Rust - How far gone is too far gone?

Long story, short - I impulse bought a partial NU50 engine on eBay last year after I bought my NU50. The original intent was just to have it for spare parts, and maybe just getting used to taking an NU50 engine apart. I just tore into it for the first time a couple of weeks ago, and holy rust.

I thought I would take a shot at cleaning up some of the parts with Evapo-Rust and see what happened. To be fair, Evapo-Rust has done a pretty good job at getting rid of the rust. However, there seems to be a lot of pitting from the amount of rust that has built up over time. That makes me wonder, are these parts even usable at this point? I would guess that the pitting isn't a huge deal on the kickstart gears/shafts/etc., but what about on the drive faces, drive boss, and clutch bell? Is there a good way to smooth out these surfaces, or is it even worth the effort?

There are other parts with an equal amount of rust, but I haven't started working on them yet. I guess if nothing else, taking things apart will be good practice before I work on my bike.





Re: Rust - How far gone is too far gone?

its fine

Re: Rust - How far gone is too far gone?

Rust, scarring, pitting and scratches are part of the well earned patina of a old bike. Most of it seems to be just surface blemishes so just make sure the technical surfaces (gear teeth, splines, rubbing surfaces, etc) are still serviceable and within tolerances.

The parts in your pictures look to be good for service.

Re: Rust - How far gone is too far gone?

Jack Rutherford /

Usually the rear pulley is the problem area. Any pics? I've been able to sand it back to relative smoothness.

Re: Rust - How far gone is too far gone?

It's good to hear that these parts should be of some use. The teeth on the gears seem to be OK. Some of the surfaces on other parts might need some light sanding or other work down the road.

The rear pulley will be interesting once I get everything apart. I had to order a socket so I can remove the big nut (I used to have one but must have lost or sold it at some point), but there's clearly a decent amount of rust back there too.


The flywheel had its own rust, but I was able to get most of it to go away too.


Re: Rust - How far gone is too far gone?

Jack Rutherford /

Evaporust did a nice job. Pitting from the rust in the rear pulley where the belt runs will be what to look out for. I've taken the pulley halves to a belt sander and got a pretty good surface to use out of it. You can get a new GY6 clutch for $30ish as well.

Re: Rust - How far gone is too far gone?

The socket that I ordered should be here on Friday. I'll post some pictures when I see what I am getting into. Luckily, all of this is just on my spare engine. I am crossing my fingers that the engine on my running bike will be better when I get into it...but I did pick up a new GY6 clutch in my order from treats last year.

Re: Rust - How far gone is too far gone?

As promised, here is what the rear pulley looks like on my spare engine.


I also started taking apart the running engine on my NU50 today so I can get it cleaned up. I already got the big gear off the crankshaft, now I just have to get the seals swapped out and the the gear back on. Overall, the parts from the running engine have much less rust and have been easier to clean up.


Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account