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oil circulation or just pressure?

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ebola

ebola

Automotive
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Nov 3, 2003
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Im building billet two cylinder engine for half scale dragster.It is built from plain alluminium block.Im wondering if I really need conventional oil pump? Im not sure how much benefit we have from oil circulation in dragrace engine.Isnt just enough to keep oil lines under pressure while running? It is pushrod engine, runs a minute maximum.Im wondering if I pressurise little oil tank and give a constant pressure thru engine lines to my gauge, would it any unexpected problems occur or not?
Thanks for input.
Andrius
 
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"would it any unexpected problems occur or not?"
No, it'll just give expected problems.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
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ok, sir, and what problems would You expect from such system? Bearing bite from oil cooking? Id doubt on that.
Its just one minute hard run...Ok, I could do say quarter galon circulation per minute - it still wouldnt require pump.Would it make sense You think?

Thanks
Andrius
 
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I also would expect a problem with bearings nipping and spinning when oil supply ran out.

I think it will be difficult to accurately predict oil flow as it with change a lot with temperature and with clearance changes from differential expansion of components.

If I was racing you, I would delay as long as possible during staging.

Regards

eng-tips, by professional engineers for professional engineers
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its not difficult to meassure it.If I rew engine under some load and check outcoming oil temperatures, it could be possible to do so.Thanks for input anyway.
 
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Certainly it would be possible to design a pressure-fed once through lube oil system.

Once through systems were common on radial aircraft engines, although I think they were pumped.

It seems that the weight and complexity would be more than for a conventional pump. The reduction in parasitic power use from the pump might or might not make up for the added weight.

Since it is clear that you are going to try this anyway, despite any advice to the contrary from folks with some significant automotive experience, good luck. Let us know how it works out.
 
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Are you refering to the "rotary" type (as opposed to 'radial') engines, that used a total loss oiling system, I think castor oil?
 
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Before about 1920, certainly before about 1915, virtyally all cars had a splash or total loss oil system. they were generally limited to about 1000 to 2000 rpm due to tendency to melt and seize bearings above this speed.

You can do the sums under presumed conditions, but without I would think you would need a large safety factor to cover variables already listed. This is only based on supposition as I do not have data on this.

Another point to consider is that oil pumps vary delivery with engine speed. Your system would be constant flow, or at best 2 step for idle and loaded conditions. This I expect will make a large supply of oil and pressure source necessary.

If you do get delayed while oil is flowing, you may very well run out and do serious damage. Some motor cycles use a chain driven small pump. These should be really easy to adapt.



Regards

eng-tips, by professional engineers for professional engineers
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Ebola, here are some things to think about.

Lawnmower engines and simple tractor engines do not have oil pumps. They rely entirely on oil-splash lubrication from a "flinger" extending down from the connecting rod. I do not know how they prevent the main and con-rod bearings from blowing up. But, those are very low-performance engines, and they are not designed for long life. (I believe lawnmower engines are designed for a life of around 100 hours running time. In a car with average driving, that's only around 6000 km.)

If the bottom-end of the engine uses entirely rolling-element bearings, you can get away with a lot of things that you couldn't do with a plain-bearing bottom end. This type of design is common in 2-stroke engines, but there are also a lot of scooter and small motorcycle engines that have rolling-element bottom ends. One thing to think about is that the crankshaft has to be a pressed-together design, because there's no other way to put the connecting rod (with its rolling-element bearing ...) onto the crankpin.

If your bearings are designed for pressure lubrication, you COULD store up the oil in a pressure vessel and discharge that into the oil lines, but why? If you got stuck spending longer than usual staging before the race, you're in trouble. The volume and weight of the pressure vessel may be significant, and the oil you pump through the bottom end has to go somewhere.

Personally, for a two-banger, I'd either go with an oil pump, or use a rolling-element bottom end and splash lubrication. Don't forget about the cam-follower lubrication, and how you're going to lubricate the piston pin.
 
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ok, Patprimmerss arguments are more than enough.I know two strokes lubrication, and there are even split ball bearings quite common on marine multicylinder twostrokes.The problem is - ball type crank bearings do not survive load without high rpm.I dont know, this is old rule, maybe modern technologies make better balls/needles?:)But I wouldnt go for them. I dont realy need high rewing engine.I need big torque at bottom.
 
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MintJulep - The Gnome was a rotary engine (the crankshaft is fixed and the cylinders spin with the propeller).


Induction was through the crankcase, intake valve was on the piston & exhaust was on the top of the cylinder. Lubrication was total-loss with castor oil.
 
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Surestick:

In an In-line engine the pistons are all in line with each other when viewed from the end of the crank.

In a "V" engine, the pistons are arranged in a V shape when viewed from the end of the crank.

In an opposed or flat engine, the pistons are opposed to each other when viewed in line from the end of the crank.

There are actually "W" engines, in which the pistons are arranged in the shape of a "W" when viewed in line from the end of the crank.

In a radial engine, the pistons are radially arranged, when viewed in line from the end of the crank.

Wikipedia's page notwithstanding, the fact that the entire crankcase of the Gnome rotates about a fixed crank does not alter the radialosity of the engine.

A rotary engine does not use reciprocating pistons. Examples would be the Wankle or a scroll expander.
 
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MintJulep

In early aircraft engines Rotary and Radial are 2 different configurations.


While most Rotary Engines had their cylinders arranged 'radially' they are not generally referred to as ‘radial’ engines.

Rotary in this context is not the same rotary as Wankel.

I'm afraid you're mistaken on this one.


KENAT, probably the least qualified checker you'll ever meet...
 
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All the Radial aircraft engines I know of were dry sump lube system, with scavenge pumps at various locations to recover the oil and send it back to the reservoir.
And some AC engines used ball mains if memory serves, and I don't consider 2300 rpm very high.
Since your talking minumal lube, you would need an antifriction bearing. But you said you don't want them?
Then you better find some good grease. How high do you think the torque will be? Maybe 150 lb ft at the most?
 
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The problem is - ball type crank bearings do not survive load without high rpm.I dont know, this is old rule, maybe modern technologies make better balls/needles?:)But I wouldnt go for them. I dont realy need high rewing engine.I need big torque at bottom.
Click to expand...

Ball bearings are great for outer crank bearings but not always for rods. Many large bore 4-stoke single motorcycle engines use needle bearings on the big end of the rod and they hold up well under some extreme conditions.

Large bore 2-strokes use the same thing and they don't spend most of their time at high RPM.

This is a rod for the Honda XR650 single.

XRCR.jpg
 
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Speedway motorcycle engines use a total loss pressure system.High compression alcohol burners with ball and roller bottom ends.A race is 4 laps....on our local track that takes around 60 seconds.
 
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Pre 1997 Husaberg engines (350cc 501cc and 600cc singles) did not have oil pumps, the top end is splash feed by the cam chain, the bottom end is essentially a dry sump, very small crankcase volume much like a 2-stroke (and full circle crank webs)with a reed valve to alow oil to be pumped out on the down stroke. These engines also didnt rev very high, max power was at about 5500-6000 rpm in the 501
 
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