MZ 175/2 ES - connecting rod problem

[matzika]

Hello everyone,

I recently bought an MZ 175/2 ES, and the connecting rod needed a replacement after engine disassembly. Since I couldn't find any ES connecting rods in the online stores (MZ-B, ost2rad), I've researched and found that connecting rods are the same for ES and TS, and I ordered TS 250 connecting rod from MZ-B.

After the delivery, I've seen that they are not compatible. In the picture below, you can see the difference (the right one is the original ES, left one is the new one for the TS 250), as the big end on the ES is narrower and the small end for the piston pin is a bit wider compared to the TS 250.

Since I couldn't find any info on the internet that ES and TS have differences regarding the connecting rods, I'd like to get some additional information if someone here has some experience regarding it, and also could provide me with where I could get one that would fit for my ES.



The TS have a serial number 43.008, mine for ES has 43.095.

Thanks.

[Blurredman]

I wonder if there is a difference in conrod between the earlier 4 speed and the later 5 speed. Certainly the crankshaft itself is different according to on-line sources, but coming accross your prediciment I wonder if the reason is due to the conrod. However, 4 speed models take 6305 main bearings, and 5 speed has 6304 size.

[matzika]

I've come to an interesting finding, and that's that the big end size of the ES conrod is actually a bit narrower than the needle bearing, so the needle bearing sticks out of it (bearing size is 28x35x20), and an interesting thing came that the conrod from the TS 250 has the exact same bearing size, meaning that they are the same size, but the conrod is just of the same width as the bearing. Also, the small end of the ES has the exact same width as the bearing, but the TS conrod is a bit narrower and the bearing sticks out a bit, and they are again of the exact same size. This all should mean that in the end, they are the exact same, but visually you could get confused, as I did.

The ES had no washer/distances on both sides on the big end, so I'm just gonna do the same with the TS conrod, install it without them, and it should be just fine.

[Blurredman]

Ah yes, I forgot. You mentioning that reminded me.

The ES's conrod is centralised by the piston. The TS (5 speed i'm guessing) onwards the conrod is centralised by the crankshaft! I also was confused with the gap either side of my ES when I rebuilt the engine and then came to that realisation with help from others when comparing to later design.

[matzika]

Thanks Blurredman for confirming my assumption regarding this. I was really confused at first, but luckily the situation is now resolved.

[Blurredman]

That's okay. Of course, What you say makes sense about the conrod being fine to use considering the constraint is now at the bottom instead of the top (and that's probably better in itself anyway). But i'm unsure whether I would try it myself- make sure the new conrod has similar oil passeges etc to the old one too! Good luck!