High Schooler Needs Da Guidance

Hey guys,

I finally picked up my first motorcycle. Actually, it’s not really a motorcycle. I bought an XS400 completely disassembled. I’ve been into motorcycles since I was in 5th grade, but quarantine and junior year of high school are not compatible. I was wondering if I could get some tips or links to manuals on how to assemble the engine. I have no clue what year it is, nor whether it’s a DOHC or SOHC, but I do know that I’m not giving up on this and I’m turning these boxes of parts into a cafe racer. Any help is greatly appreciated. Thanks!

Woof. That's a tall order. Assembling an engine from boxes that you didn't take apart can be tricky in normal circumstances.

Figuring out which engine you have should be first order of business, besides verifying that no mechanical problems were the cause for disassembly in the first place. Do you have pictures of the bike or pile of parts for us to go from? Identifying SOHC vs. DOHC is pretty easy from a variety of parts, cases, heads, or even the bike it came from would do it.

Some things to check before you get too far in are piston and cylinder wall condition, valve seat and valve condition, and tooth condition of all gears.
Are we talking completely apart? Down to absolutely individual parts? Or are assemblies (head, gear clusters, etc) still together?

Welcome, dont touch anything! haha.

The VIN will be stamped on the right side case on the top, where the oil fill is. The VIN prefix ( first 3 digits) will tell you the model and year of the bike. The frame should have a matching VIN on the steering neck.

The SOHC and DOHC look different and arent very much compatible at all. I dont know much about DOHC but I think all of them will have a YICS logo.

Is the engine assembled or apart? Get photos. Rebuilding an engine is not cheap at all.

I built my bike from the frame up using the Haynes XS400 manual.

Easy to figure which you have, just look at the valve cover. You either have a spot for 1 or a spot for 2 shafts. Dohc has a cover that has a clear separation, where sohc is just 1 lump. It also has the 4 access bolts to adjust valves whereas dohc does not.