If you like our site, please consider joining our club!
By joining you will help ensure that we can continue to provide this service
JOIN HERE!

R69S pistons

jimkav
Posts: 170
Joined: Wed Apr 03, 2013 9:55 pm
Has thanked: 2 times

R69S pistons

Post by jimkav »

How can I tell if these are the original pistons in my 62 R69s?
Looks like someone at one time put incorrect plug in?
Attachments
6C758D5C-0B8B-469F-8F4F-E8EA9477A98A.jpeg

User avatar
schrader7032
Posts: 9014
Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX
Has thanked: 2 times
Been thanked: 29 times

Re: R69s pistons

Post by schrader7032 »

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.
Attachments
LeftPistonCrown2.JPG
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

jimkav
Posts: 170
Joined: Wed Apr 03, 2013 9:55 pm
Has thanked: 2 times

Re: R69S pistons

Post by jimkav »

Thanks!

jimkav
Posts: 170
Joined: Wed Apr 03, 2013 9:55 pm
Has thanked: 2 times

Re: R69S pistons

Post by jimkav »

Cylinders scored
Attachments
952F5531-2E8E-433B-B048-6D157FC5B266.jpeg

User avatar
schrader7032
Posts: 9014
Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX
Has thanked: 2 times
Been thanked: 29 times

Re: R69S pistons

Post by schrader7032 »

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.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

scottiesharpe
Posts: 135
Joined: Mon Apr 18, 2011 11:23 pm
Been thanked: 2 times

Re: R69S pistons

Post by scottiesharpe »

I agree with you Kurt. But keep in mind, the early Nural pistons were crap and are well known to fail in this manner.
Scottie Sharpe, Proprietor
Scottie's Workshop, 3282 E Hwy 4, Murphys CA
Full Service Workshop for vintage and classic BMW Motorcycles http://blog.scottiesharpe.com

jimkav
Posts: 170
Joined: Wed Apr 03, 2013 9:55 pm
Has thanked: 2 times

Re: R69S pistons

Post by jimkav »

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
Attachments
533A4DB2-7669-44B7-B30D-8BCCFDCA5A84.jpeg

Tinkertimejeff
Posts: 146
Joined: Thu Jan 20, 2022 5:49 pm
Been thanked: 8 times

Re: R69S pistons

Post by Tinkertimejeff »

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.
Attachments
BarnBike5.JPG

User avatar
jwonder
Posts: 784
Joined: Wed Nov 23, 2016 7:50 pm
Location: Long Island, New York
Has thanked: 3 times
Been thanked: 7 times
Contact:

Re: R69S pistons

Post by jwonder »

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!!!! :-)
James Wonder
Vice President, Vintage BMW Motorcycle Owners
2022 BMW Friend Of the Marque
Long Island, New York

jimkav
Posts: 170
Joined: Wed Apr 03, 2013 9:55 pm
Has thanked: 2 times

Re: R69S pistons

Post by jimkav »

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

Post Reply