I have an M type of uncertain origin which developed low oil pressure. The engine was removed and carefully stripped and in the sump was found in three pieces a bronze washer which appeared to have come from the front of the crank. Having had the crank reground and new big ends cast I am rebuilding the engine. I am new to the M type and would like some advice on the correct assembly order and adjustment of the dynamo drive gear/oil pump gear/Washers??/Oil scroll.
The engine appears to be an early type with only the front main ball race. The bronze washer appears to be a running clearance against the engine mount casting. Is it a thrust washer seems like zero end float.?
There were three washers. Keyed steel washer and one steel and the bronze washer that both float over the keyed washer.
Having made a bronze washer of the same thickness as the broken one and gently reassembly of the parts with the original brass/paper gaskets the whole lot nips up the crank which I guess was the problem in the first place as the broken washer is exploded and blued.
Judging by the hammer marks on nearly ever part of the engine I think to say the least it has been bodged up in the past.
I have been unable to find a drawing of this type of engine.
Can anyone advise the correct assembly/Parts/clearances of this end of the crankshaft.
You should have a worm gear for the oil pump, a bevel gear for the dynamo / cam drive and a "top hat" bronze bush. You need to position the bevel gear with shims so there is a slight click when you turn the dynamo shaft. This can be adjusted with shims under the dynamo but if you use too many it will strain the flexible coupling to the cam gear. Best to aim for about 10 thou under the dynamo. Originally the rim of the top hat bush ran against the front casting to take thrust and the tube section fitted in the casting with a reverse scroll to stop oil leakage. This system is useless. It's best to machine off the scroll and bore the front casting to take a modern lip seal. Regarding the thrust I would speak to Richard Hardy who goes under the name "Yorvik" He was recently selling high quality split inner race bearings to replace the front crank ball bearaing. These are quite expensive but are more than capable of taking the thrust.
Sorry to pile on the work but if your engine has been abused it is important to make certain the dynamo lines up with the vertical cam dive gear. You can do this by attaching a DTI to the dynamo fork and running round the bore in the cylinder head. Before you do this you must make certain that the head is properly located by two dowel studs. Another way is to turn up a pointed mandrel to fit into the cylinder head bore and see if the point coincides with the centre drill mark on the dymamo shaft. If the alignment is out you will have to shimm or rotate the bottom bevel gear housing - may even need for the dowels to be repositioned.
Robin I would suggest as a starting point that you get hold of a copy of the excellent catalogue produced by Sports and Vintage Motors which has an exploded view of the engine. There is also an excellent article by Barry Foster on crankshaft end float which will help you. If you E mail me directly I will scan this and send to you by reply. Another source of information for you is Malcolm Greens book called MG Road Cars Volume 1 the Four Cylinder Cars which has a chapter on engine building by Bob Jones.
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Posted - 23/01/2009 : 14:55:59
