Piston Rings

Basic info on DKW NZ 350's

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ztitus713
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Piston Rings

Post by ztitus713 » Fri Nov 23, 2012 10:51 pm

Hello

I need new piston rings for my NZ 350 motor. Greiner has them for sale however the only problem I am having is figuring out what size I need. Does anybody know what size I do need? I looked in the manual and they listed 3 or 4 different sizes. Thank you

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Zack
TM250
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Re: Piston Rings

Post by TM250 » Mon Nov 26, 2012 12:44 pm

Hello Zack!

That would depend upon what size (diameter) of piston or cylinder bore you'll want to fit them on. Does not your existing piston have the diameter indicated on the top surface? Otrherwise you would have to measure it.

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Gorm
martdapp
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Re: Piston Rings

Post by martdapp » Sat Dec 01, 2012 2:21 pm

That would depend upon what size (diameter) of piston or cylinder bore you'll want to fit them on. Does not your existing piston have the diameter indicated on the top surface? Otrherwise you would have to measure it.

Indeed, but does any-one knows the tollerance between cylinder and piston?
So, when I have the smallest (or bigger) piston, to wich size I do have to bore the cylinder?
PS. pistonrings do also have their measures, You should use pistonrings wich belong to your (or a new) piston.

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martin
Frank
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Re: Piston Rings

Post by Frank » Sat Dec 01, 2012 3:45 pm

Hi Martin,

The tolerance according to the ws-manual should be 0,17mm +/- 0,01mm(huge, compared with nowadays engines!). This is the tolerances for the old original German pistons.

Many of the post war pistons have the tolerance stamped on the dome of the piston and it can vary quite much depending on the manufacturer of the piston and also on the material used in the piston.

Normally a good engine repair workshop with equipment to grind the cylinder, knows quite well how the job should be done in a proper way.

// Frank
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Re: Piston Rings

Post by TM250 » Sat Dec 01, 2012 6:02 pm

Please note also that the "Stossmass" i.e. the gap in the ring when placed inside the cylinder should be 0,4 to 0,6 mm on the NZ. Repro pistons from Italy which are quite common today need a higher "Kolbenspiel" than the original german pistons. That I have learned from experience!

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ztitus713
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Re: Piston Rings

Post by ztitus713 » Sun Jan 20, 2013 4:25 pm

MY piston does not have the size stamped on it. I looked all over it and couldnt find anything. I guess I will have to measure the existing piston ring that I have.
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