Crankshaft butchers.

[sleepy]

Just thought I'd share the latest bit of butchery I have come across.
Had an RM125B crank turn up for a rebiuld and the first thing that looked funny was the rub marks on the sides. Measuring it I found it to be almost 1mm wider than others I had seen. After it pressed apart I found a stepped pin and a later rod fitted with a larger big end bore. Thats ok but the thrust washers were to big for the recess and that's why it was to wide. The next strange thing was the appearance of the wear on the pin, looked almost like it had milled flats machined into one side which I hadn't seen before. The pin had been properly made by the look of the grinding finish on the un-worn sections but after a quick file test I found it hadn't been hardened.
Makes me groan to see stuff like this and am amazed at how shops could charge for such work.

[Nathan S]

That's kind of perversely impressive.

I'd hazard a guess that a bike shop (or "helpful" uncle) farmed the machine work out to someone who didn't know what they were building.

[Tim754]

Bloody sad really Still I think there seems to be a lot of hospital surgeons that caught the same plane......

[sleepy]

Thought I'd upload a photo(if it works) of the pin. Also pretty sure I know who made it or at least who sold and had it fitted, won't post the name publicly. 

[shelpi]

Iv'e seen it but I don't believe it ahh yes I do, recently bought a YZ80C fuba come's to mind to give you an idea of dodgie back yard work done to it both front and rear brake actuator arms are welded on
still I got what i paid for! well almost, maybe

[sleepy]

Iv'e seen it but I don't believe it ahh yes I do, recently bought a YZ80C fuba come's to mind to give you an idea of dodgie back yard work done to it both front and rear brake actuator arms are welded on
still I got what i paid for! well almost, maybe

I'd forgive a back yarder for this type of work but it didn't come from one.

[Lozza]

Thought I'd upload a photo(if it works) of the pin. Also pretty sure I know who made it or at least who sold and had it fitted, won't post the name publicly. 

That can't have been heat treated correctly/if at all  The bearing has just been rocking back and forth. Had the big end disintergrated?

[sleepy]

That can't have been heat treated correctly/if at all  The bearing has just been rocking back and forth. Had the big end disintergrated?

The rod and bearing look quite ok. Definetly not heat treated or completly wrong steel used. The quality of finish on the pin is quite good but that didn't help the poor guy that paid good money for a crank build. 

[Mick D]

Who ever produced this has thought of it only as a crankshaft pin, Instead of a crankshaft pin and Bearing journal
Hardened bearing journals don't disintegrate in the way that this surface has.


Although Bearing Manufacturers use slightly different nominations of high carbon high chrome steels.   
52100 bearing steel is a good choice for such one offs.
It will still produce a very good high performance result.
A couple of reasons why:
52100 will machine well in the hands of any competent turner.
No need for induction hardening(as performed by manufactures prior to grinding).
It can simply and safely be case hardened at home.
Then sent to a Cylindrical grinding machine to finish the bearing journal surface.

[Mick D]

Steel is no longer malleable after hardening.
These raised up ridges are a characteristic indication of still malleable

[sleepy]

Who ever produced this has thought of it only as a crankshaft pin, Instead of a crankshaft pin and Bearing journal
Hardened bearing journals don't disintegrate in the way that this surface has.


Although Bearing Manufacturers use slightly different nominations of high carbon high chrome steels.   
52100 bearing steel is a good choice for such one offs.
It will still produce a very good high performance result.
A couple of reasons why:
52100 will machine well in the hands of any competent turner.
No need for induction hardening(as performed by manufactures prior to grinding).
It can simply and safely be case hardened at home.
Then sent to a Cylindrical grinding machine to finish the bearing journal surface.

I have a piece of EN36A sitting here waiting to be turned into oversize pins. The plan is to machine up a batch of 24 and 25mm pins that are .5mm oversize, get them case hardened and then grind to suit honed out rods for hard to get stuff. It's a good way to bring back cranks that are worn but only if they haven't had an overheat. Just got to get the time to do it and decide what to make them for.

[Mick D]

I have a piece of EN36A sitting here waiting to be turned into oversize pins. The plan is to machine up a batch of 24 and 25mm pins that are .5mm oversize, get them case hardened and then grind to suit honed out rods for hard to get stuff. It's a good way to bring back cranks that are worn but only if they haven't had an overheat. Just got to get the time to do it and decide what to make them for.

That's a great time saving alternative for blokes like me in those difficult to get rod situations Sleepy.
I am not quite set up to do it.
So the next one that is difficult to find, but existing is savable, you will be hearing from me

[djr]

rather than making a pin from scratch, if this engine has been fitted with a later rod, which has a larger big end, could you use the matching pin for that rod and machine out the crankshaft halves to suit that ?   
 {assuming there is enough space/clearance  to do this}
or make a stepped pin out of the later type pin ?   
at least it would be the correct material and the bearing area wouldn't need machining
just a thought { I am usually wrong on this sort of subject}

[sleepy]

rather than making a pin from scratch, if this engine has been fitted with a later rod, which has a larger big end, could you use the matching pin for that rod and machine out the crankshaft halves to suit that ?   
 {assuming there is enough space/clearance  to do this}
or make a stepped pin out of the later type pin ?   
at least it would be the correct material and the bearing area wouldn't need machining
just a thought { I am usually wrong on this sort of subject}

Machining the crank wheels is the way I normaly do it if the original is no longer available and there are others available that match the lenght but with bigger pins. The owner of the crank in this case managed to find a NOS rod which has been fitted.
The stepped pin option is OK if made properly but each time a new rod kit is needed a new stepped pin is needed as well but with machined out wheels the new kit goes straight in.

[Lozza]

Only the bearing journal need be hardened made heaps of stepped pins that way. There should always be a small radius from the journal to the step down EDM wire cutting the crank webs works very well too. Mick the pin must be hardened and EN36 A/B is the only material to make it from. Has to be hardened then ground to final size.