NSR125 rough engine?!

[skatefreak]

Hey all,
desperatly need some ideas!
I have a spare engine for my NSR, came with the bike, the bike is the best bits of a crashed and a donor bike (suspect this spare engine was in the crash).
I have had the top end off, flywheel side and clutch side off in the past (but not split the casings), in the past the engine had been left in a garden in bin bags for a while and generally neglected.

The top end looks absoloutly fine when I took it appart though there was gunk holding the crank shaft rock solid which took a fair while with fresh oil and rocking to free up. I did see a little spot rust on surfaces in there to.

After swapping the engines in my NSR, this one runs, pretty well actually but it sounds in a bad way.

I do have a video I will upload but I cant untill I get home.

At first it sounded like the piston was running *dry* and catching on something but I have warmed it up and taken it around the block (maybe not the wisest idea) thinking that if its some of the crud that was holding the crank shaft it should clear out. It hasnt though and if it were the piston catching something I would have expected it to have demolished itself by now.

Using the old screwdriver to the ear trick I can safely say the noise is loudest around the clutch housing (bottom end, front) which would put the money on the big end bearings having degredated but the engine seems more than willing to rev and runs well without to much vibration.

All else I can think of to describe it is its loud, much louder than my other engine, almost sounds like a plane .

The piston is a generic and had no sizing/indication of which way round it should go in, i put it with the piston ring gaps facing towards the exhaust port, could the piston being the wrong way round cause this?

Any thoughts would be very very much appreciated.

Best regards

-Jvr

[P.addy]

Big end.

My RS was catching for a while, then seized solid at 20mph.

[HD]

I read somewhere that if you put the piston in the wrong way it can take just few seconds to fuck up completely. Can't remember if I read it on here.

Have you literally put this engine in and now this is happening or have you had it a while?

If you've just popped it in the it could be something to do with crash damage?
____________________
Rusty '02 Vito Camper + CBR600F3

[skatefreak]

I'v had it for ages but this is the first time i'm running it...
I was thinking it could be the piston is in backwards but i have litterally taken it around the block and it seems to run pretty well so i wouldnt expect it to be that...

i fear it may be the big end bearing

rediculously noisey though....

-Jvr

[SuzukiTom]

yeah man, time to split that motor in two! id be checking for play on big ends and main bearings as above!

to be fair if that motor has had all the sh1t in it then id replace them anyway they cost pennies and you know its done!