Restoration of BMW R69s engine

[malmac]

What a pain! I thought this was a new crank set. And if so that it should be ready to go. Well at least you have the equipment to deal with it. And the machine tools to make what you need. I never had a lathe or mill to make what I needed I just had to bodge something together and try to get a precision result. Thinking back the only shop I worked in that had a real press was in college.

Yes this is a reproduction crankshaft. Nicely machined but not nicely assembled. I am confident if this had been a genuine BMW part, it would have been ready to fit. But the days of those cranks being available are just a fond memory.

Let me tell you, I could have bought an R69s out of the US sent it to Barringtons for a full rebuild, paid freight and import duty and I would of had money to spend left over Vs setting up the workshop.
But then again some things are not about money. I don't want a pristine bike that is an advertisement for someone else's restoration finesse. I want a bike that I know inside and out. The bike may not be perfect but at least I will have a pretty good idea of why it is less than perfect.

I hope that makes sense.

Mal

 

[Tozguy]

It does to me.

 

[C-Bag]

Yes this is a reproduction crankshaft. Nicely machined but not nicely assembled. I am confident if this had been a genuine BMW part, it would have been ready to fit. But the days of those cranks being available are just a fond memory.

Let me tell you, I could have bought an R69s out of the US sent it to Barringtons for a full rebuild, paid freight and import duty and I would of had money to spend left over Vs setting up the workshop.
But then again some things are not about money. I don't want a pristine bike that is an advertisement for someone else's restoration finesse. I want a bike that I know inside and out. The bike may not be perfect but at least I will have a pretty good idea of why it is less than perfect.

I hope that makes sense.

Mal

I feel like I do too. None of my VW’s were showy. The paint often worn, but mechanically they were as good as I could make them. In so many ways my machines around the shop are the same. I fix them to suit me. Don’t worry about the paint, it’s whether it will do what I want. I can’t imagine how much you paid for that crank by your description. I hope you let whoever you bought it from it was NOT up to snuff.

 

[malmac]

I feel like I do too. None of my VW’s were showy. The paint often worn, but mechanically they were as good as I could make them. In so many ways my machines around the shop are the same. I fix them to suit me. Don’t worry about the paint, it’s whether it will do what I want. I can’t imagine how much you paid for that crank by your description. I hope you let whoever you bought it from it was NOT up to snuff.

Hi Tony

I would like to get the crankshaft to with in spec before I consider feedback to the supplier.
It is getting ever closer but it will be the last 10% that takes 90% of the patience - or maybe I am just a natural born pessimist.

Cheers


Mal

 

[malmac]

This is how I have named the locations on the crankshaft which are used in the measurements.
Just for those who are really really really curious..... which I hope for your sanity is none of you fine folk.

 

[petertha]

...what I have done is I have just purchased the mandrel and grinding stones and grinding oil. The current project to make up a tool which is basically a custom universal joint with a threaded adjuster to expand the mandrel to the exact dimension.

Just landed on your post, very cool. I was looking at honing tools similar to what you are showing. The price was a show stopper so I had to resort to other methods in my application. But now you have me curious, how did you incrementally set the taper wedge or whatever the mechanism is that expands the stone(s) ever so slightly as you progressively enlarge the bore? I've never seen a Sunnen type machine in real life but on some videos looks like the operator turns an adjustment wheel as its stroking which I assume is pulling or pushing on the wedge?

About how much material did you have to remove from the bore? What grit of stone & how long did it take?

 

[malmac]

...what I have done is I have just purchased the mandrel and grinding stones and grinding oil. The current project to make up a tool which is basically a custom universal joint with a threaded adjuster to expand the mandrel to the exact dimension.

Just landed on your post, very cool. I was looking at honing tools similar to what you are showing. The price was a show stopper so I had to resort to other methods in my application. But now you have me curious, how did you incrementally set the taper wedge or whatever the mechanism is that expands the stone(s) ever so slightly as you progressively enlarge the bore? I've never seen a Sunnen type machine in real life but on some videos looks like the operator turns an adjustment wheel as its stroking which I assume is pulling or pushing on the wedge?

About how much material did you have to remove from the bore? What grit of stone & how long did it take?

Hi Peter (I assume)

Here are some pics that I hope will help you understand.
I also balked at the total price of the P180, which is why I fabricated the most expensive part.
I notice in the catalog that grit size ranges from 150 to 600 - 150 to 280 being the most popular in the tooling I was using. That is if I understand the catalog correctly.

I built in a small turn wheel using a 5mm x .8mm pitch thread which I found lifted the stone in a controlled manner.
I did not devise a gauge, I used feel. I kept the stone low and inserted the stone into the bore. I then lifted the stone with the drill stopped but the stone well lubricated with honing oil. When I had some light pressure on the stone in the bore I use a relatively slow speed of approximately 100RPM and moved the mandrel in and out of the bore steadying the tool with my hand.
I then stopped the tool and progressed the stone until again it lightly touched the bore. Repeated the process. It generally took three such applications to resize the bores from slightly over 20.00mm to 20.05mm.
It only took an hour to do all four bores, even with careful measuring and testing and thinking etc.
I don't think they adjust the lift of the stone while the hone is rotating. I think they have to stop the tool, adjust and then recommence. I know I had to.


I hope this helps.

Regards Mal

 

[petertha]

Aha, I get it now. Your self made collar is acting on the ramps & that extends the stone.
Reason I'm asking is for liners on my model radial engine... well... the NEXT engine I build because this was a bit of a chore. Lapping is quite controlled but such a slow process that requires the bores to be within a thou or so to begin with. I've watched some Sunnen hone vids & that stroking / pseudo-grinding action looks to be a better, more established way of achieving a target bore with better removal rate. But I will never own a machine like that so had some ideas of making one from scratch. Looks like you adopted their fiddly-to-replicate component & worked out how to achieve the radial expansion.

So about how much bore diameter did you remove & what was the native material?

Sorry for the interruption to your post, this has gotten me inspired.

 

[malmac]

Aha, I get it now. Your self made collar is acting on the ramps & that extends the stone.
Reason I'm asking is for liners on my model radial engine... well... the NEXT engine I build because this was a bit of a chore. Lapping is quite controlled but such a slow process that requires the bores to be within a thou or so to begin with. I've watched some Sunnen hone vids & that stroking / pseudo-grinding action looks to be a better, more established way of achieving a target bore with better removal rate. But I will never own a machine like that so had some ideas of making one from scratch. Looks like you adopted their fiddly-to-replicate component & worked out how to achieve the radial expansion.

So about how much bore diameter did you remove & what was the native material?

Sorry for the interruption to your post, this has gotten me inspired.

Peter

If you were able to make those cylinders then what I did would be a breeze for you.
I think if you had the option of honing in a controlled manner you could perhaps adapt the mandrel to fit into your tail stock without the universal joint and use it more like a drill with an adjustable diameter. The screw adjuster process could work with a slot for adjustment.
The main difference being that the wear pad would not be stabilising because the centre of the tool would be constant and the hone stone would expand out from that centreline. The quill on the tail stock could provide the in and out motion in a controlled manner. I think that is right but correct me if I am mistaken.

I only took out about .03mm. But I am sure more could be removed

Mal

 

[malmac]

Special tools - often with these old bikes the work is very difficult without at least some special tools. I certainly make more special tools than a normal sane person requires, but that is my obsession. Well the penny dropped yesterday as I was upgrading my data collection sheet, that really it is a special tool of the "aid to thinking" category.
I got to a stage where this crankshaft is really playing hard to get. The reason being that instead of the misalignment being aligned to the quadrants it is now slanting across the webs and making my earlier datasheet, not as helpful as it could be. So I have added some larger diagrams which can act as thinking templates, to save me sketching the situation to improve my grasp of what the measurements are telling me.

Mal