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+--- Thread: How to measure big end & crank for sizing new bearing shells (/showthread.php?tid=4896)
How to measure big end & crank for sizing new bearing shells - fcp - 09-12-2013
I plan to replace all of the big end and crank bearing shells on my 606 build as I will have the crank assembly and pistons out for balancing.
MB list repair sizes for both Big end and bearing shells. Question is how to determine correct sizing.
For example, putting a mic on the crank and taking several sample measurements shows big end to be 50.88 diameter which (*if* I have have read WS manual 'testing repairing con rod') correctly means a 0.767 variance to average of range showed for 'Bearing shell basic bore) which is 51.600 - 51.614 ?
.767 seems like a lot of wear though?
Bearings don't look especially worn and mileage is <100K on engine before strip down.
I suspect I am either measuring the wrong thing.. making the wrong assumption about what wears or misunderstanding purpose of 'repair size' i.e they are for use only when big end on rod is re-machined?
Perhaps all I need is new standard size?
Pics of removed shells here:
![[Image: 9720536259_aa35e81fb0_b.jpg]](http://farm4.staticflickr.com/3757/9720536259_aa35e81fb0_b.jpg)
2 sets of big end shells. Wear on lowers only. Others have said unneccessary to replace, but they are out now and I would rather be certain that they are done.
RE: How to measure big end & crank for sizing new bearing shells - hansendk - 09-12-2013
well the 51.600-51.619 mm is the big end of the conrod on the crankshaft its 47.950-47.965 mm
so if your crankshaft is STD. thats how it has to be.
remember that the con rod bearings for turbo and no turbo is not the same
turbo is sputter type bearing meaning that the half in the rod is designed to take higher load.
RE: How to measure big end & crank for sizing new bearing shells - fcp - 09-12-2013
"if your crankshaft is STD" - you mean like not reground right?
The measurement I took was on the crank not ID of rod big end. Which is the ts 47.950-47.965 mm measurement you refer to?
this is Turbo engine 606.962. I have been reviewing con rod spec in WS manual here http://www.w124performance.com/service/w124CD1/Program/Engine/605_606/03-6111HA.pdf
One thing I don't get - crank has oil feed holes @ big end, yet bearings have no holes?
RE: How to measure big end & crank for sizing new bearing shells - hansendk - 09-12-2013
to 1 first yes
second also yes
oil is comming from the main bearings to the con rods that why they have no oil holes
messure your crank pins and they schuld be 47.95-47.965 mm or 1.8877-1.8883 inch.
RE: How to measure big end & crank for sizing new bearing shells - fcp - 09-13-2013
(09-12-2013, 07:14 PM)hansendk to 1 first yes
second also yes
oil is comming from the main bearings to the con rods that why they have no oil holes
messure your crank pins and they schuld be 47.95-47.965 mm or 1.8877-1.8883 inch.
Cool, so that makes sense. Apologies if this stuff is very basic to be teaching, but I'm a software architect by trade.. this stuff I'm learning as I go along a bit :-)
RE: How to measure big end & crank for sizing new bearing shells - hansendk - 09-13-2013
no need to apologies that's what the forum is all about helping each other and it happens that my job is workshop manager engine remanufacturing but that doesn't mean I know everything.
if it comes to software you have to teach me the basic.
its better to ask than make mistakes