Cluch slipping

[r.rocchelli]

I'm restoring my 1942 350 NZ , the motor runs regularly,but after a few Km the cluch start slip !!
I open the motor and the cluch rings seems to be quite goods (originals) , the thikness is around 4mm. , normal??
may be the cause is the not correct oil?? I used a new normal oil for two stroke gearboxes of good quality but may be not compatible with the cork friction material of the 350 NZ ??
or may be the load of the springs??
Can some body give me help??
Regards Rino

[Rob Hickmott]

Hi Rino,

I am having the same trouble, my clutch is about the same thickness of cork plates, I am using good transmission oil for motorcycle clutch and gear box.
I am going to try tightening the clutch springs some more. I cant find a proper setting for these springs in the workshop manual, somone who has more experience might be able to give the correct settings.

[thomas591]

Hi there,

the manual says that the adjuster nuts on the clutch cover should be tighted in a way that aprox. 1 mm of the threaded stup is visible. Make shure that all studs protrude the same abount. If this is not sufficient, then try to tighten the nuts some more. No measurements for the clutch adjustement is given in the manuals.

regards


Thomas

[r.rocchelli]

,Finally i decided to change the old corks disks
Be carefull to the number of teeths my NZ has 6 the 350 -1 has 8 the disk often in E-bay are non goods for an aluminium motor NZ!!
Rino

[thomas591]

Hi Rino,

Stemler (see "vendors" page) sells the 6 teeth version for the NZ 350 for EUR 17,16 each. These are the steel clutch disks which are covered with modern material, not with corks. They work excellent and they save you from messing around with the corks. The Stemler part number is 00 00 0 001 615.


Best regards


Thomas

[flamsmidt]

i had also some problems whit the clutch at firts wrong plates whit 6 taps insted of 8 no trouble i tought i had another housing of an 250 nz but in such a housing only fit 3 plates after long surching on markets i found plates whit 8 taps they came from an NSU "lux" the plates are thinner and i fitted 5 plates in my clutch now works great but the big problem is that after all those years the iron plates "druckplatten"are bend so the clutchplates have to little of frichtionground .
to check if youre plates are bend use a steel ruller .
repro steel plates are hard too get so if you place al the bended sides in same direction it will work and reed the "werkstad handbuch" for military use plain motor oil only !! civil use gearbox oil {page 90 of the instandsetzungsanweisungen} greetings and good luck
m.markerink

[thomas591]

Hi there,

I just talked to this guy: http://www.erb-computertechnik.de/resta ... %20tip.htm about DKW cork clutches. He seems to know what he was talking about, because he told me that annually he converts about 70-80 SB clutches from cork to modern materials.

We were talking about the SB500 clutch and he said that this is the most difficult one to convert, because of the drilled clutch cage. Therefore the price is 270,00 Euro + 19% Tax + postage. To convert a NZ clutch to new friction plates and new steelplates is much cheaper. He can also make new clutch cages for the NZ, which is a big relief when your teeth of the primary chain on the clutch cage are badly worn.

Another topic that we discussed is the question about the oil. Originally the SB Gearbox should be filled with a mixture of 3/8 Ambroleum and 1/8 engine oil. He claims that this gives very hard shifting for the first 20-30 miles, because the grease is still quite hard. He recommends a very simple classic gearbox oil with no additives and advises NOT to fill the gearbox to the normal level, but only that far, that the teeth of the gears are immersed in oil. That is sufficient to lubricate the gears and bearings, while giving a very good clutch performance the only disadvantage is that you have to check the oil more frequently.

REGARDS


Thomas

[thomas591]

Following are some picures of the repaired/converted SB500 clutch. Excellent workmanship!

Thomas

[Rob Hickmott]

Hi Thomas,
I have an SB 500 as well as the NZ, What exactly do you get for your 270 Euros?. I am using cork at the moment running in Silkolene medium gear oil. Which works OK, but will need replacing at some time.

Thanks rob

[thomas591]

Hi Rob,

these are the steps performed:

1. Clean all components.
2. Glassblast the friction disk and the clutch cage
3. Make new friction discs.
4. Glue modern friction material on the new dics and machine the friction material to the appropriate thickness.
5. Using a late, turning small plates which equal the diameter of the old corks and glue them into the cork-holes of the clutch cage. Now there is a flat surface in the clutch cage.
6. Manufacture new friction material rings and glue them onto the now level clutch cage.
7. Machine the new friction material in the clutch cage to the correct thickness.

Regards

Thomas


P.S. No financial interest from my side into redoing the clutch, I just can recommend it.


P.P.S. The guy wants your complete clutch for the repair, not just the discs, so he can match ALL parts to each other.

[flamsmidt]

hi there.

the right choise of oil is not dificult use single grade sae 30 oil !!
al these oils are wrong gearbox oil,15w40,80/90 dif oil,aditives like slik 50 and others.

and thomas an sb gearbox is not an nz gearbox no offence but there are
in an sb box no bronze bearings on main gear shaft

fill the nz box whit sae 30 on normal markings.

otherwise bronze bearings will seize up the clutch push bar will seize up.
i had that once .

the problem is where to get sae 30 oil on suplier ships on rivers they have it, and other wise order it at an auto parts shop .

good luck m.markerink

[thomas591]

Hi Flamsmidt,

you are absolutely correct, when stating that the SB500 gearbox has nothing to do with the NZ. Maybe my postings should therefore be placed in an SB related forum...

Not quite (to my believe)! My postings and remarks can be related also to NZ clutches. I was facing a problem when I restored my NZ350/1943. The clutch cage and discs were totally worn. If I would have had the address of the above mentioned specialist, I would have solved my clutch problem much easier. On my bike I was lucky to find a NOS 350-1 clutch which works very well. But after all, I would have preferred to have an alu-engine clutch.


Regards


Thomas

[iz350]

One cure for clutch slipping(had this problem when I was using a sidecar on my DKW clone IZH-350)was use of Castrol MTX gearbox oil.It is used lot in wetclutched motocross bikes to reduce clutch sliping.Worked for me.But it needs good condition gearbox seals to avoid leaking.