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Regular readers may recall that I raised a concern about slightly low oil pressure a couple of months ago.  I think it was Mick who suggested it could be down to excessive end float on the crank.

I have the gearbox out at the moment so I put a dial gauge on the end of the crank and levered it back and forth to get a repeatable figure of 0.18mm or 7.1 thou.  This is outside the recommended workshop manual range of 4 to 6 thou.  Is it significant and should I be thinking about replacing the thrust washers?

Rgds Ian

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+1 because it will only get worse.

I recommend Scott Helms at custom thrust washers.

Customthrustwashers.com

plus a simple job to do giving you the opportunity to get an idea of how good the main bearing shells are as you have to remove the no.4 bearing cap and also clean the sump out!

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" how good the main bearing shells are as you have to remove the no.4 bearing cap and also clean the sump out!"

Dave,

There ain't no number 4 main bearing on a 4 cylinder crank ! I know...I've looked :P

Mick Richards

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+1 for scott helms

Quality product with good delivery time

If your in there change the b end shells..can only help to get your pressure back and will give u a heads up on the mains...cant remember if you can change the mains in situ

Good luck

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Just remember guys, don't go chasing pressure, it's flow that counts. As long as the loss of oil from sides of bearings etc is balanced by the incoming flow.

Mick Richards

Edited by Motorsport Mickey
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37 minutes ago, Motorsport Mickey said:

Just remember guys, don't go chasing pressure, it's flow that counts. As long as the loss of oil from sides of bearings etc is balanced by the incoming flow.

Mick Richards

1920`s LeMans Bentleys only ran 8PSI oil pressure but had several gallons of it sloshing round the engine

Stuart.

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I’m eager to learn:

Why would the thust washers impact oil pressure when worn?

On a 6-pot the other 3 main bearings are of a similar design with no TW at all, so why would it matter?

Additionally. the TW is only on 180 degrees of the circumference.

Or is the 4 pot of a different design?

Thanks,

Waldi

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Just my 2 Cents:

- Thrust washer in a 4-pot consist of 2 half-circles each
- Impact on oil pressure - why?
- there is just one set of thrust washers as this bearing is designed as the one taking the load. If there would be more than one , there would always be only one "working": So keep it simple (and cheap) and skip the others…..

- pressure is necessary to make a fluid flow. So without pressure: No flow at all.
- The pressure is measured in the oil gallery - this pressure is dependant from the oil pump, setting of pressure restrictor  AND the flow resistance of the oil channels after the measuring point.
- first (and main?) factor is the main bearings. Worn bearings loose as t lot of oil -> thus the oil pressure is reduced.
- The flow through the big end bearings depends on the flow through the main bearings: So worn main bearings reduce flow in the big end bearings
- the oil flow into the head depends (4-pot) on the rear main bearing: Worn bearing -> less oil in the head

Rebuilding my engine gave me much higher oil pressure with much more oil in the head - so (TR3 with "open" oil cap) so I lost oil by dripping out of the oil cap

 

Regards, Johannes

(Sorry for my english …)

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"pressure is necessary to make a fluid flow. So without pressure: No flow at all."

Well I know what you mean Johannes but that is not really true - it's actually the other way around.  Pressure results from a restriction of flow.  If you ran the pump with nothing attached to its output  there would be plenty of flow but no pressure.   Its the restriction due to tight clearances in the bearings which produces the pressure at the pump by reducing the flow.

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Rob: even then you need some pressure (even a milli-psi is pressure). And just lifting the oil from sump to head needs some pressure too

You are right: 

1 hour ago, RobH said:

Pressure results from a restriction of flow.

But keep in mind that any kind of pipe or passage is a restriction of flow - and high flow until the main bearing with direct exit into the sump doesn't help you with lubricating the big ends or the rockers

 

Regards,

Johannes

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Of course it's not pressure, but a difference in pressure that's needed for fluid to flow.

Cheers, Richard

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  • 1 month later...

Morning all

too cold to do much in the garage so thought i’d check the end float on my 6

i had a lot of difficulty finding somewhere suitable to mount the dti, eventually the magnetic base was attached to the block and i got a reading of 14

its a metric dti so this equates to 5.5thou so ‘acceptable’

however i’m not confident in the reading, as i’m new to using the dti and wasnt happy it was mounted stably enough

does anyone have a picture of how they mounted a dti to a 6pot in the car successfully?

steve

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I can't help with where to mount the DTI Steve but all I was concerned about was getting a repeatable reading.  So I moved my DTI around a couple of times and confirmed that I was getting the same reading each time.

If I were you I would be looking to do the same sort of thing.

Rgds Ian

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Hi Steve,

the DTI should be on the block, not on the frame, but this is Obvious.
I messured mine when the engine was on an engine stand with camshaft chain cover off so had no issue then.

You could check if it is firmly mounted by adding a feeler gave between the point of the DTI and your pulley, then check if the reading changes the same rate.

Regards,

Waldi

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Hi Steve,

          I know this is silly but to interpret your reading of '14'  without conversion tables. Place the DTI on a flat surface and slide feelers under the tip to get near your reading.

As for stability. When attached to the engine block can you get ANY movement on the pillar of the DTI.  You should not.

 

Roger

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4 hours ago, RogerH said:

I know this is silly but to interpret your reading of '14'  without conversion tables. Place the DTI on a flat surface and slide feelers under the tip to get near your reading.

Alternatively divide 0.14 by 25.4 to get the exact figure of 0.0055, (to 4 significant places)

Rgds Ian

Edited by Ian Vincent
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1 minute ago, Ian Vincent said:

Alternatively divide 0.14 by 25.4 to get the exact figure of 0.0055, (to 4 significant places)

Rgds Ian

Yes, maths is your friend!

i’m planning to measure a few more times and see what results i get.

if the endfloat is within limits i’ll leave well alone, otherwise it’s off with the sump, fit std washers, retest, order the correct size.

thanks for the input !

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With metric DTI’s “we on the mainland” normally work in hundreds of mm.

25,4 units on the scale equals 25,4/100 mm which is 0.254 mm which is 10 thou (or 1 thou equals 0.0254 mm)

I had to get used to thou’s too.

Waldi

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After much trial i found a solid location for the dti and obtained repeatable end float readings of 16-17=6.2-6.6 thou

so i guess i’ll be having the sump off !

wonder what i’ll find, as the engine is ‘bespoke’ ie i dint know whats been done exactly......

steve

Edited by Steves_TR6
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