Twin Disc 502 - Noise in forward and reverse

[JC]

Have TD 502MG attached to Cummins 250HP 1.5 gear ratio. Had trouble with the gear while backing down at the dock... the gear started making this metal grinding sound.... So I stoped the engine and checked for fluids etc..... Everyting looked OK. No noise in neutral.

After some thought I then decided to deatach coupling and shaft and test without shaft attached. The sound improved but I think could still hear some sound.

So I needed to decide what to do. I dont know anyone in my country with good knowledge about Marine Gears so I read me the service manual and decided to take the gear out of the boat for dissasembly. I already took gear out of the boat and split the transmission apart. The forward and reverse shaft assemblies look fine. The bearings and all the gears look good. So then it was time to pull the output shaft from the rear case. It was hard to take out the bolt and the coupling but I was able to do it and took out the coupling with an extractor. Now I am at the last part and am having difficulties. I want to pull the shaft and gear (all in one) from the rear tapered roller bearing) but I cant do so. What I want to do is check that last bearing to make sure it is OK. For some reason I smell burt oil smell in that portion of the gear. I have made a tool like is in the manual to try and pull the shaft out of the roller bearing but as hard as I try it seems to be stuck. Am i Doing something wrong?? Help Please!!!

Could it be something else?? Cutlass Bearing?? Damper PLate?? I posted on Boatdiesel forum but sometimes it takes a long time there to get an answer and I would like to get to the problem as soon as possible in case I need to ship a replacement part.

Thanks,

JC

[AndreF]

Good luck, JC.
I have the same set-up in my boat.
Keep us posted......

[Dave Kosh R.I.P.]

JC , Have you called a Twin disc dealer? They will usually tell you how to do it over the phone if you expalin your situation. After all they would want to sell you parts . I know it's a long distance phone call but your down right now. I also have the MG502's , 2-1 gears with Volvo 250 HP's.
Dave K

[Bruce]

JC,
I use a press for shafts and bearings and don't have a problem. A portable screw type bearing puller can be very tough to remove items.

Unless you see a bearing cage that came apart or a galled roller, doubt thats where the noise was.

I would look at the damper plate first. There should be no play.

I take it before you yanked the gear down that you did not check for gear wear and backlash both of which can create quit a bit of noise but not be a major problem.

Cutlass won't make a sound like that unless theres no rubber left and the shaft is laying on the outer shell.

Heavy metalic sounds in gear boxes leave pieces of metal laying around for you to find easily. Not hearing the sound myself, I can't comment how bad your sound was.

[JC]

Hi all. Thanks for the very usefull information. This is my situation at the moment.....

I have the case open with forward, reverse and output assemblies out.... everything is cleaned up.. did find tiny ground up pieces of metal trapped in the screen and inside of the case but I cant say it was alot of volume....Probably from normal clutch plates when changing gears fighting marlin etc....

The rear output shaft bearing looked ok to the eye but I decided to get a replacement now that it is out because I did have to put allot of pressure to pull out and am afraid some damage could have been done... one "snap piston type ring" on the reverse clutch was broken but it could have happened at dissasembly...


So now I am at the point where I will reassemble and start looking somewhere else...

Bruce I have been told now by 3 differente persons to look at the torsional coupling... Here is a pic...

What should I llok for?? How does it work???




Thank you for taking of your time to help someone in need!!!!

JC

[Harry Babb]

JC
Take a good look at the drive plate. I see a shiney area.........a diameter slightly smaller than the springs.............something could be rubbing

Check the Crankshaft endplay..........if its excessive the drive plate may be rubbing a bolt head on the gear ???????

I recently disassembled a 6BTA and found that one of the flanges on the thrust bearing had fallen off of the bearing itself..............crankshaft endplay was WELL in the excess of 1/8".........not good.

Harry Babb

[JC]

Thanks Harry. Good observation. I hadnt really payed attention to that but now that you say it I can also see it... My boat is an hour away so I will check when I get there. I have never gotteh this far "into" the engine. Normally I have only had to do minor stuff like changing filters, impellers, starting motor etc... How do I measure endplay at the crank shaft?? What would be a cause for this?? Why would the noise be audible only when "in gear"???

One thing that I am trying to relate when putting pieces together is that the same engine Ive had this issue with I was troubleshooting at the time this happened. My problem was that the engine once hot was hard to start and stalled when going from forward to reverse...

If the engine was cold it would fire right up... but after engine warmed up and being used for a while if I would go to idle and then into reverse the engine would stall. When I engaged the starter motor I had to advance the throttle to get the engine to start or it would take a longer time...

Could this be related???

JC

[Harry Babb]

JC
I do not know if there is any relationship between the noise and hard starting and stalling when the engine is hot.

To measure the Crankshaft endplay you will need a "Dial Indicator". What you do is mount the "indicator base" on the engine flywheel housing and put the stylus on the flywheel itself, then use a pry bar to gently pull the harmonic balancer all the way in one direction and ZERO out the indicator. Then use the prybar to gently move the harmonic balancer in the other direction and take the reading on the indicator dial. The end play should be .004" minimum to .017 maximum.

The pic that you posted looks odd to me. The drive plate should be flat. It looks "bulged" to me..........it could possibly just be something with the pic

I have a real interest in following this post and finding the problem since I found one thrust flange completely missing from the main bearing and laying in the bottom of the oil pan on one engine that I am rebuilding and there was a definate problem with the drive flange.

Harry Babb