I just bought a used ns12s3, bad idea. There was supposed to be a gallon on the engine but its completly out of compression and there is a very large amount of play between the crankshaft and connecting rod. Does anyone know appropriate running dimensions for the connecting rod end and crankshaft end where they meet? Should I replace the connecting rod or just the crankshaft? Would a rod from an mr12 fit? Also would it be a good idea to get the p/s squeezed or better replaced? And one last question, what size head shim does this engine normally come with stock, this guy had 7mm clearance, I am used to running 3mm.

Any help greatly appreciated.

Wow, that sucks man. I would replace the rod and get the sleeve pinched. www.rc-mushroom.com has the rods for $19. I just ordered 3 from them. I don't know exactly the size of the shim thats used but it should be just one silver shim. It's pretty thick so I think the .7mm would be about right. Someone else correct me if I'm wrong. Oh, and leave him negative feedback if you got it off ebay. Do you mind me asking how much you payed for it?

Standard crank pin should be 4.27mm. Crank should be changed when it gets to 4.23mm. Now if your crank is in between that range, most probably is conrod bushing out of measure, conrod should be changed if play is .05mm with crank, provided crank is between above measures.
I wouldn't do p/s squeeze on such a high revving engine, better change p/s.
As per head shim, standard shim for Nova based engines is 0.3mm (silver aluminum shim) which is good for running engine with up to 30% nitro, but if you are running 20% nitro you would do better with a 0.17mm shim. If you are running 25% nitro you should have a 0.21mm shim.
AFM

Just a quesion AFM. Why wouldn't you want to do a pinch on a high revving engine? I just sent out my NS5 out this week.

With the micrometric tolerances on todays high end engines, I just don't trust a process which I doubt has the exactness and quality control needed for such engines, plus your piston is allready worn out and the coating gone, they only reduce the skirts diameter but nothing is done to the piston (correct me if i'm wrong).
Sure it will work, but I just don't think it will be the same as a new p/s. Would have to try it to believe it. When you get yours back let me know how ypur engine performs. Prove me wrong.
AFM

Ok, I should get it back this week. I've sent out a modified RS12 that had extensive work to the crank and it ran really well. I'll let you know how it goes.

Thanks for the help guys.

I bought the engine off ebay for close to $140. The crank pin reads 4.15mm at the worst area and 4.20mm at the best area with my digital calipers. The conrod is 4.28-4.32mm so there is probably .15mm of play. This guy was running 2 .3mm shims and 1 .1mm shim for a total of .7mm head clearance. That is definately wrong.

Thanks for you help though guys. I guess I will need to replace a crankshaft, rod, and piston/sleeve. I could probably buy a new ns12s3 for that price since they are only like $220-230 new. No more used engines for me. I am gonna request a refund from the seller cuz this engine is complete junk, it looks good cosmetically but the guy had no clue as to what he was doing.

Just some FYI for you NS3 owners. I have a buddy that owns a Hobbytown. He tried to order a NS3 for stock. He told me that they discontinued them. And could not get any. Very interesting, considering that the engine is not that old.

os rocket is the bomb! especially since is work is now like $11 on ebay. you might just like it man....

Yup, got to running in Sunday and a little bit today. Motor is running great so far. It runs hot (about 230) but that's cause the fitment is really tight. Gonna change out the rod pretty soon.

The S-3 has not been cancelled. Nova Rossi does not have an importer right now. It used to be trinity but they droped them. So no one is importing nova. That is why no one can get them. Also .03 is the stock shim the comes with those motors. And if you keep that old motor I would be interested in the carb??

True... I got mine a week before Tower discontinued them... PHEW... That was close. I too recommend changing the p\s, it is like ~$100, Crank is like ~$45, and that would be mainly what you need, I would suggest checking the bearings... I think you may be better off selling the carb to kt racing and selling the crank case to someone else, I dont know how much they go for, but remember it is not new, so maybe half to 3/4 new price as there is not really anything that can wear on the case other than the thread, how is the thread on the case?