nz 350 piston to cylinder clearance

Basic info on DKW NZ 350's

Moderator: Mods

Post Reply
andyy1
Novize
Posts: 10
Joined: Thu Dec 29, 2016 10:06 pm

nz 350 piston to cylinder clearance

Post by andyy1 » Sat Feb 18, 2017 12:37 pm

hi guys, does anyone know the piston to cylinder clearance size. need to find out for the machine shop to rebore. also the ring gap when inside the cylinder. thanks in advance, andy
martdapp
Master Mechanic
Master Mechanic
Posts: 949
Joined: Sat Jan 19, 2008 9:46 am
Location: Hoensbroek Niederlande

Re: nz 350 piston to cylinder clearance

Post by martdapp » Sat Feb 18, 2017 10:39 pm

Hi Andy,

I had this question also for a time ago;
Here the answer from Frank;

Its normally the manufacturer of the piston who tells the tolerance between piston and cylinder, depending on the materials and manufacturing methods used.

Those tolerances stated in the DKW wartime workshops manuals are for the original DKW pistons and they are not valid if you use a modern repro piston.

Normally the cylinder is grinded to exact measures, for example 72.50mm, 73.00mm, 73,50mm and the manufacturer of the piston has took care of the tolerance when manufactured the pistons.

Normally the tolerance is stamped on the piston dome, for example 72.85mm, when cylinder then is grinded to 73.00mm, the tolerance is 0.15mm.

//Frank
andyy1
Novize
Posts: 10
Joined: Thu Dec 29, 2016 10:06 pm

Re: nz 350 piston to cylinder clearance

Post by andyy1 » Sun Feb 19, 2017 8:24 pm

hi martin
there is no markings on the piston size wise. i suppose i will just have to take it down to the borers and tell them the tolerances of the wartime ones and then see what they say. i have looked up an old post on here and it says that .17 is the clearance but modern pistons it can be .05 according to the guy i got the piston of its a nos izh one made in the 70's so do the wartime tolerances apply ? on the good news front i have sorted out the damaged fins on the cylinder you sold me. i took them to a professional welder to do and guess what ! as soon as i got it back and started to clean it up the repairs broke. so i did the welding myself, put it in the oven at 250 degrees to see if the welds would crack and they didn't. so a self taught welder like myself is better than a qualified welder. quite pleased with myself. cost me 45 pounds tho in his charges. posted a picture on here for you to see the cylinder. cheers, andy
martdapp
Master Mechanic
Master Mechanic
Posts: 949
Joined: Sat Jan 19, 2008 9:46 am
Location: Hoensbroek Niederlande

Re: nz 350 piston to cylinder clearance

Post by martdapp » Sun Feb 19, 2017 8:50 pm

Here the cilinder from Andy.
I let weld several cilinders, never had a crack again.
thumbnail_20170203_172146.jpg
thumbnail_20170203_172158.jpg
thumbnail_20170202_191707.jpg
You do not have the required permissions to view the files attached to this post.
Post Reply