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The small side on the right
Posted: Thu Nov 10, 2011 9:57 pm
by Bruce Frey
The small side on the right as you sit on the bike and the left if you face the rear mean the same.
I think the arrow is the small symbol preceding "Vor" and points to the right of the picture. If that is correct, the small side of the piston should be on the top of the picture.
Bruce
I have measured and found the
Posted: Fri Nov 11, 2011 10:31 am
by 515PHOTO
I have measured and found the narrow side--Had Rusty at MAX measure a new piston, find the offset and compare to the arrow. OK, based on the perponderance of evidence I'm gonna fit this piston. Only confusion is Bruces last comment. Now, imagine you are sitting above this piston, the arrow is pointed ahead of you, the smaller side is to the right. When looking at the photo, assuming the arrow is pointing to the right, would the smaller side not be on the BOTTOM of the picture? My mind is starting to hurt!
Sorry....you're right. If
Posted: Fri Nov 11, 2011 10:19 pm
by Bruce Frey
Sorry....you're right. If the arrow points to the right in the picture, small should be down.
It appears that the old saying, "he doesn't know which end is up," applies to me.
Bruce
Thanks Bruce. I figured it
Posted: Sat Nov 12, 2011 12:45 pm
by 515PHOTO
Thanks Bruce. I figured it was just a 'oops' but the older I get the more confusion that swirls around me. Just ask my kids!
Thanks all for the help. I am sure more questions are to come. Stay tuned.
Now, where did I put those valves????????????
Sad tale of woe...
Posted: Sun Dec 25, 2011 4:04 pm
by R68
...I rebuilt a Universal 2B, a seldom seen Swiss made motorcycle from the 50's, somewhat similar to a BMW R67 or Zundapp KS601. The aftermarket pistons were not labelled, and I put one in "upside" down. After 330 km, the connecting rod bearing on that side seized, the alloy rod exploded...(Duh, I'm an idiot)...this piston orientation is a really important topic to be aware of!...
Re: piston orientation
Posted: Fri Jan 14, 2022 11:09 am
by Darek1967
Hello All,
This is my first time on the forum so apologies if my question is misplaced. I'm trying to make sure I'm installing my Nural pistons correctly since there is no VORN markings on both pistons - see picture. Any help is appreciated. Thanks
- R69US Nural Piston
Re: piston orientation
Posted: Fri Jan 14, 2022 11:16 am
by schrader7032
Welcome to the forum! I believe the /2 bikes don't have the "vorn" or arrow marking meaning they can go in any direction. The reason for the orientation would be due to the offset of the wrist pin...if it is not in the center of the piston, then it needs the offset. On my R69S rebuild, I put the pistons in so that I could read the writing. I just wanted something that I could remember or write down as to the orientation.
I went to the Barrington manual and I'm a little disappointed in what is written. It says "should there be a front-rear orientation demanded by the piston". Seems to me that the manual could have spelled it out for stock pistons. I suppose they're hedging their bets for someone installing non-stock pistons.
Re: piston orientation
Posted: Fri Jan 14, 2022 11:30 am
by Darek1967
Thanks for immediate reply. I'm at the end of R69US rebuild, top end and gas tank left to install. Will post pictures soon.
Thank you again
Re: piston orientation
Posted: Sun Jan 16, 2022 11:55 am
by jwonder
schrader7032 wrote: ↑Fri Jan 14, 2022 11:16 am
Welcome to the forum! I believe the /2 bikes don't have the "vorn" or arrow marking meaning they can go in any direction. The reason for the orientation would be due to the offset of the wrist pin...if it is not in the center of the piston, then it needs the offset. On my R69S rebuild, I put the pistons in so that I could read the writing. I just wanted something that I could remember or write down as to the orientation.
I went to the Barrington manual and I'm a little disappointed in what is written. It says "should there be a front-rear orientation demanded by the piston". Seems to me that the manual could have spelled it out for stock pistons. I suppose they're hedging their bets for someone installing non-stock pistons.
To be clear, for people reading the forum and to ensure that the proper information is disseminated, some models have an offset piston, while others do not.
See
https://vintagebmw.org/library_data/Wor ... R60S69.pdf Page 26 of the PDF, 25 of the doc. R 50 and R 50 S have the offset while the R 60 and R 69 S do not.
For the R 27 see
https://vintagebmw.org/library_data/Wor ... rm_R27.pdf on page #23 pf the PDF, page 21 of the document, both the R 26 and the R 27 have offset rod bores in the pistons on the thrust side.
I hope this helps clear this up.
Re: piston orientation
Posted: Sun Jan 16, 2022 2:57 pm
by schrader7032
I guess Darek's original piston tells it all for him...no "vorn" or arrow means no offset.