Crankshaft centre main bearing thrust washers

[Paul Kelley]

My engine is being rebuilt and we've hit a problem. The crankshaft regrind has resulted in the width of the centre main bearing being increased beyond the size of the available oversize thrust washers at +10 thou. These are the 'half moon' ones that stop float. First question please: the width across the centre main bearing is now 28 mm. Do you know what it should be as standard (I assume this would have been an imperial measure), so that we can work out what size thrust washers we are even trying to find. Second question: do you know of anyone who supplies, or could make up, oversize thrust washers to the size we need, probably about + 30 thou at a guess? As ever, any help would be much appreciated.
Paul

[richardthestag]

ouch, any feedback from the machine shop on what was going through the mind of the operator or how they can fix this?

I do not have a crank, outside and engine handy. Ring Trevor (sorry barkerwilliams I cannot recall his surname) at Faversham Classics. He is a superstar when it comes to the engines and tolerances.

I guess you could have an oversized shim made up but many machine shops these days need drawings and stuff. I am going to guess that another crank is going to be the easiest answer and this one is moving towards boat anchor territory

Keep us posted.


P.S. I had a machine shop destroy* a set of "skimmed once" cylinder heads. They had bags of life left in them but the machine shop was trying to get rid of the corrosion from the blind coolant passageways. fortunately he had the foresight to stop before they were rendered complete scrap, but they will not take another skim without the use of savershims.

[NeilR]

One way to overcome that is too use a suitable size bearing shim (probably about 20 thou thick) & cut it in half.
If inserted between block & thrust washer, it can't fall out.

Just a thought.

Neil

[jbuckl]

Just measured the block thrust faces to be 22.25mm
STD thrust is 2.34mm
so standard gap is 26.93.
your crank is 28.00?
that means with 30 microns of end float the new washers need to be 0.535mm thicker...2.875mm each.
maybe they’ll knock you up a pair in bronze?

[Paul Kelley]

Many thanks all three of you for these helpful suggestions. The original crankshaft was already at + 60 thou so, as Richard says, better off at the bottom of the sea (or possibly as a garden sculpture). The s/hand one which we now find has the over-ground centre main was sourced from Stag Classics (Paul McLaughlin) and supplied pre-ground and toughened. He's a good bloke and found this one in his yard and will see if he can replace it if needs be, so all done in good faith and fair. Using jbuckl's measurements I can get a pair made up (Drakes in Bradford or Ganley's in Kent will do it). Thanks for that info jb, really helpful (sorry, I don't know your name). Plus I'll talk to my mechanic about your idea Neil. So, the choice is either make the most of what we've got and get non-standard thrust washers made up, or try again with another unknown crankshaft. Mmm. Any views on the wisdom of fitting very oversize thrust washers? It is a manual car so arguably more pressure on the washers, especially the back one.
Thanks again, much appreciated. Paul

[NeilR]

The pressure on the thrust washers will always be more on a manual, the front one, because clutch releasing tries to push the crank forward.

Neil.

[Paul Kelley]

Thanks Neil, that's what I meant, just back to front!

[Lingen]

Neil.
If you push the crank forward, surely it pushes against the rear thrust bearing as Paul said?
Mike.

[NeilR]

No it doesn't - if you push the crank forward then it pushes against the forward thrust bearing. Pretty obvious really.

Neil.

[wilf]

Err ??

[jbuckl]

If the forward direction thrust is at the rear, which it is, the clutch opening force is reacted against the rear thrust washer.
The front most washer becomes unloaded as the crank is pushed away from it.
Paul, I’ve sent a pm about bronze oversized thrusts.
Julian

[Lingen]

Thanks Julian. That is what I thought. The thrust bearing that is stopping the crankshaft from being moved forwards by the action of the clutch against the flywheel, must be facing in the opposite direction= towards the driver = backwards. Pretty obvious really!
Mike.

[NeilR]

When the clutch is released, it pushes the crank towards the front of the car, this pushes on the thrust in front of the crank centre journal.
Do I have to draw you a picture !!!!!.

[Phil S]

most engineering suppliers will sell shim steel. this is easily cut with tin snips and may be a way to overcome the problem if you don't have any luck with thicker thrusts. worn thrusts are a problem on the straight 6, they can get so bad they stall when the clutch is disengaged

[wilf]

When the clutch is released, it pushes the crank towards the front of the car, this pushes on the thrust in front of the crank centre journal.
Do I have to draw you a picture !!!!!.

I think you might need to. With the greatest of respect, I think you might have your geometry wrong.