First time engine rebuild

[DB90]

So, I acquired a large amount of XS parts a while back and in that bunch of parts is what I believe to be a 78 basket case motor. The heads, jugs, pistons, cam chain, and cam chain guides have already been taken off. I know absolutely zero history about this motor. Judging by the condition of the pistons, they appear to be scorched like they got really really hot, I think this was taken apart for a top end rebuild but I don't know for certain.

I figured that this would be a good motor to learn how to work on these motors more in depth. I have zero experience with rebuilding motors. The extent of my knowledge ends at adjusting timing, points gaps and dialing in carburetors.

I know, before anyone says it that I need a manual which should be ordered within the next couple days. Suggestions on which manual is superior are welcomed!

So with all that said, what do y'all think my starting point should be? Should I dig into the bottom end and see if there are problems there before just doing a top end? I kind of figured since it's already almost all apart anyways that I might as well.

What do you gurus think?

I will post some pics this evening.

 

[MrBultaco]

Build or buy an engine stand...

 

[DB90]

Build or buy an engine stand...

Already on it!

 

[Jim]

The bottom end can be checked out without disassembly pretty well. I wouldn't disassemble it unless you do run across a problem or an unknown. First thing I'd check is the copper cladding inside the con rod little ends. Give us some good pics of 'em.

I like the Yamaha book better than the rest of 'em... cept it don't go into great detail for engine rebuilds. It covers it, just not as thoroughly as it could.
For that, look on Amazon for an XS650 engine book by Hans Pahl.
Edit: found it. https://www.amazon.com/Yamaha-XS650-Engine-Including-Electric-ebook/dp/B071W5SSPY

Also, for just the top end, some yahoo here wrote a thread on putting 'em together. It's in Tech. I've never used it, so I can't vouch for how good it is...
https://www.xs650.com/threads/xs650-top-end-buildup.52041/

 

[Jim]

Unless you really want a hard copy, the Yamaha manual is available on PDF.

 

[DB90]

The bottom end can be checked out without disassembly pretty well. I wouldn't disassemble it unless you do run across a problem or an unknown. First thing I'd check is the copper cladding inside the con rod little ends. Give us some good pics of 'em.

I like the Yamaha book better than the rest of 'em... cept it don't go into great detail for engine rebuilds. It covers it, just not as thoroughly as it could.
For that, look on Amazon for an XS650 engine book by Hans Pahl.
Edit: found it. https://www.amazon.com/Yamaha-XS650-Engine-Including-Electric-ebook/dp/B071W5SSPY

Also, for just the top end, some yahoo here wrote a thread on putting 'em together. It's in Tech. I've never used it, so I can't vouch for how good it is...
https://www.xs650.com/threads/xs650-top-end-buildup.52041/

Thanks Jim! I'll get some pictures of the con rod small ends!

I downloaded the Hans book on Kindle just now. Great info in there! I'll definitely be buying the hard copy!

I'll download the PDF but I really enjoy having the hard copies. I love sitting down in the shop and just reading through them.

 

[Jim]

I love sitting down in the shop and just reading through them.

Me too.... gearhead!

 

[DB90]

First thing I'd check is the copper cladding inside the con rod little ends. Give us some good pics of 'em.

To my eye they appear to not be damaged but they are rusty.

My second image won't upload but it looks almost identical to the one in the image

 

[Dunc]

Replace em!

 

[Raymond]

That little end don't look happy. Shade tree test, just for fun, if you push a gudgeon pin/wrist pin in it should be a very close sliding fit. But if you can wiggle the ends of the pin up and down it's boogered.

Come to that, if you can feel roughness with a finger tip on the bearing surface, it's boogered.

 

[DB90]

Replace em!

Dang! I was hoping that wouldn't be the case Wheres a good source for them?

 

[Raymond]

Others are far more expert than me, but I think it might be easiest to find a crank with better conrods - might be cheaper and easier than buying new conrods and rebuilding/having the crankshaft rebuilt.

 

[DB90]

Others are far more expert than me, but I think it might be easiest to find a crank with better conrods - might be cheaper and easier than buying new conrods and rebuilding/having the crankshaft rebuilt.

Yeah I had that thought. The hunt begins! Lol

 

[MrBultaco]

Someone had 2 cranks for sale a few days ago...free. iirc. See classifies

EDIT: https://www.xs650.com/threads/cranks-for-sale-free.65471/

 

[DB90]

Someone had 2 cranks for sale a few days ago...free. iirc. See classifies

EDIT: https://www.xs650.com/threads/cranks-for-sale-free.65471/

Awesome! Just messaged about them. So now, how do I identify if they are right for my motor? I know there are some differences between the 447 and the others but how do I know which one I have?

 

[Jim]

So now, how do I identify if they are right for my motor?

Any crank from a 447 motor should work. Look for a 447 casting stamp somewhere on it... usually on the con rods iirc.

 

[DB90]

Any crank from a 447 motor should work. Look for a 447 casting stamp somewhere on it... usually on the con rods iirc.


View attachment 259316

Awesome! Thanks Jim!

 

[DB90]

So I was digging into the head on this motor. Taking everything out so I can get the whole motor vapor blasted. I came across what looks like a poor attempt at porting.

Pretty sure the valve seats need recut and the valves replaced. The angles on the valve seem kind of concave which I'm pretty sure in no bueno.