No amount of sludge in the crank sludge trap is going to effect the vibes caused by two pistons going up and down together......However over the years I have found it can restrict th oil flow to the drive side big end....... That sludge could of been building up since the motor was first built many decades ago and who is to say that the previous owners did not run around with blocked oil filters only flowing oil through the filter bye pass thus shoving crap back to the oil tank and then back into the motor????
However the REAL IMPORTANT REASON for examining the inside of the crank is to ensure the pratts at AMC / whatever they were called when the motor was built have not left a perfect example of a stress raiser within the Drive Side crank half DIRECTLY BENEATH AND IN PERFECT LINE with the big ends outer 90 thou STRESS REDUCING radius which is rather pointless when some pratt leaves a stress RAISER directly beneath it enabling that crank half to easily become two piece taking much of the motor with it as it does so. The drawings showed that the drill used to clean out the inside should be taken right into the web leaving the sharp outer edge also within the web where it would do no harm and many years later Mr Negus had the drawing amended to ensure the instructions were a lot more prominent but as the test maching of new crank halves was so expensive he told me non were to be produced.
When my olde 99 crank cracked but stayed together at this point as it sounded like a totally knackered traction engine I ASSUMED the crank grinder had cocked things up but when our olde Atlas crank failed big time when leading a race at Oulton Park I sent the two bits of drive side crank to a friend for examination to determine why it had failed. With 20 years experiece as a metallurgist in th steel industry and with his own public works metallurgical lab up in Gateshead he quickly phoned asking ' Who was the idiot who introduced that stress raiser into the crank at a point of maximum stress...your crank shows that it had been slowly breaking for a long time before finally going bang'. The Gentleman then explained to me all about stress raisers(G.E.C. were paying for the phone call!!) and described stress raisers as ' something every Engineering student learns about for a few hours but which they then forget in later life resulting in many innocent people losing their lives' quoting as examples the De Havilland Comet airliners that fell out of the sky till someone eventually realised there was a problem!! and the early U.S.A. built Liberty ships that would break in two very easily and probably doing in the middle of the Atlantic during a force 8 /9 gale in a convoy and suddenly disappearing beneath the waves damn nigh instantly taking all the crew with it as it carried to us the steel, guns, aircraft, food, bombs, tractors, thermionic valves, aircraft etc etc we were incapable of producing thanks to previous decades of government and industrial incompetence.(Nothing has changed since either ..I dont refer to the C.B.i. as The Confederation of British Incompetence for nothing!!)).
A friend and I had a certain aircraft company who shall remain nameless check our spare D.S cranks and a couple went straight into the scrap bin.
I phoned one friend to tell him all about the stress raiser I thought I had found and he replied, not for the first time I should add, 'Oh I thought you knew all about it, i have been removing it from my and customers road and race cranks for years, they break if you dont'. I will NOT say what I then said.
Suggested reading for many Commando and Dommy owners is
http://a20b767e.magix.net/#xl_xr_page_1
Read and learn. Belt users might like to paruse the section on belts and all owners suffering from cam failure should read the section on that subject!!......
Of course one day soon when death attacks for the 5th and hopefully final time I will stop learning but till then..... Some of us have had the gods look after us.....exactly why I have no idea unless it is to wind up Norton owners!!!
Remember that Commando serialised rebuild in Classic Bike a while back?? Was there ant mention of checking the crank for the stress raiser or reinstalling into the crankcases the camshaft oil bath Mr Hopwood and others so very carefully designed into the original Dominator crank cases to ensure the cam was correctly lubricated????
