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Discussion Starter #1
Hi

I have experienced big end bearing failure this past weekend for the third time this race season. I have a 2L moderately tuned Nord engine in my race car. Other than the usual causes of big end bearing failure such as dirt, incorrect clearances and oil starvation, are there any Alfa specific causes of big end failure? I have a high capacity oil pump and baffles in the sump, so I pressume I can rule out oil starvation. I really need to get to the bottom of these bearing failures as it is becoming a hugely costly exercise.

Thanks
 

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Hi Rubel,
What do the failures look like? can you post some photo's? Are only the rods bad or mains as well? What clearances are you using? What mfg bearing shells? Do they fail all at once or from rear to front? What is the crank surface like, & has it been treated/hardened or anything? Let me know, perhaps I can help. Gordon Raymond
 

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2000s are noted for losing crank oil gallery plugs, but I presume on a race engine you've solved that already?

Andrew
 

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What big end? #1, 2 or 3, or 4 (or is it random)? The 2 and 3 big ends are both fed through # 3 Main (and also feed 2 and 4 mains, whereas # 1 and 4 each are fed only by one main, therefore 2 and 3 big ends can suffer from inadequate pressure and volume.

Has the crank been ground? A few times and not been rechamphered? I would ever only use a good standard nitrided crank in a race engine.

Two tricks are encreasing the oil pressure by shimming the pressure relief valve (there is plenty of capacity in the pump), and restricting the feeds to the head (6, 1 mm restrictors in the top of the block).

Have you cross drilled the block?

Old rule of thumb is 10 psi for every 1000 rpm: that means, you should have at least 75 - 80 psi in a full race Alfa engine under race conditions.

Moderately tuned? What does this mean? 160 bhp at 6300? If so and you only have 60 psi, and you are revving it to 8000 rpm: problem found!
 

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Clayton, although I have heard the suggestion before, I don't understand how shimming the relief valve will increase oil pressure? For example, my race engine would easily exceed 100 pounds when cold if the relief valve were not bleeding off pressure. However, the fact that I see nearly 100 pounds cold tells me that this is where the valve is releasing. On the track at 50, 60, 70 pounds, the relief valve should be completely closed. Shimming it wouldn't increase pressure hot. What am I missing?

Erik
 

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Discussion Starter #8
Hi

Thanks for all the advice.

Unfortunately the bearing let go in a big way so there aren't really any pieces worth photgraphing.

Although the main bearings seem fine, they were damaged by the shrapnel from thedisintegrated big end bearing.

According to my engine builder we are running standard clearances with AE bearings. Someone has suggested we try an Australian made bearing known as ACL?

The three failures have all been on different cylinders. We have always started with a standard crank and machined it to 10 thousand. I don't think we've ever re-hardened or nitrided the crank.

We haven't in the past replaced the plugs with allen screws but will do it this time round.

It doesn't seem as though it was as a result of oil pump failure.

What is an accusump?

We have not cross drilled the block but will do it this time.

Moderately tuned meaning 160bhp at 6 300. Our oil pressure runs at between 60psi to 70 psi. One thing that is worrying me is that since we installed an oil cooler the oil is running very cool at about 150 degrees F. Is this too cold?

Thanks again for all the advice. It is much appreciated
 

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Good question! I love this sort of thing… So I take it that this is what is actually happening, not a likely scenario or situation?

My question to you is: how long since you had your engine down? Are you sure your relief valve is operating as it should? And are you asking what is wrong with your engine or how does shimming work?

I will try to answer all as I think it is of value to the topic.

There are a few intertwined concepts to understand here: The first is that an oil pump itself is a positive displacement pump (in theory only, as there is some leakage around the gears). The volume of fluid that is displaced is relative to the speed of the pump (engine speed). That means, at idle, there is very little flow out the pump and the oil pressure will be quite low. From what I remember, a standard Alfa has about 5-10 psi at idle. However, as the revs rise, what changes? Think about it… The flow out of the pump will rise as a function of engine speed, but will the demand for oil? The answer for this is no. While the engine parts are spinning, this does not mean that the clearances in the bearings will increase relative to pump output. Oil pressure is a hydrodynamic function of flow rate, restriction and viscosity. Flow rate from the oil pump is governed by engine speed. The oil pressure (taking out of the equation the pressure relief valve) is governed by the volume that is delivered by the pump to the restrictions in the lubrication system. That is: the pump pushing the oil past the bearings: these are constant no matter what the speed of the engine. The bearing clearances will change minutely as the engine heats, but for this case we can assume they are also constant. I am not sure of the effect of a spinning shaft on the calculate-able restriction in the bearings, and I know there is a self pumping phenomenon, I will also assume it is negligible. As viscosity of oil is also a function of heat (not linear), for this explanation, we can ignore this also.

Therefore: without a pressure relief valve, we have a system where there pressure will rise in a linear fashion with engine revs. When the pressure relief valve (PRV), opens the pressure should remain constant as the revs rise further. If it does not open, theoretically the pressure will keep rising with engine revs: not acceptable and the reason for the well known Alfa burst oil filter syndrome (when the PRV is stuck closed).

The PRV should not be open at idle. If it is that says that the pump capacity is way too high. If you have a standard pump, then something is just not right…

Shimming the PRV will delay the point at which the PRV begins to relieve the pressure, therefore effectively raising the oil pressure. The amount that the PRV is open to maintain the oil pressure at a particular temperature is governed by the principle explained above. That is: the relationship between volume, restriction and viscosity.

In you case, it sounds as though you need either an oil cooler, or there is something slightly amiss with the relief valve. I would not be racing with less than 70 psi in any case!
 

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Why grind the crank? Speaking as a person who used to work in an engine reconditioning centre (and has ground cranks) i.e. knows the tricks of the trade....

Engine reconditioners love racers: they get to do all this unnecessary work and earn more $$$$.

A standard alfa crank can have mega miles on it and be perfect for racing with nothing more than some screw in crank dowels. They are nitrided as standard and balanced within a nat's dick so tell the engine dudes to check and adjust the balance after putting in the dowels and then leave the bloody thing alone!

If you are blueprinting the engine and the crank is good, the BE clearances should be set by resizing the rods.

There are main bearings (Federal Mogul?) available that have a groove running around the inner circumference on all 5 bearings to distribute oil. Drill 2 and 4 to suit your cross drilled block and use these in conjuction with the other mods I recommend above and the bottom end should be cool for 7000 all day.
 

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Thanks for the reply to my question, Clayton. You confirmed what I thought to be true, shimming the relief valve will only be useful if it is bleeding pressure at a lower pressure than you want it to. In other words, if you want 75 pounds hot, and the the relief valve doesn't open until 75 pounds or greater, it won't help your situation.

Rubel, if you don't have threaded plugs for the crank galley's, I would at least hope you have drilled the plugs out and THOROUGHLY cleaned the crank after each mishap. It's amazing how much debris can remain in there! I am quite sure your problem isn't with the bearings you are using. Lots of us have used AE's without incident. Drilling your block for direct oiling of the 2/4 mains is a good idea (don't forget you need the grooved bearings). These mains oil through the #2 and #3 rods on a stock block. But I wouldn't expect a rod problem without the modification.

An Accusump is a very good idea. It serves as a reservoir of pressurized oil. Should the oil pump pick-up lose contact with the oil in the sump, the Accusump will save your engine. Of course, you don't want to have to rely on it any more than you have to. A good system of baffling will keep the oil around the pickup. I use the one sold by Paul Spruell. It is relatively cheap and effective.

Finally, you didn't mention what type of oil you are using, but I wouldn't run anything other than a quality synthetic in a race engine. And 150 degrees F is WAY too cold! You must have a massive cooler. My race engines run between 220 F to 240 F when they are right.

Erik
 

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Discussion Starter #13
Thanks again for all the advice. We use fully synthetic Castrol Edge Sport 10W60 oil. The engine builder has confirmed that the crank has been thoroughly cleaned out after each mishap.

Where on the engine do you put the sender unit for your oil temp gauge? Our sender unit is on a T - piece inserted into the block where the oil pressure guage sender unit normally goes. Do you think it will make a difference to the temp reading where the sender unit is placed?

When you speak of baffling are you referring to baffles in the sump or a windage tray?
 

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I wouldn't think you would get dramatically different temperature readings from one point to another? My oil pressure and oil temp readings come off the oil galley at the top passenger side rear of the block. I believe this is the location of the stock oil pressure sender. If I'm not mistaken, the stock low oil pressure light sender was on the drivers side just behind the filter fitting. Either location would read the oil temp shortly after it returns to the block from the oil cooler and before it is delivered to the journals.

The baffling I referred to is an sheet aluminum piece that is attached to the stock sump to "trap" oil around the pick up when cornering. I use it in conjunction with a windage tray. They both come from www.paulspruell.com . Modern race tires generate a lot of traction that can move the oil away from the pick up. A "trap" and an accusump are good ideas in my opinion.

Since 2L cranks are relatively plentiful, I would rather find a good used crank than cut one undersize. If not re-nitrided, they will be soft and are more likely to score with less use. That shouldn't be the cause of your problem however.

After I spun a rod bearing a couple years ago, a couple of the people I consider experts suggested that I try to determine if the cylinder was detonating. If you were getting detonation, you could tear up rod bearings, although you'd expect to see piston/rings/head damage as well. One last thought is to make sure your oil cooler is thoroughly cleaned out after each incident. I know racers who will throw away an otherwise good cooler after an engine failure. Since the cooler should be after the filter, that seems like overkill. But it's a good idea to make sure no debris has collected.

Hope that helps!

Erik
 

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I was also wondering about the oil cooler, with previous major failures did you replace the oil cooler or have it ultrasonic cleaned. My suspision is that something is not clean.
 

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Discussion Starter #16
Hi guys

I've just been speaking to our engine builder and he is not sure how to go about cross drilling the block as you have suggested.

Could you please post a "step by step guide" on how to go about it.

Thanks again for all the advice.

Cheers
 
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