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piston orientation

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Bruce Frey
Posts: 536
Joined: Fri Oct 27, 2006 3:00 am

The small side on the right

Post 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

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515PHOTO
Posts: 94
Joined: Tue Feb 09, 2010 11:58 am

I have measured and found the

Post 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!
82 R100RT, 64 R60/2, 2018 R1200RT
61 R27 and boy do I need parts-- got any?
Oh no, wifes coming home- get the engine out of the oven!
"Are those bearings in the freezer?!" she calmly inquired

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Bruce Frey
Posts: 536
Joined: Fri Oct 27, 2006 3:00 am

Sorry....you're right. If

Post 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

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515PHOTO
Posts: 94
Joined: Tue Feb 09, 2010 11:58 am

Thanks Bruce. I figured it

Post 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????????????
82 R100RT, 64 R60/2, 2018 R1200RT
61 R27 and boy do I need parts-- got any?
Oh no, wifes coming home- get the engine out of the oven!
"Are those bearings in the freezer?!" she calmly inquired

R68
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Sad tale of woe...

Post 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!...

Darek1967
Posts: 10
Joined: Thu Jan 13, 2022 6:27 am
Location: New York

Re: piston orientation

Post 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
R69US Nural Piston
Darek
'69 R69US

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schrader7032
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Location: San Antonio, TX
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Re: piston orientation

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

Darek1967
Posts: 10
Joined: Thu Jan 13, 2022 6:27 am
Location: New York

Re: piston orientation

Post 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
Darek
'69 R69US

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jwonder
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Re: piston orientation

Post 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.
James Wonder
Vice President, Vintage BMW Motorcycle Owners
2022 BMW Friend Of the Marque
Long Island, New York

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schrader7032
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Re: piston orientation

Post by schrader7032 »

I guess Darek's original piston tells it all for him...no "vorn" or arrow means no offset.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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