Dead RD400 resurrection

[m in sc]

yeah that def looks like it was submerged at some point.  does the crank roll over?

[JBeasty]

First, throw the Haynes manual as far as you can. Then, seek and download a Yamaha repair manual and a parts manual for your year (graphics seem to be for a '77). Then, purchase a good JIS (Vessell) screwdriver before doing any more disassembly. Many of the parts mentioned are readily available (dowels, etc.) There are vendors online for many parts (Economy Cycle, Yambits, many others). You just need to do the "leg work" to find them. More major parts like the cases/covers will need ebay searching, forums searches, or finding a good welder to repair.

By the amount of rust in the oil pump cavity, I would guess that the bike has been in a flood and never drained after (in that case, the crankcase is probably full of rust, too) or left outdoors for rain water to fill the cavity - for quite some time. Remove the pump and closely inspect it. If no pitting, I would clean the outside and send it to Arrow for a rebuild. If any water made it to the crank area, it will probably need rebuilt.

Got it. I just ordered a Yamaha repair manual, and downloaded the parts catalog from this site. I'll proceed slowly with the Haynes manual. I think (hope) water got into the pump area via the cable port (the cable is broken). The points on the left side don't look near as bad.

[JBeasty]

yeah that def looks like it was submerged at some point.  does the crank roll over?

Yes, it kicks over. Drained the transmission oil and it looked dirty, but no evidence of water. The crank area remains a mystery for now...

[m in sc]

pull the jugs. its only 8 bolts. thats where the real story is.

Ive seen bikes sit in a junkyard for 20 years rusted solid in the crank but the transmissions look almost new. 

[JBeasty]

Made some progress. Doesn't look too bad. The left piston looks pretty cooked on top. No major scoring on the cylinders. Lots of gas/oil in the crankcase - maybe that's what preserved things a bit.

[JBeasty]

cylinders, head

[JBeasty]

Reed valve, intake

[JBeasty]

more...

[m in sc]

left piston was on way out at some point, almost sunroofed. (holed). note the metal errosion.    def bore, piston and crank seal time on that topend. But, not terrible overall. I also spot boysen reeds.

regarding the head, doesn't look like its been cut to correct squish, daytona heads need that on non daytona cyls, that will need to be addressed as well in the future.  .02

[JBeasty]

left piston was on way out at some point, almost sunroofed. (holed). note the metal errosion.    def bore, piston and crank seal time on that topend. But, not terrible overall. I also spot boysen reeds.

regarding the head, doesn't look like its been cut to correct squish, daytona heads need that on non daytona cyls, that will need to be addressed as well in the future.  .02

Just wanna say thanks for all your (and everyone else's) input and help. I feel like I'm not alone in this journey. 

[JBeasty]

Stupid question #x 
Are there any parts (or assemblies) I should be measuring/checking BEFORE I disassemble them, or is all that done once everything is taken apart? The Haynes manual has me pretty much taking it all apart, then has a following section on inspection and reassembly.
Also, looks like the chain broke at some point. Nice hole in the case - is this fixable?

[JBeasty]

Found another (repaired) hole! Just in front of the kick starter. How do you even get a hole there? Starting to price paired crank cases and side cases...  Also exploring repair options. Neither holes are near gasket surfaces or mounts, and the hole in the top case doesn't lead into the transmission.

[JBeasty]

Got bored (as if I didn't have enough to do) and disassembled the oil pump. Maybe economy cycle can salvage it? It will need more than just a rebuild. I'll give them a call or email with pics.

[Striker1423]

For the oil pump, contact a fella here named Arrow. You'll be glad you did. Ed Toomey can also rebuild the pump. Pick your poison. Ed's in South Carolina, Arrow's in the UK. My pump was done up brand new by Arrow and I'll sing the lad's praises 'til the cows come home.

Case holes can be welded shut.

All the seals, etc. need done. The crank would be suspect at this point as well. Lots of competent rebuilders around.

 

[m in sc]

hole near sprocket looks like a previous chain failure . agree with the rest above.