21 replies to this topic

[knighty]

I have just been browsing about the Nicholson McLaren web site and came accross this picture of some crankshaft drillings, I have never seen this method employed before, It appears that the oil is fed via the front and rear of the crank only, I'm asuming this allows for thinner main bearings to be used, allowing a more compact engine design?????....... I think I have heard of this method refereed to as a "nose feed crank"........anyone got any ideas?........I cant seem to make my mind up if the crank is a V8, 10 or 12???.....

cheers

stephen

[Engineguy]

Looks like a 4 main bearing, 6 pin 12 cyl crank with the two center-most pins clocked together (i.e. cyls 5, 6, 7, and 8). :

Main, pin at 12:00, pin at 4:00, main, pin at 8:00, fat counterweight, another pin at 8:00, main, pin at 4:00, pin at 12:00, main.

[Halfwitt]

Originally posted by Engineguy
Looks like a 4 main bearing, 6 pin 12 cyl crank with the two center-most pins clocked together (i.e. cyls 5, 6, 7, and 8). :

Main, pin at 12:00, pin at 4:00, main, pin at 8:00, fat counterweight, another pin at 8:00, main, pin at 4:00, pin at 12:00, main.

I agree, a nose-feed type V12 4 main-bearing crank. On F1 engines, the oil is fed in at the front, and power is taken from the rear.

[knighty]

Thanks guys, OK so it’s a nose fed V12 crank, could someone please educate me why you would want to drill the crank like this?.......would I be right in assuming that its in the interest in making the main bearings shorter (due to the lack of feed grooves) therefore making the overall engine length shorter………not to mention the fact the cylinder block will be much more simplified with the lack of crank oil feed galleries and drillings?........how is the oil fed into the nose of the crank?.......I’m assuming some sort of trick coupling is employed?.........

[McGuire]

With center oiling there is constant, full-time oil supply instead of just one shot every 360 degrees when the galleys line up (or every 180 degrees with a cross-drilled crank, which is a real mess). More precise metering, less volume and reduced windage.

[zac510]

I keep trying to grab that image and spin it around a bit. It would make it far easier to understand what is going on!!

I can't tell where the oil is reaching the bearings. Is this depicted in the image?

[WPT]

Not sure, but think end fed cranks allows one to reduce the operating oil pressure. WPT

[McGuire]

Originally posted by zac510

I can't tell where the oil is reaching the bearings. Is this depicted in the image?

No, the short drillings from the rod and main journal surfaces to the center oil galley (shown) have been omitted for some reason, "clarity" I suppose.

[McGuire]

Originally posted by WPT
Not sure, but think end fed cranks allows one to reduce the operating oil pressure. WPT

That's exactly it. Lower pressure and volume, less oil being thrown out through the bearing clearances and flung all around the crankcase.

If you ever get the chance to see it, high speed photography of crankshaft windage is a remarkable sight. It does not resemble a cloud of oil droplets so much as a "rope" of oil wound around the length of the crank like a helix. The crank and reciprocating gear must plow through that bog...

[zac510]

Originally posted by McGuire


No, the short drillings from the rod and main journal surfaces to the center oil galley (shown) have been omitted for some reason, "clarity" I suppose.

I suspected as much, thanks for the reply.

[Engineguy]

Originally posted by WPT
Not sure, but think end fed cranks allows one to reduce the operating oil pressure. WPT

More to the point, at F1 RPMs it becomes almost impossible to pump oil inward from the main bearing shell inward toward the center of the crank... the centrifugal force on the oil column in the drilling flings the oil out... if you crank the oil pressure way up the oil will still follow the path of least resistance; out the side clearance of the bearing shell... no way in hell it can fight its way toward the center of the crank to get to the rod journal supply drillings. Hence the need to input the oil at the end, where you can start at the center.

[McGuire]

Originally posted by Engineguy
More to the point, at F1 RPMs it becomes almost impossible to pump oil inward from the main bearing shell inward toward the center of the crank... the centrifugal force on the oil column in the drilling flings the oil out... if you crank the oil pressure way up the oil will still follow the path of least resistance; out the side clearance of the bearing shell... no way in hell it can fight its way toward the center of the crank to get to the rod journal supply drillings. Hence the need to input the oil at the end, where you can start at the center.

Even at half F1 speeds it becomes damn difficult...or why "cross-drilling" is generally such a bad idea. It will actually starve the rod bearings, have seen it a hundred times. It will also greatly increase windage losses, needlessly tax the oil rings, etc etc.

David Reher on the subject, link and excerpt below:

http://www.rehermorr...techTalk/51.htm


I’ll begin with a rather bold statement: Don’t use a cross-drilled crankshaft. There are a few exceptions to this rule, but under most circumstances, a cross-drilled crank is going to cause big problems.

Unfortunately cross-drilling is one of those terms that’s become part of the jargon of hot rodding. People who know very little about racing engines have heard of a “cross-drilled crank,” and mistakenly believe they’ve got to have one. In fact, cross-drilling simply refers to the position and routing of the holes that carry pressurized oil from the main bearing journals to the connecting rod bearings.

In a cross-drilled crankshaft, oil feed holes are drilled completely through the main journals so the passages are open on both ends. Holes from the rod journals are then drilled at an angle to intersect the holes in the main jouranls at the centerline of the crank. This system was thought to ensure a continuous supply of oil to the rod bearings because one end of the passage drilled through the main bearing is always exposed to the pressurized oil in the upper main bearing insert.

So what’s wrong with this picture? The pressurized oil that enters the feed hole through the main bearing journal must overcome the centrifugal force created by the rapidly spinning crankshaft before it can reach the passage to the rod journal. If the pressure created by the oil pump is not strong enough to counteract the centrifugal force that is pulling the oil away from the rod journal feed hole, then the rod bearing is starved for lubrication. Since the pinwheel effect of the centrifugal force increases with rpm, when the rod bearing does run dry and seize, the resulting carnage is usually catastrophic.

I learned my lesson about cross-drilled crankshafts the hard way. Back in the early ’80s we started to turn our engines faster. We’d been running stock Chevy cranks in our 287-cubic-inch small-blocks and B/ED motors without any problems. Eventually the supply of usable cranks became exhausted, so we ordered aftermarket cranks – “California cranks” as my Texan friends called them. These cranks were much prettier than the factory forgings, and they all had trick cross-drilled main bearings. It didn’t take long for those cranks to turn blue when the rod bearings burned, sometimes on the first or second dyno pull. Then we’d bolt in an old 283 crank and the engine would live forever. So what was the difference? The difference was the cross-drilling.

Today most racing crankshafts have a “high-speed” oiling system, which is essentially just how Chevy drilled those stock cranks. The oil feed holes for the rod bearings intersect the main journals at or near the surface of the journals. The pressurized oil does not have to overcome centrifugal force to reach the oil feed holes for the rod bearings, so the supply of lubrication is constant even at high rpm. There have been some refinements made to the angles and positions of the oiling holes to “time” the oil supply, but the basic design hasn’t changed significantly.

It’s easy to spot a cross-drilled crankshaft. Insert a piece of welding rod or coat hanger wire into the oil hole drilled in the main bearing. If the wire comes out the other side, the crank is cross-drilled. My advice is not to use it.

It is possible to crank up the oil pressure high enough to overcome the negative effects of cross-drilling. However, excessive oil pressure creates its own set of problems, increasing parasitic losses due to windage, excessive oil on the cylinder walls, and the power that’s consumed by turning a high-pressure oil pump.

[knighty]

Interesting reading!.........so on a nose fed crank, like in f1, how is the oil fed into the crank nose? what sort of seal is used?........it must be something pretty special

[McGuire]

Not really, it's all inside the timing cover. This is another example of nothing new under the sun. Some Japanese motorcycles use center oiling, also some big outboards. One Detroit OEM was doing considerable R&D on it 35 years ago. In that setup, picture an automatic transmission-style pump on the front of the block, concentric to the crankshaft. One or two dozen of these engines were built for the Trans-Am sedan racing series... but the division cancelled its race program so the Generous Manufacturer never released the engines.

[Canuck]

Harley-Davidson (and all the clones) run a nose-fed crank. Course they also run caged roller bearings for the rods and one 'main', and a pair of tapered Timken bearings on the other main so hot operating oil pressure at idle is often under 10psi. Lots of extra weight to accelerate.

[Hellenic tifosi]

Originally posted by knighty
Interesting reading!.........so on a nose fed crank, like in f1, how is the oil fed into the crank nose? what sort of seal is used?........it must be something pretty special

Nowadys most of the engine oil seals are made of teflon, which has excellent dry running capabilities. In fact.

[Kevin Johnson]

Sigh. Just make the feedline a cross section of a curve that imparts vector impetus towards the centerline of the crank because of crank rotation handedness.

I think it is the entrained air in engine oil in standard engines that makes most of the problems. A cross drilled crank simply gives more opportunity for localized areas of pressure fluctuation and these allow the expression of pockets of neat air to the bearings.

Originally posted by McGuire


Even at half F1 speeds it becomes damn difficult...or why "cross-drilling" is generally such a bad idea. It will actually starve the rod bearings, have seen it a hundred times. It will also greatly increase windage losses, needlessly tax the oil rings, etc etc.

David Reher on the subject, link and excerpt below:

http://www.rehermorr...techTalk/51.htm


I’ll begin with a rather bold statement: Don’t use a cross-drilled crankshaft. There are a few exceptions to this rule, but under most circumstances, a cross-drilled crank is going to cause big problems.

Unfortunately cross-drilling is one of those terms that’s become part of the jargon of hot rodding. People who know very little about racing engines have heard of a “cross-drilled crank,” and mistakenly believe they’ve got to have one. In fact, cross-drilling simply refers to the position and routing of the holes that carry pressurized oil from the main bearing journals to the connecting rod bearings.

In a cross-drilled crankshaft, oil feed holes are drilled completely through the main journals so the passages are open on both ends. Holes from the rod journals are then drilled at an angle to intersect the holes in the main jouranls at the centerline of the crank. This system was thought to ensure a continuous supply of oil to the rod bearings because one end of the passage drilled through the main bearing is always exposed to the pressurized oil in the upper main bearing insert.

So what’s wrong with this picture? The pressurized oil that enters the feed hole through the main bearing journal must overcome the centrifugal force created by the rapidly spinning crankshaft before it can reach the passage to the rod journal. If the pressure created by the oil pump is not strong enough to counteract the centrifugal force that is pulling the oil away from the rod journal feed hole, then the rod bearing is starved for lubrication. Since the pinwheel effect of the centrifugal force increases with rpm, when the rod bearing does run dry and seize, the resulting carnage is usually catastrophic.

I learned my lesson about cross-drilled crankshafts the hard way. Back in the early ’80s we started to turn our engines faster. We’d been running stock Chevy cranks in our 287-cubic-inch small-blocks and B/ED motors without any problems. Eventually the supply of usable cranks became exhausted, so we ordered aftermarket cranks – “California cranks” as my Texan friends called them. These cranks were much prettier than the factory forgings, and they all had trick cross-drilled main bearings. It didn’t take long for those cranks to turn blue when the rod bearings burned, sometimes on the first or second dyno pull. Then we’d bolt in an old 283 crank and the engine would live forever. So what was the difference? The difference was the cross-drilling.

Today most racing crankshafts have a “high-speed” oiling system, which is essentially just how Chevy drilled those stock cranks. The oil feed holes for the rod bearings intersect the main journals at or near the surface of the journals. The pressurized oil does not have to overcome centrifugal force to reach the oil feed holes for the rod bearings, so the supply of lubrication is constant even at high rpm. There have been some refinements made to the angles and positions of the oiling holes to “time” the oil supply, but the basic design hasn’t changed significantly.

It’s easy to spot a cross-drilled crankshaft. Insert a piece of welding rod or coat hanger wire into the oil hole drilled in the main bearing. If the wire comes out the other side, the crank is cross-drilled. My advice is not to use it.

It is possible to crank up the oil pressure high enough to overcome the negative effects of cross-drilling. However, excessive oil pressure creates its own set of problems, increasing parasitic losses due to windage, excessive oil on the cylinder walls, and the power that’s consumed by turning a high-pressure oil pump.

[bobqzzi]

Originally posted by Hellenic tifosi


Nowadys most of the engine oil seals are made of teflon, which has excellent dry running capabilities. In fact.

teflon? really, I don't recall seeing an teflon seal in an automotive engine in quite some time.

[Hellenic tifosi]

Originally posted by bobqzzi


teflon? really, I don't recall seeing an teflon seal in an automotive engine in quite some time.

Well, I was exaggerating when I said that most oil seals have a PTFE lip, but it is a fact that more and more constructors are choosing PTFE over the traditional elastomer seals, the main reason behind the switch beeing it's superior reliability.

At the moment I don't think that there is any truck engine (where reliability counts the most) with a conventional elastomer seal.

[Kevin Johnson]

http://www.hastingsm...valve_seals.htm

I remember the horrible touble with OEM watercooled VW valve stem seals in the late 70s and buying Teflon replacements.

Guess this guy remembers too:

http://www.joesherlo...og-2004-07.html

"The only 'oil-burner' I ever owned was a Volkswagen Scirocco and that was a factory defect. It began to burn oil (400 miles/quart) at 30,000 miles or so. Volkswagen's water-cooled engines from that era were notorious for being early blue-smokers. During a routine service, the Volkswagen dealer slapped a stick-on printed ring around the gas filler hole which read: 'Check oil at each fill up.' This was the Weasels of Wolfsburg's response to the apparently well-known oil burning tendency of all water-cooled Volkswagens: Get some stickers printed. "Eef you haf ein problem, it is obviouzzly your fault für nicht reading das sticker vitch ve haf now printed at great expensze to us. Guten tag." Jerks! That's one of the reasons why I'll never buy anything - ever again - from Volkswagen. Für the rest uff mein life. Ja wohl!"


Ein bisschen zu schwer meine Ich.


Bit of searching -- OEM on many Porsche and Ferrari -- must be good.

Works well for crank scrapers too.

[hydra]

Its funny this thread came up when it did. I was thinking about nose-fed cranks yesterday, and why they're not more commonplace on production engines. I can't think of any disadvantages to them. Lower FMEPs, superior oil-control, and thicker crank webs can't be all that bad.

Also, if you're going through the trouble of making a billet crank, how hard would it be to set up an existing block for nose-feed oiling?

[CFD Dude]

Originally posted by hydra
Its funny this thread came up when it did. I was thinking about nose-fed cranks yesterday, and why they're not more commonplace on production engines. I can't think of any disadvantages to them. Lower FMEPs, superior oil-control, and thicker crank webs can't be all that bad.

Also, if you're going through the trouble of making a billet crank, how hard would it be to set up an existing block for nose-feed oiling?

For production engines the major reason it isn't used is packaging. The crankshaft protrudes from the engine at both ends; for the clutch/torque converter at one end and the crankshaft damper at the other. It would required exterior plumbing to get the oil to the end of the crankshaft past the crankshaft damper (I can't see how one could go in the other end). The exterior plumbing introduces parts that could leak due to newly introduced joints, including an additional rotational seal, and it's exposed so it's subject to being damaged by road debris. It also encapsulates the accessory belt so one would have to take the plumbing apart to replace the belt.

In short, it would introduce parts that, increase costs, could leak, and it increases maintenance costs. It’s an interesting idea, but I don’t think that it’s going to replace bulkhead drillings anytime soon.