Hello everybody,

I am David, 31, from Germany and I started my Yamaha vintage 2 stroke path in 2018 with a '72 R5F, then completely rebuilt a RD350LC, then got a DT175MX and got it road- and dirt worthy again and now I got something really interesting to me:
I pulled out a MX175A from 1974 out of an importer's garage yesterday. All in all in a very good condition, seems to be really original and complete.
I bought it to have fun with it on classic moto cross events (and because it's absolutely beautiful and rare and I just HAD to buy it)

However, the engine is stuck and the reason is a broken crankshaft, connecting rod has seized. Looking for spare seems to be difficult, does anybody know if there are cranks from other Yamaha models that eventually fit? Or do I have to buy an after market connecting rod and let somebody press it in my broken crank? Of course I would like a new complete crankshaft  

Researching for specs and information seems to be a little bit difficult as well, so I wanted to ask if anybody knows where I can find some basic information and specs around this model. I already found something at cmsnl and ordered a service manual for this specific model year, but I feel like you can never get enough information. It also seems like these bikes were much more popular in the US than in Europe, as my bike for example was imported from California.

Really appreciate any help and hints!

I would like to share some pictures as well by the way, how can I post them in here?



 

 from near Salisbury, UK.

Just in case you didn't already know, if you select a part on CMSNL, then scroll down a little, you will see which other models used that part. You can do a similar thing on Partzilla, but there you need to look on "Product Fitment" after selecting a part.

To accurately identify your model, look up the VIN/engine number (they will have been the same originally) in the VIN table on this forum - see "Tech Library" on the top toolbar. There might also be some manuals in the Tech Library.

Regarding uploading photos, we need to use a third party host such as Imgur and, as a security measure, you need to have made about twelve posts before you can upload.

I'm sure you will, but replace the front and rear brake shoes!

New rod, pin, bearings, washers are available new from Yamaha still.  

Pretty common to rebuild the crank.   Several Yamaha models used that crank, probably won't be easy to find a complete new assembly and a used assembly probably should be rebuilt with a new rod, so might as well do yours.  

I've heard PJME in the UK does good work and not too far away from you.

Thank you very much for your help, really appreciate it! 

In the meantime actually nothing really has happened, had too much work to do towards the end of last year. At least I made it to dissemble the engine completely and I am really happy with the condition of the parts inside. Transmission and clutch basket show minimal wear only. 

And I've also done my homework and research and found the other models which shared the same rod. What still confuses me: The number on my rod is 248, in the parts list from cmsnl it's 3R2 in front. Anyway I will give it to a trusted racing shop here in Germany, he's done a very good job on replacing the standard copper head gasket with O-Rings in the cylinders of my RD350LC. Also I want to clean up the ports of the cylinder, fit a VForce 3 reed valve block with glass fibre reeds and give it a rebore to the next size, which would be 66.50 (2nd over size). 
Does anybody know where to get good quality after market pistons? I found a local dealer who bought lots of TKRJ pistons for Japanese bikes, but I've seen only pistons for the DT175MX, which I also own so I could compare those two. Actually it would fit, but I spotted three differences: The MX piston has a L-ring, the gap between the pins for the piston rings is bigger, and the transfer windows are much smaller than the DT's. Especially the last two make me think I should not try to fit a DT piston into the MX cylinder. Any opinions on that? 

It will surely take some , and hope to have it race ready for the season! And I will also upload some pictures, as soon as I am allowed to hehe. 

CMSNL have the pistons and rings in stock, but presumably their prices are too high for you? You could always try and negotiate with them.

Enduronut on this forum might also have what you need, but postage costs from the US to Europe are truly outrageous now! 

Thanks man! Indeed I felt that 185€ for piston and rings together would be a little expensive, especially for NOS while there might be better after market parts out there. Weirdly the 3rd over size would only be a little more than 100€. Maybe I should follow your advice and try to negotiate with them. 

Oh yes, postage costs are crazy at the moment. If I can I try to avoid buying anything from the US (still looking for the joint from air filter to carb, only found on eBay in the US  ) 

www.aliexpress.com/item/33035024764.html...%7C_p_origin_prod%3A

No offense RT325...  here are pictures Enduronut posted of what happened to one of those cheap aftermarket Chinese pistons almost immediately.  Ruined the cylinder when the exhaust side failed.