ETZ 250 Main Crankshaft Bearings

[Kruh]

Interesting point on that 'f' addition. If it means a low noise bearing, then it reffers to the plastic cage bearings.

[nice2day]

Also, I've heard that the standards back then in DDR weren't the same as the ones today. So a C4 bearing back then is equivalent to a modern C3. Maybe someone can confirm this? Seems likely.

Also Puffs seems to say the same thing:

C3's should also be considered in the gearbox where the manual specifies C4f's. The extra clearance should reduce the chance of jamming.

Hi Kruh and Puffs...from what you are saying as quoted above, you seem to be saying that a C4 clearance is tighter than a C3 which is not the case. In order of tightness or from tight to slack is:

C2 -/ CN (normal)- / C3 / - C4 /- C5. where C2 is very tight and C5 is very loose.

Hope this clarifies the standard.

Les

[Puffs]

Hi Les, no I don't think I was saying that, apologies if that was unclear. I said "The extra clearance" but that was intended in comparison with standard bearings which one can currently buy. I do not believe we can still buy those DDR C4f's anymore, so I wasn't comparing with those.

The relevant clearances are specified in tables in the PDF I posted earlier. Pertaining to modern bearings, not DDR produce.

Yes, Kruh is quite possibly correct in that the current C3's are equivalent to the DDR C4f's. I read similar opinions on the German forum. Yes, I do believe that the DDR had some different standards compared to modern/western standards, so that DDR classifications with a similar name are not necessarily equivalent to modern day / western standards. So the clearance in a DDR C4f might be different to that in a modern day (SKF/FAG/NTN) C4, and closer to that of a modern day C3 (or indeed equivalent).

On 'low noise': I think that means the surfaces of the races is polished smoother, compared to the standard issue. It's roughness in that surface that makes bearings loud, not so much the material used for the cage.

[nice2day]

Thanks for the clarification Puffs. It was just the way I read it.
Out of some historic interest regarding the nylon caged roller bearings. Way back in the mid '80's, many MZ ETZ's suffered main bearing failure where the nylon cage collapsed completely letting the balls run freely or even falling out. I guess the heat and petrol/oil just weakened the material...Les

[Puffs]

Ta, that I did not know. Only in '98 I got my MZ, and only after that I started to look at MZ.

Might be temperature related? Plastics are quite sensitive to that.

Of course ball bearings are assembled without cage & with all the balls on one side, so that the inner race can be placed, and then comes the cage to distribute the balls along the circumference & fixate the races. If the cage fails, the bearing fails dramatically.

[Blurredman]

Hi Guys,

I've attached my old bearings from one of the engines I have disasembled. This should clarify everything concerning the ball cage.

I really would like anyone who is re-building their engine to inspect what main bearings they have. If they don't have the attached DDR bearings then it is quite likely the engine may have already been re-built.. In which case the manufacturer identifier should be inspected.. The original bearings are actually labelled DDR.. You can take the cage out and have the bearings run sperately.

If the Nylon disintegrated into nothing (which I don't think is likely, actually) for whatever reason and all the bearings ran free, then it would be likely they would all freeze up the lack of ball roll woud rub away material on the ball and then they might fall out then when enough material is removed..

I myself have however experienced the cage being a potential issue however. On the last engine I rebuilt, one of the cages was cracked but it was still in a single piece and balls in their right place.. How long had it been like that? I don't know. I personally think it might not have been a product of a poor re-build, whereby the bearings weren't replaced. The crank had been re-built it seems with both copper shims on the one side. If it was built like that, then I also think the cage was broken by poor manhandling by whoever re-built it last. I think the two were historic poor workmanship by the last owner.
That said, I had put an extra 10,000 miles on it before MY re-build, so as above- was it a product of dodgy re-build, or did it happen naturally?

I not sure about the ETZ auto lube causing an issue, I do think that at full throttle, the pump gives a more oily ratio then the standard 50:1 that everyone was told to use with the TS's?

[nice2day]

An excellent interesting post Blurredman. Thanks for showing...Les

[Puffs]

Yes, thanks BM, yes, that does make it clearer: they are open on one side. That mitigates the concern I had on lubrication.

That cage makes assembling/disassembling easy! Move all balls down & you can pop-up the inner race.

I am suggesting that even in DDR times the MZ factory did not produce bearings themselves, but had various suppliers for that. Not necessarily only from the DDR, bearings were/are also made in Russia, Poland, Czechoslovakia, ... . So then there would be variation in the bearings they installed.

I think mine had never been apart before I got it, yet I'm quite sure I never saw bearings like that before. I once again looked in the box of old bearings I have. In this size I have 1 set without legible markings, and a few others from SKF & Koyo (all C3). All have a metal cage.

I read somewhere that the Mikuni pump delivers oil equivalent to an average premix ratio of 1:50. So with a closed throttle it'll be leaner, and with an open throttle richer.

I wasn't sure when that 1:50 recommendation came, so I browsed some more in manuals: for the ES they still recommended 1:33, and changed that to 1:50 for the earlier TS (engine: MM250/3), which incidentally still lubed the main bearings with gear oil. Also interesting to see that for both those engines they specify "6305 c 003 f (geräuscharm)" as main bearings, for both. So those are C3's, 25x62x17, while for the later MM 250/4, where lubrication of the main bearings was done by premix, the recommendation changed to the 6306 C4f.

At least that's the recommendation in German, the English manual says 6304 C4f, which is odd, as 6304's are just 20x52x15, while the 6306 ones are 30x72x19. Apparently bearings shrink when translated to English, which is of course quite a frightening process.

[Blurredman]

I wasn't sure when that 1:50 recommendation came, so I browsed some more in manuals: for the ES they still recommended 1:33, and changed that to 1:50 for the earlier TS (engine: MM250/3), which incidentally still lubed the main bearings with gear oil. Also interesting to see that for both those engines they specify "6305 c 003 f (geräuscharm)" as main bearings, for both. So those are C3's, 25x62x17, while for the later MM 250/4, where lubrication of the main bearings was done by premix, the recommendation changed to the 6306 C4f.

At least that's the recommendation in German, the English manual says 6304 C4f, which is odd, as 6304's are just 20x52x15, while the 6306 ones are 30x72x19. Apparently bearings shrink when translated to English, which is of course quite a frightening process.

Where were those English translations for the bearings from? Haynes?

It's a good thing I just replaced what was already there..

[Puffs]

Yes, that's always good idea - have a looksee what's there.

See on page 92 of the "MZ_TS250-1977-Official_Service_Manual.pdf" that it says:

6304.JPG (7.29 KiB) Viewed 48 times

In German they fit bigger ones in their Supa5.

[Blurredman]

I was looking at my spare engine in bits, and looking through the bearings. And also found this little guy.