Crankshaft primary side end slightly out of true and bent.

Peter Waller

Peter Waller

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May 16, 2021
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I have fitted a Alton starter motor kit to my 74 850 Commando and it is impossible to get the 10 thou air gap on one point. We put a dial gauge on the end of the crank where the engine sprocket goes and it has a 3 thou runout/wobble. After grinding down the alton stator poles as low as they can go the alternator poles still touch the magnet ring on the alternator at high revs and when hot. I have a 14 thou gap nearly every were and a tight 9 thou gap at the tightest spot. But every time I check the primary oil there is a little shimmer of silver in the oil where i presume the stator pole are touch the magnet ring on the alternator at revs when under load as I can see the score marks.
My question IS can the shaft on the end of the crank that holds this assembly be straightened if I remove the crank assembly as a winter project? It also has a fair amount of end play.
 
Peter,
I have an Alton. I think your rotor to stator clearances might be ok and not causing the silvery oil.
Are you seeing wear/score marks on the Alton rotor after you skim the stator?

On my install I found that the primary chain was intermittently touching the case when the chain bounced down.
There were three telltale grooves carved by the primary chain.
This was the underside of the primary top chain touching the protruding casting that is to the left of the top inspection hole.
Dennis
 
The crank could be cracked at the where it comes out of the cheek, so if you remove the crank that is the first thing to check. You can look for a good used crank as an option and check it for true and for a crack. If it has 3 thou where the triple sprocket goes there would be more run out the father out, you go.
 
Peter Waller said:
I have fitted a Alton starter motor kit to my 74 850 Commando and it is impossible to get the 10 thou air gap on one point. We put a dial gauge on the end of the crank where the engine sprocket goes and it has a 3 thou runout/wobble. After grinding down the alton stator poles as low as they can go the alternator poles still touch the magnet ring on the alternator at high revs and when hot. I have a 14 thou gap nearly every were and a tight 9 thou gap at the tightest spot. But every time I check the primary oil there is a little shimmer of silver in the oil where i presume the stator pole are touch the magnet ring on the alternator at revs when under load as I can see the score marks.
My question IS can the shaft on the end of the crank that holds this assembly be straightened if I remove the crank assembly as a winter project? It also has a fair amount of end play.
Click to expand...
Have you had the crank out and taken apart? Means an engine strip, but that would be my first thing to check. Crank out, check it on a set of vee blocks sitting on the bearing registers, note the readings and then strip the crank, clean and deburr the flange faces and bolt holes on the crank cheeks and flywheel. Then reassemble, torque up the bolts to the correct torque and then recheck it on the same vee blocks. Check for cracks at the same time. You will be surprised at the result.
 
Carl H said:
The crank could be cracked at the where it comes out of the cheek, so if you remove the crank that is the first thing to check. You can look for a good used crank as an option and check it for true and for a crack. If it has 3 thou where the triple sprocket goes there would be more run out the father out, you go.
Click to expand...
Yes, and having the rotor (Alton or standard) at the end of it would be causing some pretty terrible forces that surly over time will break something (crank, main bearing, etc.)
 
Peter Waller said:
I have fitted a Alton starter motor kit to my 74 850 Commando and it is impossible to get the 10 thou air gap on one point. We put a dial gauge on the end of the crank where the engine sprocket goes and it has a 3 thou runout/wobble. After grinding down the alton stator poles as low as they can go the alternator poles still touch the magnet ring on the alternator at high revs and when hot. I have a 14 thou gap nearly every were and a tight 9 thou gap at the tightest spot. But every time I check the primary oil there is a little shimmer of silver in the oil where i presume the stator pole are touch the magnet ring on the alternator at revs when under load as I can see the score marks.
My question IS can the shaft on the end of the crank that holds this assembly be straightened if I remove the crank assembly as a winter project? It also has a fair amount of end play.
Click to expand...
If I were you, I would consider it to be winter right now!

It's possible that the crank is not properly joined in the middle and I would be very concerned about the drive side main bearing and even more concerned about the engine coming apart at speed. The silver might be from the chain/sprocket since 3 thou at the crank is probably 5-6 thou at the sprocket teeth

Not sure there, but in the US, good cranks are not hard to find on eBay.
 
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