oil pressure to over come centrifigal force

[GT6M]

Heres an intresting topic for some,

Kastner med up a thingy called an octopuss, this to solve oil flow to the bearings.
others have put a pipe frae,t oil filter housing to NO1 galley plug

others have cleaned oot the swarf an detrius in the oil drillings.

BUTT, what aboot the bearings no being lubed at high revs by the actionee of centrifical force, stopping the oil getting doon the drilling to oil the bearing.
And also to be took into consideration, If the oil is getting flung ootwards, then will it cause a suction behint oil ..plug, and then suck air into the bearings, whicj means no lube at all,
as air has sucked the oil away,!!!

A cross drilled crank would appear to be even wuss for this, as there 2 wols for oil to be flung oot wards. and back against oil in flow.
OR, does a X drilled crank actually let moer oil in,

baffledikussed are we, well think of it like this,

at high revs, oil is flung oot by centrifical force, the bigg ends, as on a lever so to say, will get an even bigger fling.

So, if CF =say 50 PSI at 6K revs, then if yer oil pump is pumping 60 PSI at 6k revs, then there no much oil left to lube,
never mind form a cushion of oil to stop crank bottoming oot.

So hoo much oil pressure is needed to over come CF,
at high revs

M

[RogerH]

Hi Marcus,

if the crank had no Big end bearings installed then oil would be flung out and pressure lost from the mains.

However the big-ends stop/reduce the oil flow and the cross drilling would have a greater effect again.

 

Roger

[Peter Cobbold]

So the idea is that centrifugal force acting on oil in the drillings counteracts oil hydraulic pressure and messes up pressure?

Here's a back of envelope estimate based upon a short column of oil in the outer 10mm of a drilling of 3mm bore leading up to the big end bearing.

 

The centrifugal force at the main bearing looks tiny small * . The centrifugal pressure in the oil in the outer fastest moving end of the drilling to the big end bearing may be significant at ca 30psi plus ( the calculation neds to be repeated for the four 10mm increments of il column from the crnak centre) Even if the whole oil column 48mm long were included the result would be less than 5 times bigger, appreciably less than 30psi 90psi

(* When it comes to m/b the drilling bore will be bigger (but so will the area so pressure not bigger) and the radius of rotation much less than the 48mm used for the b/e. So V^2 will be tiny. I cant see cross-drilling the m/b contributing to centrifugal oil starvation there ( but do the calculations using the m/b radius) )

 

 

In a cross drilled crank journal the low centrifugal pressures across the crank m/b diameter will be equal but opposite - they will cancel out. will be the same - the extra drilling wont change pressure exerted by cf at the groove. But the bigger area will allow oil from the pump to acheive a faster flow into the crank centre.

 

Perhaps the 'pull' of the column of oil out into the b/es is involved. If the oil pressure from centrifugal fling pushes oil out of the b/e shellls faster - which is plausible- then the oil flow from the crank to the b/e will speed up. Given a limited pumped inflow that will tend to drop the pressure at the m/b.

Now we need to consider flows. Inflow of oil must match ouflow ( continuity) so if the centrifugally enhanced flow up to the b/e starts to exceed the pumped inflow from the main gallery the m/b will be 'scavenged' . Think of the centrifugal force on the b/e acting as a pump away from the m/b. Obviously at designed rpm this is not an issue. But the b/e pump gets faster with excessive rpm. It pumps oil away from the m/b faster. So the m/b pressure drops. Now if we add a crossdrilling in the m/b the restriction to flow from the gallery to the b/e is halved and the flow way form the m/b towards the b/e 'pump; speeds up. And M/b pressure drops more.

 

We can predict that the pproposed 'b/e centrifugal pump' will make a m/b feeding two b/e worse than a m/b feeding one b/e.

 

Of course the b/end centrifugal pump is always present at normal rpm, but at lower psi. It is the rise in the pressure, and flow, at excessive rpm that might tip the balance of flows.

 

 

Peter

 

 

Centrifugal force:

m v^2 /r

Errors corrected in bold.

volume of oil in outer say 10mm of drilling 3mm bore roughly 30cu mm x density

= 0.03ml

EDIT: wrong volume should be 3 x 3 x 10 or 0.09ml Final value corrected upwards three fold.

given: density: 900g per litre = 0.9g per ml

so mass = 0.9 x0.03 = 0.027 g

 

Area acted upon: roughly 9sqmm

 

radisu of rotation of oil:

stroke/2 = 95mm/2 = 48mm

 

 

At rpm 5000

tangential velocity m/sec when r=48mm

circumference = 2 pi r = 2 pi 48 = 300mm

= 30cm = 0.3m

so 5000rpm= 83 rpersec = 25m per sec

 

 

So 2.7 x 10-5 kg x 25 x 25 / 0.048m

= 1700 x 10-5 / 0.048

=1700 x 10-5 / 4.8 x 10 -2

=1700 /4.8 x 10-3 kg

=0.35kg

= 3.5 Newton (conversion error factor of ten)

 

pressure = 0.35 N over 9sq mm area

= 0.35 N over 9 x 10-6 sq metr = 0.04 /10 -6

= 400000 N per sq m

= 18 psi

 

Going from 5000rpm to 7000rpm then V^2 doubles ( ie ratio will be 25 to 49) and centrifugal pressure rises to 36 psi.

Edited April 1, 2015 by Peter Cobbold

[Lebro]

Yep, that's what I made it

[RogerH]

Spot on

 

Roger

[Peter Cobbold]

So no-one spot the deliberate mistakes?

Now corrected.

Edited April 1, 2015 by Peter Cobbold

[RogerH]

Hi Pete,

we spotted the mistake but simply accepted it as we knew you would be back to sort it.

 

 

The Fergy tractor crank has radial big-end oil holes and runs ok - at 2000rpm max.

The TR 4 pot crank is virtually identical except for the cross drilling

 

I believe 'Dick' on this forum runs a standard fergy crank with no problems.

Considering the limited escape routes for the oil in the big-end I can't see the harm of the radial oil hole or the benefit fo the cross drilling.

 

Roger

[Peter Cobbold]

Hi Pete,

we spotted the mistake but simply accepted it as we knew you would be back to sort it.

 

 

The Fergy tractor crank has radial big-end oil holes and runs ok - at 2000rpm max.

The TR 4 pot crank is virtually identical except for the cross drilling

 

I believe 'Dick' on this forum runs a standard fergy crank with no problems.

Considering the limited escape routes for the oil in the big-end I can't see the harm of the radial oil hole or the benefit fo the cross drilling.

 

Roger

Hi Roger, Yes, "I will be back"... to check. Doing sums after midnight was never wise.

 

I made a big mistake - factor of ten - in converting kg to N. So the interperation has completely changed - I now think the cf pressure at the big end might well be important. At excessivley high rpm it could act as a pump scavenging the main bearing. Then cross drilling the main journal makes it easier for oil to flow away from the journal by doubling the flow area.

Flow through the bigend journal/shell would be difficult to estimate. It wont be linear with pressure. Even in laminar flow in a pipe flow rises with the square root of pressure drop.

 

The c'f pressure at the big ends will be present at normal rpm and may help oil flow into the b/e journal. Perhaps tractor cross drilling helps that c'f flow up to the b/e at the low rpm tractors run at ??. Low rpm + high load operation may need easier flow out to the heavily loaded b/e.

 

 

 

 

Its a good advert for supercharging, as I can also drive at tractor-like rpm. even up hills.

 

Peter

Edited April 1, 2015 by Peter Cobbold

[ianc]

As ever, Peter is very thorough in his analysis.

In the hope that it may throw a little more light on the situation as it was in 1953, I've cut the section below from my 2-part article on the 4-pot engine (TR Actions 241 & 242, March & May 2010, respectively).

 

1. Big-Ends: the combination of higher engine speeds (up to 6,000 rpm), greater compression and better breathing in the TR mean that the loading on the big-ends will be much higher than in the Vanguard. Big-end failures occurred after 2-3 hours at sustained 5,200 rpm, so the bearing material was changed from white metal to indium-coated lead bronze bearings. Then, modifications were made to the main bearing shells so as to permit oil to pass more rapidly from the crankcase via the main bearings to the crankshaft, and thence through the crankshaft drillings to the big-ends. This was not a complete cure – see next!

2. Crankshaft: see Figure H2, which Neil Revington drew for me in 1976 for the Technicalities Booklet, and which was reproduced in Section A8 of the Technicalities CD. The crankshaft was originally drilled from the main bearings to the big-ends (see upper drawing), but, with the higher crankshaft speeds and the increased bearing clearances necessitated by the use of lead bronze bearings, this resulted in a considerable loss of oil owing to centrifugal action. To reduce this effect, the crankshaft drillings were modified (see lower drawing) so that the greater proportion of the oil would be discharged around the periphery of the big-end bearing, which is closer to the centre line of the crankshaft, by making a ¼ inch cross-drilling, and by reducing the diameter of the outlet at the outer end of the main oilway to ⁵/₆₄ inch. In addition, to improve the spread of oil round the bearing, the edges of the outlets were “shelled”, and this process also prevented foreign matter “cutting-up” the bearing shell.

Ian Cornish

[iain]

Ian

 

any chance of a pdf of your article? I rejoined TRReg later that year.

 

Many thanks

 

Iain

[GT6M]

Ian, wheres all the pics ye relating too,!!

 

there got to be some thing init that ruins the NO 1 big end

 

Kas wid his octopussy thingy said it was to give pressure to that bearing,

as his tests showed little oil pressure there,

BUT, was this oil pressure no there cos of CF acting on all the bearings,

and NO1 being furthest frae,t pump, got all the others CFs that were going back into the oil gallerys,

thus mek,n no pressure at high revs.

 

M

[Peter Cobbold]

Ian, wheres all the pics ye relating too,!!

 

there got to be some thing init that ruins the NO 1 big end

 

Kas wid his octopussy thingy said it was to give pressure to that bearing,

as his tests showed little oil pressure there,

BUT, was this oil pressure no there cos of CF acting on all the bearings,

and NO1 being furthest frae,t pump, got all the others CFs that were going back into the oil gallerys,

thus mek,n no pressure at high revs.

 

M

Markus,

No 1 m/b only has one bigend to suck away oil centrifugally. while m/b 2 and 3 have two each.

So my guess would be Kastner's measurements indicate the oil not getting from the pump at sufficient pressure.Because the cf action at m/bs #2 and 3 steal it first.

 

Flow along 'pipes in parallel' is well understood in fluid dynamics, as is the multiple reservoir problem. But calculating the flows is waaay beyond me.

 

What I think is happening is that the flow to m/b1 is OK at normal revs. So psi there will also be OK. But as rpm go higher than Triumph designed for ( and Ian C's post shows they knew all about it ) then the m/bs 2 and 3 will take more oil away from the main gallery due to the centrifugal flow rising to b/e 2, 3 4 and 5. That leaves less flow for m/b1 so psi drops there. As you say it's furthest from the pump. So m/b 2 and 3 get to feed first, its the easier route for oil to take.

 

If I were trying out a Mkll Octopus I'd connect an external gallery or hose from m/b 4 to m/b 1. Mb 4 only feeds one b/e and may have 'spare' pressure available to help out #1m/b. It also gives a sort of circular gallery as used in some fuel injection systems.

Would that be a monopus or a bipus?

 

Peter

 

Edit. Or, better I think, make a 'tuned octopus'. Look upon the oiling as a feed pump supplying six b/end centrifugal 'scavenge pumps'. To equalise the flow though each scavenge pump the feed from the main gear pump needs to be divided up as:

1 unit of flow to mb#1, 2 to m/b #2, 2 to m/b #3 and 1 flow unit to m/b #4.

The oil flow from the pump could be distributed like that by keeping the length of all tubes identical. But the bores will be different to control flows. The bore dimension is absolutely critical. A pipe with laminar fluid flow only needs its bore to be 19% bigger to take double the flow for the same pressure head.

Why? - see Poiseuille's Law *: flow is proportional to the fouth power of the radius of the bore: r^4

*http://hyperphysics.phy-astr.gsu.edu/hbase/ppois.html )

Fourth root calculator here: http://www.calculatorsoup.com/calculators/algebra/fourthroots.php

We want a flow 2 times bigger so the bore has to be 4th root of 2 bigger. That's 1.19-fold, or 19%.

 

The oil flow is more likely to be turbulent, not laminar, so Poiseuille cant be accurately applied. But it would be a start.

So we need four equal length pipes taken off the oil pump, the bores to m/b #2 and 3 should be 19% bigger than those to the front and rear m/bs. Also make sure all the bends are the same. So if one pipe needs a right angle bend the others must have too. And the main oil gallery isnt used.

Or did Kastner do that?

Edited April 1, 2015 by Peter Cobbold

[ianc]

If back copies of TRA 241 & 242 are not available from the Office (please check first!), then send an email to my home - the address is on page 82 of TRA.

Ian Cornish

[Peter Cobbold]

Simple formula for calculating centrifugal force at any radius and rpm:

 

""The force exerted on a particle in a centrifuge is a simple function of the rotation speed of the centrifuge and the radius of rotation. The actual equation is:

G-force= 1.12 x R x (RPM/1000)²

R is the radius of rotation measured in millimetres ""

 

source:

http://clinfield.com/2012/07/how-to-convert-centrifuge-rpm-to-rcf-or-g-force/

 

So the G-force can be caculated for tthe crank radius, big end radius. For any rpm.

It rises rapidly with rpm!!

 

Peter

[oldtuckunder]

 

What I think is happening is that the flow to m/b1 is OK at normal revs. So psi there will also be OK. But as rpm go higher than Triumph designed for ( and Ian C's post shows they knew all about it ) then the m/bs 2 and 3 will take more oil away from the main gallery due to the centrifugal flow rising to b/e 2, 3 4 and 5. That leaves less flow for m/b1 so psi drops there. As you say it's furthest from the pump. So m/b 2 and 3 get to feed first, its the easier route for oil to take.

 

FWIW

 

I think there may also be a problem with pressure to MB 1 at low revs. By chance I wanted to trigger the illumination of the big red light in my start button on zero oil pressure (i.e. engine not running) I almost took a second feed from the pressure switch in the plugging under the distributor, but by chance found I already had a spare wire handy towards the front of the block, so I screwed a second pressure switch into the plug in the gallery next to MB1. Its only reading this thread that has reminded me that quite often at tickover and low revs I would see this ineffect secondary oil warning light flicking, but on checking the oil pressure guage it would be at 60+ and the main oil warning light wouldn't be flicking, I just put this down to possibly a faulty **** new pressure switch and didn't really worry about it as the oil pressure was excellent! and the light stopped flicking as the revs increased. I'm just wondering if it was actually an indication that oil pressure was low at the front of the gallery?

 

NB when stripping my engine MB1 and BE1 looked perfect so I have no evidence that it caused a problem.

[RogerH]

Hi Folks,

are we talking about the 6 or 4 cylinder engine. I thought it was the 6 but it is not stated as such.

 

On the 4 cylinder engine I have quite often found the rear (#3) MB badly pitted ( I believe it is called galling).

This could only happen with poor lubrication (probably). But I've never seen one seized or uniformly worn through to the base metal.

 

Roger

[stuart]

Hi Folks,

are we talking about the 6 or 4 cylinder engine. I thought it was the 6 but it is not stated as such.

 

On the 4 cylinder engine I have quite often found the rear (#3) MB badly pitted ( I believe it is called galling).

This could only happen with poor lubrication (probably). But I've never seen one seized or uniformly worn through to the base metal.

 

Roger

Its a 6 Roger.

Stuart.

[Peter Cobbold]

FWIW

 

I think there may also be a problem with pressure to MB 1 at low revs. By chance I wanted to trigger the illumination of the big red light in my start button on zero oil pressure (i.e. engine not running) I almost took a second feed from the pressure switch in the plugging under the distributor, but by chance found I already had a spare wire handy towards the front of the block, so I screwed a second pressure switch into the plug in the gallery next to MB1. Its only reading this thread that has reminded me that quite often at tickover and low revs I would see this ineffect secondary oil warning light flicking, but on checking the oil pressure guage it would be at 60+ and the main oil warning light wouldn't be flicking, I just put this down to possibly a faulty **** new pressure switch and didn't really worry about it as the oil pressure was excellent! and the light stopped flicking as the revs increased. I'm just wondering if it was actually an indication that oil pressure was low at the front of the gallery?

 

NB when stripping my engine MB1 and BE1 looked perfect so I have no evidence that it caused a problem.

The " gauge pressure section" is helpful:

http://en.wikipedia.org/wiki/Oil_pump_%28internal_combustion_engine%29

 

"Despite the frequent comparison to hydraulic engineering theory, this is not a “closed system” in which oil pressure is balanced and identical everywhere. All engines are “open systems”, because the oil returns to the pan by a series of controlled leaks. The bearings farthest from the pump always have the lowest pressure because of the number of leaks between the pump and that bearing. Excess bearing clearance increases the pressure loss between the first and last bearing in a series."

 

That is what Ive been trying to say, and why I think the centrifugal flows become important at excessive rpm. Cenrrifugal force intriduces extra 'leaks' at high rpm.

 

Peter

[GT6M]

Thats what ive been thinking Peter.

with all the oil loss at every bearing, then No1 actually gets little oil.

BUTT, some hoo it manages quite well if not thrased to bits.

 

Intresting thing that one aboot an oil light on NO 1 galley plug.

Kas said he got v little oil there too.

 

M

[oldtuckunder]

with all the oil loss at every bearing, then No1 actually gets little oil.

BUTT, some hoo it manages quite well if not thrased to bits.

 

Just finished cleaning, you know when its really clean as it becomes like the forth road bridge, its already started rusting at one end before you get to the other (nightmare). But anyway considering oil loss I surprised me the size of the oil feed hole to the distributor shaft spindle about the same size as the feed to a MB, yet if you look at the feed to a camshaft journal its way way smaller rotating at the same speed (infact faster at the bearing surface) and takes way more punishment. There must be oodles of oil escaping back down that shaft to the sump.

 

On No 1MB managing, if you look at the crankshaft flexing post that Peter put up last week? you can see that No 1 MB and No1 BE actually get way less of a thrashing than the journals further down the crank, might explain why it manages on an oil starvation diet utill really pushed.

 

Have to go "Rust Never Sleeps"

[Peter Cobbold]

Thats what ive been thinking Peter.

with all the oil loss at every bearing, then No1 actually gets little oil.

BUTT, some hoo it manages quite well if not thrased to bits.

 

Intresting thing that one aboot an oil light on NO 1 galley plug.

Kas said he got v little oil there too.

 

M

Markus,

I am pretty certain that the cause is excessively high rpm.

The m/b is fine at 5rpm but killed at 7k. That's a tight rpm range and 'fits' the idea that centrifugal forces are at play. Because they will double

between 5 and 7k. And in the crank assembly the b/ends are at the biggest radius so the velocity out there is highest. Its the square of velocity that dictes the cf force. Hence the leaks there will double between 5 and 7krpm. Thats why I focus on the flows out there.

 

I don't see anything else that is so sensitive to rpm. The oil pump - as long as it is air-free- as Nick mentioned should still pump. And with a flow in proportion to rpm.

What is the relief valve doing? Typically its open at midrange rpm so dumping oil above say 3k rpm. Is it still open at 5 to 7k ??? That could also steal flow before it reaches #1. But then why is the m/b psi so lowif theres pressure to open the rv? I do wonder if the centrigual scavenge start to take so much flow that the relief valve shuts as rpm rise above 5k.

 

Do the big ends ever suffer? because you'd think an oil starved m/b would also have its b/end equally starved: the mb and be would expire together. AFAIK they dont and the b/e survives when the main fails, despite the hugec ompressive loads on it. To me, that's a clue to centrifugal support of oil flow and pressure at the b/e.

 

I'm convinced the explanation for zero op at #1 m/b is centrifuging of oil away from the bearings at excessive rpm. And the cure would be to eqaulise flows between bearings according to the centrifugal scavenge - with the tuned octopus I mentioned. And I think I'd relocate the relief valve to the manifold in the octopus. So all the pipes see equal pressure, and equal with the rv, and the flows are matched.

 

Peter

[Guest ntc]

A six pot will do 7000 rpm with no oil issues,so I do not get the question.

[GT6M]

think ive sorted the oil flow to number one end,

the drillings thru the dizzy area were only 7 mm,

but got too and med em all 11.6 mm all the way along the gallerey.

so nee moer bottleneck at the dizzy bush part.

 

 

 

 

M

[Stanpartmanpartwolf]

Correct Neil. Steel 95mm race cranks are not cross-drilled & for a reason. Oilway diameters are critical & that's it. Best to clear of Moldex cranks IMHO.

[GT6M]

NTC says, A six pot will do 7000 rpm with no oil issues,so I do not get the question.

 

an Stan Wolf says, Correct Neil

 

Seems as thou some folk have had some luck so far, and other aint.

It cannot be denied that there is less pressure at NO1 end, as others test have shown,

and also some of the blokes I no have had NO1 go.

 

And Mr KK found this out yonks ago, and med a contraption to remedy it.

 

So, whos correct, the ones with probs,or the ones woes just been lucky so farr,!!

 

M