2 stroke 50cc Rebuild

[DarrenJ]

Due to a very long story and a stupid chav trying to fraud me with PayPal I'm left with a 50cc Piaggio NRG which has the piston off with the rings snapped.
I was wondering if there is a guide on the internet on how to rebuild them, I've limited mechanical knoledge but from what I've heard not much can go wrong with them if you take your time and do it properly?

[tatters]

here you go.



https://www.poetonaptec.co.uk/technica/mpc2top.htm
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Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650,KZ750 Present:G650XC,C12,CRF450X,1190ADV

[tatters]

by the way is it a air cooled or watercooled NRG?
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Past:NRG50,AF1125(x2),NSR125RR,ZZR250,CX500,VFR400,KR1S,ZZR600(x2),CB400N,YZF1000(x2),KH125,Z200,FX400R,CBR954RR(x2)GPZ500S,GT550,VFR750F(x2),RD350N,XR650R,CBR600F,CB250,KDX250,YZF750R,CRM250,400EXC,KLR650,TTR600RE,DR350S,R100GSPD,RGV250,VMAX1200,DL650,KZ750 Present:G650XC,C12,CRF450X,1190ADV

[TomC]

As you say just take your time, it isnt difficult you should be fine.

[DarrenJ]

Air cooled.
Thank you for the link again excuse my utter newbism when it comes to engines. Ignition timings etc. is all over my head at the moment.
Am I right in thinking on a 50cc 2 stroke you place the new piston in the cylinder obiously attach it and thats it?
I've heard different stuff about ignition timing and valve clearance which confuse a sixteen year old. But I got my 125 coming when I'm 17 next month so I've got to shift the NRG.

[Kye]

Doing an NRG top end couldn't be simpler.

Assuming the bodywork is off or you have enough room to work on the engines top end...

Remove the air flow plastics (I'm assuming you've already got them off by the sounds of it)

There are 4 Nuts on the top of the cylinder, undo them in a star like pattern (i.e 1,3,2,4 not 1,2,3,4) Take the nuts completely off and place them somewhere safe.

Slide the head (top bit) off the studs and you will see the piston inside the barrel.

Undo your exhuast and take it off now if you havent already done so, and slide the barrel off the studs.

You can now see the piston, there is a pin that holds this onto the conrod, and 2 circlips (round clips) are either side of this pin in some groves to stop the pin coming out. There should be 2 little slots in the side of the piston that allow you to slide a small screwdriver in there and wedge a circlip out. Then push the pin out from the other side, which then allows you to remove the piston.

Goto the shop and get a new piston kit matched up to your old piston/barrel. This should contain a Piston, rings, grudgeon pin and circlips. You also require a top end gasket set.

Remove the base gasket from the crankcases, most should lift off fairly easily although you might need a flat head screwdriver to scrape any stuck bits off, make sure this surface is totally smooth. Repeat the same with the gasket in between the barrel and head, but this is usually an O-Ring or Metal so they don't tend to stick.

Slide the rings over the piston carefully, until they seat in their grooves.

Oil up the piston with 2 stroke on a rag, and oil the inside of the barrel up too.

Start by applying some more oil to both sides of the base gasket, this ensures it makes a proper seal. Slide it over the studs and onto the crank casings.

Fit 1 circlip into the piston whilst it is loose, then slide the grudgeon pin through the piston just until its showing on the underside of the piston, then line this up over the conrod, making sure the bearing is still in place, and slide the pin through; holding the piston in place.

Now the next fiddly bit is fitting the other circlip whilst the piston is in place, I just tend to get one half in, then force the other side down with a screwdriver wedged in the little gap in the piston that you used to get it out. Getting circlips in is very fiddly and annoying if you haven't done it before, and if you seriously deform them trying to get them in, get another pair because once they loose their tension they need replacing. You need the 12mm ones if you do happen to require replacments.

Once the circlips are in, slide the top of the barrel down over the studs until it just lines up with to top of the piston.

Now you have to make sure the ends of the rings line up with the little pins that are in the ring grooves, these hold the rings in place and stop them from rotating in the bore. Now careful lower the cylinder down with one hand, and keep pressure on the top piston ring with the other, keeping it tight and seated down enough so it will slide into the cylinder properly. Repeat for the second ring and slide the barrel all the way down to mate with the base gasket.

All the difficult parts are now done, and you can slide the head gasket and head on, and put the nuts on the studs fingertight. Then just turn the engine over by hand a few times, just to get the cylinder aligned up with the piston properly, and make sure its free.

Do up the bolts in the 1-3-2-4 pattern like you undid them, connect up your exhuast and it should fire up.

With a new piston and rings you are advised to run it in carefully, and an important thing to do whilst running it in is making sure you let it warm up properly everytime you start it before setting off, and don't hold it wide open throttle for extended periods of time, but do try to vary the revs a bit too.

If I remember correctly the exhuast manifold bolts should be 8mm, and the head nuts should be 10mm I think.

Ignition timing is all pre-set on the NRG's and they do not have valvles to set clearences or anything like that, just basically what I described.

Hope this helps,

Kyle
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Ducati 600SS
Vespa PX125

[Simonbt]

you've gotta love 2 stroke engines