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MG MGA - Clutch /Flywheel dowels

Hey everyone,

I'm in the midst of putting a B clutch in my A and have been to Barney Gaylord's site for details on the conversion.

One of the issues with the conversion is that if you use a MGA flywheel with the B clutch you have to relocate one of the dowel/pins and add a third.

My question is this- Why not just use one of the dowel/pins and then rely on the six bolts that attach the pressure plate to the flywheel for alignment?

Also, I was planning on having the flywheel balanced with the new pressure plate in place.

Thanks for any input!
John
John Bries

John,

The tolerances used in originally drilling and tapping the bolt holes in flywheel and the holes in the pressure plate cover are too great for correct, and permanent, alignment. These large tolerances were necessary for quick production line assembly at the factory. Only the dowel holes were drilled with the required accuracy.
This can be demonstrated as follows;
With no bolts fitted, only the dowels, try and move the pressure plate cover in all directions. Almost no movement can be observed.
Now with all the bolts fitted but not tightened, and no dowels fitted, try and move the pressure plate cover in all directions. You be surprised at the large amount of movement.
You cannot use the fully tensioned bolts to prevent movement with no dowels. The force applied to the pressure plate under strong use will move the pressure plate relative to the flywheel no matter what is the torque on the bolts.
A bit of load while slowing down against engine compression and the pressure plate will move back etc. etc.......
Eventually the pressure plate cover will come loose and cut through the bolts, and/or ruin the threads in the flywheel.

Mick
Mick Anderson

John,

The previous comments also apply if you use only one dowel. The movement is just not as much.
Try moving the pressure plate cover with one dowel and all the bolts fitted, but not tightened.

Mick
Mick Anderson

Why not just go to e-bay or a local autojumble to get a early "B" flywheel. It is lighter than the MGA and can be lighten a little more for a quicker rev. It will then just bolt in and save on machine costs.
JEFF BECKER

Mick. We said. Les
Les Bengtson

John...there are far more MGB (than MGA) flywheels available. If I pull my engine/trans again...I'll go the route Jeff is suggesting. You'll do well to consider it yourself. The lighter weight will do more than give a quicker rev...it will add a few horsepower and should add a bit more life to the bearings (assuming proper installation and maintenance of course).
Mick...well said...
The front transmission cover has also been referred to as the "scatter-shield". This is what happens when mechanical failures occur (also caused by mickey mouse modifications to high-speed-rotational misalignment) behind the engine's rear plate. Catastrophic failure has caused quite a few unexpected amputations. If anyone thinks I'm trying to scare someone...you better believe it.
It's not wise to hand-drill locating pins...this is precise work best left to a machinist with a vertical mill. It's also worth a little more to have these parts balanced.
Jon Bachelor

A lightened flywheel transforms the engine into a free revving unit. A great improvement.

I have a drawing somewhere for the machining of the dowels, was generously given by another regular on the board (search teh archives)

Would be easier to start with a B flywheel, but you can take weight even off these. Just make sure the machinist knows what he is doing, this is spinning by your feet, you cannot expect the bell housing to contain any failure. Mkae sure that any machining has a smooth radiused edge, and that a suitable thickness is left in all places.
domnic

This is all about balance. Cranks, flywheels and clutch covers are all balanced within reasonable degrees of accepability individually and during manufacture. If you have to replace any one of these you can do so and be assured that the overall balance will still be within factory acceptable limits which are not perfect. Now if you fit an alternative flywheel and or clutch cover it must also be reasonably balanced as an assembly and in order to ensure that you can dismantle and rebuild again at some future point all parts must be marked and dowelled. Dowelling must be in at least two places (three is unnecessary) and spaced diametrically opposite one another. Dowels must be drilled and fitted AFTER balancing the whole assembly as this is what you are trying to maintain. They are for alignment only and do little to transmit torque otherwise they will be sheared off in short order and I have never seen a sheared flywheel dowel.

The lighter flywheel will certainly give a more responsive throttle but will make no difference whatsoever to horsepower. Additionally a fully balanced assembly will do much to reduce engine vibration and so enhance main bearing life.
Iain MacKintosh

I did the drawing and will be glad to forward a copy.
Doug
doug.sjostrom "at" smith-nephew."com"
D Sjostrom

I recently looked into doing this - I have an MGB engine + flywheel for my Magnette and was considering getting the dowels moved to suit the clutch in the car.
The Machinist said that the factory jig would accurately place the holes, but doing it after the event he wanted to balance the flywheel and clutch cover together after re-drilling.
Dan Smithers

Dan,

Remember that there are two separate issues here. Alignment and balance. Absolutely correct placement of the dowels is required to prevent the clutch running off centre.
It would be a good idea to balance the flywheel and clutch as an assembly.
I must ask though, have you considered fitting an MGB diaphragm clutch? You would not have to drill the dowel holes nor do the balancing (from about 1959 BMC engines had the flywheel and clutch balanced as separate units).
Has anybody fitted a MGB clutch with a Magnette gearbox? With the MGA gearbox you need to fit the front gearbox cover and clutch operating lever from an early MGB.
The MGB diaphragm clutch is light years ahead of the old coil spring type.

Mick
Mick Anderson

Mick, I am definitely thinking about the MGB clutch. Probably not this time roud though. My engine rebuild has just cost a whole lot more than I expected, so it will probably wait until I get round to doing the gearbox.

dan
Dan Smithers

Mick,
Re your comment " MGB diaphragm clutch is light years ahead".....what performance improvements should I expect if I fit one?

Thanks,
GTF
G T Foster

This thread was discussed between 18/11/2004 and 23/11/2004

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