Can do. So I understand, what’s the reason?
Good question, made me think about why I always give this advise.
I don't have a good answer other then all the really great mechanics I've had the good fortune to work with and all the instructors at the various factory schools would say this.
After thinking about it, here are my feelings.
1. Free revving an engine provides no useful information and can only cause problems. I have had V8 automotive based engines with tuliped valves in 4 cylinders and they would still spin up over 4K RPMs.
2. I would be worried about spinning a cold engine faster then 2K RPMs. A engine won't get up to full operating temp without a load on it. It takes 10-20 minutes working under a moderate load to reach full temp. I have tried to let engines idle at the dock for 30 mins to try and shorten this time and it really doesn't help much at all.
3. Engines weren't designed to spin that fast without a load. I'm guessing combustion chamber temps and pressures are pretty low when this is done so it could affect the bearings, rings and valve train.
I know that this doesn't apply to your engine, but never free rev a 2 stroke outboard engine. These engines use roller bearings for the crankshaft and rods. Rapid acceleration of these engines will allow the rollers to "skate" on the crank. We were taught what this looked like in the O/B classes so we could instruct the customer when we came across this.
