Crank thrust washer problem and solution

[227bhp]

One for our delicate Filet perhaps as I know you like a ponder

I took an engine apart which hadn't done many miles, the crank thrust washer (TW) which takes the load from the uprated push clutch was completely buggered as was the crank. Owner says there is nothing wrong with how the clutch is set up (it's an aftermarket twin plate with hydraulic concentric slave), however I think he's wrong as the groove worn into the diaphragm tells me otherwise. Obviously he's going to check and remedy that, but I think I need to make a mod to prevent it happening again as (faulty fitment or not) it is a lot of pressure on just one half moon splash fed bearing. Looking on the 'net it's not an uncommon failure no matter what the engine, the World over and there is a mod which won't work on this as the bearing layout won't allow it.

So, to the point: The oilway which feeds the main bearing runs through the block, i've realised that if I drill a small hole through to this gallery behind the TW seat I can feed my TW with pressurised oil. If I drill at 90' to the surface then the oil will enter (via a hole I will drill) the bearing through one of its two grooves. This I believe will be no good, so i'll drill at maybe 45' and it will then come through to the central flat section.

The problem is what diameter hole to drill and am I in danger of starving the main of oil?

It's the furthest bearing from the oil pump, I'm thinking maybe 1mm perhaps, the hole which feeds the main is 8mm.
Maybe I could put a shim under the pump relief spring to compensate, but i'm wary of having too much oil pressure too.
Wondered what your thoughts were...

[Mignon]

If this is an engine which does not normally suffer thrust washer failures then logic suggests it must be being caused by whatever has been modified. If there is a constant pressure acting on the washer then it's going to wear out a damn sight faster than otherwise. I suggest an exercise to see if the clutch is exerting a constant pressure.

As to feeding more oil to the washer the main problem is that thrust washers are flat (usually*) and are not able to generate hydrodynamic lubrication wedges such as exist inside a curved journal bearing. Also the front/rear clearance on a thrust washer to the crank faces is usually about 6 thou or more hence not tight enough to generate hydrodynamic lubrication. As such you're probably going to just squeeze out any oil over and above what gets there by splash anyway.

However more oil is usually a good thing n'kay and there's an easier way to achieve it. If you file a small chamfer on the end (split line) of one of the two main bearing shells on that journal on just the rearward facing half of the shell from the centre out it will direct oil to the thrust washer directly from the high pressure hydrodynamic wedge existing inside the journal. A chamfer so as to generate a gap about 1 mm square in area should suffice. You can potentially play with that chamfer size just for the cost of a set of bearings without having to drill holes in the block.

• Manufacturers have played about with slightly curved thrust washer geometries to try and generate hydrodynamic lubrication effects. I'm no expert on the theory or practice.

[stevieturbo]

227bhp said:

One for our delicate Filet perhaps as I know you like a ponder

I took an engine apart which hadn't done many miles, the crank thrust washer (TW) which takes the load from the uprated push clutch was completely buggered as was the crank. Owner says there is nothing wrong with how the clutch is set up (it's an aftermarket twin plate with hydraulic concentric slave), however I think he's wrong as the groove worn into the diaphragm tells me otherwise. Obviously he's going to check and remedy that, but I think I need to make a mod to prevent it happening again as (faulty fitment or not) it is a lot of pressure on just one half moon splash fed bearing. Looking on the 'net it's not an uncommon failure no matter what the engine, the World over and there is a mod which won't work on this as the bearing layout won't allow it.

So, to the point: The oilway which feeds the main bearing runs through the block, i've realised that if I drill a small hole through to this gallery behind the TW seat I can feed my TW with pressurised oil. If I drill at 90' to the surface then the oil will enter (via a hole I will drill) the bearing through one of its two grooves. This I believe will be no good, so i'll drill at maybe 45' and it will then come through to the central flat section.

The problem is what diameter hole to drill and am I in danger of starving the main of oil?

It's the furthest bearing from the oil pump, I'm thinking maybe 1mm perhaps, the hole which feeds the main is 8mm.
Maybe I could put a shim under the pump relief spring to compensate, but i'm wary of having too much oil pressure too.
Wondered what your thoughts were...

More details. What engine, what clutch, who built the engine, where thrust clearances and faces all good when it was built...etc etc etc ?

It would take a pretty serious clutch, and some serious foot on the clutch time to cause most thrust bearings any problems at all. And generally most clutches arent like that. And multiplate clutches less so....as that's part of the reason for going multiplate. So you can have more grip without huge pedal effort.

Or are you somehow suggesting the slave/bearing has had excessive travel and somehow forcing the crank against the thrust ?

Again...what setup, engine, box, clutch, how many DIY'd parts etc ? Presumably the pedal felt fine, clutch worked ok etc ?

But feeding oil to the thrust faces has been done before. If they are loose thrusts, engines where I've seen it done, they've also bolted the thrust to the block with countersunk bolts. You dont want the oil feed to actually get behind the bearing and push it onto the crank.

1mm should be plenty though, as it would be additional oil, over the normal oil supply it sees from the mains themselves. I wouldnt worry about it having any affect on the main oil supply.

[99hjhm]

Clutch issue. seen it done on mini's, 1mm hole and 2mm in the thrust, just on the loaded rear thrust .Have done the filing the parting line on bearings in the past and seems to work, certinally where there is a centre groove through the bearing shell.

[227bhp]

Mignon said:

If this is an engine which does not normally suffer thrust washer failures then logic suggests it must be being caused by whatever has been modified. If there is a constant pressure acting on the washer then it's going to wear out a damn sight faster than otherwise. I suggest an exercise to see if the clutch is exerting a constant pressure.

As to feeding more oil to the washer the main problem is that thrust washers are flat (usually*) and are not able to generate hydrodynamic lubrication wedges such as exist inside a curved journal bearing. Also the front/rear clearance on a thrust washer to the crank faces is usually about 6 thou or more hence not tight enough to generate hydrodynamic lubrication. As such you're probably going to just squeeze out any oil over and above what gets there by splash anyway.

However more oil is usually a good thing n'kay and there's an easier way to achieve it. If you file a small chamfer on the end (split line) of one of the two main bearing shells on that journal on just the rearward facing half of the shell from the centre out it will direct oil to the thrust washer directly from the high pressure hydrodynamic wedge existing inside the journal. A chamfer so as to generate a gap about 1 mm square in area should suffice. You can potentially play with that chamfer size just for the cost of a set of bearings without having to drill holes in the block.

• Manufacturers have played about with slightly curved thrust washer geometries to try and generate hydrodynamic lubrication effects. I'm no expert on the theory or practice.

Thanks for the reply, sadly that was the mod I mentioned and won't work as it only has a 180' thrust bearing on each side, obviously as they are against the block they are uppermost too so even gravity is against it.
Clearance is between .0019 to a max of .007 and I guess the washer only about 8mm wide so not much area either, although in its favour the oil could be pumped behind the washer as well as in front which would create a cushion and reduce the clearance - a bit like a hydraulic tappet maybe.
The question still remains, if I was to try it what diameter hole and would it tend to bleed off the pressure from the main, only way is to try it maybe.

I did ponder over putting the block on the miller and machining a groove to sit a bearing on the other journals, but the shape of it and amount of metal on crank and block wouldn't allow it.

Edited by 227bhp on Monday 5th December 22:09

Edited by 227bhp on Tuesday 6th December 14:38

[crossy67]

How's about machining the flywheel so you can fit in a large flat plane bearing. Not the nicest option but would hopefully last longer than the thrusts and not as bigger job to change.

http://www.ball-rollerbearing.com/sale-7693853-ax4...

[Mignon]

227bhp said:

Thanks for the reply, sadly that was the mod I mentioned and won't work as it only has a 180' thrust bearing on each side, obviously as they are against the block they are uppermost too so even gravity is against it.

I wouldn't fret too much about any of that. The thrusts are fed by the oil that spills out of the side of the main bearing and that gets carried round everywhere and flung out. The chamfer on the end of a shell just increases the supply. It won't all go onto the thrust obviously but some of it will.

As for losing pressure if you do that or drill a hole, I wouldn't worry about it either. The pump won't be short of capacity. An easier way than trying to drill a very small hole is drill or even better, ream, a bigger one and make a little brass or aluminium jet to press in to limit the size down again.

[227bhp]

Mignon said:

227bhp said:

Thanks for the reply, sadly that was the mod I mentioned and won't work as it only has a 180' thrust bearing on each side, obviously as they are against the block they are uppermost too so even gravity is against it.

I wouldn't fret too much about any of that. The thrusts are fed by the oil that spills out of the side of the main bearing and that gets carried round everywhere and flung out. The chamfer on the end of a shell just increases the supply. It won't all go onto the thrust obviously but some of it will.

As for losing pressure if you do that or drill a hole, I wouldn't worry about it either. The pump won't be short of capacity. An easier way than trying to drill a very small hole is drill or even better, ream, a bigger one and make a little brass or aluminium jet to press in to limit the size down again.

If I fixed the washer to the block as Stevie says I could use the hole in that to regulate the flow, this would have the advantage that you would just have to drop the sump and either make the hole bigger or put another washer in without taking the engine out.

[Mignon]

That's a good suggestion from Stevie to screw the washer to the block. I agree that this with a hole through the washer (the leading end obviously for preference) leading directly to an oilway would be the optimum solution.

[GavinPearson]

I would recommend that you look at the surface finish on the crank thrust faces in case that is wearing the washer out.

You may need to lap or regrind and lap those surfaces and fit oversize thrusts.

[227bhp]

Mignon said:

That's a good suggestion from Stevie to screw the washer to the block. I agree that this with a hole through the washer (the leading end obviously for preference) leading directly to an oilway would be the optimum solution.

What you mean here is that if the crank revolves like the hands of a clock we introduce the oil at 3 o' clock and it does 180' before getting to 9 o clock.

Yes, we're forming a plan here

Then my thoughts went to the two grooves in the bearing, these are now working against us I think in losing oil. So what I will do is to fix the washer through these grooves with the screws thus partially blocking them off, options here are to use a screw with a hole drilled through it so the oil passes through it, but it's not really early enough in the 180' arc. The other option is to use a plastic or aluminium c/s screw so I can get it just below the surface safely, if the crank munches into the bearing and hits the screw head at least the head won't eat the crank.
The bearing backing still will though

[99hjhm]

Are you not reinventing the wheel here? Whats the engine and is this a common issue with it?