Right, whilst surfing Ebay one night i came across a nc30 motor that was about 20mins up the road from me and actually on my way to work, it was listed as seized but with a good gearbox and complete.

I thought this would serve 3 purposes perfectly them being -
A - i can take it in bits and teach myself how they are built etc, i can rebuild 2 stroke motors but i have never been inside a 4 stroke. As this engine was already broken i could not do any harm to it and ruin a complete motor with muppetry!

B - A good gearbox could very much come in handy for my track bike when/if 2nd goes crook on it

C - general spares, shims casings covers etc etc, all handy to have.

So i won it off eBay for less than 4 pints at my local!

Sure enough as I took it in bit it wouldn't turn over, only about half a turn, but as i began to take the heads off etc it became apparent that the motor was only refusing to turn over as one bore had a load of surface rust on the bore, I cleaned it out with a lollipop stick so as not to do any damage to the bore and some oil and eventually got it clear.

I can turn the engine over now by pushing the pistons seem ok, i have taken it completely to bits now and was wondering what to do with it next.

The bore that had the surface rust will be down on compression, now can i get it honed out get some new rings and put it back together. I know rings head gaskets and the rest will be more than a decent second hand motor, but it'd be for my trackbike. So was thinking i can clean up the inlets, lap the valves, plastiguage the shells, generally get it all refreshed and then have a motor that i know will be good for years to come with only valve clearances and oil?

Or will the damaged bore always be down on compression and make this a fruitless and pointless task. If so i will leave it in bits and use it as needed for spares.

The way I see it, if you can hone the bores and it really is nonsense / superficial surface rust you'll be A for away. If not you may need to bore it (as soon as you are through the rust layer you are hundreds again). The issue is that boring requires oversize pistons. So hopefully all that is needed is a clean up and you are good to go, otherwise plan B, new pistons and you're good, or plan C = spare parts.... that's my 2c

it seems pretty superficial, im tempted to just use some emery cloth on it and clean it up, but when i get it all back together and compression on that bore is down its all a bit of a waste of time effort and more importantly ££££ that could have been sunk into tracktime.

I didnt think you could get oversize pistons for the NC30, also i need to be careful with oversize pistons as the race rules only allow an oversize of so much, cant remember what it is off the top of my head.

What do i need to measure the bore of the cylinder?

Also anyone got any recomendations where to send it for media blasting/soda blasting? I'd like to get it back to bare metal and then seal it like that rather than powder coat it up.

The other thing you can do is have that cylinder sleeved (they bore it out, put a new lining in, and then bore it to original factory spec or at least that's what they do on cars) Again you may end up spending more money on it than a replacement would cost. To measure the bore you would need a micrometer (which I suspect is expensive). I think you should take it to a professional to measure and have a look before you make your decision.

I 'd just run a hone through the bore and see what you get. There is a bit of scope with bore-to-piston to stay within serviceable limits, so you'll probably find that it'll be good to go.

I'd just be keen to diagnose why it got rusty in the first place i.e blown head gasket or cracked head and ended up with coolant in the bore or simply left out in the rain etc. Could lead to a bigger issue, which you would want to know before you start spend $$ on it.

Yeah fair point Luke, i "think" its been left sat with no plugs in and got some water into in, it was full of oil still when i picked it up, when i drained it it wast white so it doesnt look like its been mixing its fluids.

Oh, I forgot to answer the bore measuring question. The best solution would be use a dial bore gauge, but they tend to have a fairly small range and are quite expensive, so buying one for NC30 bores, will proabably only be able to measure in the ~45-60mm range.

I think you'll get more mileage out of a set of telescopic gauges which you then take the actual measurement using standard outside micrometers:



They are a little tricker to use but once you get the hang of it, they are pretty accurate. This way you will already have the tools to measure the main bearing journals (though I also confirm my measurements with plastigauge) and any other inside diameters that you may come across.

Here are some quality bore gauges:

http://www2.mitutoyo.de/ebooks/english/ ... html#/152/

They have a set covering the 18-150mm range for 275 gbp:
http://www2.mitutoyo.de/fileadmin/user_ ... _small.pdf