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This is probably a daft question but what is the purpose of the crankshaft spigot bush.  I appreciate that the gearbox input shaft fits into it but once the gearbox has been fitted to the engine with the driven plate clasped firmly between the pressure plate and the flywheel, the spigot bush would seem to me to be redundant.  What am I missing?

Rgds Ian

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Hi Ian,

the flywheel and the GB input shaft become independent parts with the clutch depressed. They rotate separately.

You do not want a steel flywheel spinning with a steel shaft in it.

So you have the oil'd bronze bush.

 

Roger

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When I rebuilt the gearbox in my TR6 last year I thought that while it is in bits I will do the clutch and spigot bush as well, I was amazed to find that there was no spigot bush fitted  just a big hole where it should be.

I have owned the car since 1997 and have done an enormous mileage in that time with no problem, I have ofcourse fitted a bush but can't detect any difference in the way the car behaves.

George 

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1 hour ago, harlequin said:

When I rebuilt the gearbox in my TR6 last year I thought that while it is in bits I will do the clutch and spigot bush as well, I was amazed to find that there was no spigot bush fitted  just a big hole where it should be.

I have owned the car since 1997 and have done an enormous mileage in that time with no problem, I have ofcourse fitted a bush but can't detect any difference in the way the car behaves.

George 

That’s where I am coming from George, my car didn’t have one either. 

Rgds Ian

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8 minutes ago, Ian Vincent said:

That’s where I am coming from George, my car didn’t have one either. 

Rgds Ian

The plot thickens! Maybe it was an upgrade back in the day. The super duper big bore spigot bush.

It does seem a bit strange, someone has gone to the trouble of removing the bush but not replaced it 

George 

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You preferably want the clutch release bearing pressing symmetrically on the clutch, an even distribution. So the clutch friction plate uses its full surface to engage the clutch. A clutch plate not working symmetrically can induce local heat stress on the flywheel surface which can further result in clutch/gear failure. A radial movement (for whatever reason this occurs) should be limitted as much as possible. The pilot bush is merely a guide in this matter. And as Roger mentioned, steel on steel is no good.

There are a lot of things that CAN happen. But I am sure, they don't always do.

There is lots of debate whether the bush should be pressed in the flywheel (short back cranks) or loose fit etc....eventhough the WSM states loose fit, mine was pressed fitted. So far no irregularities found and doing its job.

Jochem

Edited by JochemsTR
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Good morning @ all,

the ingoing gearshaft has only one bearing at its end in the gearbox and the end in the crankshaft has some radial play.

I always thought the spigot bush is needed to keep this end as exactly as possible in the center of the crankshaft to avoid the friction plate spinning out of center?

This seem reasonable to me because to see the friction plate spinning a minimum out of center with only 1.000 revs on my late (I already did that) gave me very much respect.

Ciao, Marco

 

Edited by Z320
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+1  It's asking a lot of the single ball race in the gearbox to keep the other end of the shaft central.

Bob.

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Yes , car manufacturers are well known for fitting items without any engineering benefits costing a couple of quid onto cars (which cannot be seen and polished by owners) because they just feel like it...Hmmm I don't think so.

Mick Richards

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Thks All,

I figured it was an alignment issue and I would agree that if the driven plate is allowed to wobble only a fraction off line when the clutch is depressed it does represent a big out of balance force.

Rgds Ian

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