750 SF2 Engines - Mods & Fixes?

sfcpiet said:
Seeing the condition of some flanges and the mating surfaces of the sprocket, it really is no wonder the joint sometimes gives up.  Not only do the camshafts need to be a rather tight fit in the flanges, the flanges and the sprocket surfaces have to be dead flat to be able to stay assembled in use.  Any high points on either surface that cause the mating surfaces not to contact over the entire surface will compromise the strength of the joint.  Once movement sets in, everything else starts moving around, not long to go until the final death rattle chimes in.

Heating the flanges before re-fitting helps to preserve the interference fit.  Care should also be taken to ensure the camshaft ends are properly de-burred and smoothed so that they actually pass through the flange without taking metal with them.  Pressing the flanges on cold will most likely remove a sliver from the flange bore.

Using star or spring washers under the small nuts at the connecting studs cannot be recommended.  Schnoor-type washers are a far better option.  Using Loctite would also be an option, if it wasn't for the pita it causes involving future dis-assembly.

The entire camshaft assembly relies on the interference fit of the shaft/flange, as well as reliable cohesion between flanges and sprocket.  Neither the key nor the studs are able to transmit the forces present.  The key is only for location, the studs afford the tension required for the flange/sprocket cohesion.

piet
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Piet, would you recommend to change the screws of the Flange/sprocket assembly every time they are removed? or can they be reused? in case they have to be changed... do they need to be special elastic screws, or normal ones would do the job?

I admit I had to google "schnoor-typ washer", good idea to change them! I had star washer installed as original.

Regards and thank you!
Miguel
 
Never had to change the studs, Miguel - but when I rephased my cams for a 270 crank I used hi-tensile cap screws and schnoor washers and new std M6 nuts (the factory ones have a 9mm head rather than the usual 10mm) ... I cut a 5mm allen key down to fit in the hold while tightening the nut - no need for nylocs. But the std studs and a 9mm nut on each end is fine. Just saying, there are alternatives.
 
Thankfully, cheap indian-made drop-forget 9mm open end spanners usually slip over the hex nut before the stud thread is stretched.  Backyard bodgers rarely use anything else.  Despite that, I have had to replace quite a few studs because of damaged threads.  I find plenty cracked star washers and mangled nuts, these are replaced as a matter of course.

Re-using studs and/or nuts is up to everybody to decide for themselves.  Tight threads are a pita to work with in the confined space of the chain tunnel.

piet
 
The cam flanges came lose on my 750GT that had never been apart and had only a few thousand miles from new. I was told by a Laverda dealer when fixing this problem that when the bikes were built that the flanges were available in three different ID sizes to get the proper very tight press fit.
 
1200ts said:
The cam flanges came lose on my 750GT that had never been apart and had only a few thousand miles from new. I was told by a Laverda dealer when fixing this problem that when the bikes were built that the flanges were available in three different ID sizes to get the proper very tight press fit.
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I think your dealer my have been a fake news trendsetter.
 
sfcpiet said:
Thankfully, cheap indian-made drop-forget 9mm open end spanners usually slip over the hex nut before the stud thread is stretched.  Backyard bodgers rarely use anything else.  Despite that, I have had to replace quite a few studs because of damaged threads.  I find plenty cracked star washers and mangled nuts, these are replaced as a matter of course.

Re-using studs and/or nuts is up to everybody to decide for themselves.  Tight threads are a pita to work with in the confined space of the chain tunnel.

piet
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I think I make the mistake of forgetting the DPO factor, Piet. Even something as basic as tightening a couple of 9mm nuts goes awry for them!
 
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