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small block stroker autopsy #2761164
04/07/20 04:21 PM
04/07/20 04:21 PM
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Atlanta, GA
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mgoblue9798 Offline OP
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New to me stroker small block of unknown build origin, on tear down found #6 has a spun rod bearing. It was not from an oiling issue as there was no discoloration or signs of heat.

Noticed very little rod side movement on all journals. The spun bearing rod journal had zero side clearance but the bearing was lapped over itself and material squeezed out the side.

Closer inspection showed all rod bearing outer sides worn down into the copper on the edges.

Crank has fillet rod journals, whoever build the motor used regular P series bearings. Obviously going back with HN bearings and guessing the wrong bearing being used is the likely cause for the spun rod bearing.

Sound right?

Re: small block stroker autopsy [Re: mgoblue9798] #2761177
04/07/20 04:37 PM
04/07/20 04:37 PM
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Auburn WA
Dave_J Offline
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My guess too.


Retired, US ARMY 1973-1994
ASE mechanic, Electrical 1994-1997
Retired GTE/VERIZON/FRONTIER 1997-2015


Posting cheap tech help (CRAP) here since Nov 97, 1000's of posts, some may be good.

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Re: small block stroker autopsy [Re: mgoblue9798] #2761310
04/07/20 11:15 PM
04/07/20 11:15 PM
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Romeo MI
MR_P_BODY Online content
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You can have way more side clearance than the book calls for with out issues
wave

Re: small block stroker autopsy [Re: MR_P_BODY] #2761321
04/07/20 11:44 PM
04/07/20 11:44 PM
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Fulton County, PA
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CMcAllister Offline
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Yes, WAY more with the right pistons. The side clearance has nothing to do with oil getting off of the bearing.

So it grabbed the bearing, turned it and piggy backed it and there's no heat? Crank hurt? Rod has to be junk, right?


If the results don't match the theory, change the theory.
Re: small block stroker autopsy [Re: mgoblue9798] #2761385
04/08/20 08:59 AM
04/08/20 08:59 AM
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New York
polyspheric Offline
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Really loose side clearance is harmless, unless it allows the rod's pin eye to use the inner face of the pin boss as a thrust surface.


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Re: small block stroker autopsy [Re: polyspheric] #2761450
04/08/20 11:47 AM
04/08/20 11:47 AM
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Southern California
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BIG DRAG Offline
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Excessive side clearance will cost hp from adding more windage in the crankcase, it will also lower oil psi due to the clearance being larger. The oil has to go somewhere. I wouldn't bandaid an issue with excessive rod side clearance.
Now it's not huge hp being eaten up but it all adds up.
I learned this from an accomplished stock/superstock engine builder a long time ago.

What is the clearance at now?

Last edited by BIG DRAG; 04/08/20 11:51 AM.
Re: small block stroker autopsy [Re: BIG DRAG] #2761453
04/08/20 11:51 AM
04/08/20 11:51 AM
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Washington
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madscientist Offline
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Originally Posted by BIG DRAG
Excessive side clearance will cost hp from excessive windage in the crankcase, it will also lower oil psi due to the clearance being larger. The oil has to go somewhere. I wouldn't bandaid an issue with loose rod side clearance.



This just isn’t true. Side clearance has zero affect on oil loss through the bearing. None.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: small block stroker autopsy [Re: madscientist] #2761458
04/08/20 11:56 AM
04/08/20 11:56 AM
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Southern California
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BIG DRAG Offline
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Originally Posted by madscientist
Originally Posted by BIG DRAG
Excessive side clearance will cost hp from excessive windage in the crankcase, it will also lower oil psi due to the clearance being larger. The oil has to go somewhere. I wouldn't bandaid an issue with loose rod side clearance.



This just isn’t true. Side clearance has zero affect on oil loss through the bearing. None.


Then why is it that when bearing clearance is excessive that oil psi goes down? Clearance is like a controlled leak, more clearance more leakage.

This has been my experience.

Re: small block stroker autopsy [Re: BIG DRAG] #2761483
04/08/20 01:03 PM
04/08/20 01:03 PM
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Bend,OR USA
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Think about what you said about the bearing clearances being excessive and how the rod side clearances affect oil flow out of the bearings and crankshaft work
There many misunderstood myths spread about racing and motors, if the rods have .0025 bearing clearances and .012 side clearances will they let more oil out than with .0035 bearing clearances and .008 rod side clearances?
How about having .0030 bearing clearances with .030+ rod side clearances like most stock Street Hemi motor came with from the factory shruggy
I've built and race a bunch of BB stroker motors with BB Chevy type H and I beam rods that had over .0035 bearing clearances and well over .035 side clearances using 5W20Wt oil and had the oil pump bypass spring set so it allow the motor to have 70 lbs. pressure with hot oil at 7000 RPM, many motors like that with no bearing problems so far up
I have torn down a bunch of Mopar BB, SB and Hemi V8 that had way over .030 rod side clearances from the factory, only one early (October of 1965) production 1966 street Hemi motor had less than the factory recommended max .016 rod side clearances, it was between .012 to .015 on all of them shock shruggy


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: small block stroker autopsy [Re: BIG DRAG] #2761490
04/08/20 01:40 PM
04/08/20 01:40 PM
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Fulton County, PA
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CMcAllister Offline
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Originally Posted by BIG DRAG
Excessive side clearance will cost hp from adding more windage in the crankcase, it will also lower oil psi due to the clearance being larger. The oil has to go somewhere. I wouldn't bandaid an issue with excessive rod side clearance.
Now it's not huge hp being eaten up but it all adds up.
I learned this from an accomplished stock/superstock engine builder a long time ago.

What is the clearance at now?


Old wives tale. And a long time ago, that was accepted. Side clearance is not relevant to keeping oil on the crank. Get the weight out of the rod and the pin. You do have to use the correct piston design to control the rod.

[Linked Image]

[Linked Image]


If the results don't match the theory, change the theory.
Re: small block stroker autopsy [Re: BIG DRAG] #2761491
04/08/20 01:41 PM
04/08/20 01:41 PM
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Posts: 5,690
Downtown Roebuck Ont
Twostick Offline
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Originally Posted by BIG DRAG
Originally Posted by madscientist
Originally Posted by BIG DRAG
Excessive side clearance will cost hp from excessive windage in the crankcase, it will also lower oil psi due to the clearance being larger. The oil has to go somewhere. I wouldn't bandaid an issue with loose rod side clearance.



This just isn’t true. Side clearance has zero affect on oil loss through the bearing. None.


Then why is it that when bearing clearance is excessive that oil psi goes down? Clearance is like a controlled leak, more clearance more leakage.

This has been my experience.


Bearing clearance will affect oil pressure, side clearance can't.

Picture the bearing clearance as the garden hose on the side of your house. Say you're pumping 5 gallon per minute at 45 psi running it wide open watering the flowers. The flowers are your side clearance, zero effect on what comes out the end of the hose.

Another way to look at it is ask yourself if attaching a 2" firehose to the end of your 5/8" garden hose will fill a bucket any faster.

Kevin

Re: small block stroker autopsy [Re: BIG DRAG] #2761496
04/08/20 01:54 PM
04/08/20 01:54 PM
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New York
polyspheric Offline
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Quoting myself from my book ("Chevrolet Stovebolt Performance"*), the math using its 2.311" rod journal for this example:
The only leak, or outlet path, for oil pressure in the rod’s journal to bearing clearance space is at the sides of the rod big ends. This annular clearance area is easily calculated. The journal OD is 2.311”; with a bearing clearance of .003” (generous, but possible), the leak area is the bearing ID area minus the journal OD area. Here, it’s 4.205 in2 ((2.311+.003)2 × Π ÷ 4) minus 4.195 in2 (2.3112 × Π ÷ 4).
The leakage from each side of the rod is .0109 in2. The radial clearance between the rod and journal cheek is the surface area of a horizontal cylinder 2.314” OD times the width of the side clearance, or 2.314” × Π × W.
For the side clearance to control the oil escape volume, the side clearance area must be less than the annular clearance; in this case, less than .0109”. If the side clearance area is equal to the known leak at .0109”, W is .0015”, or 1½ thousands. Therefore any value of W higher than .0015” (the rod is .003” narrower than the journal’s cheek-to-cheek width) has no effect on oil pressure or the volume released.
Since the side clearance is always much larger than this, any more clearance is, of course, harmless.

* http://victorylibrary.com/235BK.htm


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Re: small block stroker autopsy [Re: polyspheric] #2761499
04/08/20 02:00 PM
04/08/20 02:00 PM
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Fulton County, PA
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CMcAllister Offline
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Originally Posted by polyspheric
Quoting myself from my book ("Chevrolet Stovebolt Performance"*), the math using its 2.311" rod journal for this example:
The only leak, or outlet path, for oil pressure in the rod’s journal to bearing clearance space is at the sides of the rod big ends. This annular clearance area is easily calculated. The journal OD is 2.311”; with a bearing clearance of .003” (generous, but possible), the leak area is the bearing ID area minus the journal OD area. Here, it’s 4.205 in2 ((2.311+.003)2 × Π ÷ 4) minus 4.195 in2 (2.3112 × Π ÷ 4).
The leakage from each side of the rod is .0109 in2. The radial clearance between the rod and journal cheek is the surface area of a horizontal cylinder 2.314” OD times the width of the side clearance, or 2.314” × Π × W.
For the side clearance to control the oil escape volume, the side clearance area must be less than the annular clearance; in this case, less than .0109”. If the side clearance area is equal to the known leak at .0109”, W is .0015”, or 1½ thousands. Therefore any value of W higher than .0015” (the rod is .003” narrower than the journal’s cheek-to-cheek width) has no effect on oil pressure or the volume released.
Since the side clearance is always much larger than this, any more clearance is, of course, harmless.

* http://victorylibrary.com/235BK.htm


thumbs

Oil acts as a coolant. It needs to flow, not be trapped. Oil pressure is not what keeps the parts from contacting each other anyway. It's the hydrodynamic wedge.

I'd still like to see pictures of the OP's parts. Never saw a rod bearing grabbed and piggybacked with out getting hot and destroying the rod.


If the results don't match the theory, change the theory.
Re: small block stroker autopsy [Re: CMcAllister] #2761504
04/08/20 02:07 PM
04/08/20 02:07 PM
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New York
polyspheric Offline
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I would expect a color change and spalling.


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Re: small block stroker autopsy [Re: CMcAllister] #2761775
04/09/20 01:00 AM
04/09/20 01:00 AM
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WA
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pro451bee Offline
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How long does it take to polish the entire crank shaft ! That is a thing of beauty . I am sure it sheds oil good too.

Re: small block stroker autopsy [Re: polyspheric] #2761780
04/09/20 01:41 AM
04/09/20 01:41 AM
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Originally Posted by polyspheric
I would expect a color change and spalling.
iagree
The damage done depends on how long it was run with the bearings stacked one over or under the other one, if you run them long enough that way they will usually break a rod bolt and then the rod cap unwinds and breaks the rod and block puke
Seen more than one BB Chevy have that happen at the drags in SO CA whiney


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: small block stroker autopsy [Re: madscientist] #2762154
04/10/20 06:41 AM
04/10/20 06:41 AM
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Carson City, Nevada
Biginchmopar Offline
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Originally Posted by madscientist
Originally Posted by BIG DRAG
Excessive side clearance will cost hp from excessive windage in the crankcase, it will also lower oil psi due to the clearance being larger. The oil has to go somewhere. I wouldn't bandaid an issue with loose rod side clearance.



This just isn’t true. Side clearance has zero affect on oil loss through the bearing. None.


iagree

Re: small block stroker autopsy [Re: CMcAllister] #2762155
04/10/20 06:42 AM
04/10/20 06:42 AM
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Carson City, Nevada
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Originally Posted by CMcAllister
Originally Posted by BIG DRAG
Excessive side clearance will cost hp from adding more windage in the crankcase, it will also lower oil psi due to the clearance being larger. The oil has to go somewhere. I wouldn't bandaid an issue with excessive rod side clearance.
Now it's not huge hp being eaten up but it all adds up.
I learned this from an accomplished stock/superstock engine builder a long time ago.

What is the clearance at now?


Old wives tale. And a long time ago, that was accepted. Side clearance is not relevant to keeping oil on the crank. Get the weight out of the rod and the pin. You do have to use the correct piston design to control the rod.

[Linked Image]

[Linked Image]



iagree

Re: small block stroker autopsy [Re: CMcAllister] #2762296
04/10/20 01:07 PM
04/10/20 01:07 PM
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Atlanta, GA
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mgoblue9798 Offline OP
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Crank will need to be turned but is not bad. Rod does not show any heat, going to measure the big end and decide if it is junked or not. I have never seen a bearing so mangled before.

Re: small block stroker autopsy [Re: mgoblue9798] #2762391
04/10/20 04:05 PM
04/10/20 04:05 PM
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Are you feeling lucky on that rod? If not replace it ,please up twocents


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)

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