Help! Too new to an XS to help myself

[Vintageriding]

Hi guys,

My first time posting on the forum, I recently just got my hands on a frame and engine of an unknown '400 and I'm thinking about returning it to its original state. First, the engine # reads 1MO and frame # 2L0, could someone please kindly help me with the ID of this bike?
Secondly I'm taking apart the engine since it's not running, and I notice it's missing a triangular piece of metal (supposedly sitting right behind the clutch basket). I looked it up on the schematic and some docs call it oil pump cover, while others oil guide plate, I've attached a photo showing a crank case with that piece in case you guys can't remember. But all search by those keywords came back with nothing on ebay. So my question would be what exactly is it? What does it supposed to do? Most importantly if someone happens to have a spare piece could we make a deal?

Thanks in advanced!

 

[xschris]

I am not aware of any xs400 motors with the 1mo code. The frame is either a 78e or a 79f. The build date will tell you for sure. A date of 77=78 and a 78=79. Post some pics of what you have so we can see. As for the part you can look up it's part number on the yamaha web site then google the number then see what comes up. That part is not usually missing or broken so it may be hard to find. Welcome to the forum.

 

[Vintageriding]

Thanks mate, I'll see if I still keep some photos of the engine before it was taken apart. It looks exactly the same as any XS400 engine from 78-81, but I just went through the scrap box that it came with and found a side cover with "GX400 SP" does that ring some bell?

As for the missing piece, what does it do? I'm not an expert with yamaha engines so I have no idea what it's for, and if I could live without it. I was thinking of the unconventional way to replace it with a random piece of aluminum, would that kill the machine by any chance?

 

[xschris]

I think the gx400 was the xs400 for the Japanese market. I would think that part is a baffle/splash guard for oil control on the clutch gear. I don't think they would have put it there for no reason

 

[Lupe]

1M0 was the model code for the XS250C.

The missing plate is for guiding oil to the gear box as Chris said.

 

[xschris]

1M0 must be for the German market. It's not listed in the U.K. bikes and how it got to the u.s. is another mystery

 

[Vintageriding]

1M0 was the model code for the XS250C.

The missing plate is for guiding oil to the gear box as Chris said.

Thanks Lupe, but that would be really weird... Is there any difference between the 250 and 400cc crank case except for the piston size?

 

[Lupe]

No, not German market. I found a list on the internet some time ago. Maybe Japan?
I just copied a "1M0 XS250C 1976".

Edit: The XS250 is missing in the Haynes US model list;-)

The crankcase might be not 100% the same. I am not sure. On the early XS360 the hole for the cylinders was a bit smaler than on the XS400 (see picture) and I guess on the old XS250 that might have been the same. But it is possible to remove that edge and use a 400cc cylinder.

Yamaha changed that later and all crankcases were equal.

 

[xschris]

Check to see what is stamped into the front of the cylinders. I think most xs250's had a square top end. If yours is the rounded style it could be the 391cc (400) top end. The xs250 was never offered here in the states from what I have been told and I have never seen one even on ebay.

 

[Vintageriding]

Here it is, the cylinder head is round and the stamp is 392 . The crankcase came with a 6 speed transmission. Do you guys reckon it could've been a rebuild? The I got it out of a junkyard so can't really check with the previous owner (junkyard owner).

If that is the case could it have been the crankcase swap that stopped the engine from running?

 

[xschris]

On a motor that old who knows what has been done Post a pic on the case numbers and the cylinder number. All the xs400 motors I have ever seen they all say 391cc but never 392cc. By the looks of the cases they where not from the same motor.

 

[Lupe]

The 392 on the top end is interesting. I only know the 391 as Chris wrote.
The early Yamaha documents say 392, for XS400D for example. Haynes says 392 in the front and 391 in the extra capter in the end I guess there was a measuring eror somewhere

Could you post a picture of the right crankcase cover too?