Custom build of a crankshaft trueing stand

[malmac]

DAY ONE
We have a couple of 1960 vintage BMW motorcycles. I want a crankshaft trueing stand so that eventually I can press the old cranks apart and rebuild them. In the short term this stand when completed will permit me to check cranksahfts sources from elsewhere and confirm their alignment.

Day one was get the base machined off. I was quite happy with the result.

Mal

 

[tq60]

We did not use a press to straighten cranks.

In books there would be photos of that but not how we did it in the engine shop.

Hammer and chisel.

Turn in centers to locate high spot and the trick is to determine where the "bend " is, journal or main...

You place it low spot DOWN then place chisel in top corner and tap with hammer and roll chisel around the top of the arc.

Rakes a bit of practice and convincing brain that hammering down on something causes it to rise is difficult for brain to understand.

You are relieving stresses in crank and it moves.

Less chance of breaking things...

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

[DavidR8]

I presume this is the process you're doing @malmac

Overhaul of a 2-cylinder crankshaft - Salis Parts

The photos are a compilation of the work done on different crankshafts: R67/2, R60/2 and R69S.

www.bmwclassicmotorcycles.com

 

[mattthemuppet2]

wow, that is not a trivial undertaking!

 

[DavidR8]

wow, that is not a trivial undertaking!

I recall reading an article about rebuilding Carillo crankshafts with roller bearing rods. It basically said there's no way you're getting it apart without a whole lot of cursing.

 

[malmac]

I presume this is the process you're doing @malmac

Overhaul of a 2-cylinder crankshaft - Salis Parts

The photos are a compilation of the work done on different crankshafts: R67/2, R60/2 and R69S.

www.bmwclassicmotorcycles.com

David we have an R69s so that link is exactly what I plan to do, eventually. We have a 30 ton hydraulic press and as I gradually manufacture the jigs and press tools required I guess it will all come to pass. Timeline is open ended.

Thanks for posting the link I had not seen that before.

Mal

 

[malmac]

We did not use a press to straighten cranks.

In books there would be photos of that but not how we did it in the engine shop.

Hammer and chisel.

Turn in centers to locate high spot and the trick is to determine where the "bend " is, journal or main...

You place it low spot DOWN then place chisel in top corner and tap with hammer and roll chisel around the top of the arc.

Rakes a bit of practice and convincing brain that hammering down on something causes it to rise is difficult for brain to understand.

You are relieving stresses in crank and it moves.

Less chance of breaking things...

Sent from my SAMSUNG-SM-G930A using Tapatalk

The R60/R69s cranks are actually pieced together cranks with roller bearing big ends.

However I have no doubt working with fine tolerances and runtouts is generally a character building experience.

I hope I can muscle up to the challenge.

Mal

 

[malmac]

Some advice on setting up the next machining task would be appreciated.

I am going to cut 60 degree dovetails on the feet of my stand legs.
This will allow me a certain amount of adjustability.,
My problem is that the two feet need to be as close as dam it to being exactly the same width.
If they are not the same width then they will either be sloppy in the dovetail slides or one will be tight and the other sloppy.

I thought I might spot them together using my TIG with 4 small tacks.
That way I can do one end and then reposition them in the 3 way vice to machine the other ends without them getting out of position.
Then machine them up as one piece before taking the tacks off with a small bevel.

But maybe there are much better options that you know of that would achieve the goals in a better way.

Thanks in advance.


Mal

 

[Liljoebrshooter]

Scrape them to fit. Just like a dovetail on a machine.

Joe

 

[francist]

Or slot them part way in from the ends so you could tap in or thread in small wedges to fine tune the fit?

-frank