OH Sh*t - ZF gearbox

Well i guess its time, My new to me '05 420 DA/8.1s has started a nice "clunking" sound on the port gearbox. It started last Saturday on a cruise for fathers day - sounded like a stick or something around the shaft hitting the hull.
Noticed it again as i was backing into my slip - only in reverse this time. I have had a couple of mechanics look it over - one said its normal chain/gear backlash on the ZF. The other called the bank to see if my check would clear.

He finally came to the conclusion after speaking with Marysville marine that its the dampening plant and that its worn and needs replacing that he can do in the water??
I am alittle skeptical about this and concerned that maybe there is something more going on??

It sounds like a loud "clunk" at times but at normal idle is just a "knock" - any thoughts on this oh SeaRay GODS???????

thanks
chris

Mine would sometimes do that and I was told it was dampening plates too. Can you hear or experience it beyond idle? If its only idle I think you are ok. Also, check your RPM at idle if its too low. Next, mine went away with new plugs and wires.....
Good luck.

Dampeners do fail.

Been through that before - replaced in the water on my previous boat. There is some variability about replacing in the water. Requires separating the engine and transmission - so some type of lift has be used - not every mechanic will have the lift.

I had mine done by ZF, and yes it was expensive.

Not saying conclusively that this is your issue - but it is feasible, and doing in water is ok - if the mechanic has an ability for the lift.

If that is the direction you go, make sure that re-alignment is included and a sea trial with the mechanic to confirm correct alignment.

The symptom that led me to the problem was I starting noticing particles around the transmission. Started as a fine rubber dust, then morphed into larger rubber particles.

But before I jumped into replacing a dampener - I would make sure the engine was running smooth.

My first direction would be spark plugs and maybe even new wires.

The job of the dampening is to even out the rougher bounces that occur at idle. As the engine rev's up - things even out and are smoother.

A rough running engine that may have a subtle miss - is asking for the dampener to do a bigger job.

Your problem may not be the dampener - rather how the engine is running at idle.

I have had 8.1's before (not on the dampener boat, a different one) - new spark plugs can make a huge difference.

Maybe another opinion before jumping into a dampener replacement.

I am sure there will be some folks who are much knowledgeable than I jump in case I am off base.

Mark

The flywheel has tortional coupler built into the flywheel. There are rubber parts vulcanized to the steel flywheel to dampen the shock of the engine turning the input shaft on the transmission. If those rubber "pucks" come loose, the transmission loses its cushioning from the engine. It isn't a serious problem, it isn't hard to fix and can unually be fixed in the boat, but only if there is enough room in front of the v-drive to separate it from the engine and swing it out of the way so the mechanic can get his hands in between the engine and the bell housing to do the work. It almost always requires a lifting aid (portable crane) to take the weight off the transmission, but I have seen it done with 2-3 very strong young men.

Notice that I did not use the word cheap in the above description. This is a very labor intensive repair and requires a haul out and shaft removal with a good part of the work needing 2 men.

The test for a bad coupler is to see the black debris around the vent holes on the bell housing. Unfortunately, your engines/transmissions are painted black so you probably canot see the black dust. Try wiping the bell housing with a damp paper towel to see if you can see and rubber particles.

Make absolute sure your engine has had all the typical tune up parts before diving in for the damper plate.

An ignition problem from a fouled plug or bad wire will make the sounds you refer to.....

100% agree with AO'N!
Engine performance noise gets transferred and loud speaker through the drive tranny!
Most likely not the tranny. But if it is then very confident it's the dampener plate.

The inside of the hurth drive is very very simple. It's just gears, bearings, clutch plates and ATF. Seriously if any of those failed your boat would no go!

Thanks to all the replies - I will check for debris or "dust" around the housing just to be sure. I replaced all of the plugs and wires last year and the motor sounds and acts smooth as silk. I will review all suggestions above and greatly appreciate the advise, from what i have researched these drives are pretty bullet proof.
Chris

Plugs replaced a year ago - could still be the issue. Only need one slightly fouled to start a low idle miss.

FootballFan said:

Plugs replaced a year ago - could still be the issue. Only need one slightly fouled to start a low idle miss.

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Good point thanks!!!