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Crankshaft repair ideas ?!

Proxule

Proxule

Ultra Member
Howdy folks,

I am rebuilding a little some thing I picked up a wile ago. I wont share just yet because I am right in the middle of things. What I can say is this shaft is 95 years old!
It is a single cylinder and the shaft on the driven side is worn down about .015 from the original dimension, the keyway is also wallowed out.

I am deathly scared of using heat. I normally would whip up the old smokey and weld the shit out of her, But this isn't a part I can source, If and or when I do screw it up.
Or Braze it, low fuming braze temps are around 900C
but again - High enough to distort it bend it like banana!

For certain, This is a drop forged steel crank, I am 100% sure of this.

1. Braze weld
2. SMAW - aka old smokey
3. Turn down further for a total of .060-.0100 undersize and make a sleeve and use loctite 620 / 638
4. Turn down further for a total of .060-.0100 undersize and use Devcon Titanium putty ( I used this product a lot and is literally bomb proof stuff ).
5. Turn down further for a total of .060-.0100 undersize and make a sleeve and use high silver content braze ( 50% silver mix rod melts at about 650-700C )
6. Spray weld it - Not an option, The cost is very* prohibitive.

I cant just make a sleeve and leave it unsupported where the keyway is wallowed out. I need to address that at the same time as the undersize.

Any and all opinions appreciated and entertained.
Thanks
 

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I wonder if cutting the keyway deeper and not touching anything else would be a viable option. I personally would braze it up and machine down where necessary.
 
DPittman said:
I wonder if cutting the keyway deeper and not touching anything else would be a viable option. I personally would braze it up and machine down where necessary.
Click to expand...
On second thought I think there would be lots of choices of epoxies that could handle the environment the crank would be in.
 
You don't say anything about what the crank is from, but it appears to be an old engine. If so, what is the purpose of the shaft extension and keyway. I have a Lister (clone) diesel which was designed 80 or 90 years ago. It uses a removable handle on a shaft extension for starting. A pawl in the bore of the handle engages the keyway in the crankshaft. The wear on your crankshaft looks a lot like what I would expect as wear from a starter handle like that. If that is the case, There is relatively low loading on the shaft but the direction of the load is quite variable and (a person cranking the engine) exerted through a sliding fit. The handle is removed when the engine starts. There is a spring that allows the drive pawl to be overrun by the crank (hence the damage in the small area of the key).

Therefore a solution that would be fine for a properly fitted hub or pulley, may not be suitable for a hand operated handle.
So, is this the starting method for the crank you are trying to repair?

Chris
 
Could you use a heat sink at the journal side of the keyway and then slowly build up the damaged area with weld? By slowly I mean two or three seconds of weld and let it cool for a while then go again until it's built up enough to machine.
 
cjmac said:
You don't say anything about what the crank is from, but it appears to be an old engine. If so, what is the purpose of the shaft extension and keyway. I have a Lister (clone) diesel which was designed 80 or 90 years ago. It uses a removable handle on a shaft extension for starting. A pawl in the bore of the handle engages the keyway in the crankshaft. The wear on your crankshaft looks a lot like what I would expect as wear from a starter handle like that. If that is the case, There is relatively low loading on the shaft but the direction of the load is quite variable and (a person cranking the engine) exerted through a sliding fit. The handle is removed when the engine starts. There is a spring that allows the drive pawl to be overrun by the crank (hence the damage in the small area of the key).

Therefore a solution that would be fine for a properly fitted hub or pulley, may not be suitable for a hand operated handle.
So, is this the starting method for the crank you are trying to repair?

Chris
Click to expand...
Thanks for the reply.
Yes its an old engine, Not a lister. I am familiar with your engine and how it starts. This engine is spin by hand and not handle is used. This end is the drive end, It will have a flywheel and a smaller pulley that gets a flat belt to drive machinery.
This area that is worn away is the area that gets the small pulley.

The set screw must of worked loose and allowed to flop around for 2 decades.
 
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YotaBota said:
Could you use a heat sink at the journal side of the keyway and then slowly build up the damaged area with weld? By slowly I mean two or three seconds of weld and let it cool for a while then go again until it's built up enough to machie
Click to expand...

This in indeed an option, But I can imagine how long it would take to do 2 or 3 seconds of weld worth, over the entire area needing to be built up.
Suppose it is an option. Thanks
 
I would hesitate to heat the piece. Do you need to re install the original pulley? Is it in equally rough shape? Once this is fixed will it be used with a load (belt) on that pulley? I would think about using a sleeve. Could you incorporate a split tapered bushing into a repair of the pulley? That would clamp the sleeve. Also you could consider relocating the keyway into undamaged metal, maybe 180 degrees away.

Chris
 
cjmac said:
I would hesitate to heat the piece. Do you need to re install the original pulley? Is it in equally rough shape? Once this is fixed will it be used with a load (belt) on that pulley? I would think about using a sleeve. Could you incorporate a split tapered bushing into a repair of the pulley? That would clamp the sleeve. Also you could consider relocating the keyway into undamaged metal, maybe 180 degrees away.

Chris
Click to expand...
No I do not need to reinstall the original pulley but I will keep it original and put it back on, Either for show or for actual work.
It is in equally bad shape, or worse. It is cracked in several spots and the bore is is questionable, Have yet to confirm concentricity. It is in the electrolysis tank right now.
Not relocating the key-way, but a good idea!
Split bushing would be slick but there is no room for this idea, Sadly.

I have thought of turning the crank down past the key-way and making a press fit sleeve. And machining a whole new key-way. But that its pretty extreme move. ( I would need to remove a lot of material to get below the key-way ).

Thanks
 
If you cut the shaft back to the end of the key way then taper it down to a point you can submerge the crank in water and weld an oversized piece of shaft to the crank then turn it true and recut the keyway.
 
I wonder why there is so much stick out of the keyed portion. I presume there is a bearing surface inboard of the key way. Perhaps you can just cut off the damaged portion and use the good part. The pulley will sit closer to the bearing and thus have less leverage on the shaft (a good thing)

Alternatively, turn down the damaged section to get it nice and round. You mention the pulley hub is damaged. One could make a new (extended) hub. It would have a bore sized for the keyed section, then a step down for the new turned section of the crank shaft. The pulley would maintain it present spaced out location. No heat required in the repair.

Something like this (pulley with extended hub is red; stepped bore is black):
F40AA3C4-414F-4079-ABB0-FA2AF479DB71.jpeg
 
Thomas said:
If you cut the shaft back to the end of the key way then taper it down to a point you can submerge the crank in water and weld an oversized piece of shaft to the crank then turn it true and recut the keyway.
Click to expand...
Thats so wild lol. Great idea. What a adventure it would be !
Thanks !
 
Oh, you will need to make a key way to a shoulder (like a blind hole). You do that by drilling a hole at 90* to the bore at the base of the key way so the chips will break at the shoulder. The hole will not affect the strength of the hub.
 
RobinHood said:
I wonder why there is so much stick out of the keyed portion. I presume there is a bearing surface inboard of the key way. Perhaps you can just cut off the damaged portion and use the good part. The pulley will sit closer to the bearing and thus have less leverage on the shaft (a good thing)

Alternatively, turn down the damaged section to get it nice and round. You mention the pulley hub is damaged. One could make a new (extended) hub. It would have a bore sized for the keyed section, then a step down for the new turned section of the crank shaft. The pulley would maintain it present spaced out location. No heat required in the repair.

Something like this (pulley with extended hub is red; stepped bore is black):
View attachment 29184
Click to expand...
Great ideas. All valid. But I have no free play in the lenth at all.

A picture is worth a thousand words I hope.

Thanks for the opinions.
 

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