Drive shaft,Transmission noise when cold.

[highseas]

My boat which has new engine and transmission has started making rattling, noise before it warms up.Was fine first couple of months,but recently started making funny noise which lasts 15 to 30 min. when I load up prop above 1500rpm.I thought it was coming from transmission,but I now believe its coming from driveshaft.Noise dissapears and all is good after a bit.Cutlass bearing?, was apparently replaced also but not sure.It is a hurst trans.,has anyone else experienced a similar situation?Pretty sure install was done right,all looks ok,no other problems.Not ready to pull apart at this point.

[highseas]

Did I say Hurst,I meant Hurth HBW 50.Engine is Universal M3-20B,with only 250hrs. on both.Recently changed ATF with DextronIII,made no difference.Getting about 5 drops per minute through stuffing box.The rattle is accompanied by a faint slipping feeling,turn down rpm,s noise fades.After a bit dissapears altogether.Then hours of motoring causes no further noise.Sounds more like coming from further back in driveline,which is why I think it is shaft.Any ideas?

[svHyLyte]

Have you got a zink on your prop-shaft? If it has spent itself one of the screws may have come loose or separate allowing the zink to slid up and down the shaft. In reverse the water flow will push it up and away from the strut. Forward will spin it and allow it to slip back down to the strut where it can impact the strut but continue spinning. Backing off will slow/stop the spin allowing the zink to settle to/against the strut after which there is no noise.

FWIW...

s/v HyLyte

[Alan Wheeler]

A couple of possibles. First place to check is prop. Ensure it is not fouled causing cavitation. Next is the shaft play in the bearing. These are least likely due to the noise going away, but easiest to do so worth looking. Next is the shaft coupler to transmission. Lastly is the dampner plate. This is the most likely and quite common. It is a plate that is mounted between gearbox and engine that couples the two together. This plate has springs around it's outside and it's job is to take the "injector shock" out of the drive train. These plates fail and cause the issue you describe. Eventually it will fail and you will have no drive, providing that is the issue. You have to split the box away from the engine to get at it.

[highseas]

Replaced zinc 3 months ago on shaft,no strut on hull,only about 6 or 8 inches of exposed shaft.I tightened,hammered and retightened.When I tried to move shaft side to side there was maybe a sixteenth inch of play.Maybe after breakin period I need to realign,not sure though.Like I say after a 15 min. noise goes,even if I shut down motor for a bit.I think it may be slowly getting more regular,makes me not want to go too far from homeport.Seems to want to clear up sooner when I rev engine up to cruising rpm and down again briefly a couple of times.then all of asudden its gone.

[highseas]

Hi Allan,thanks for your advice.I think you may be right about Dampner plate,not to happy about it but it sounds like most likely scenario.Boat sat for a year or so,which may have introduced problem according to Hurth manual.Sounds like an off season project for me.Hopefully it lasts till end of our sailing season in the PNW.

[Whimsical]

Originally Posted by highseas

no strut on hull,only about 6 or 8 inches of exposed shaft.

Slight thread drift.
Nothing to do with the noise but I gather there is nothing supporting that 6-8 inches of shaft. AFAIK the shaft should only stick out about 1.5 times the diameter so for a 1.5 inch shaft about 2 inches

Mike

[highseas]

Its more like 3 to 4 in.,enough room for zinc,(2 in.),plus an inch or so .I dont think that amount requires a strut or it would have one.I think Allan is right about Dampner plate,tranny has to come out.

[highseas]

Still a mystery; dampner plate checks out o.k..Pulled tranny,all looks good,brand new looking, no rust.Still have the rattle,not sure but have feeling may be bad bearing in trannyHow can I explain this noise?when you speed up from idle to above 1500 rpm,under load,it starts,sort of a rattling ringing sound,possibly slight slipping sensation,drop Rpm ,down noise dissapears.Cruise at slow speerd for 15 or 20 min.then boost revs up and down a few times,noise sounds harsh then suddenly stops,drive full speed rest of day ,no problem.Next day,engine cold, same thing.Now I am thinking cutlass bearing ,although when you spin shaft by hand seems smooth.Or worse a not fully engaging mechanism inside trans.Its almost like when it warms up something occurs to make full engagement.Noise only happens in gear under load.Now I will reinstall trans. and try to drive it till it breaks,Or should I send barely broken in unit(now 260hrs on engine\trans.) back to Hurth in Florida for analysis?

[highseas]

Do I have a bearing on shaft?Is the cutlass bearing on the strut? if so I guess it isnt cutlass bearing,as I have no strut.Could this sort of noise originate in stuffing box?I have an idea it is possibly a skipping tooth sound(clutch plates),just not sure.

[GordMay]

MP3 ?
A Stethoscope or an MP3 player (with built-in microphone) could help identify the exact source and character of the noise.

While stethoscopes can cost anywhere from $200 for a standard type to more than $500 for electronic and digital models, small MP3 players cost about $90.
With an MP3 device, sounds can be recorded and filed for future comparison. MP3 files could also be transmitted over the phone or via the internet, allowing distant experts to help analyze a problem in a remote setting.

[never monday]

Originally Posted by highseas

Its more like 3 to 4 in.,enough room for zinc,(2 in.),plus an inch or so .I dont think that amount requires a strut or it would have one.I think Allan is right about Dampner plate,tranny has to come out.

3-4" is still to much. This can induce shaft whip at the unsupported end.

You still have a bearing. it's in the hull where the shaft comes out.

When was the repower done? how old is the engine? not in terms of engine hours, but purchase date?

[GordMay]

Originally Posted by never monday

3-4" is still to much. This can induce shaft whip at the unsupported end.
You still have a bearing. it's in the hull where the shaft comes out...

See dimension 'D".

[highseas]

Purchase date I believe is around 2001,previous owner put 120 hrs on engine/trans.Boat sat at dock,as liveaboard,with regular haulouts till now.Noise started at 240 hrs,now at 260.Engine is Universal M3-20B,trans. is ZF5M(no longer listed on ZF website?)(A=2.05,B=1.86)Professionally installed.Waiting to talk to installer to see what they say.I feel maybe it is to light duty for 20,000 lb. boat,Specs. dont cover ZF 5,but must be same as ZF6,as ratios are same.When boat was hauled in June I spun shaft at prop ,it was smooth,no play.If it was shaft whip why did it not do it first 2 months I used boat?,(lots of motoring).Not sure if prop can go further forward due to clearance issues.A ringing rattle that dissapears leads me to believe it is internal.

[highseas]

Trans. is stamped 2001,install was 2003 I think.Will find out after long weekend.Thanks.