1957 R50 Recent restoration New Pistons -problem!

[schrader7032]

As for the right side oil passage, if it were me, I'd probably try to get complete access to the engine case if possible. Here's a pictorial on what that process is:

http://bmwvmca.org/joomla/index.php?opt ... &Itemid=37

[westeagle]

Thanks for that info!

[wa1nca]

IMO
I would think the crankshaft should be removed so that any drill filings can be cleared that feed the rear main bearing

I have 2 bikes 55 R50 and 54 R51/3 that don't have the extra feed for the right side and never had any problems

Dont know why that side failed

Tommy

[malmac]

Hi Folks -First Post on this forum, and it's good to be here!

So...Over the past year, I restored a 1957 R50 (my first-ever machine restoration) - I made a Youtube video documenting the restoration:

https://www.youtube.com/watch?v=eQXqBSgzs2M

In general, I'm very pleased with how the restoration came out: I did all of the dismantling and re-assembly myself: slingers, new bearings & seals (huge thanks to the Ed Korn video, Betjemann bible and this Forum!); subcontracted the frame powder coating, bodywork and painting, crankshaft rebuild, cylinder re-boring, and wheel rebuilding.

After it was all reassembled, I was off to a great start with the bike starting on the First Kick! Over the past few weeks, as weather permitted, I have been venturing out further and further on a series of "shakedown" rides. A couple of days ago I was returning home from a 5 mile outing and was accelerating up a long hill when the bike started to decelerate on its own. I pulled over for 30 minutes and noticed the right cylinder fins were very hot. Once it cooled down I was able to hobble the last mile home, presumably on 1 cylinder, while the bike emanated quite a clatter from the right side (piston slap?)


Beautiful restoration really bad news about the pistons.

Where did you source the new pistons that you installed and what brand are they?

Also what clearance did you bore the cylinders too?

I ask these questions because I am in the thick of doing up my engine with new pistons and naturally would like to avoid a similar disaster as you have just had.

You have done such a beautiful job of the restoration, I would think that both pistons need to be replaced, it might add to the expense but will feel better knowing all is well.

Also check out duane asherman's article of pistons.
I notice you have non standrad mufflers and he mentions mufflers in his article.
Maybe more free flowing mufflers can lead to the engine running more lean and therefore hotter, but I am just guessing.

Cheers

Mal

Once home, I started taking the right cylinder apart to look for damage, and found that the piston and cylinder wall had substantial scoring wear. See pictures.

My preliminary "diagnosis", (from my novice perspective), is that it looks like the right side was starved of oil. Of course, I took the left side apart to see what condition it was in, and there is also some sign of same phenomenon, although much, much less.
On hindsight, one of my failings was not paying enough attention to cleaning out the small oil passage holes (just used compressed air when I should have really gotten in there) Plus, I am now becoming aware of the importance of the mod of drilling the new oil hole on the right side (using one of the available templates)...



So... A few questions to the experienced friends out there:

1: I'm assuming I need to re-bore the right side, to the next size up and replace the piston?

2: Based on the photos, Does the damage on the left side warrant doing a rebore and new piston there too?

3: When I drill the new hole into the block for the right side, is there any way to do it safely without taking the engine out of the frame?

4: I would have to do an aggressive clean out of the existing oil passages as well. Again, does this mean pulling the engine?

5: Any additional input, ideas or theories of why this occurred would be much appreciated!

btw, I am using Valvoline VR-1 SAE 30 motor oil and the early spring outdoor temperatures I have been operating at are in the 40's F.

Best regards,

Henry

[westeagle]

Well that was my thought originally. I never expected to take it out on a cross country tour, so thought the current design must be fine, for short jaunts on a Sunday. Hence my decision to not pursue the extra oil hole originally. That is why I am also looking for other ideas on why this might have happened.

[schrader7032]

Sounds like you had piston seizure. Duane Ausherman has a discussion on this:

https://w6rec.com/bmw-motorcycle-defect ... -the-r602/

[schrader7032]

What were the clearance specs with the piston and the bore when the engine was rebuilt?

[westeagle]

So they were new Kolbenshmidt 69.500mm pistons

Measurements of bore/ clearances for both sides as provided to me:

2.7345"
+.00197"
=2.73647

[westeagle]

The mufflers being non stock are something I’ll have to look at. Come to think of it the original pistons I removed for the restoration had the same damage and used the same mufflers...That would be a pity as I love the sound of those non stock mufflers. But if changing to stock mufflers is what it takes, then so it must be...

[westeagle]

Hi Folks -First Post on this forum, and it's good to be here!

So...Over the past year, I restored a 1957 R50 (my first-ever machine restoration) - I made a Youtube video documenting the restoration:

https://www.youtube.com/watch?v=eQXqBSgzs2M

..And another Youtube video of the very ride where my problem occurred, although its not shown in video

https://youtu.be/Q6PNy7g6kaw

In general, I'm very pleased with how the restoration came out: I did all of the dismantling and re-assembly myself: slingers, new bearings & seals (huge thanks to the Ed Korn video, Betjemann bible and this Forum!); subcontracted the frame powder coating, bodywork and painting, crankshaft rebuild, cylinder re-boring, and wheel rebuilding.

After it was all reassembled, I was off to a great start with the bike starting on the First Kick! Over the past few weeks, as weather permitted, I have been venturing out further and further on a series of "shakedown" rides. A couple of days ago I was returning home from a 5 mile outing and was accelerating up a long hill when the bike started to decelerate on its own. I pulled over for 30 minutes and noticed the right cylinder fins were very hot. Once it cooled down I was able to hobble the last mile home, presumably on 1 cylinder, while the bike emanated quite a clatter from the right side (piston slap?)

Once home, I started taking the right cylinder apart to look for damage, and found that the piston and cylinder wall had substantial scoring wear. See pictures.

My preliminary "diagnosis", (from my novice perspective), is that it looks like the right side was starved of oil. Of course, I took the left side apart to see what condition it was in, and there is also some sign of same phenomenon, although much, much less.
On hindsight, one of my failings was not paying enough attention to cleaning out the small oil passage holes (just used compressed air when I should have really gotten in there) Plus, I am now becoming aware of the importance of the mod of drilling the new oil hole on the right side (using one of the available templates)...



So... A few questions to the experienced friends out there:

1: I'm assuming I need to re-bore the right side, to the next size up and replace the piston?

2: Based on the photos, Does the damage on the left side warrant doing a rebore and new piston there too?

3: When I drill the new hole into the block for the right side, is there any way to do it safely without taking the engine out of the frame?

4: I would have to do an aggressive clean out of the existing oil passages as well. Again, does this mean pulling the engine?

5: Any additional input, ideas or theories of why this occurred would be much appreciated!

btw, I am using Valvoline VR-1 SAE 30 motor oil and the early spring outdoor temperatures I have been operating at are in the 40's F.

Best regards,

Henry