure from the spec.

[Kevin Johnson]

Well yes, that's why we don't use it for bolts.

try thermal expansion coefficient

Yes, the same relative ordering is present.

https://www.engineeringtoolbox.com/line ... -d_95.html

One of the factors supporting the use of Magnesium versus Aluminum is its superior damping of NVH. It is even superior to cast gray iron in applicable ranges.

https://apps.dtic.mil/dtic/tr/fulltext/u2/640465.pdf (See Table IV)