11 replies to this topic

[mini.rich]

Right I'm near to finishing my twink engine, just need to put the flywheel/clutch assembly on. I'm just checking the end float on the primary gear and realised I don't have a haynes manual to hand I've got a DTI set up and waiting=P could someone give me the correct figures please?

Also whats the tolerance on how much 'play' or side to side movement there should be in the bushes? I have 0.14mm front and back.... I'm guessing it could do with re-bushing??

By the way they are standard MPi drops.

Any help would be greatly appreciated

[MRA]

End float is 0.003" to 0.0065" on the primary gear.

Bush to shaft clearance should be no greater than 0.005"

[dklawson]

Martin, 0.005"? Can it really be that much? I thought it was about 1/3 of that value, closer to 0.0015"

[mini.rich]

End float is 0.003" to 0.0065" on the primary gear.

Bush to shaft clearance should be no greater than 0.005"

Cheers, looks like I'll need to have it rebushed then. End float is 0.08mm, so thats ok, but means bugger all until I can get it rebushed and check again, ha!

Edited by mini.rich, 17 May 2011 - 04:59 PM.

[MRA]

Doug, the earlier white metal bush was between 0.0015" & 0.0002"

And the later Bronze bush should be from 0.003" to 0.005" aim for a tighter fit on a road car and a slacker fit for a race car, don't forget that the very early type was oil fed.

[MRA]

Also found in a 1970 BL workshop manual .... the lubricated bushes (oil fed) with a running clearance of 0.0025" to 0.0030" which differs from my previous information of 0.0015" to 0.0020" these figures were from my trusty BL 1100 / 1300 workshop manual for an 1100 with the oil fed bearings.

The Mini 850 & 997 were the only models that used the oil fed primary bearings..

[Guess-Works.com]

Use feeler gauges to measure the end float on a primary gear between the outer bush and backing washer.

Rebushing may not solve an endfloat issue unless the outer bush is worn, which is why there are different thickness primary gear thrusts.

Also try rotating the C washer and reinserting.

Edited by Guess-Works.com, 17 May 2011 - 05:21 PM.

[Cooperman]

If the latest bushes don't have a good radial clearance the primary gear can seize onto the crank. I've seen that and the guy who built the engine said that it had been machined to give a sensible running fit - obviously not 'running' enough. I must confess that I took if off and opened it up with a flap-wheel in an electric drill until it ran easily and I judged it to be suffiiciently clear then polished it with metal polish. I do well know it's not the recommended way, but it seems to have worked (this time!), the guy wanted his car back on the road the same day and it's still running O.K. well over 17 months later.

[MRA]

They do, and then you have a very stiff clutch with lots of crunching

[Cooperman]

They do, and then you have a very stiff clutch with lots of crunching

The one which was brought to me (on a trailer!) was so solid the drive was absolutely solid. The primary gear had the latest manganese-bronze bushes and, the owner said, had been machined out before fitting and ran smoothly when turned by hand,. I think I believe him, but it was just that when run, the bushes must have expanded and seized onto the crank. With the older phos-bronze bushes I can't remember ever having this issue, but more clearance is definately needed to ensure no seizure. I reckon your figure of 0.005" max is about right, maybe with 0.002" as a minimum for new bushes.

[morley]

That happened to me, i had the top hat bush replaced and changed the bush to one of the floating bushes which apparently dont cause any issues. Few miles later after running my engine in.. metal on metal squealing, clutch not disenganging and the pedal not returning. It was very frustrating after the engine had just been rebuilt. I ended up removing the seized gear - which took alot of effort! and replaced it with a second hand item and new primary thrust washer to suit! Those things are expensive when new for what they are!

If the latest bushes don't have a good radial clearance the primary gear can seize onto the crank. I've seen that and the guy who built the engine said that it had been machined to give a sensible running fit - obviously not 'running' enough. I must confess that I took if off and opened it up with a flap-wheel in an electric drill until it ran easily and I judged it to be suffiiciently clear then polished it with metal polish. I do well know it's not the recommended way, but it seems to have worked (this time!), the guy wanted his car back on the road the same day and it's still running O.K. well over 17 months later.

[Cooperman]

It's for that reason I won't use the manganese-bronze valve guides either. I've had no problems with them, but I know a couplke of people who have had valves stick after fitting them when the engine has got a bit warm. I guess with M-B you need a bit more running clearance wherever they are used.