Restoration of BMW R69s engine

[C-Bag]

I never had a bike crank apart. Back in the 70’s you could get roller cranks for VW’s and it was more a thought exercise than reality for me. in thinking about what you are up to it almost seems building the crank up from scratch with precision flats to press each “layer” to would be easier than trying to fix a bad assemble.

 

[malmac]

I never had a bike crank apart. Back in the 70’s you could get roller cranks for VW’s and it was more a thought exercise than reality for me. in thinking about what you are up to it almost seems building the crank up from scratch with precision flats to press each “layer” to would be easier than trying to fix a bad assemble.

Tony

I do not have the experience - and maybe never will, so what I say has to be seen as theoretical rather than based on 40 years hands on experience.

1. While it seems that pressing up the crank can be done carefully or less carefully - even so maybe even with much care it is probably not guaranteed that care will result in immediate perfect alignment and runout - though it should mean generally less tweaks needed afterwards.
2. The forces involved in pressing together the cranks is quite high so it is rather easy for the slightest deflection to result in some level of misalignment.

In due course I have a crank which needs a total rebuild so then I will explore turning theory into practice.

Regards Mal

 

[C-Bag]

To be sure Mal I don’t have the specific experience either. I was just thinking out loud. I can only think this does take a lot of force to press one of these cranks together. And it’s got to be crazy to get all these parts together while exerting so much pressure on the parts already assembled. not trying to second guess you.

 

[malmac]

To be sure Mal I don’t have the specific experience either. I was just thinking out loud. I can only think this does take a lot of force to press one of these cranks together. And it’s got to be crazy to get all these parts together while exerting so much pressure on the parts already assembled. not trying to second guess you.

Tony

I did't think of you second guessing me - I am the sort of person who would spend a month making a jig that would allow me to assemble cranks perfectly. I did see a jig that looked good on Youtube but after they pressed it together, they still had to go through a certain amount of what I have done. That was also just a single cylinder crank. I am blown away by the fact that folks were pressing up 4 cylinder Kawasaki Z1 cranks and getting it all work out....... that is really impressive or should I joke and some compressive.

Mal

 

[Joe in Oz]

Allan Millyard (https://www.youtube.com/user/millyardviper) has some great videos on building crankshafts. He even made a 12 Cylinger Kawasaki engine.... Most of his build videos are quite inspiring, actually.

 

[malmac]

Allan Millyard (https://www.youtube.com/user/millyardviper) has some great videos on building crankshafts. He even made a 12 Cylinger Kawasaki engine.... Most of his build videos are quite inspiring, actually.

Joe
Allan is inspiring but sometimes I find he is a bit brief on the technical in depth stuff which a person is looking for when they are building their own flat 12 BMW special.......
Not that I am planning to undertake such a project.

Mal

 

[malmac]

Well I have arrived at a critical juncture. The crankshaft is within the factory specs so now I have ask myself, is that good enough?
There are three measurements that count.
One is to make sure that the centreline through the three crank webs are aligned. Here is the test I learnt from Salis to check the alignment. The spec is less than .02 mm. Here as you can see I have .01mm variation.

Mal
View attachment Mal Alignment.mp4

 

[malmac]

The second test is the runout on the shafts. Unfortunately my video camera was not set quite right, so the runout on the left is partially obscured.
Spec is again less than .02mm - I guess technically I am just right on .02 - so now I have to make a call - is this good enough or do I need to get back to the wrestling match?

Mal
View attachment Run out.mp4

 

[Joe in Oz]

I believe that at our age we have to become a little pragmatic....
Are you doing this to sell as a "factory blueprint standard" concourse quality example of your workmanship, or as a beautiful bike to own and ride?
If the first, then you have mailed it on specs. If the second, how many kilometres did BMW expect these bikes to run for before rebuild? Are you still likely to ride to that expectation? If not, you nailed it too....
Sounds like you are trying to prove something to yourself.....
Finish it, sell it and know you are not cheating anyone, or indeed ride it and admire it in your collection, knowing you won't wear it out.....

Cheers
Joe

 

[malmac]

I believe that at our age we have to become a little pragmatic....
Are you doing this to sell as a "factory blueprint standard" concourse quality example of your workmanship, or as a beautiful bike to own and ride?
If the first, then you have mailed it on specs. If the second, how many kilometres did BMW expect these bikes to run for before rebuild? Are you still likely to ride to that expectation? If not, you nailed it too....
Sounds like you are trying to prove something to yourself.....
Finish it, sell it and know you are not cheating anyone, or indeed ride it and admire it in your collection, knowing you won't wear it out.....

Cheers
Joe

Hi Joe

That is fair advice. I have more or less come to the conclusion that what I want is a bike that runs nicely when completed. I am not after some concourse machine and also won't be selling the bike. So I am moving along with other parts of the rebuild. Thanks for taking the time to provide that perspective.

Mal