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Rod Bearing Clearance

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Willy Nilly View Drop Down
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    Posted: 26 Sep. 2022 at 5:10pm
Are my rod bearing clearances OK?

I had my crankshaft machined, and my rods sized and balanced for .030 bearings.

The shop manual bearing clearance limits are .001 to .0019.  I would not expect rod bearings to be perfectly concentric since they are not honed, and probably deform slightly when torqued down.  But here are my measurements to the best of my amateur ability:

Rod 1:  .0027 to .0042
Rod 2:  .0034 to .0048
Rod 3:  .0035 to .0042
Rod 4:  .0026 to .0031

Side clearances are close to the upper factory limits.

Should I try another brand of bearings?


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Oldpappy View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 26 Sep. 2022 at 5:36pm
The measurements you list are not within spec, so if an accurate measure they are not OK.

What brand of bearings did you buy, and how are you measuring clearance ? 


Edited by Oldpappy - 26 Sep. 2022 at 5:37pm
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Willy Nilly View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Willy Nilly Quote  Post ReplyReply Direct Link To This Post Posted: 26 Sep. 2022 at 5:49pm
The bearings are JMP.  I might try Cleavite.

I am using a micrometer and an inside dial bore gauge.  The journals are all within .0004 of each other.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 26 Sep. 2022 at 5:54pm
So, not torqued down. 

Check the clearance using Plastigage. Plenty of YouTube videos on this method.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bill2A Quote  Post ReplyReply Direct Link To This Post Posted: 26 Sep. 2022 at 8:53pm
I agree.
Plastigage is cheaper than new bearings and might tell a different story.
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Bruce W View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 26 Sep. 2022 at 8:55pm
  Were the rods reconditioned?
BW 
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Happy Trails! Good-bye, Good Luck, and May the Good Lord Take a Likin' to You!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 26 Sep. 2022 at 9:15pm


"I had my crankshaft machined, and my rods sized and balanced for .030 bearings."

From what he said I assumed so, though I am not sure what is meant by have the rods "sized".
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 26 Sep. 2022 at 11:02pm
  “Sizing” is one of several procedures done in the process of reconditioning of the rods. The big end bore is checked for size, roundness, and parallel and corrected if necessary. I guess I missed the word “sized” in his post. 
BW 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 26 Sep. 2022 at 11:23pm
Okay, now I know what he meant, just didn't think it through.

I always check bearing clearance with Plastigage.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cpt logger Quote  Post ReplyReply Direct Link To This Post Posted: 27 Sep. 2022 at 2:36am
There is a lot to digest here. If the rods were "Sized" It means, as Bruce said, "The big end bore is checked for size, roundness, and parallel and corrected if necessary." Part of this "Sizing" is repairing any Out of Round, (OoR), of the big end bore &/or oversized big ends. The repair requires machining some metal off the ends of the rod & the rod cap where they meet. Then putting the rod together with the proper torque & then honing the big end to size. Thus, they do get honed. They also get checked for straightness, parallel bores & twist. I have done thousands of these. 

Obviously to check the big end for size, one needs to torque the rod bolts to factory specs. Then a dial bore gauge is used to find the measurements & to check for an OoR condition. I am going to ASSuME that Willy Nilly did this properly. If the rods are not clean & properly torqued, they will give very erroneous readings. The bearings are not installed when checking for any of these things, OoR, twist straightness, or parallel bores. When using Plastigage, the bearings are installed.

The measurements given are indeed out of service limits. I would take them all apart & clean them well with acetone & making sure no dust gets between the rods & the caps or the bolts, reinstall the rod bolts & torque the rods again. If the issue is not resolved, I would send them back for warranty consideration. The rods I reconditioned were always inside factory new specs, not service limits.

Plastigage is a good cheap way to check clearances. However, it will not show any OoR or many taper issues. Nor will it find twist, bent rods or non parallel bores.

IHTH, Cpt Logger.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Willy Nilly Quote  Post ReplyReply Direct Link To This Post Posted: 01 Oct. 2022 at 12:28am
I measured the bearings in the rod with an inside micrometer.  I did not mic the rod bores, but I am assuming they were sized correctly by the machinist.

Anyway, I have now Plastigauged the rod bearings on the crankshaft at the correct torque.  All four bearings came in at between .0015 and .002, which is pretty good, so I think I am OK to reassemble.

What confused me was that the machinist told me it is good to check both with a micrometer and with Plastigauge.  But he also said that direct measurement with micrometers was more accurate, and you can check out of round.  So, I still don't understand why my measurements were off, although I didn't really torque properly with the rods off the crankshaft because I was afraid of twisting or damaging them while only in a vice.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cpt logger Quote  Post ReplyReply Direct Link To This Post Posted: 01 Oct. 2022 at 4:40am
Originally posted by Willy Nilly Willy Nilly wrote:

I measured the bearings in the rod with an inside micrometer.  I did not mic the rod bores, but I am assuming they were sized correctly by the machinist.

Anyway, I have now Plastigauged the rod bearings on the crankshaft at the correct torque.  All four bearings came in at between .0015 and .002, which is pretty good, so I think I am OK to reassemble.

What confused me was that the machinist told me it is good to check both with a micrometer and with Plastigauge.  But he also said that direct measurement with micrometers was more accurate, and you can check out of round.  So, I still don't understand why my measurements were off, although I didn't really torque properly with the rods off the crankshaft because I was afraid of twisting or damaging them while only in a vice.


Bolding, italics & underlining are all mine.

The bolded part of that sentence explains the underlined portion of the sentence.

How can you expect the rods big end to be round & properly sized when you do not apply the proper torque? Would you install the rods on the crankshaft with improper torque & then expect them to work well for many thousands of miles? I hope not.

As far as a vice hurting the rods, if you use a soft metal jaws or jaw covers on the vice, the jaw can not hurt the rods. My vice has aluminium jaws. If you can twist a connecting rod in a vice with a standard torque wrench, those rods are junk already! I have never even heard of this possibly happening. Hmmm...

...Two hours later: Heck, just for grins I just used a four foot cheater bar on an air cooled VW rod just to see if I could bend or twist it. I could not & I am a big boy. I weigh close to 285 lbs & no amount of jumping up & down on the four foot cheater pipe affected the rods twist or straightness at all. You do not need to worry about that. I even Magnafluxed the rod after this abuse, it is fine.

Note: Never assume anything. Doing so makes an ass out of u & me. I usually spell this word ASSuME just to remind me of that fact.

In any case, IHTH, Cpt Logger.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Willy Nilly Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct. 2022 at 10:13pm
I was working off my own theory, which is probably wrong.  But my theory is that once you get the main bearing or rod bearing caps fairly tight, let's just say approximately half of proper torque, the bearing to journal clearances will not change.  Further tightening to proper torque will only apply more tension to the nuts and studs, but not change bearing clearance.  I have not tested this myself.  But if anyone has experimented and has actual data to refute this theory, I would be interested in knowing about it.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Bruce W Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct. 2022 at 10:26pm
  All I can say is that in EVERY machine shop, when honing connecting rod big ends to final size, the rod bolts are always tightened to torque spec. In that business, as in many others, time is money. If the job could be done properly with fewer steps, most would be doing it that way. I’m sure that tightening the bolts to spec has an effect on the size and shape of the rod’s big end. Steel is not absolutely rigid, as I’m sure you’re aware. 
BW 
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Happy Trails! Good-bye, Good Luck, and May the Good Lord Take a Likin' to You!

We Have Miles to Jeep, Before We Sleep.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Willy Nilly Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct. 2022 at 10:29pm
Originally posted by Bruce W Bruce W wrote:

  All I can say is that in EVERY machine shop, when honing connecting rod big ends to final size, the rod bolts are always tightened to torque spec. In that business, as in many others, time is money. If the job could be done properly with fewer steps, most would be doing it that way. I’m sure that tightening the bolts to spec has an effect on the size and shape of the rod’s big end. Steel is not absolutely rigid, as I’m sure you’re aware. 
BW 
That makes sense.
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