21 replies to this topic

[Spider]

The very early 850's didn't have these nuts but they appeared soon after production started.

 

Apart from wear the Thrusts out as Nick have mentioned, the real reason from them being fitted was to stop the Centre Main Cap from breaking in two.

 

And to stop the Crankshaft from being shoved in to the radiator when the Clutch Hose deteriorates.

[tiger99]

The thrust washer wear problem is probably due to bad advice which most of us believed at the time. We used to be taught, in any car, to start the engine with clutch pedal pressed fully to reduce the viscous drag of gears in the gearbox, including the transfer gears in the Mini, and so ease the work of the starter motor.

 

Nowadays it is recognised that it aggravates wear on the crankshaft thrust washers, which really need oil pressure to lubricate them. The worst affected engines were the Triumph straight 6 in the Vitesse, GT6, 2000 and 2.5PI, but the four cylinder engines were very similar. Excess wear caused the thrust washer halves to be ejected from the main bearing cap, with severe damage following.

 

The same applies to the A and B series engines, and many others. Rapid wear by loading bearing surfaces before hydrodynamic lubrication is established causes most engine wear. You can possibly get 3 or 4 times the life out of an engine by pre-pressurising the lubrication system before activating the starter. Systems are available that can do that. But if you have a turbo, you also want to keep the oil flow for up to a minute after the engine stops, the time when most turbo bearing wear occurs, for which an electric pump might be needed.

 

So always start your Mini, in neutral of course, with foot off clutch pedal, unless you have some pre-lubrication system fitted.

[gazza82]

Interesting. I was told never to start a car with the clutch depressed. Just in neutral.

A friend of a friend used to but soon stopped when he started his car (in gear it turned out) with clutch down and his foot slipped off the clutch pedal. Cost him a new front end and end wall of a concrete garage 8-}

[Homersimpson]

The thrust washer wear problem is probably due to bad advice which most of us believed at the time. We used to be taught, in any car, to start the engine with clutch pedal pressed fully to reduce the viscous drag of gears in the gearbox, including the transfer gears in the Mini, and so ease the work of the starter motor.

 

Nowadays it is recognised that it aggravates wear on the crankshaft thrust washers, which really need oil pressure to lubricate them. The worst affected engines were the Triumph straight 6 in the Vitesse, GT6, 2000 and 2.5PI, but the four cylinder engines were very similar. Excess wear caused the thrust washer halves to be ejected from the main bearing cap, with severe damage following.

 

The same applies to the A and B series engines, and many others. Rapid wear by loading bearing surfaces before hydrodynamic lubrication is established causes most engine wear. You can possibly get 3 or 4 times the life out of an engine by pre-pressurising the lubrication system before activating the starter. Systems are available that can do that. But if you have a turbo, you also want to keep the oil flow for up to a minute after the engine stops, the time when most turbo bearing wear occurs, for which an electric pump might be needed.

 

So always start your Mini, in neutral of course, with foot off clutch pedal, unless you have some pre-lubrication system fitted.

What is interesting now is that a lot of cars can't be started unless you press the clutch, my wifes focus is like this.

[nicklouse]

But which way is the clutch depressed? And where is the force sent.

[Cooperman]

The thrust washer wear problem is probably due to bad advice which most of us believed at the time. We used to be taught, in any car, to start the engine with clutch pedal pressed fully to reduce the viscous drag of gears in the gearbox, including the transfer gears in the Mini, and so ease the work of the starter motor.

 

Nowadays it is recognised that it aggravates wear on the crankshaft thrust washers, which really need oil pressure to lubricate them. The worst affected engines were the Triumph straight 6 in the Vitesse, GT6, 2000 and 2.5PI, but the four cylinder engines were very similar. Excess wear caused the thrust washer halves to be ejected from the main bearing cap, with severe damage following.

 

The same applies to the A and B series engines, and many others. Rapid wear by loading bearing surfaces before hydrodynamic lubrication is established causes most engine wear. You can possibly get 3 or 4 times the life out of an engine by pre-pressurising the lubrication system before activating the starter. Systems are available that can do that. But if you have a turbo, you also want to keep the oil flow for up to a minute after the engine stops, the time when most turbo bearing wear occurs, for which an electric pump might be needed.

 

So always start your Mini, in neutral of course, with foot off clutch pedal, unless you have some pre-lubrication system fitted.

Well explained Tiger.

 

As you say the old Triumph engines were very bad for thrust bearing failure, but they only had a half-circle thrust bearing and the thing to do was to machine the bearing cap to take a full diameter bearing, then hold the thrust bearings in with silver-steel dowels. I recall doing this on a triumph 2000 rally car engine way, way back in about 1969.

[whistler]

The original Minis didn't have those overthrow nuts. They were added by BMC after having to deal with the results of badly adjusted clutch arm stop bolts which allowed significant damage to the crank thrust bearings - all of which had to be rectified under warranty.

They are not needed so long as the clutch adjustment is correct.

 

Edited by whistler, 18 May 2019 - 04:07 PM.