18 replies to this topic

[Aridgerunner]

I know the overthrow nuts have been discussed over and over for years. I think I've read every post on the subject. And I think I've read that they are not needed when using a lightweight flywheel. What I never learned is why they're not needed.

In my case I am using Mini Spares lightweight flywheel, pressure plate, diaphragm, clutch disc and their hardened plunger and a new release bearing and new overthrow nuts. It's all new from the crank to the arm. And the arm was replaced shortly before we decided rebuild everything.

I will be most thankful to anyone that explain why they're not needed with a lightweight flywheel.

Thanks in advance.

Bill

[nicklouse]

They are needed with all flywheels.

 

mine are Ti.

[Ethel]

You'd never release the clutch if there wasn't something behind the pressure plate to push against. That something  is ultimately the crank thrust bearings and the throw out stop nuts are there to prevent you pushing on the thrusts any harder than is necessary to release the clutch.

[Aridgerunner]

Thanks. I had no plans to remove them. Was just curious.

[imack]

I run them on my KAD alloy flywheel, but I've never set them by the book as I hate the feel of hitting the throw out stops before the pedal hits the floor. I set them so the pedal hits the floor at the same time that the throw out stops bottom out. It's never caused me any issues.

[timmy850]

The earliest Mk1 minis didn’t have the overthrow nuts. They also had:
Spring type clutch (not diaphragm)
No circlip in the slave cylinder

This meant that you could pump the pedal a few times and it’d lock up the crank on the thrusts or crack the main bearing caps

On later engines there was less risk of this happening, but the overthrow nuts are a good last resort to stop too much pressure on the thrusts. If they are adjusted correctly you’ll not have any problems

If you adjust them in too tight there is a chance you’ll bend or break the end off the clutch arm. If they come loose and wind in they’ll prevent the clutch disengaging and you won’t be able to select gears

[nicklouse]

Had may a Mini in the 80s that did not have the C clip on the clutch slave. It only became a thing when the verto slaves had it. 
break the ball off? Only if very worn and that would be after bending the arm or lengthening the push rod to take up the play.

 

still very possible to lock up the crank without the stops.

 

light flywheel normally also means stronger spring.  
 

the only time I have seen the lock nuts not used was on a Grass track car with a dog box.

 

But they rebuilt the engine between events.

[Spider]

The earliest Mk1 minis didn’t have the overthrow nuts. They also had:
Spring type clutch (not diaphragm)
No circlip in the slave cylinder

This meant that you could pump the pedal a few times and it’d lock up the crank on the thrusts or crack the main bearing caps

On later engines there was less risk of this happening, but the overthrow nuts are a good last resort to stop too much pressure on the thrusts. If they are adjusted correctly you’ll not have any problems

If you adjust them in too tight there is a chance you’ll bend or break the end off the clutch arm. If they come loose and wind in they’ll prevent the clutch disengaging and you won’t be able to select gears

 

Just to clarify here, it was early in 1961 that they did fit the Over-throw Nuts and they still had the Spring Clutch. They got sick to death of fishing worn thrusts out of the gearbox under warranty,,,,

[timmy850]

My definition of early and late is based on Australian minis, not necessarily including UK

They had introduced the circlip before this manual which was 1964


It’s quite common for a lot of people to tell you to take off the overthrow nuts & the return spring for pre-verto as they claim they don’t do anything. I happen to disagree and have them fitted on mine

[68+86auto]

If the factory could've got away with removing them, they would've. They were added for a reason.

 

The clutch will of course "work" without them but that doesn't make it a good idea.

Edited by 68+86auto, 21 September 2026 - 01:18 AM.

[Spider]

They had introduced the circlip before this manual which was 1964

 

 

Yes, it was there from day 1. The Slave was unchanged up to the introduction of the Verto.
 

[plsosds]

Lightweight flywheels are typically designed with slightly altered dimensional clearances or paired with specific pressure plate setups that reduce the overall clutch travel distance. Because of this, the risk of over-disengaging or throwing the clutch arm too far is minimized, rendering mechanical overthrow nuts unnecessary. However, always double-check your specific clutch clearance during assembly to ensure the release bearing doesn't over-travel!

[Spider]

Lightweight flywheels are typically designed with slightly altered dimensional clearances or paired with specific pressure plate setups that reduce the overall clutch travel distance. Because of this, the risk of over-disengaging or throwing the clutch arm too far is minimized, rendering mechanical overthrow nuts unnecessary. However, always double-check your specific clutch clearance during assembly to ensure the release bearing doesn't over-travel!

 

The flywheels themselves may well have 'altered (fitted) dimensions' however, the Thrust Bearing will still be in about the same place as with a stock flywheel and the amount of  movement needed for disengagement the same, so it's just as possible with a lightened flywheel to experience over-throw as with a stock flywheel. If an arm was fitted with a different leverage ratio, then it might be possible not to experience it from normal usage, however, where this all falls apart is if (when) there's an issue with the hydraulics, in particular with the hose collapsing, which isn't always readily visible from the outside, it acts as a slow return or non-return valve, with each pump of the pedal, the arm gets pushed out more and more until you end up shoving the crankshaft through the radiator

[Aridgerunner]

Thanks Spider. That's a perfect explanation as to why these are needed.

[nicklouse]

It’s quite common for a lot of people to tell you to take off the overthrow nuts & the return spring for pre-verto as they claim they don’t do anything. I happen to disagree and have them fitted on mine

But I am guessing the people that say it don’t actually understand the workings of the full assy. Or why the spring is actually needed.