One more time, rod side clearance

General engine tech -- Drag Racing to Circle Track

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Kevin Johnson
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Re: One more time, rod side clearance

Post by Kevin Johnson » Mon Apr 09, 2018 9:21 am

Jay, does your AVL measure aeration as well as flow?

Thanks.

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Re: One more time, rod side clearance

Post by Newold1 » Mon Apr 09, 2018 10:42 am

Again. I am not putting forward some idea that I know how the oil in the rod bearing crank rod journal interface behaves, because I don't really know!

I would think that the oil in this area flows to the area of least resistance and that is obviously out the sides of the rods sides either between two rods or out the side at the crankshaft rod journals fillets.

My question here for the experts is does the pressure put against the oil wedge between the bearing surface and journal surface receive added pressure from the movement of the piston & rod during the complete stroke cycle? I think it probably would but that's just a guess on my part. My reason for asking this question is if that added pressure occurs and the only place for the oil under added pressures to exit is going to be out the areas where the side clearances are it would seem as though a wider clearance there would allow more oil to exit at that juncture than a tighter clearance would. Apparently from what some are saying here it that does not happen and the side clearance spaces being wide or narrow have NO EFFECT on that oil exit volume.
I understand that bearing to journal clearances in most cases are between .002" to .0035" and that in itself does not leave a lot of oil area for a pump up scenario but I have to believe that the oil system is supply under pressure enough oil to maintain the oil wedge there and as I keep saying that oil supply has to move and be replaced and can the wider side clearance increase the volume of oil exiting the sides of the rods? That's my question and how can someone verify one way or another that wider rod side clearances have no effect on that exit volume? Can it have and be shown to have any effect on running oil pressures in the engine? :?:

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Re: One more time, rod side clearance

Post by Warp Speed » Mon Apr 09, 2018 11:26 am

Kevin Johnson wrote:
Mon Apr 09, 2018 9:16 am
Jay, if the bearing witness marks on this journal are from (a) piston guided rod(s), is it your opinion that the oil holes are not optimally located? Would you accept a crankshaft like this or have the drillings adjusted in a new one?

Thanks.

question.gif
Yes, the poor alignment of the feed holes to the bearing, coupled with the angle of attack they have in that crank oiling strategy could cause leaks. Some re-design required there to be optimum.

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Re: One more time, rod side clearance

Post by Warp Speed » Mon Apr 09, 2018 11:27 am

Kevin Johnson wrote:
Mon Apr 09, 2018 9:21 am
Jay, does your AVL measure aeration as well as flow?

Thanks.
Ues, oil flow and density are both measured.

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Re: One more time, rod side clearance

Post by CharlieB53 » Sat Apr 14, 2018 7:47 am

If oil slung up into the cyl's were a problem I suspect manufacturers would have redesigned the block, partially closing off the bottom of the cyl leaving only a rod 'slot' pretty much the same as we see in the Mercury Marine 2 stroke V6. Said rod slot would block most of the oil slung off the crank, very effectively limiting cyl oiling. This could be a serious problem as it would also limit piston cooling from the lack of oil.

Piston oil squirters will provide additional piston cooling, but the added complexity of production engines may out-weight the benefit except for specialized applications, i.e., industrial/marine engines.

IIRC some rod manufacturers have 'notches' in their rod to direct slung oil into the cyl/piston? I am pretty sure I read a thread on this already. Keeping rod side clearance toward a minimum may increase this directional 'slung' oil.

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Re: One more time, rod side clearance

Post by Kevin Johnson » Sat Apr 14, 2018 8:06 am

I spoke with an OEM engine designer who will go nameless. I asked him why no more attention was paid to windage control and he explained that a target power level was successfully achieved in the initial iteration. If further improvements were made the customer could run into taxation issues in certain countries due to the increased power levels.

It is not that they do not know what can be achieved but rather does it make economic sense to spend the extra money.

Totally different engineer, different time, different engine, explained that they were encouraged (strongly) to use existing components from a factory parts bin, so-to-speak, to build a lower tier engine. This explained why a component was used that was antithetical to windage and oil control.

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Re: One more time, rod side clearance

Post by pamotorman » Sat Apr 14, 2018 9:38 am

CharlieB53 wrote:
Sat Apr 14, 2018 7:47 am
If oil slung up into the cyl's were a problem I suspect manufacturers would have redesigned the block, partially closing off the bottom of the cyl leaving only a rod 'slot' pretty much the same as we see in the Mercury Marine 2 stroke V6. Said rod slot would block most of the oil slung off the crank, very effectively limiting cyl oiling. This could be a serious problem as it would also limit piston cooling from the lack of oil.

Piston oil squirters will provide additional piston cooling, but the added complexity of production engines may out-weight the benefit except for specialized applications, i.e., industrial/marine engines.

IIRC some rod manufacturers have 'notches' in their rod to direct slung oil into the cyl/piston? I am pretty sure I read a thread on this already. Keeping rod side clearance toward a minimum may increase this directional 'slung' oil.
i believe all GM super and turbo charged production engines use piston cooling.

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Re: One more time, rod side clearance

Post by peejay » Sat Apr 14, 2018 9:57 am

Newold1 wrote:
Mon Apr 09, 2018 10:42 am

I understand that bearing to journal clearances in most cases are between .002" to .0035" and that in itself does not leave a lot of oil area for a pump up scenario but I have to believe that the oil system is supply under pressure enough oil to maintain the oil wedge there and as I keep saying that oil supply has to move and be replaced and can the wider side clearance increase the volume of oil exiting the sides of the rods? That's my question and how can someone verify one way or another that wider rod side clearances have no effect on that exit volume? Can it have and be shown to have any effect on running oil pressures in the engine? :?:
You said it yourself: The bearing journal clearance is .001-.002" radially. That is the point of restriction. All oil coming OUT of the rods has to go in through the journal. Opening the sides clearance up beyond .001-002" is not going to increase the amount of oil coming out because the limitation is the oil coming in.

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