Vintage BMW Motorcycle Owners

How can I tell if these are the original pistons in my 62 R69s?
Looks like someone at one time put incorrect plug in?

Looks like your pistons are dated more or less correct at 1/62, there should be additional info inside the piston that came from the mold. The nominal dimension should be 71.92mm so yours are twice over...I believe each oversize is 0.5mm in diameter. The triangular stamp is likely the inspection same from Nural. If they are twice over, then something happened early on with the engine that required it. Here's what my '69 R69S piston looks like.

Thanks!

Cylinders scored

The view if of the bottom third or skirt of the cylinder, right? I'm not sure, but how far down the bore does the piston actually travel?

Those marks suggest that there was lack of lubrication. But I don't have much experience with this type of thing.

I agree with you Kurt. But keep in mind, the early Nural pistons were crap and are well known to fail in this manner.

From the looks of the piston bet it was slapping back and forth in the cylinder.
We’ll see what the other side looks like.
Rt side heads stuck on (That side had decent compression). Bikes supposedly been sitting forever. Over the next few days I’ll hit it with some penetrating fluid & try again

I know the feeling. My Barn Bike had both heads stuck on the cylinders and both pistons stuck as well. I had to improvise a little.

jimkav wrote: ↑

Wed Nov 16, 2022 8:45 pm

From the looks of the piston bet it was slapping back and forth in the cylinder.
We’ll see what the other side looks like.
Rt side heads stuck on (That side had decent compression). Bikes supposedly been sitting forever. Over the next few days I’ll hit it with some penetrating fluid & try again

Jim, take the head bolts off the head and heat it to 200 degrees with a torch. Let it cool. Heat it again and it should come off. If you are going to use a plastic/rubber hammer, do not tap on the fins, you will bend them! If I have a stubborn one, I heat it 2 or 3 times and let it cool, then heat it again and put the head bolts into the heads (do not screw them in) and tap on the them for leverage. I tap, not beat it to death. Heating and cooling works because of the dissimilar metals and the aluminum heads expanding more than the cast iron! Gotta love physics!!!!

Figured the dissimilar metals would expand/cool at different rates. Wasn’t sure how hot to heat the cylinders.
Thanks