Yanmar 240 reverse at 1500rpm

[Yannis]

How stupid of mine, I was leaving port at 1500 rpm and ...decided to take a turn by just reversing the port engine.
I paused at the Neutral point, but then reversed without first dropping the revs.

I heard a relatively loud "groank" type of noise, I also felt a shaking of the boat, turned my head and saw a cloud of black smoke.
Realized my stupidity but nothing else happened...I cruised in Bertram weather at cruising speed for 35nm and the following days I returned home, another 80 nm. I reversed at numerous occasions with nothing important to announce in terms of noise or engine hesitation.
My mechanic says that these transmissions have the clutch ? attached to the housing and as a result what usually happens is that instead of breaking the gears they first break the clutch. I have no idea.
Shall I remove the trans and look inside? I would sincerely hope I don't have to. Could anyone give me some advice?
Thanks.

[Charlie J]

i wouldnt worry about it
just keep a eye on it

[Carl]

I wouldn't make a habit out of doing that...but it seems like your running fine with no strange noises noticed.
So if it where me I'd leave all alone, no good can come from removing and looking inside.

If it ain't broke, don't fix it.



Maybe your mechanic said the clutch "broke" free as in the clutch slipped a little bit, like it's supposed to.

And for what its worth, I've seen quite a few guys shift at high RPM's when docking in a panic or backing down on a big catch...know of quite a few boats that have had major hits to the running gear, stalling motors while running at a good clip.
Their transmissions came through ok. They can be pretty robust.
If any concern...change out your trans fluid and have it analyzed.

[Amberjack]

Ditto the last posts. While still new to my repower set up I popped the engines out of gear at about 3000 rpm--thought I was reaching for the throttle. Panic call to the engine dealer who said not to worry about it, the ZF transmissions I have were built to take occasional abuse. That was 15 years ago.

And if you visited the Bristol Bay gill net fishery during the opening you would see much worse engine jockeying on a daily basis than you did once by accident.

[ktm_2000]

I'm going to ask the captain obvious question, Was the cloud of black smoke from the heavy load you put the motor under and not from the transmission getting beat up? aka If you go from a idle to full throttle instantly does your boat throw heavy black soot as the boat works its way up to normal cruising speeds?

[Carl]

If you get a cloud of black smoke from your transmission...you got big problems.

[Yannis]

Ktm,

The black smoke came out of the exhaust and was like a round black cloud, say, 1 meter across.
When I saw it, it was already at the level of my head (my head was on the flybridge), say, 3-4 meters from the sea surface and 3-4 meters behind the boat.
There was nothing below that cloud, just that almost round black bulb of smoke.
Considering the time that had elapsed between the shift into reverse, and my turning my head, it seemed logical to me that it was due to the momentary extreme strain I put to the engine that couldn't be compensated by its ability to suck more air for the task, hence it was black.
No, except for a few seconds of moderate black smoke during the beginning of an acceleration, my boat does not produce black soot. Moderate, because I know that on this engine I have one dripping injector, the other engine doesn't produce anything.

[Carl]

...a dripping injector can happen with age, or so I'm told.

[Yannis]

Ha, ha ! Eat bio tomato puree, it contains lycopenium!

[Tony Meola]

Yannis

We have all done it at one time or another. Not to worry. If it is running fine with no noise, I would not worry about it. That is the one advantage of having the Throttle and clutch combined. When you go from forward to reverse the engine throttles down with the shifting. But shifting too fast, and you hear a load bang and know right away that you did not stop at neutral.

[Yannis]

Tony,

My buddy handed over the helm to his gf so he could untangle some ropes, she saw a wake and got frightened, she shifted to neutral from top speed, only it was reverse...single lever on a 200 Johnson... long story short, they didn't use the boat that summer...and...very cheap too!!!

[Carl]

Then there was the time we were running out and dad saw a big log pop up right in front of the boat. He was used to his buddies twin screw boat so instead of our single, so he brought both the throttle and shifter down quick from cruise to reverse.

The good news is the boat stopped before we hit the log...the bad news is the boat wouldn't go when he put back in gear. So he lifted the drive, I saw something was wrong but could not quite put my finger on it.
Then I realized what it was, it was gone. The wheel and the shaft coming out of the drive, it sheared right off.

So we gave a honk to a passing boat and got a tow back in...from what kind of boat you might ask.

Go ahead, ask...



A 31 Bertram FBC, fighting yellow hull with Perkins diesels, the Cheetah!

[Tony Meola]

Carl

I was always told there is the possibility of sheering off the shaft if you go from forward to reverse too fast, or went from dead still to full throttle in one shot.

[Charlie J]

think we have all banged the gear a little hard
i know i have chasing the bass and bait in the heat of the moment
to get back on them, the ZFs are tough trannys

[Yannis]

A durable tranny, a durable boat...what would we do without them Charlie!

[Carl]

Carl

I was always told there is the possibility of sheering off the shaft if you go from forward to reverse too fast, or went from dead still to full throttle in one shot.

Tony- the shafts should be able to handle that kind of abuse. When choosing shafting you plug into a calculation the motor and reduction variables to find what shaft size would be adequate...then add the safety factor which is several multiples of what a shaft can handle.

What it does not account for is running a shaft that is not aligned properly, an unbalanced wheel, bent shaft, too large an overhang of prop past strut. All those I mention cause the shaft to bend slightly with each rotation. That in of itself would be okay if the whole shaft bent equally...but the shaft bends a little more at the weakest point the keyways. Then it's the old wire hanger thing when you bend it back and forth a few times in one spot till it fatigues and breaks. Everyshaft I have ever seen break either broke at the back of the prop at the key or at the transmission coupling right where the key starts.
Little side note...that is why the shaft keyways are not cut square and ending abruptly, they transition from full depth with a radius and the bottom corners are not square, but have a small filet...larger shafts over 2" also require spooning at the ends of the key...the idea is to not centralize a fatigue point...but disperse it over a larger area.

Back to my point...the shafts are made to handle the demands if the right calculations were made and with a good installation. If not, the shafts slowly fatigue with each minute bend and it's only a matter of time before it brakes. Yes it can be at a time of hard abuse...like forward to reverse, backing down, docking...but can also be on a slow speed howdy cruise.

In the case of dads boat it was a stern drive shaft that broke, when pulled they saw it was partially cracked by the telltale discoloration so when he went from forward to reverse the shaft wasn't 100% otherwise it should have been okay.

[Rawleigh]

Carl: Don't forget scored by sand or trash in the cutlass bearing!

[Yannis]

Every how often do you need to pull them for x rays?

[Carl]

Every how often do you need to pull them for x rays?

Aside from commercial I've never heard of anyone having shafts x rayed. Check them for corrosion, abnormal wear each season...if good I go.
Prior owner had my dad make him one spare shaft...if he hit he pulled the bad one out, replaced and had us straighten...it was a yearly thing for him and me too. Lots of debris in my waters, but I digress. He had boat for 12 years and my 25 years the shafts still look great. I'd use now if they were a size up.

Carl: Don't forget scored by sand or trash in the cutlass bearing!

I've seen shafts worn pretty badly at the cutless...the prize went to Sea Tow who lost the bearing rubber but kept going and going and going. By the time they brought us the shaft was worn way under 1"dia on a 1-1/4" shaft. Yeah it made some noise, they said, but we kept getting calls, so we went. Shaft still didn't break and they push, pull tow...

The worst offender of eating up bearings is mono fishing line and the new spider wire stuff...cuts grooves in short time. Still the shaft gets worn, but no sharp edges so no fatigue points to speak of...you'll get vibration for sure.

[Yannis]

Carl,

If that vibration happens when I reverse at 1500, I’d rather have them checked.
I had mine checked twice, once because I bought the boat, and another when I changed my cutlass bearings, which now I will change again after 5-6 years.
The external progressive friction is one thing. The abrupt change of direction may create other issues, like cracks, which with my vision, the light etc. I may not be able to see in my yearly inspection.

[Carl]

If your running the correct shafting, going from Forward to Reverse at 1500rpm would not have me thinking twice about the shafts integrity.

If your coupling key is brass, it should shear before any other part of the drivetrain breaks. Its why I always used and sold brass keys with shaft setups...it becomes the weakest link in the drive system. If the key goes it can be replaces inside the boat for only a few bucks.

If it gives you a piece of mind...have shaft checked. Me, as I said, I would not give it a second thought.

[Yannis]

Nice to hear, Carl, it is soothing to know that I shouldn't be worried, thanks!

[Carl]

Nice to hear, Carl, it is soothing to know that I shouldn't be worried, thanks!

No problem...I figure you gotta save where you can before your sons bills come in.