Engine has sat idle for 3 years, still good to go?
 

I haven't been on this site for about 3 years.

A few weeks ago I dug up my old HPI R40 with a JP Modified RS12 (black with purple heatsink).

The last time I ran this was maybe 6 years ago. If I remember correctly, I ran the car and just stored it (without any AR oil, yes, rookie move).

What are the chances that this engine is still in good shape?

Just undo the rear plate and take a look on the crankschaft and bearings if you can see rust. Only some surface spots is OK.

Can you turn it over by hand? Does it feel gummy or frozen solid? If it turns freely, put some fuel in and fire it up. If it's either of the last two, it's time for engine disassembly 101:nod:

I wouldnt just fire it up...
 

Open it up, check carby and backplate seals are not dried out and cracked. Use after run or whatever you use, lubricate and clean and inspect and lube bearings. It's aluminium and it will be oxidised and you dont want the oxide running through your engine.

I had an engine, actually 2 that sat for 2 years roughly and only had some after run in them. They turned nicely by hand and I fired them up. It took some readjustment of the needles to get them back to normal but no problems.

like these other guys said, disassemble and make sure the bearings are looking good. I just had to rebuild several engines that were sitting for 10 or so years un-oiled.

The front bearing is the hardest to clean up without removing it from the block. Make sure it is free spinning. If you start it up and it makes a loud squealing sound the front bearing is probably seized up.

fuel is good at loosening up old gummed up castor. rinse the bearings out with fuel and see if they free up.

yes, I did that for an O.S. engine from 1985 last winter and it worked fine after some basic cleaning. It has worked fine since whenever I have fired her up.