19 replies to this topic

[malbear]

I was wondering where the exit hole in the crankshaft is for oil feed to the big end on most engines.
It might be logical to have this exit forward of the TDC position where most downward pressure is exerted by the conrod. Does it matter ? or is it usually drilled in the most convenient position for manufacture.

[Aussie overseas]

Are u the guy from WA who has the six stroke engine? I read about this but thought it was in West Aussie. I thought like the OX2 it was a dud. R U still working on this engine?

[McGuire]

Crank drilling is sort of an interesting subject... with the "Search BB" function you can find several previous discussions here.

[Stian1979]

exit hole?
Fedd in and the oil is leaking out from plain bearings on the crank and on the bearing in the piston where they enter trough the rod's.
Some also have driled holes that inject oil for cooling on the piston.
Also chanels for cylinder lubrication has ben made.

A exit hole is not necesary and I can not remember seing one.

Correct me if I'm wrong

[malbear]

Ive done a search and the closest to my question is this post started by knighty
Race crank oil drilling picture - any ideas???.....

"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 does not answer the question but touches on it . It is the positioning of the holes to "time the oils supply that I am trying to get a handle on.

[Greg Locock]

I'd guess that the oil has to be fed into the low pressure area on the journal, which according to Heywood is at around 2 o'clock and 8 o'clock, with respect to the conrod (fig 13-22).

However, a large part (?) of the effective delivery pressure of the oil is due to centrifugal pressure head in the transfer passage, so you may need a further study to figure the optimum out there.

I'm a bit dissappointed in Heywood, I thought he'd have more about it.

[Greg Locock]

Maybe the centrifugal head is not important, since the big end will have the same centrifugal head.

[hydra]

Wilson Kerr has a lot of good info on this subject in the 4th volume of his work on torsional vibrations...

[gary76]

Interesting discussion: As stated in previous postings the prime object in the positioning of the oil exit in the crankshaft big-end bearing is to introduce oil to the big-end where the pressure is at its lowest thus maintaining an adequate oil flow to the big-end bearing. This has been found to be between 30 to 60 degrees 'ahead' of TDC or 30 to 60 degrees 'after' TDC, depending upon notation. About 40 degrees seems to be a good average but I have seen as much as 65 degrees on some modern high speed racing engines.
On most engines oil to the big-end bearing is fed from the main bearing hence oil pressure must be sufficient to overcome the centrifugal effect of the rotating crankshaft to allow the oil to flow into the crankshaft and onwards to the big-end bearing. This centrifugal effect also assists the oil flow (pressure!) at the big-end. Now, the oil flow through the big-end (and the main bearing) is determined by its leakage area therefore if the centrifugal oil pressure generated at the big-end is too great it can create low oil pressure in both main and big-end bearings. i.e. oil pressure must be sufficient to overcome the centrifugal force opposing the entry of the oil into the main bearing journal and maintain the rate of flow at which the oil is 'flung' from the big-end bearing. This was the reason for 'cross drilling' big-end jounals creating what was termed 'low pressure' crankshafts.
Sorry that I have been a bit 'long winded' but I hope it will prompt some more thoughts since as Greg said there is little written on the subject and what is written is outdated me thinks apart from the basic theory.

[malbear]

Thanks Gary and Greg ,
your posts have helped my understanding

[J. Edlund]

Originally posted by gary76
On most engines oil to the big-end bearing is fed from the main bearing hence oil pressure must be sufficient to overcome the centrifugal effect of the rotating crankshaft to allow the oil to flow into the crankshaft and onwards to the big-end bearing.

While most engines have their big end bearings fed with oil from the main bearing, most modern F1 engines do not use this method. Instead their crankshafts are drilled all the way through and then oil is fed through the nose of the crankshaft. This is however not a new method, it was also used on the Rolls Royce Merlin to overcome some bearing issues on earlier models.

It seems like using a nose fed crankshaft makes it possible to reduce the oil pressure somewhat, earlier F1 engines not using a nose fed crank have been said to have an oil pressure around 5.5-6 bar while current (or near past) seems to use pressures of around 4-4.5 bar with higher engine speeds.

Main bearings may also have a partial grooving.

[gary76]

I have just remembered an article which I found sometime ago in one of my searches. I hope you will find it useful, I did.
www.jagweb.com/jagworld/xk-engine/page6

[ScottNC]

Anyone have a detail picture of the "nose fed" crank drillings? I'm curious how the inboard main journals recieve their oil supply by that means.

[phantom II]

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Originally posted by gary76
I have just remembered an article which I found sometime ago in one of my searches. I hope you will find it useful, I did.
www.jagweb.com/jagworld/xk-engine/page6

[Wolf]

Phantom- easily solveable problem, methinks- just add .html on the end o that link: http://www.jagweb.co...gine/page6.html . Hope it helps.

[phantom II]

Sure did. Thanks man.

Originally posted by Wolf
Phantom- easily solveable problem, methinks- just add .html on the end o that link: http://www.jagweb.co...gine/page6.html . Hope it helps.

[J. Edlund]

Originally posted by ScottNC
Anyone have a detail picture of the "nose fed" crank drillings? I'm curious how the inboard main journals recieve their oil supply by that means.

The nose fed crankshaft only supply the big end bearings as seen on the drawing below. I guess that there is some sort of spring loaded carbon face seal against the nose of the crank.

[ScottNC]

J. Edlund, thanks for the drawing. I see the drillings for two rods fed by two mains but still don't understand how the oil gets to.....no wait I think I figgured it out. The crank is fed from both ends, the way the rod journals are drilled from the mains on either side allows oil to procceed on to the next main via the intersecting hole?

If this is correct doesn't the oil (pressure) have to fight against centrifugal force after every rod pair?

[gary76]

Answer to Scott NC: yes, the oil will have to overcome the centrifugal force generated at the big-end to feed the adjacent main bearing but if you refer to the crankshaft sketch shown on the Jag link you will see that the longitudinal oil ways drilled in the crankshaft are 'offset' hence the effective radius at which the centrifugal force acts is reduced. This together with the short stroke (crank throw) of high speed engines greatly reduces the effects of centrifugal forces on oil pressures within the crank. This was refered to by the article in the 'Hot Rod' magazine but not very clearly.

End fed oil to the crankshaft can be done in several ways: a spigot into a hole as the AJS 7R/ Matchless G50 engine: a spigot on the end of the crankshaft into a oil sealed cavity in the front cover plate: a carbon face seal (similar to a water pump seal) on the end of the crankshaft. I am sure there are pros and cons for any of these but I have used the oil seal on a crankshaft spigot successfully for many years on and engine with a max. speed of 8000 rpm. (not very high!!)

[J. Edlund]

Originally posted by ScottNC
J. Edlund, thanks for the drawing. I see the drillings for two rods fed by two mains but still don't understand how the oil gets to.....no wait I think I figgured it out. The crank is fed from both ends, the way the rod journals are drilled from the mains on either side allows oil to procceed on to the next main via the intersecting hole?

If this is correct doesn't the oil (pressure) have to fight against centrifugal force after every rod pair?

The whole crank is drilled from the front to the end and go to each and every crank throw. There are no drillings in the main bearings, instead the crank is fed at the front like seen on the Ferrari engine below. Since the drillings are centred around the crankshaft centre there should be no problems with the centrifugal forces.



However, some crankshafts are still fed from the mains with the same type of drilling.