Screw (prop) keeps turning

[rebel heart]

I hadn't fired up my engine in a few weeks, so I fired up my Yanmar 4JH2 (52 hp / non turbo / installed in 2000 new). I was checking all my levels, and am happy to report that oil pressure, engine temp, and coolant levels are all fine. I'm sitting in the cabin right now as I let it run for another hour or two.

I'm ashamed to admit it, but while poking around looking at my fuel filters (dual racor 500's), I notice the shaft spinning ever so slightly. Something I should have id'd long ago to establish whether this is common or abnormal. I'd estimate maybe 1 revolution every 30 seconds or so, and it's timed with the engine. Rev up, and it spins faster. This is in nuetral.

I put it in gear, then gave forward throttle. Boat goes forward.

I put it in gear, then give reverse throttle. Boat goes backwards.

This is normal for me to have a bit of constant motion on the shaft, even when I'm not in gear?

[David M]

Hey rebel...
Depends...some trannys I have seen do this. My guess is it has something to do with the viscosity of the tranny oil spinning oil from the engine side to the shaft side although the clutch is in neutral...similar to what an automatic transmission does. Does gripping the shaft (safely) stop the turning? I have never seen anyone in the know worry about it. If it seems a concern you could always call the manufacturer to see if this is normal.

[SkiprJohn]

Aloha Rebel,

My Velvet Drive trans have always done it. Both boats had Velvet Drives. Both did it.

Kind Regards,

JohnL

[Alan Wheeler]

Yep they will turn. No worries, it is normal. However, you should have the thing in gear when warming up anyway. I place you on detention. Punishment is go to the StudyHall and read about warming up the engine. :-)

[never monday]

Originally Posted by Alan Wheeler

Yep they will turn. No worries, it is normal. However, you should have the thing in gear when warming up anyway. I place you on detention. Punishment is go to the StudyHall and read about warming up the engine. :-)

detention isn't good enough for this felon.

Double Secret Probation for you sir.

Next time you abuse your engine this way, put it in gear and pull on the ropes.
This will stop the freewheeling that is normal and give the engine a healthy workout.

[David M]

One practical problem with warming up your engine while in gear...the wash and your neighbors. I guess it really depends on the size of your screws. My 24"x24"s wreak havoc. The guy behind me in the little sailboat probably has a 4 knots of current (close to hull speed) under his boat when I do that! (I am stern in to the dock)

I would probably end up in detention FOR doing that!

In all practicality, I let my engines fully warm up after getting out of the marina at just above an idle before going full ahead.

[rebel heart]

Well, I do put it in gear (forward and reverse) for a bit to get it to temperature, but then I put it back in nuetral and it manages to keep the temperature from that point onwards.

The whole idea of "having load on it" is for the temp, right?

[Alan Wheeler]

Even if you can let it run at low revs while engaged in gear is better than nothing, ONLY if you are tied to the dock. But if you are intending to head out, then don't pre warm the engine. Simply get ready to go, start and then throw off the lines and motor. You won't be doing any great speed out the marina, so that is a good initial warming, then once you get out, you can start to place some load on it. Not full throttle, you do have to be sensible about it.

[Alan Wheeler]

The whole idea of "having load on it" is for the temp, right?

No it is to stop your bores from glazing up.

[stevensc]

A turning shaft is very dangerous! They love to grab and wrap loose clothing or long hair depending on how fast they are turning can rip your sleeves or pants legs right off with your arm or leg sill in them. This includes shafts while not powered but freewheeling while sailing or drifting. Don't get near them if they are turning even slowly!
Steve

[SkiprJohn]

Steve,
My propshaft will stop turning with hand pressure while in neutral.
JohnL

[Celestialsailor]

I have a 4JH also...It is older than your rated at 44hp. Great engine. Yes, it does slowly spin when cold and very slow when warmed up. My other engines did it too. A Volvo 2003(junk), and Westerbeke 4-107(the leaky legend). It is nothing to worry about. As Skiperjohn pointed out, they can be stopped by hand. Although my 4-107 had a paragon trans and if not adjusted perfectly it could spin uncomfortably fast.
Perhaps this could lead to a thread about sailing in gear or free spinning. I think that depends on tranny design. Anyone want to touch that one?

[rebel heart]

I checked my 4JH2 manual and it told me to sail with it in nuetral. Which is great, because I had been doing it for a year before I bothered to check the manual. Fortune favors the foolish.

[Celestialsailor]

See...There you go. I have not read the manual. I just do not seem to have that gene. Im not sure if it is bad to sail with it in gear. I doubt it. I do know with some hydralic trannies, it is suggested not to let the screw free wheel. Mostly I let mine free wheel unless I hear a whine, then I put it in gear. Seems to me though that free wheeling would be less drag. Interesting topic I think.

[SkiprJohn]

If you do a bit of search on this forum you'll find the big discussion on "free wheeling" vs "in gear" controversy and how it effects the life of tranny and speed. The Velvet Drive folks have come to the conlusion that it doesn't hurt to have it free wheel. I'm not certain of the other trans makers.
JohnL