Crankshaft repair

[Maker]

Dad's just got this old "Pank" pump, should look quite nice cleaned up but internally it's in quite a bad way, one of the conrods is missing, the other is very worn and the crankshaft has a little bit of pitting.

I think the conrods are just short enough to fit in the swing of my lathe, if not I'll need a boring head for the mill but I'd offered to make them before I saw the state of the crank. Chances are I'll just leave it as is, he's never gonna run it long enough to wear out a new conrod but it got me wondering if it could be repaired, how would you hold a part like that though? Obviously in a four jaw chuck and indicate on the journal but what do you do at the tailstock?

Once I've got it held I can turn it back to good metal and either make new conrods to fit that or weld a sleeve on and turn it back to it's original size.

Surprisingly, the crank end of the remaining conrod doesn't look too bad, the piston end on the other hand...

I assume the wrist pin is similarly pitted and I'll be making a new pair of those too.

 

[eLuSiVeMiTe]

Good question.

Tack a bit of flat bar on the unsupported end and center drill the 3 centers?

 

[Barking Mat]

Cor blimey governor!

 

[Maker]

Good question.

Tack a bit of flat bar on the unsupported end and center drill the 3 centers?

I considered that but aligning it is the issue, unless you can somehow set it up unsupported at the tailstock, maybe with a fixed steady on the journal to be machined and then drill the center bang on where it needs to be, you'd never get your drilled bar lined up. I suppose it's not that critical, you could be about a 1/4" off where it should be and it would still work just fine. I might go with this actually.

The other idea I had would be to mount a four jaw chuck on a bearing on a morse taper to fit the tailstock, then dial it in just like you would at the headstock end. A bit like the boring head idea you deleted. Biggest problem here is I don't have another four jaw.

 

[eLuSiVeMiTe]

I considered that but aligning it is the issue, unless you can somehow set it up unsupported at the tailstock, maybe with a fixed steady on the journal to be machined and then drill the center bang on where it needs to be, you'd never get your drilled bar lined up. I suppose it's not that critical, you could be about a 1/4" off where it should be and it would still work just fine. I might go with this actually.

The other idea I had would be to mount a four jaw chuck on a bearing on a morse taper to fit the tailstock, then dial it in just like you would at the headstock end. A bit like the boring head idea you deleted. Biggest problem here is I don't have another four jaw.

Lol you saw that. Would need the other 4 jaw to rotate and could be driven by the spindle via the crank.

Center spots is probably the easier option with a fixed steady to get it dialed in.

 

[Morrisman]

Considering it was still running like it is, would it be possible to simply smooth out the journal with a flat file, emery strip etc? Or is it too lumpy and bumpy for that?

 

[Agroshield]

Biggest problem here is I don't have another four jaw.

If you ignore all the people in the thread saying don't do it, there are some good ideas here:

https://www.practicalmachinist.com/...stock-end-crankshaft-turn-rod-journal-183194/

You do not need two four jaws. A Keats angle plate on a faceplate at the chuck end would free up the four jaw for use at the tailstock end.

See: http://s3.cnccookbook.com/CCLatheEccentricTurning.htm

 

[Agroshield]

One of these (revolving tailstock chuck adapter with Myford thread - also available with Boxford thread):

https://www.ebay.co.uk/i/370603921920

could be a good start. Major thing to think about is when used in T/S, the chuck will try to unscrew. Could be overcome by running in reverse with upside down tool.

Look on YT for 'crankshaft grinding' as some typical setups there. E.g.

 

[the snooper]

If your making new conrods you may aswell find someone that can take the big ends back to a decent surface and make the conrods to suit

 

[Maker]

If your making new conrods you may aswell find someone that can take the big ends back to a decent surface and make the conrods to suit

It's a rusty old pump he paid about thirty quid for, someone kitted up to do it properly would charge ten times what the thing is worth. For the use it's going to see when it's repaired, leaving the shaft as it is would honestly be fine, I'm really just doing it because I can (Or rather, considering doing it because I like to think I can ).

 

[eLuSiVeMiTe]

It's a rusty old pump he paid about thirty quid for, someone kitted up to do it properly would charge ten times what the thing is worth. For the use it's going to see when it's repaired, leaving the shaft as it is would honestly be fine, I'm really just doing it because I can (Or rather, considering doing it because I like to think I can ).

I spent ages making a fixed steady to repair a motor shaft. Probably wasn't economic but I enjoyed it and have a steady to use for other projects

 

[Maker]

I spent ages making a fixed steady to repair a motor shaft. Probably wasn't economic but I enjoyed it and have a steady to use for other projects

It won't be much use if the lathe ever sells.

 

[eLuSiVeMiTe]

It won't be much use if the lathe ever sells.

Aye. Easy come easy go.

Made my office a much nicer place to be though and given everyone a lot more space

Can't find any pics of how it used to look but that whole wall was covered by a big black kalex unit and stacked filing cabinets. Made the room feel dingy and tiny

Easy to find another lathe when the time comes

 

[pressbrake1]

For cranks I use a block bored out to crank diameter then bolt it to a face plate and clock in
Split block on tailstock end
Minor faffage but works well

 

[Maker]

I'm more into listening to music than making it (I did have six months of guitar lessons when I was 10 ) but the gear looks very cool. I can't see me swapping my workshop for anything but a bigger workshop though. The painting above the monitor caught my eye.

For cranks I use a block bored out to crank diameter then bolt it to a face plate and clock in
Split block on tailstock end
Minor faffage but works well

I was hoping you'd have some input. Can you elaborate on the tailstock end? Are you clocking the part in then drilling your spilt block for a live center?

 

[pressbrake1]

I'm more into listening to music than making it (I did have six months of guitar lessons when I was 10 ) but the gear looks very cool. I can't see me swapping my workshop for anything but a bigger workshop though. The painting above the monitor caught my eye.


I was hoping you'd have some input. Can you elaborate on the tailstock end? Are you clocking the part in then drilling your spilt block for a live center?

Correct, sounds hoochy but works well especially if you can cobble up a toolpost grinder

 

[Seadog]

Major thing to think about is when used in T/S, the chuck will try to unscrew.

Why would that be? It's a right hand thread.

 

[Maker]

I'll give that a try then. Hopefully it's not been hardened, I've got a nice motor stashed away for a toolpost grinder but I'll be going back to uni in a couple of weeks so I doubt I'll have time for such a project.

It's only just occurred to me the tool will have to be some long skinny boring bar type thing to fit down between the webs, now I really hope it's not hardened.

 

[eLuSiVeMiTe]

I'll give that a try then. Hopefully it's not been hardened, I've got a nice motor stashed away for a toolpost grinder but I'll be going back to uni in a couple of weeks so I doubt I'll have time for such a project.

It's only just occurred to me the tool will have to be some long skinny boring bar type thing to fit down between the webs, now I really hope it's not hardened.

Old style tool holder maybe.

 

[Maker]

I've got a couple of those actually but no 1/4" HSS to fit them. I've got some big blanks I reckon will do it, must be 5/8 or 3/4". A parting blade might do the trick too