Strange crankshaft wear pattern

[swampbuggy]

Since we are talking about Crankshafts, I thought you guys might enjoy seeing this one. Its a Winberg SBC. -Mark

[smeg]

Yes Winberg do beautiful work, we have used his cranks before.

[pamotorman]

this issue january/march of engine professional has a article on rods and the one illustration of what happens to the rod bearing bore at TDC exhaust is interesting.

[MadBill]

Captain Obvious says the bore gets tall and skinny...

[Warp Speed]

Captain Obvious says the bore gets tall and skinny...

LOL

[swampbuggy]

Assuming that you are agreeing with Madbills remark Warpspeed, do you figure that Pankl rods do the same thing or not ? If NOT is that the main reason the ELITE of NASCAR started using Pankl rods ? Thanks Mark H.

[ptuomov]

Here's a question (not a statement): When a high-level specialty components manufacturer makes a high-budget small-series crankshaft, say for a very high budget factory-backed racing operation, how much design support do they get from the factory? I've assumed a fair bit, but that's just an assumption.

In terms of the crankshaft oil passages, I think the thinking has indeed evolved over the years. It looks like me (a total outsider) that 25 years ago designers put a high premium on continuous oil flow from the mains. Now, they seem to put more of a premium on angles of the passages. For example, the straight shot single drilling oiling used to be popular. But I think the rod bearings got so short that the oil passage needs to be as normal relative to the journal surface as possible, so now the initial hole from the rod journal surface towards straight the center seems to intersect the long passage in an angle. Another example is main journal vs rod journal diameters. The new BMW engines that have electronically controlled oil pump flow volume have rod journal diameters that are larger than the main journal diameters. I can't read people's minds, but it seems to me that this will reduce the required main supply pressure and simultaneously allow even shorter rod bearings (because of the larger diameter). This in turn allows the bore spacing to be much smaller for the turbocharged unit. I'm rambling, but of course stuff evolves, and I'd very much like to understand why.

If you go back to the original poster's observation, it's the following. The rod bearing is worn at one spot and the rod journal is worn at another spot. Usually, rod journal does not wear without the bearing wearing too on the other side, as the journal is a lot harder. When you align the rod journal and the bearing shell such that the damaged parts are aligned, that's not at an angle at which there are any obvious tension or compression forces at the worn location. So the question is what's going on? Any ideas? My guess was that it's cavitation where the clearance expands dynamically, which can create forces that are large enough that damage both the journal and the bearing. But that's just a guess.

[Kiggly]

As an update, it appears the additional ~20psi oil pressure is helping. The bearing wear pattern is smoother and shinier, rather than a bit striped and more of a digging in look it had with lower pressure. Unfortunately, I moved to a crank where it already had some passes and I’m not going to be able to answer the crank wear question. Given the ride bearings have looked better at service intervals, the crank is probably seeing less abuse as well.

The only gotcha is valvoline changed the formulation of their 50wt vr1 oil. It is darker and smells different. I don’t know if this is an influence, all of the effect, or no relation at all to how the bearings look now.

[naukkis79]

Changing oil from 50wt mineral to some narrow-viscosity index synthetic probably would make wonders to rod bearing life. For high stress use rod bearings need lots of oil flow and with 50wt viscosity that flow is really hard to achieve, resulting high rod bearing temperatures and high wear.

Those whole VR1-line of oils seems to be done for lawn movers and other low-rpm engines, for 10K rpm use there's much better suited oils available.

[peejay]

Changing oil from 50wt mineral to some narrow-viscosity index synthetic probably would make wonders to rod bearing life. For high stress use rod bearings need lots of oil flow and with 50wt viscosity that flow is really hard to achieve, resulting high rod bearing temperatures and high wear.

Those whole VR1-line of oils seems to be done for lawn movers and other low-rpm engines, for 10K rpm use there's much better suited oils available.

Then why do people run straight 50, 60, or even 70 in TA engines?

This is a legit question. I thought the idea was that you had to run fairly open clearances so that when everything flexes and walks around it won't bind up, and then you needed to run super thick oil so that it actually stays in the journals, combined with having to combat the typical oil dilution you get with a high powered engine. Has time moved on?

[naukkis79]

Then why do people run straight 50, 60, or even 70 in TA engines?

I don't know why anybody would want to lubricate engines with asphalt and expect them to last.

This is a legit question. I thought the idea was that you had to run fairly open clearances so that when everything flexes and walks around it won't bind up, and then you needed to run super thick oil so that it actually stays in the journals, combined with having to combat the typical oil dilution you get with a high powered engine. Has time moved on?

You need to use super thick oils if there is minimal flow to rod bearings. Many old-school engine design don't have adequate flow to keep rod bearing temperatures in control. Worst oil for conrod bearing temperatures are expanded viscosity-index(5w-50 etc) as viscosity expanders only prevents oil to flow, it isn't actually helping lubrication at all. Straight 50 mineral oil is much better than 5w-50 synthetic but proper not viscosity expanded synthetic oil is much better. Nowadays engines mostly use very thin 0W-0 5W-5 grades but for large bearing clearances some 10W-30 might be spot on. It will flow much more than 50wt mineral and still has at least as good or better high temperature lubrication properties.

[peejay]

Then why do people run straight 50, 60, or even 70 in TA engines?

I don't know why anybody would want to lubricate engines with asphalt and expect them to last.

Well, given that these are engines that typically do not have water jackets, and only see WOT for five seconds or so while 60+psi of boost is thrown at them, "last" implies different priorities than most engines.

Worst oil for conrod bearing temperatures are expanded viscosity-index(5w-50 etc) as viscosity expanders only prevents oil to flow,

Wonder why BMW has had so many problems with the M six cylinder engine, then! They specify 5W50 (or was it 5W60?) and they need rod bearings every 60kmi or so.

I thought the bad thing about viscosity modifiers was that they broke down more quickly, and increased aeration.

[smeg]

Changing oil from 50wt mineral to some narrow-viscosity index synthetic probably would make wonders to rod bearing life. For high stress use rod bearings need lots of oil flow and with 50wt viscosity that flow is really hard to achieve, resulting high rod bearing temperatures and high wear.

Those whole VR1-line of oils seems to be done for lawn movers and other low-rpm engines, for 10K rpm use there's much better suited oils available.

By what experience do you have with VR1 oils to make that statement?
We use VR1 10-40 in lots of our engines, offroad race, street strip, drag race and have never had a problem ever ziltch.
Horses for courses, if I was doing an engine for 10,000 rpm, I wouldn't be using VR1. Your statement about lawnmowers and low rpm?????
High rod bearing temp and wear with 50 wt oil?? Our sprint car engines going 8500 + don't tell us that.

[Kevin Johnson]

I agree with debris, but not sold on it being actual dirt. I dot see how any dirt could or would get into the system, everything is filtered to the outside world. ...

The passages to the cross-drilled rod pins extend diagonally through the cross passage and are plugged by the factory (visible in your photo). This short diagonal blind hole could capture and retain detritus from the previous wear you observed/remarked-upon and incrementally release it by being disturbed by pulses from the cross-drilled mains (mentioned SAE paper available on this). Every factory piece (crank forging) is going to be somewhat unique in external and internal morphology and this could help explain why you only began observing this wear on this particular crank. I am assuming you also subsequently switched cranks in addition to the increase in oil pressure* and noted physical differences in the lubricant. Good plan to move to a dry sump.

*A good thing which helps to suppress free air bubbles thereby combating their coalescing into larger bubbles.

P.S. With great difficulty I restrained myself from creatively invoking radon gas this time. I apologize for just now seeing the thread. I wasn't feeling very well in January.

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