Revving Engine in Neutral

[caltrop]

Hey Guys,

I'm new, but you'll probably see me around more, most likely with silly questions. I'm a in-training aircraft mechanic (decade of handyman experience) looking to fix up my friend's '81 GS450L. Never really done automotive work before, but I like the familiarity of an air-cooled engine.

I want to check the alternator output to make sure the stator's still good. Both manuals I have and the stator papers all say rev the engine up to 5000 RPM for this, but my friend is uncomfortable doing so in neutral. I know it can be bad to rev an engine hard without any load on it, but I don't know the limits of this engine. Thoughts on what RPMs/durations one should actually worry about?

Much obliged.

[gearhead13]

The engine redlines at 9-9.5 k rpm so revving it to 5 k for a short time would be ok.
But, generally revving an unloaded engine is not a good thing.
I only took mine to 4k rpm and still got 60v+ ac.

[Larry D]

Because these are air-cooled engines, get a box fan and keep it blowing on the engine while tuning to keep it cool. No problem with revving it, we've all done it and these engines are designed to rev.

[bwringer]

Won't hurt a thing. Just don't wind it up to redline for more than 10 minutes or so.

[tkent02]

Won't hurt a thing. Just don't wind it up to redline for more than 10 minutes or so.

This.
It's not like an airplane engine.
It's not like a car engine.
Its a motorcycle engine, it's made to spin. 5,000 RPM is nothing.

You don't need a fan either, it only takes a few seconds to check the stator voltage. Nothing will get hot.

Edit, warm the engine up before revving it up to 5,000, that should make your buddy feel better about it.