VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Wear on Mains vs Rods

Ok ::: I have some good numbers now and can talk out of the front of my mouth.

I have measured my 1938 Chevy 216 crank accurately for Wear (average of 4 readings of the reduction of diameter of journal, 2 axially along the journal top to bottom and 2 associated with each of these but side to side[90 degrees to first set]), Out of Round (difference between two diameters chosen randomly but at 90 degrees to each other) and Taper (difference between the diameter at one end of journal and diameter at the other end of the journal along the axis of the crank).

Before I present the numbers let me ask if anyone knows if the rod journals for these 216s generally wear more than the main bearing journals or do the mains wear more than the rod journals??? This may shed some light on the issue I have repeated raised here about the error in journal dimensions listed for 37-38 versus 39 on by Chevrolet Shop Manuals. If the 37-38 Manuals are in error, then the smaller diameters (by .002 inches) of the journals for mains are correct. Whereas the rod journal diameters are listed the same for both the 37-38 listings and for the 39- listings. I hope you see what I am getting at?

First the 39- listing Specs:
Main # 1 = 2.6840 +/- .0005 inches
Main # 2 = 2.7150 +/- .0005
Main # 3 = 2.7460 +/- .0005
Main # 4 = 2.7770 +/- .0005

Now the 37-38 listings Specs:
Main # 1 = 2.6860 +/- .0005 inches
Main # 2 = 2.7170 +/- .0005
Main # 3 = 2.7480 +/- .0005
Main # 4 = 2.7790 +/- .0005

For All years (both 37-38 listings and 39 onward listings) Rod Specs:
Journal Diameter = 2.3115 +/- .0005 inches

My measurements of Crank:
Main #1=2.6790 to 2.6808 inches[OutofRd = .0018:: Taper = .0008]
Main #2 = 2.7102 to 2.7106 [O.of R. = .0004::: Taper = .0004]
Main #3 = 2.7410 to 2.7418 [O.of R. = .0008::: Taper = .0008]
Main #4 = 2.7728 to 2.7728 [O.of R. = .0000::: Taper = .0000]
Main #4=2.7736 to 2.7739 (frwd,rear on journal) [O.of R. = .0003]

Rod #1 = 2.3067 to 2.3070 inches [OofR = .0003::: Taper = .0005]
Rod #2 = 2.3059 to 2.3077 [O.of R. = .0003::: Taper = .0018]
Rod #3 = 2.3069 to 2.3061 [O.of R. = .0008::: Taper = .0010]
Rod #4 = 2.3052 to 2.3068 [O.of R. = .00015::: Taper = .0007]
Rod #5 = 2.3052 to 2.3064 [O.of R. = .0013::: Taper = .0003]
Rod #6 = 2.3066 to 2.3063 [O.of R. = .0003::: Taper = .0009]

Main # 1 Wear = .0041
Main # 2 Wear = .0046
Main # 3 Wear = .0046
Main # 4 Wear = .0042
Main # 4 Wear = .0033

Rod # 1 Wear = .0047
Rod # 2 Wear = .0047
Rod # 3 Wear = .0050
Rod # 4 Wear = .0055
Rod # 5 Wear = .0057
Rod # 6 Wear = .0050

All of the above wear readings are based on the 1939 Chevy Shop Manual Specifications. If one uses the 1937-1938 Chevy Shop Manual Specifications then the numbers for wear are:

Main # 1 Wear = .0061
Main # 2 Wear = .0066
Main # 3 Wear = .0066
Main # 4 Wear = .0062
Main # 4 Wear = .0053

Rod # 1 Wear = .0047
Rod # 2 Wear = .0047
Rod # 3 Wear = .0050
Rod # 4 Wear = .0055
Rod # 5 Wear = .0057
Rod # 6 Wear = .0050

As you can see, if the 39- dimensions for crank are used, then the journals of mains are wearing slightly less than or about the same as the rods. Were as if the 37-38 dimensions are used, then the mains are definitely wearing more than the rods. To add to this I see that the mains are more scored and rough than the rod journals regardless of these reported numbers.

So which pattern is to be expected for the 216 nozzle-fed and oil dipper lubed powerhouse??? Now you see why this information may shed light on the error that has been driving me crazy? Any help would be appreciated.
Mike

From my memory - back when these engines were newer, the rods loosened up more than the mains. That is the babbit wore/compressed faster on the rod bearings. This depended a lot on how the engines were driven/maintained. The highway car engines in general required fewer rod and main bearing adjustments than the short trip city cars. But then the rods will make noise a .002" and the mains will not make noise till about .004". The pressure oiling to the mains may make the difference by have a constant oil feed.
Very few mechanics ever measured the shafts when overhauling or adjusting bearings.They usually just removed shims if everything looked good. If the rod journals had a raised area in the center (in line with the oil grove in the rod) they knew that the journal was worn. Usually this did not happen until the car/engine had a lot of miles or was getting very old and just removed more shims or filed the rod caps. When things got too bad they just installed a new short block but this was seldom done due to the expense.
I would say that your wear pattern looks normal. I doubt if there is any general rule. If the engine was well maintained and never run with loose bearing the bottom end would be good for 100,000 miles with the poor oils of the day. Probably would go twice that with moden oils. The 1948 and up bearings that had thinner babbit required far fewer bearing adjustments.

As you can see, if the 39- dimensions for crank are used, then the journals (foreget the babbit) of mains are wearing slightly less than or about the same as the rods [Average Wear of 4 Mains = .0044 inches and that of rods = .0051 inches]. Were as if the 37-38 dimensions are used, then the mains are definitely wearing more than the rods [Ave Wear Mains = .0064 and Wear on rods = .0051]. To add to this I see that the mains are more scored and rough than the rod journals indicating possibly they wore more (?). I need a cranshaft man who has measured cranks ??? Any comments on crankshaft wear???
Mike

Mike
In most cases the conrod journals will wear more than the main journals as they take the brunt of the load and the mains only rotate therefore wear less.
Tony

Tony's observations of rod wear vs main wear supports the 1939 Specification numbers (as opposed to the 37-38 Specifications) as being correct. The case for an error in the 37 and 38 Shop Manual is getting very solid. {Shame on you Chevrolet}
Mike

The Taper and Out of Round Readings are also higher for the rod journals than for the main journals. This could indicate more wear, and support the 1939 Spec as being correct. I am puzzled by the score marks on the main journals. Since the mains are pressure fed, perhaps dirt can get trapped easier there than the scooper (and nozzle feed) feeding for the rods?
Mike

I just recently installed a set of main bearing inserts in my 1957 283. Three of the five bearings had the score lines, and that engine has a full flow oil filter.

I still believe that the 1937-39 cranks were the same demensions when new.

The evidence that the 37-39 crankshafts were all the same and consistent with the 39-Specs is very high and supported by one of the best sources of knowledge of that era: ChevyNut. What has thrown me into this unrelenting pursuit of the truth is the apparent error in the 37 and 38 Chevrolet Shop Manual and its repetition in the 1935-1952 Motors Manual. I very appreciate ChevyNut’s comments and insight into this matter. Also all the others who are contributing to my obsession to understand this. If any others have data or evidence of rod journal vs main journal wear, I appreciate hearing it. Thank you all.
Mike