330 main bearing groove installation

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carello
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330 main bearing groove installation

Post by carello » Wed Aug 28, 2013 8:20 am

In reviewing the main bearing shell installation for a 330, I find the grooved shell insert installed in the lower cap rather than the upper crankcase. The loading takes place in the lower cap, so why are these grooved half shells reverse from normal engine design practice (groove in upper half)?
Maybe I am misreading or misunderstanding the parts list?
Cheers
Craig
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DWR46
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Re: 330 main bearing groove installation

Post by DWR46 » Wed Aug 28, 2013 11:33 am

This has been discussed to death on the Vintage lamborghini Forum. The oil feed from the block is routed through groves in the block and main caps to behind the lower bearing shell, then through the shell, so the fresh oil is placed under the crank to cushion the combustion downward powerstroke pressure on the crankshaft. The groove in the lower shell itself promotes the oil flow to the rod bearings via the drilled passageways in the crank itself. People have gotten far more techincal, but this is a quick summary.

330Jim
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Re: 330 main bearing groove installation

Post by 330Jim » Wed Aug 28, 2013 2:52 pm

It finally occurred to me that this is why many (if not all vintage V12s) see an oil pressure variation when you let off the gas. I have seen it on a couple of 330's, when you are on the gas the oil pressure is higher, when you let off the gas the oil pressure drops even though the RPM does not change. Under load, the bearing to crank clearances are tighter and therefore the oil flow is reduced increasing the oil pressure.

Technically speaking I am not a fan of the grooved lower bearing. It reduces the load carrying capability of the bearing in half.

Cheers Jim

DWR46
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Re: 330 main bearing groove installation

Post by DWR46 » Wed Aug 28, 2013 8:09 pm

Jim: Usually, it is the other way around. Main bearings with excessive clearance will usually manifest themselves by the oil pressure taking a dip when the throttle is opened and junping up when the throttle is closed quickly. Obviously, as the revs build the oil pressure will still go up, but there will be a dip as the throttle is opened. The pressure variance is caused by the crank moving around too much in the bearings. When I inspect or test a car, this is always something I take a look at.

330Jim
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Re: 330 main bearing groove installation

Post by 330Jim » Thu Aug 29, 2013 2:46 pm

True for a typical bearing that has the oil feed in the upper bearing. These engines have the oil feed in the lower bearing so they are the opposite, that is what was puzzling me.

Cheers Jim

DWR46
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Re: 330 main bearing groove installation

Post by DWR46 » Thu Aug 29, 2013 5:31 pm

JIm: All I know is that is the way the oil pressure gauge reacted in every Ferrari I have seen with excessive main bearing clearances. Heavier weight oil will mitigate the situation.

jroswell
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Re: 330 main bearing groove installation

Post by jroswell » Thu Aug 29, 2013 8:41 pm

330Jim wrote:It finally occurred to me that this is why many (if not all vintage V12s) see an oil pressure variation when you let off the gas. I have seen it on a couple of 330's, when you are on the gas the oil pressure is higher, when you let off the gas the oil pressure drops even though the RPM does not change. Under load, the bearing to crank clearances are tighter and therefore the oil flow is reduced increasing the oil pressure.

Technically speaking I am not a fan of the grooved lower bearing. It reduces the load carrying capability of the bearing in half.

Cheers Jim
Jim - you appear to be saying that because the groove divides the bearing in half, it reduces its capacity by half. This is not true; the load capacity is determined by the area of the bearing, and would only be reduced by the width of the groove as a percentage of the total width. Example: If the bearing is 50 mm wide and the groove is 2.5 mm (I'm estimating as I don't have a bearing handy) then the area is reduced by 2.5/50 or 5%.

330Jim
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Re: 330 main bearing groove installation

Post by 330Jim » Thu Aug 29, 2013 11:55 pm

jroswell wrote:
330Jim wrote:It finally occurred to me that this is why many (if not all vintage V12s) see an oil pressure variation when you let off the gas. I have seen it on a couple of 330's, when you are on the gas the oil pressure is higher, when you let off the gas the oil pressure drops even though the RPM does not change. Under load, the bearing to crank clearances are tighter and therefore the oil flow is reduced increasing the oil pressure.

Technically speaking I am not a fan of the grooved lower bearing. It reduces the load carrying capability of the bearing in half.

Cheers Jim
Jim - you appear to be saying that because the groove divides the bearing in half, it reduces its capacity by half. This is not true; the load capacity is determined by the area of the bearing, and would only be reduced by the width of the groove as a percentage of the total width. Example: If the bearing is 50 mm wide and the groove is 2.5 mm (I'm estimating as I don't have a bearing handy) then the area is reduced by 2.5/50 or 5%.
That is what I thought at first too. However you have to look at the pressure profile across the bearing face. A bearing with no groove in it has a full arc that goes from one side of the bearing to the other (axially). The area of that arc, represents the load carrying capability of the bearing. On a bearing with a groove in it, you have two arcs, one from the outside edge to the groove and the same thing on the other side. Since the pressure profile is interrupted your pressure profiles are much smaller. The net result for a grooved bearing is the area of the pressure profile is half that of a bearing with no groove in it. This results in half the load carrying capability. Note the pressures in this profile are much higher than the engine oil pressure, so the engine oil pressure is a very minor factor. Don't get to worried about it thought, even with the reduced bearing carrying capability these engines still have enough bearing area to support the loads they are experiencing. It is just something you would not do in a modern engine. Back in the fifties and sixties engine design was more seat of the pants, as a result you had some interesting approaches compared to what we are used to today.

Cheers Jim

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carello
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Re: 330 main bearing groove installation

Post by carello » Fri Aug 30, 2013 8:12 am

The crankshaft is drilled to receive oil feed from the oil pump thru the main bearings. In turn, these mains feed and distribute oil under pressure, thru the crankshaft, to the rod big ends. Would the drilled passages in the crankshaft have any bearing on where the grooved/holed shell half is placed?

Since this grooved main shell is so opposite to modern(?) practice, why is this not more clearly understood after 50 years with 330?
Thanks
Craig

330Jim
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Re: 330 main bearing groove installation

Post by 330Jim » Fri Aug 30, 2013 2:50 pm

carello wrote:The crankshaft is drilled to receive oil feed from the oil pump thru the main bearings. In turn, these mains feed and distribute oil under pressure, thru the crankshaft, to the rod big ends. Would the drilled passages in the crankshaft have any bearing on where the grooved/holed shell half is placed?

Since this grooved main shell is so opposite to modern(?) practice, why is this not more clearly understood after 50 years with 330?
Thanks
Craig
Yes the drilled passages in the crankshaft are related to the grooves in the bearing. Off the top of my head I do not remember the configuration Ferrari was using in these cars so I cannot comment on the design. There are several ways to drill the crank with various pros and cons. High end engines tend to use cross drilled cranks to minimize over scavenging the main bearings due to the centrifugal loads on the oil at the rods from high RPM. Lower end engines tend to have a straight through hole to minimize cost. This works fine until about 6000 RPM then the cross drilled cranks tend to be needed.

I don’t understand your second question, what is not understood? I see nothing wrong with the 330, it just appears they choose to maximize slightly different aspects then we would typically choose today. This is not uncommon for the era these engines were designed.

Cheers Jim

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