Yes but are some grooved and others plain?

 

On s4 I have all main lower halfs solid...top half has a midline groove and holes....this top half goes on the block side.

 

"Early" cars had split front bearing with all bearings grooved...except the thrust bearing, which had "narrow" faces.

"Dimensions" are all the same, with the exception of the thrust bearing.

Porsche "superceeded" the early bearings and made the front bearing one piece. The "lower half" of the main bearing shell had very short grooving, resulting in approximately 200 degree of oil groove.

These have been the only bearings that have been available, for years.

An "early set" should be dimensionally the same as a "late set" of bearings, with the only exception being the thrust bearing.

I've never seen or been able to order a set of bearings with overside OD.

 

Might be helpful to know what you wish to accomplish.....lots of experience on the forum...You may not be asking the right questions...

 

for those that know, here is what i calculated as main bearing oil clearance and rod bearing clearance, if someone disagrees, let me know....

mains: .0027-.0035 "

rods: .0020-.0028"

so according to my calcs, you have .0008" leeway to play with.

 

Not that it much matters but I recently took an '84 (USA version) apart that had 1 piece front bearing. And I am pretty certain the engine was never apart before....

 

RE: clearance on the mains, unless you have a TBF crank that has been chewed on by the dying thrust bearing, has anyone ever seen a crank whose mains would have justified .25mm undersized bearings?

 

Sure...but we threw it away. Used cranks are plentiful and cheap still. Noit sure you can have one correctly machined undersize, for the price of a perfect used one.

 

Really? I guess it's the measure of "correctly" that is in play.

I had an old Buick crank undersized recently on the mains and journals for $107. Not much more than a polish and inspection.

 

I've got a "shelf" full of standard/standard 5.0 cranks that I'd be thrilled to get $250 each. They will sit around for years and finally get thrown into the recycle metal bin, long before they are "rare".

Getting a crankshaft turned undersize, correctly, is a really tough thing, at least in my area. (Turned undersize, not polished, inspected, and cleaned.) Not many crank grinders want to spend the time to correctly shape the edge of the stone to match the different radius requirements of various crankshafts (and the ones that do take this time want to be paid to do it.....so getting a grinder that takes the time to do this, is usually expensive....more than $250.) The "result", if the stone is not shaped correctly, is a "chatter" in the radius of the journals.

If the radius isn't perfect and has these "chatter" marks, the result will be a stress riser, where a crack will form. I will not use any crankshaft with a "chatter" in the radius....they are complete garbage, to me.

 

Thanks for the clarification. The level of custom work for these cars is high.

Perhaps the shop (a big crank specialist in Minneapolis) has the tools for a Buick crank on its shelf. Always nice when the counterman IDs a part faster than I can say it.

 

Over the last couple of days, I've been trying to measure a 928 crankshaft more accurately, purely for fun.

So what is the spec for the rod journals? I am guessing something like the following, some from the service manual and some from the specs of other V8 crankshafts:
Rod journal diameter: Nominal size - 0.01mm, tolerance -0.02mm
Rod journal fillet radius: 2.5mm, tolerance -0.5mm
Rod journal surface roughness Rz: 2µm, tolerance -1.2µm
Maximum rod journal taper per half the journal length: 0.01mm? 0.02mm? (pure guess based on other V8 crankshafts)
Maximum rod journal out of round: 0.005mm? 0.01mm? (pure guess based on other V8 crankshafts)

(If somebody searches for this later, don't believe any of it. Nobody should assume I can read prints or specs. Go read WSM pages 13-21, 13-21. And the last two are guesses.)

I don't understand why that would be hard for a crank grinder to accomplish, what's unusual about that spec? It's not financially worth it to turn them to the next undersize bearing, I am not arguing that. The number of good used S4 cranks is large and, importantly, declining slower than the number of blocks in which they can be used. Just wondering where's the difficulty?

 

Only crank worth working on is GTS. All other variants can be found really cheaply.

 

+1.

 

At the Munk auction, cranks went for about $50 there were several, couple had spun bearings still $50