weld up or weld in a new bush

Vincent Brake

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Hi out there,
Question: would i weld this hole (mains in primary side) of round 70 mm up or would i weld in a whole new bush?
i am not toying arround with shrunk in bushes, as they are in a to weak seat now.

please your opinions and if a new bush what material would i use? like 6082, AlMgSi1, old name 51ST?

thanx

Vincent




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timetraveller

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Vincent, there is a very nice mod which might save you doing either. I think it originated in Canada but am not sure. The idea is to machine out just enough of the casting to ensure that the hole is round and on the correct centre line. Then a top hat bush is made which has a flange on the outside (the chain side) with holes to take countersunk screws. Inside this outer end is a left hand thread to take an oil seal. Part way down the inside of the top hat bush is an inward boss. The idea is that back to back taper roller bearings are used on the mains haft. It will depend upon what diameter main shaft you are using as to the bearing size. By careful measuring and or shimming one can organise it so that there is about a two thousandths of an inch nip on the bearings when the shock absorber is tightened up. Thus the drive side main shaft and the whole flywheel assembly is solidly supported by these pre-loaded taper bearing. You will have to machine a small amount off the chain side of the main bearing boss to take into account the flange with the securing screw and tap into that flange for whatever thread you want to use. The screws themselves can be secured by punch locking and/or Loctite once the whole assembly is correct. Robert Watson and others have this mod and can tell you more about it. The advantage to someone with your machining skills is that you can make everything just the right size to prevent having to weld the crank case up. If you do think that what is left of the crank case is too weak to accept the above mod then welding in an ali ring and then machining for size and position is something I have seen done which has worked well. Good luck with it.
 

davidd

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Norman's advice sounds good. I would be concerned that so much aluminum is missing that the support may be weak.

I have sleeves on the racing singles because the single motor flexes enough during road racing that the bearings will walk, eventually. The flexing used to loosen the primary cover screws and it would wear out the gasket.

Drive02.JPG


The timing side is sleeved also.

The journal on your engine is so thin I might be inclined to weld in a new ring to get some support back.

David
 

Vincent Brake

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thanx David and Norman

Indeed the remains there tend me to go welding, and annealing again.
i am a bit futher (toying arround where to put the flange of the bush) and the problem merging seems the welding on the chain side, as theres little room for a TIG welder to go all the way round. so am playing arround boring out til 86 (now cast 80 mm) and hold the Boss on the primary side, and weld only where the chain pulls, (thats good reachable with weld gun), and of course the whole inside.

Vincent
 

Robert Watson

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What about boring it out and making it like an "A". Cheers Bill.
That's what timetraveller suggests in post 3. Yes, one of my Rapides (post war) is done like this. It works very well, as there is no fiddling with getting bearings together (excepts on the timing side) and replacements are really cheap! I only changed them out on a rebuild as they were cheap, and have now been in for around 65K miles.
 
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