High Winding Port Transmission * ADVISE *

3

340Sundancer

Member
Aug 11, 2015
33
Great Lakes
Boat Info
2005 - 340 Sundancer
Blue Hull
V-Drives
Generator
Engines
Twin 8.1 MerCruisers
Hi everyone. I need your experience and thoughts on this one....I'll keep the story short and to the point.

Last week while reversing out of the slip I had the port in reverse and the starboard in forward (spinning the boat left) and a passenger bumped the port transmission lever from the full reverse position all the way to the forward position (without stopping in neutral). During the turn, I had a little throttle on the port (reverse) side as the wind and current were stronger than normal that day. So when the port transmission lever went from full reverse to full forward (with throttle added) there was a slam sound. Grrrr!!! So after calming down, we proceeded to exit the channel and out into the bay. Getting up and on plane was normal, then after a few minutes on plane, I could tell something was off.....the RPM's were higher. I usually run at 3,200 or 3,300 RPM's at about 28-29 MPH. Now I was at 3,600+ RPM's and about 26 MPH. The boat is on plane, but it feels like the boat does not have its normal power and like your dragging a bath tub behind you........

After all the passengers left, I went out on the calm lake to diagnose. I opened the engine hatch and listened.....
* Both engines are in neutral and idling they sound perfect. Strong. Healthy.
* Starboard is neutral and throttle is applied to 2,500 RPM's the engine sounds great. Strong. Healthy.
* Starboard is in forward gear and throttle is applied to 2,500 RPM's engine and transmission sound good. Strong. Healthy.
* PORT is in NEUTRAL and throttle is applied to 2,500 RPM's the engine sounds great. Strong. Healthy.
* PORT is in forward gear and the throttle is applied to 2,500 RPM's the engine sounds good, but the transmission has a high increasingly winding sound as you increase RPM's!! When you come back to idle it goes away.

I am wondering if the transmission on the PORT side is: slipping? Bad bearing? Bent prop rod, Bent prop......etc?!?!?!?

Could this be the reason why I am running at a higher RPM with less speed? Feeling sluggish?
Secondly, I also noticed that my throttle levers are no longer even anymore. The PORT side is forward of the Starboard side by about 2 inches when @ 3,200 RPM's. (Could the slam on the port transmission during the pivot turn have an effect on the actual port throttle???)

Strangely enough (maybe to my paranoia) the wake looks different too? Possible or just me?
What are your thoughts??? The boat is scheduled to come out and go into heated storage in a month (September 30th) but what are your thoughts I should do before then? Anyone had something like this? Its very odd.......and of course I want to get it fixed before the winter....

Ugh, thanks everyone.
 
Check your running gear(but based on your story they should be clean), then onto the tranny. If this is a V drive system, they hate going through the gear range quickly(which happened) and with power applied. You might need to get into a repair. I lost a tranny on my old 340 when it was shifted from forward to reverse without hesitation in neutral by the PO. Had to rebuilt tranny for our deal to work.


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I suspect that there is some slippage within the transmission (probably caused by the event). Even though your engines are sync'd if the tranny is slipping, the props won't be sync'd which may be evident in your prop wash while on plane. Not sure how to determine if there is slippage, but have you checked the condition of the ATF in that tranny - how does it look, or how does it smell compared to the other?
 
From the description, sounds like your trans is slipping due to shifting from rev to forward with power applied instantly. I would change the oil in the gear box immediately and try again. Oh, and never let that 'friend' back on the boat.
 
Could it be as simple as changing the transmission fluid? Really? I have a mechanic coming, but anymore advise from the club would be good! Thanks!
 
Seems to me that if the transmission was slipping the engine RPM's would be higher at every given throttle position. Given the description, that doesn't seem to be happening - buy maybe I'm reading it wrong. Having to advance the throttle further to achieve the same RPM seems to indicate additional power needs to be applied to reach the same rpm as the starboard engine. To me, that points to a drive line issue (prop, shaft, engine alignment, etc) or perhaps a bearing issue in the transmission or gearbox section (there is additional drag/friction somewhere in the system).
 
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julietbravomike said:
Seems to me that if the transmission was slipping the engine RPM's would be higher at every given throttle position. Given the description, that doesn't seem to be happening - buy maybe I'm reading it wrong. Having to advance the throttle further to achieve the same RPM seems to indicate additional power needs to be applied to reach the same rpm as the starboard engine. To me, that points to a drive line issue (prop, shaft, engine alignment, etc) or perhaps a bearing issue in the transmission or gearbox section (there is additional drag/friction somewhere in the system).
Click to expand...

Hi Julietbravomike, No there is no additional drag in the system.
Yes the RPM's need to be higher just to have the same output as before the shift slam. Its very odd, but I understand the mechanics of it. I was also starting to think that it could be a filler cap seal sucking in air? Would that cause poor performance and the high pitch noise?
 
340Sundancer said:
Hi Julietbravomike, No there is no additional drag in the system.
Yes the RPM's need to be higher just to have the same output as before the shift slam. Its very odd, but I understand the mechanics of it. I was also starting to think that it could be a filler cap seal sucking in air? Would that cause poor performance and the high pitch noise?
Click to expand...

So to sync the engines at 3200 rpm you now have to advance the port throttle two inches past the starboard when before the incident they were even?

Or are you saying to get an even wake or output (from looking behind the boat) you have to advance the RPM's on the port engine to where - for example - the port is running 3400 and starboard is at 3200?

If it's the latter, then yeah, I'd agree your transmission is probably slipping.
 
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julietbravomike said:
So to sync the engines at 3200 rpm you now have to advance the port throttle two inches past the starboard when before the incident they were even?

Or are you saying to get an even wake or output (from looking behind the boat) you have to advance the RPM's on the port engine to where - for example - the port is running 3400 and starboard is at 3200?

If it's the latter, then yeah, I'd agree your transmission is probably slipping.
Click to expand...


Now after the "event" my if I am running at 3400 on both the port and starboard engines, the PORT throttle is 2 inches further up the travel than the starboard throttle. Where as before the "event" both throttles at 3400 were pretty much even (inline) with actually the starboard throttle just slightly forward of the port.

Let me know if you want further explanation.......I really appreciate it!!!
 
So after the event it's taking more engine power to make the port propeller turn the same speed as the starboard propeller. I don't think your transmission is slipping - if it was slipping the port engine would have to turn more RPM's to turn the propeller the same speed. Something is wrong, but I don't think it's that the transmission is slipping.

My advise is to check your port trans fluid and wipe a little on a white paper towel. Under some light you'll be able to see if it's full of metal particles. Not sure if your trans has a filter, but if so, now would be a good time to check it. My money is still on some other drive line issue.
Are you sure the whine wasn't there before? It could just be something simple like a bad spark plug, plug wire, etc. and your engine just needs a tune up. Bad plugs, etc. will keep an engine from developing full RPM.
 
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Recently some one in our area purchased a 39 footer with twin diesel strait shaft engines. He seems to not have had a survey of the boat's mechanical system. He took it for a sea trial and was able to get to expected speed. He said one engine smoked more than the other and the other would over rev. After a few days his mechanic said it was either a slipping transmission of a low idle bypass valve in the transmissions was not working correctly. We have not seen them since.
Does any one know if boat transmission have bypass valves for low idle?
 
Hey guys, well, I have the answer to my problem........

Today, I had a mechanic come out to diagnosis the PORT transmission issue......and well, it was as simple as a loose spark plug wire to the #3 cylinder on the port engine! This caused the port engine to work harder, and the fluctuation to the port RPM's, and the feeling of dragging a bath tub behind me. A well as having the port throttle pushed forward to achieve the same RPM as the starboard. I check this during my original look over and I did not see it. UGH! :-/

Anyways, the mechanic plugged in his laptop and we took the boat for a ride, and I have 304 hours on the engines, and only about 50 hours at high RPM's and the rest at either idle or below 1500. He said these 8.1's like to see high RPM's and basically said that I need to run at speed more often! (NO PROBLEM THERE!!) Carbon likes to build up if these engines are not run and they like to RUN! So that's my good news for the day......no repair cost, and I got to take a boat ride on a Tuesday morning!!!!!

Now onto the last month of summer before she goes into heated storage.....

Thank you all for your help, I appreciate it, and I am glad that it was nothing serious!!
 
That is fantastic news. Now you also have more money for fuel


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