Minimum Bearing Crush?

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AA Performance
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Re: Minimum Bearing Crush?

Post by AA Performance » Sun Jun 24, 2018 12:26 am

engineguyBill wrote:
Sun Jun 10, 2018 4:30 pm
bentvalves wrote:
Sat Jun 09, 2018 4:15 pm
I have an engine blueprinting book in which the author states measuring bearing crush is simple -

torque main cap/rod cap into place with both bearing halves in place, release tension from one fastener, and the amount the cap springs up on that side measured with a feeler gauge is what you have for bearing crush.

not sure how accurate this is, just thought I'd toss it out there.

No, not accurate at all and does not make any sense. If you torque the cap, then release the torque from one of the fasteners, and "the cap springs up" AT ALL, you have serious problems related to the caps.
Try it for yourself Bill and I think you will find that you too have problems with your caps. I have found that the problems are worse with 2 bolt mains compared with 4 bolt.

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Re: Minimum Bearing Crush?

Post by modok » Sun Jun 24, 2018 1:20 am

If it doesen't work one way try another. Not a big deal, unless feeler gauges is the only tool you have, It's no crime to be poor.
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Re: Minimum Bearing Crush?

Post by modok » Sun Jun 24, 2018 3:41 am

but being lazy, can be a sin. I am guilty.
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Re: Minimum Bearing Crush?

Post by Warp Speed » Sun Jun 24, 2018 8:01 am

Measuring rod bearing crush is much easier than the mains, as most main caps use an interference register, and typically the have too much interference. This is probably due to people assuming this will help limit main cap walk.
Anyway, with rods we measure the bearing clearance, break both rod bolts loose, and torque one to 120in lb. Then, you measure the opposite parting line as close to the bore as you can. This has proved Very accurate and consistent, and is done to EVERY rod we measure.
You do the mains the same way, just remember if the caps are not aligned by dowels or pins, they may require a slight wiggle prior to the torque of one side. Do this a few times, and check for consistency of readings.
Bill has mentioned that you should trust the bearing manufacture, and that may be true to a point. But if that was true across the board, you could just measure the shell thickness, and the housing bore, and do the math to come up with bearing clearance. This works to a point also, but so does plasti-gauge! Lol

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Re: Minimum Bearing Crush?

Post by jed » Sun Jun 24, 2018 8:34 am

You raise many questions???
1. You infer mains don't need a main cap register to keep from walking?? What kind of crush number are u looking for on mains??
2. What kind of crush number is acceptable on rods??
3. Approximately how long does this process take to measure bearing crush??

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Re: Minimum Bearing Crush?

Post by Warp Speed » Sun Jun 24, 2018 10:49 am

jed wrote:
Sun Jun 24, 2018 8:34 am
You raise many questions???
1. You infer mains don't need a main cap register to keep from walking?? What kind of crush number are u looking for on mains??

Registers or dowels/pins are for locating the part during assembly. It is the fasteners clamp load and the supporting structure (main cap cross section) that keeps the part from moving during service. Tight registers (over .0015) are only really needed when using splayed outer outer bolts and questionable center bolt clamp load. It is needed to keep the outer bolts from pulling the cap one way or another during assembly.
Main bearings can tolerate a little more crush due to there increased thickness compared to a rod bearing. .0055-.0075 is typical. Cap material amd cross section also plays into this a little.

2. What kind of crush number is acceptable on rods??

Typically .0045-.0065

3. Approximately how long does this process take to measure bearing crush??

About as long as it takes to loosen both fasteners, maybe give the cap a little wiggle, and torque one side. 45-60 seconds each?

...

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Re: Minimum Bearing Crush?

Post by Jeff Lee » Tue Jun 26, 2018 1:55 am

I just went through this on 2 different engines. Building a 4.6L Modular Ford with stroker crank & bore .020” for 4.9L. Block was line bored. Parting lines at main bearings were evident and I measured with snap gauges and truthfully, couldn’t figure out what was creating the problem. Took the block, caps and bearings to a NASCAR shop close to home which I am now using. They found the line bore / hone was offset to the caps but straight across. They ordered King +.001” main bearings and checked crush and all is well. That was simple.
2nd block is my race 390 AMC. Same issues. Found the line bore was tilted; cut more at #5 main saddle and more on the #1 cap. No bearing crush on #5. These blocks were at two different shops. The AMC was fixed by using a FAA certified CNC shop to get it right. A little above the normal equipment but that’s what it took to fix a screw-up.
And since this, I have heard from others that have line bore screw-ups at various shops. I’d say this sounds like a common problem so the OP is right in triple checking everything. I don’t know if this problem is prevalent (is it?) due to bad machinery or bad operator. Or both.
NHRA SS/H
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Re: Minimum Bearing Crush?

Post by jed » Wed Jul 04, 2018 12:37 pm

Monday I checked a new Dart LSNext block. There was .015 difference in parting lines from block to caps and .005
difference in the block parting line front to back. I don't know if it is a problem but it seems to be common.
I guess that's what u get for being curious and checking everything.

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Re: Minimum Bearing Crush?

Post by cjperformance » Wed Jul 04, 2018 8:06 pm

jed wrote:
Wed Jul 04, 2018 12:37 pm
Monday I checked a new Dart LSNext block. There was .015 difference in parting lines from block to caps and .005
difference in the block parting line front to back. I don't know if it is a problem but it seems to be common.
I guess that's what u get for being curious and checking everything.
So long as everything else is machined based off of that given crank centerline there is no problem. Unless you start looking for core shift as well ! Haha now you just have to go look dont you!!
Craig.

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Re: Minimum Bearing Crush?

Post by pamotorman » Wed Jul 04, 2018 10:24 pm

if the bore diameters are correct the crush will be correct even if the block/cap parting line is not on dead center of the bore.

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Re: Minimum Bearing Crush?

Post by joe 90 » Thu Jul 05, 2018 3:29 am

pamotorman wrote:
Wed Jul 04, 2018 10:24 pm
if the bore diameters are correct the crush will be correct even if the block/cap parting line is not on dead center of the bore.
Of course.

So no need to measure crush. Just make sure bore size is correct.

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Re: Minimum Bearing Crush?

Post by smeg » Thu Jul 05, 2018 7:59 pm

engineguyBill wrote:
Sun Jun 10, 2018 4:30 pm
bentvalves wrote:
Sat Jun 09, 2018 4:15 pm
I have an engine blueprinting book in which the author states measuring bearing crush is simple -

torque main cap/rod cap into place with both bearing halves in place, release tension from one fastener, and the amount the cap springs up on that side measured with a feeler gauge is what you have for bearing crush.

not sure how accurate this is, just thought I'd toss it out there.

No, not accurate at all and does not make any sense. If you torque the cap, then release the torque from one of the fasteners, and "the cap springs up" AT ALL, you have serious problems related to the caps.
The bearing manufacturers book tells you that is the correct way to measure crush and that is the way it should be done, no more argument needed.

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Re: Minimum Bearing Crush?

Post by modok » Thu Jul 05, 2018 9:24 pm

I don't care what way you do it as long as you get an accurate measurement.
You should be able to measure it three ways and get the same answer if you know what your doin
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Re: Minimum Bearing Crush?

Post by shoedoos » Sat Jul 07, 2018 5:01 pm

In the case where rod caps are aligned with dowels....how is the crush measured?

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Re: Minimum Bearing Crush?

Post by modok » Sat Jul 07, 2018 5:25 pm

The same. Why would a dowel make a difference? I don't really get it.

Here is a challenge
how about a cracked rod
Glen Urban

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