crankshaft radius

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John leathers

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Oct 24, 2014
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Just got the crankshaft back from engine shop and found that they had ground 10 thou of crank and also of the radius.now the journals are ground at right angles. Any help would be great. Bike is 1971 commando 750, I should have copied the workshop manual when sent to engine shop cheers john
 
John leathers said:
Just got the crankshaft back from engine shop and found that they had ground 10 thou of crank and also of the radius.now the journals are ground at right angles. Any help would be great. Bike is 1971 commando 750, I should have copied the workshop manual when sent to engine shop cheers john
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Hi, Welcome. Sounds like you know what to do... Send it back to them, have them re-establish the radius. Or, if they went too wide, then, well, um, crap, we can't ever "grind a little ON"
 
The right angles will work as a stress raiser, and seriously increasse the risk of crankshaft breakage.
I know my words do not offer much comfort, but you should never have this job done by a shop that is not familiar with Nortons.
I have no idea know how to solve this, other grinding the crankshaft again if this is possible , and if not, than you should explain to this shop that they messed up your crankshaft, and demand financial compensation.
 
Unfortunately, there's no way to regrind the crankshaft to get the .090" radius back without making the side clearance huge, or grinding the journal WAY too small. You need a replacement crankshaft.

Ken
 
Peter R said:
...you should explain to this shop that they messed up your crankshaft, and demand financial compensation.
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lcrken said:
Unfortunately, there's no way to regrind the crankshaft to get the .090" radius back without making the side clearance huge, or grinding the journal WAY too small. You need a replacement crankshaft.
Ken
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It's possible that the journals could be flame-sprayed and then ground to size, but the cost may be prohibitive (for your machine shop). There's a number of businesses out there just for this operation. http://www.mbicoatings.com/content.cfm/ ... age_id/171 is just one example. You might try getting a quote from them and forwarding that onto your machine shop. My condolences...

Nathan
 
Ken Canaga found Peel's nitrided crank too bent-distorted and too undersize ends to use so considered it trash till I found this place that recovered fast and cheap and correct. Ping em to see what they might be able to do on fill in to radius.
http://www.marinecrankshaftinc.com/
 
What about an undercut fillet radius as used on modern cranks. These are rolled using pressure to increase strength. Even grinding this into a Norton crank would be better than no radius. It might just be worth a try. If not, it's the scrap bin!
 
Hard chrome and regrind. A good hydraulic marine machine shop should be able to do it. Call out the radius.
 
mike provence said:
Hard chrome and regrind. A good hydraulic marine machine shop should be able to do it. Call out the radius.
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The stress raising sharp corner is in the base metal of the crank it's self and so building up with chrome or other types of coating will not improve the strength of the component just hide the problem from the eye.
The amount of metal that will need to be removed to reform the radius will also affect the strength of the component so best action is to replace it and see if the machine shop will come to some agreement with you about the cost..
 
The stress raising sharp corner is in the base metal of the crank it's self and so building up with chrome or other types of coating will not improve the strength of the component just hide the problem from the eye.
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This is not strictly correct - correctly applied hard chrome, or flame applied metal powder, becomes PART OF THE METAL, and should correct the problem.

I've seen craftsmen flame welding cranks on the footpath in India.
And having previously travelled in a Bedford bus that was in its 5th reincarnation at least,
can vouch that such crankshaft refurbs can work well..
 
Rohan said:
The stress raising sharp corner is in the base metal of the crank it's self and so building up with chrome or other types of coating will not improve the strength of the component just hide the problem from the eye.
Click to expand...

This is not strictly correct - correctly applied hard chrome, or flame applied metal powder, becomes PART OF THE METAL, and should correct the problem.

I've seen craftsmen flame welding cranks on the footpath in India.
And having previously travelled in a Bedford bus that was in its 5th reincarnation at least,
can vouch that such crankshaft refurbs can work well..
Click to expand...


I have seen chrome repairs done by skilled men fail and does a bus crank have the inherent weak point that calls for the rad in the first place. Also does it spin at the same speeds as a Norton crank. I am full of admiration of the skill and ingenuity of people in poor countries who can keep things going with no tools or spares but they only need to make their bus move an that's all they care about.

I would not put the crank in my engine as i would always be worrying about the crank and trying not to stress it. If it fails then it will need replacing and so will many other things that will be damaged when it lets go. So its safer and cheaper to replace it now but it is obviously not a pleasant experience or cost you wished to spend.
 
Find a shop that can do it for aircraft engines, and they will know what that are doing.
It won't need all the paperwork either, so the cost won't be excessive.

These process are commonly used in agricultural equipment, sometimes even as oem,
big horsepower, so it works...

The norton crankpins are good quality steel, so will take a good weld job.
Avoiding distortion is where some experience will come into it.

And if the crank is scrap otherwise, nothing to lose seeing if it works out OK.....
 
Welding could fix it if it was done correctly. Of course the only way to know if it was successful is to see if it breaks.

Hard chrome would likely make the problem worse due to hydrogen enbrittlement. It would add no strength to the fillet.

Norton cranks are not so hard to come by. I would get another one and start over with someone who knows what they are doing. Jim
 
The hardchroming doesn't need to 'add strength", it simply needs to add material to the
parent metal so the stress reducing radius can be ground back into the crank. (?).
Heat treating to remove H2 embrittlement is routine part of hardchroming cranks.
Not that hardchroming introduces much of this anyway.
This is not exactly new or untested technology...
Likewise, flame welding to reclaim cranks etc is an extremely common procedure, many industries do it.
Some as oem manufacture.

I'm sure an aircraft welder could be found that is more than familiar and capable of doing this.
That fleet of footpath craftsmen maintaining an ancient fleet of buses could probably teach us a thing or 2 too.
A refurbed crank on its 10th ? incarnation hauling a few tons of passengers has been truly well tried and tested...

Whether this is cheaper than simply finding another (good) crank is another matter....
 
Reclaim the current crank and grow an ulcer every time you ride your bike, or
Find a good one and ride with confidence that it won't crackup/lockup midway though a high speed corner beside a sheer dropoff.
Tough choice - your choice, I say.
 
Crankshaft shops and aircraft welders do this sort of stuff all the time.
Its exceedingly likely you've flown on a plane with something vital welded.
Do pilots look worried. ?

Only if they are feeling suicidal lately, it seems.

Didn't we see hobots welded crank recently, with provision for screwed in weight plugs.
Whats the difference, when it comes down to it....
 
Indian footpath welders are kept employed by:
A. Fixing pristine crankshafts that just broke?, or
B. Bodging up bodged-up crankshafts that keep breaking at the previous bodgy welds?

Original poster: Longevity of your crankshaft is directly proportional to your longevity, choose wisely.
"They said it would be ok" is not a great tombstone inscription.
 
Silly words ?

Indian footpath welders were refurbing cranks that had done millions of miles.
They flame welded them up, and then the extensive machine shop inside ground them back to std.

The old Bedford I had travelled in was 1953, , across a desert, I was told that it had been travelling that route ever since.
 
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