Sudden loss of power during ride; subsiquent inability to start

[xschris]

If the other motor is good just swap it out. With that bad of a failure on the currant one I would think bits of metal have made there way into other parts of it.

 

[burr]

I'm completely unsure of how "good" the second engine I have is… so far I've removed the Valve cover, the cylinder head, and cylinder and pistons from it. They all look OK, not amazing though.

the problem is the second engine I bought was stored without side caps – both the stator side and clutch side have a TON of grime on them and I don't know how many Miles was put on it at all

 

[burr]

Been reading a huge amount of rebuilding threads, and I'm ready to do it. really just wondering how you feel about swapping operating parts between engines, rather than paying machinists to do cylinder boring, etc etc

 

[xschris]

Used and worn parts with other used and worn stuff is not a good way the build a motor. If you want a good one all parts need to be specked out for wear and cleaned. New seals gaskets, bearings, rings should all be done. Also honing and valve lapping. If you just through one together with unknown stuff you will have the same results as the other motor.

 

[Jeff0133]

I sense an engine rebuild thread coming on....

 

[burr]

@Jeff0133,

As long as it has lots of pics that's ok right??

 

[Jeff0133]

Mmmm...engine porn...

 

[pbr206]

Correct me if im wrong, but dont covers need to be matched because of the factory grind on the gasket faces?

Maybe a workaround would be to grind the two donor parts to assure the same "flatness"?

Either a machine shop can do it, or buy a porcelain tile from home depot and glue 120-180 grit sandpaper to it and sand the surfaces flat. (Porcelain tile is flat to within 1/1000th of an inch)

 

[burr]

Hey @pbr206, thanks for the input. Just to clarify:

I'm planning on using the bottom end on the current bike, and mating it to the Jugs, Cyl Head, and Valve cover of the old engine. That makes only 1 mismatched face on the Frankenbike. Plus I'll be using new gaskets everywhere.

Not sure what factory grind you mean – aren't two otherwise identical engines just going to have the same gasket area?

 

[xschris]

The only matched parts on the motor are the head and rocker box. They are numbered and line bored for a cam. If your using a entire top end off one motor there shouldn't be any issues with this.

 

[pbr206]

The only matched parts on the motor are the head and rocker box. They are numbered and line bored for a cam. If your using a entire top end off one motor there shouldn't be any issues with this.

Good to know!

As for the grind, and i am just relaying tech talk, the factory typlically grinds down mating surfaces so they "pair" as mentioned by chris with the cam cover/rockers and the cylinder head. However sometimes through normal wear, an engine's shape will warp, causing the surface to not be flat thus allowing gasses to escape through holes other than the appropriate valves, resurfacing them is an attempt to get back to factory.

For example, my cylinder head had some combustion scar the surface at the edge of the cylinder/cumbustion chamber, this was probably just normal wear or it could have been minor warpage that allowed a gap to develop. The gasket kept it in check, but to remove the scarring, and increase the effectiveness of a new gasket, i DIY'd a piece of tile and resurfaced the bottom face of the cylinder head. I only needed to take off a few thousandths of an inch, worked like a charm, now we will see if it solved the problem of escaping combustion gasses.

 

[burr]

Thanks XSChris, that's comforting to know.

And pbr206 - I didn't think about warpage. Makes sense though. If this doesn't work for some reason, I'll now know the reason