I read somewhere that Crank and rod journal clearance should be .004"-.006" and my manual for the 3E to 8E trucks with 259 or 289 engines shows the use of oiled paper shim or Plastigauge of .002".
I am assuming {yes I know what AssUMe means} that the .004-.006 measurement is a total number as if you installed the bearing cap and use a bore gauge micrometer to measure the inside diameter of the bearing. Then you use a micrometer to measure the actual diameter of the crank journal. The difference should be .004" with a max of .006".
If that is the case, then you use the .001"-.003" plastigauge as the book states to actually measure ONE side of the oil clearance.
The reason this came up is an auto parts store employee and I were having a difference of opinion on what the clearances should be. He insisted that the oil clearance is .002" and if a motor were .004" that would be sloppy. But my counterpoint would be it is .002" on ONE side. There is NO WAY that the plastigauge is measuring TOTAL clearance, ESPECIALLY on a crank main journal. It could NOT pull the crank over tight to one side to measure total clearance because that would mean the crank was flexing under the EXTREME load of a tiny strip of soft pliable plastic...?
By my reasoning the number of .004" is correct and perfectly in agreement with the use of .002" plastigauge to check the clearance.
Am I correct or is the plastigauge calibrated to read total clearance? And if so how would that be possible?
If I am not clear on my description please ask and I will try to re-describe what I am discussing.
PS. Please feel free to clarify any spec I have wrong, and this is definately an opinion and input request thread so kick it out there.
I dont believe this is a Tech forum question since I am asking for more of a discussion of an idea.
I am assuming {yes I know what AssUMe means} that the .004-.006 measurement is a total number as if you installed the bearing cap and use a bore gauge micrometer to measure the inside diameter of the bearing. Then you use a micrometer to measure the actual diameter of the crank journal. The difference should be .004" with a max of .006".
If that is the case, then you use the .001"-.003" plastigauge as the book states to actually measure ONE side of the oil clearance.
The reason this came up is an auto parts store employee and I were having a difference of opinion on what the clearances should be. He insisted that the oil clearance is .002" and if a motor were .004" that would be sloppy. But my counterpoint would be it is .002" on ONE side. There is NO WAY that the plastigauge is measuring TOTAL clearance, ESPECIALLY on a crank main journal. It could NOT pull the crank over tight to one side to measure total clearance because that would mean the crank was flexing under the EXTREME load of a tiny strip of soft pliable plastic...?
By my reasoning the number of .004" is correct and perfectly in agreement with the use of .002" plastigauge to check the clearance.
Am I correct or is the plastigauge calibrated to read total clearance? And if so how would that be possible?
If I am not clear on my description please ask and I will try to re-describe what I am discussing.
PS. Please feel free to clarify any spec I have wrong, and this is definately an opinion and input request thread so kick it out there.
I dont believe this is a Tech forum question since I am asking for more of a discussion of an idea.
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