GN125 Top End

[deadly_penguin]

So a few months back, I started getting a nasty sporadic top-end rattle. Turns out the drive gear on the oil pump had disintegrated, so I took it in to a local garage who flushed the motor and stuck on a replacement gear, and the noise went away for a few weeks.

The same noise came back, but constantly - so I popped off the crankcase cover to check the oil pump gear, which was fine, and then popped the head cover and found the rockers and camshaft were toast.
I replaced those, and it's still rattling;
I've not checked oil flow properly yet (there's a chance a bit of drive-dear is blocking an oilway, or the gauze in the sump is blocked) but I can see ~some in the well in the head with the valve caps off.

At this point I'm considering either a new head or just getting a second-hand chinese-branded lump and having done.

[WD Forte]

I'll assume it doesn't have an oil light so who knows how long
it was suffering and what other damage and excess wear was done?

I'd want to cut my losses in money and time
and look for a decent SH lump.

I can't recall the Chinese designation of the Gn125 lump
FMI125 or summat like that I expect so a bit of research will
give you list of bikes that use it.
You may even find a pukka Suzuki one for a good price.

then you can just bung it in and ride like the wind!!!
____________________
bikers smell of wee

[ThunderGuts]

Can you drop the oil and shine a light up at the gauze through the plug hole? Unsure of the position of it on that bike, but on my C90 you can see if there's crud on it that way. Might give an indication of crap in the oil if you can get line of sight to it.

In terms of where to go, depends how much time you want to invest. Chinesium heads will probably be OK, but unlikely to last as well. OEM heads - are they obtainable? Likely to be expensive. Either way that assumes the problem is either in the head and/or you're going to be able to identify and resolve any other issues. If you can't easily suss the issue, I'd be tempted to try and find a s/h engine somewhere. Alternatively, if you do want to go for a Chinese engine, again going off my C90 experience, see if you can get a Chinese clone but fit the carb from your bike - they're usually much higher quality than the Chinese ones and will make setting the engine up much easier. This obviously is only going to work if the engine is a clone though!

Rattling generally suggests movement where there shouldn't be any, either something loose or something worn. It sounds probable it's the latter, whether due to oil starvation or accelerated wear from the previous incidents.
____________________
TG.

[B1N]

Is this the same engine?
https://www.ebay.co.uk/itm/154981995348?hash=item2415a59354:g:HLQAAOSwZ21idQaL

[deadly_penguin]

[ThunderGuts]