More Crankshaft woe?

Inspect the centre holes carefully, probably have light damage throwing things out.  

Put the crank on a pair of vee blocks, running on either the shafts themselves or the roller bearings if still fitted. That way you get a better, more accurate picture of how the crank is aligned.  

Ive just checked a customers 850 bottom end with 17k miles on it. 3 thou total runout at the Primary drive end. Are the crank halves a matched pair?  Do you know if your crank has suffered some trauma in the past? If not, i would be tempted to believe that this is a good example of somewhat questionable manufacture when it was made. To get the crank into better alignment, start by addressing the flange faces to get the shaft ends as close as possible to zero runout. Then regrind the crank to get the big end journals parallel.

I remember reading about the Rawlings Baker 850 Commando that at the time was the fastest 'production' road bike on the drag strip. The crank on that engine had the crank cheek flanges scraped and blued to get it as rigid and true as possible.

I thought that the crank connection had two of the six (?) holes reamed to size for fitted dowel bolts which should be fitted first.  Is that correct?  If so, it would be easy to assembled incorrectly.  And if a bolt is driven in, it's easy to get unseen swarf between the faces.  Perhaps it needs taking apart and reassembling with more care than the PO?

It would originally have been turned on a lathe after assembly, so it's difficult to imagine how it could have any measurable eccentricity between the machined parts.

Naming and shaming! Hmm. I'd like to see you get away with that on this site!

Did you take a runout reading whilst set up between the case halves, and does the crank spin freely once all is bolted up.

Take readings from close to the crankcase halves on the shafts and then gradually outwards this way it may indicate where the run out starts and therefore give you an idea as to "Trauma" or it came out of the machine shop in this condition.

I would be inclined to suspect the latter as AMC machining left a lot to be desired at times.

Can you set the shafts up individually in the lathe chuck to enable a clock gauge to have it run true and then set the gauge up against the faces that fit up to the flywheel to see if your problem lies with these faces not machined square to the shaft.

This way you will know where the run out originates from.

I can't remember if the crankpin halves have a centre in the flywheel faces as this could help with the setting up if things are tight at the chuck end.

It may well be that this crank has been run in the past in this state without any problems.

Do the big end journals show any witness marks to suggest the run out is causing uneven contact?.

If the runout was machined in, the journals would have been ground to suit it by default.

Make of this what you will.

Is the lathe large enough to remove the chuck, replace it with a centre,  and set it up fully assembled between centres?  Of course there's no way of knowing if any crank centres were used as the reference point for final machining of the entire assembly.

Matthew.

               Another consideration of importance is the alternator rotor/stator clearance of .008" all the way round for the air gap. Catastrophic failures have occurred if this is not addressed due to the rotor creating friction with the stator to then grab it tightly enough to seize the engine.

If it was my choice, I'd go for the engineering shop route and find out how competent they are before you entrust the job to them.

As a matter of interest did you check the run out on the first crank that you posted? Maybe this could give you some idea as to what to expect re run out.

A chap on the Access Norton site has found that his crank has a run out of .007" at the rotor end without any apparent issues.

Rgds.

Paul.

Hi Matthew,

 I have just searched the forum, back to when I asked about runout 10 years ago. Looks like I had 3 thou runout possibly due to a belt failure. When I put the rotor on and clocked it the reading went up to 10 thou which had destroyed a new stator, hence my enquiry. I had to cut a thin shim to put between the shaft and rotor to true it up. Rather annoyingly, I’ve just had the same thing happen on a different bike, again another new stator destroyed! Shimmed this one again now and sanded the stator inside diameter for more clearance. If you ever get chance to buy shares in a stator manufacturing company then take it!  You would have thought I’d learnt a lesson but I’ve had a lot of sleeps in the last 10 years!  Best regards, Al.

A tip in Norman Whites, Norton Commando Restoration Manual advocating machining the stator retaining bolts to allow more jiggle room whilst air gapping the rotor stator set up.

By machining the bolts to the core diameter of the threads should give sufficient movement to gain enough air gap between the components.

Cant add anything re. your crank, but for the alternator airgap, Hitchcock motorcycles (the Enfield people) sell a useful item, that is very easy to make yourself. 

Cut some paper just a bit shorter than the circumference of the rotor and laminate it!

The one I bought before seeing how simple it is, is just that- an 8-9 thou thick plastic coated piece of paper 3" wide and sround 9" long. Wrap around rotor, slide on stator and nip it up,  pull out plastic and hey presto, perfect clearance all round. Worked very well for me earlier this year. 

Hope that you get it sorted, 

George 

Just a thought.

Have you checked the runout with the crank assembled onto the flywheel?

... cut from a screenwash bottle which is about .008" thick to centralise the stator. Works for me (and of course is very cheap!)