Technodrive TM170 TM880A, TwinDisk engaging failure, low hours

[vas]

Re: port gearbox works only on reverse

On the first of your pics on post 70, the groove you can see in the middle of the circumference of the shaft, with the circular hole in it, that is the groove that fills with oil, transferring pressure to the clutch pack via that hole and down the centre of the shaft. It is fed oil via the outer casting that you have unbolted, from the control valve. It's a groove so the feed of oil is continuous as the shaft turns. Ahead and astern of that oil groove as kevb says above you can see a difference in the surface of the shaft- a ring- these are the worn down to flush piston rings. They are made of a different material prob cast iron, hence the different texture. Incidentally, the astern shaft doesn't look too clever either! Have a look at the other gearbox to compare. Here's a random Google image showing what you should have, without the rings in place
http://i.ebayimg.com/images/i/261633908672-0-1/s-l1000.jpg

Thanks NU, however having examined carefully and measured the distances and worn marks, it is definite that there was NOTHING in the two narrow grooves. All the marks are from wobbly axle touching as it's been pushed offset from the gear (most likely due to wrong preload).

A labyrinth seal works on the principle of pressure drops and flow across a restriction. As the oil floes through the restricted area its pressure drops. So by creating some zones with grooves the flow speed reduces and the pressure momentarily increases, creating a back pressure to the preceding restriction, the sequence repeats and the pressure drop is controlled effectively.

Was widely used to sealing the high pressure side of steam turbines to prevent the steam pressure blowing the oil out of the bearings amongst other engineering devices.

OK, SH this matches the scores on the cast iron bit.

Discussed it with machinist, Vangelis is not particularly happy as it's a tough job creating a properly balanced "base" plate, bolting the casting on it and making it true on the lathe. Then he'll use some bronze alloy for the ring, heat press fit et al. Doubt it's going to be extremely cheap but curious to see if the stbrd box has similar wear on the other shaft (opposite rotation props obviously, so the astern forces go to the other side...)

Wonder if/where I can try and source this part (maybe keep on in stock in case of a failure on the move as it's only going to be half an hour to replace)

Also seriously considering swapping the set of diverter valve/cover assemblies from port to stbrd so that the untouched and unharmed bits go from the reverse to ahead axles
Should keep the system running a bit longer.

Finally, I'm curious if this is a recurring fault of these boxes or a plain coinsidence that the service manual for the 170 shows a rebuilting of the box with replacing the diverter body only (only the part that is worn on mine!)

cheers

V.

 

[superheat6k]

Re: port gearbox works only on reverse

I would surmise that the taper roller bearings were not correctly pre-loaded with the assembly shims, so likely an error from original manufacture. If correctly set up these boxes will run forever (in pleasure boat terms).

For a fix this is a job for someone with a jig borer, or possibly a decent mill.

The fix I would consider would be ...

Obtain a cast iron cylinder liner with ID just below the ID of the damaged bore in an undamaged area.

Westwood in the UK used to supply ours, but it is a while since we needed any. If you give me the approx sizes I can see it we have some in the factory and can send you a piece. http://www.westwoodcylinderliners.co.uk

Machine the damaged bore to the OD of the liner less ~ 0.005" (or as Westwood suggest for interference)

Cut the liner section to just over the entire hole depth.
Measure up the bore to the position of the oil transfer annular groove, then drill several radial holes about 5mm diameter around the liner at the same height to allow oil pressure to transfer to the shaft
Freeze the liner overnight, or if available dip in some liquid nitrogen.
Heat the casting to about 90oC in an oven
Drop the liner into the hole - you will only get one go at this.
Trim off the slightly protruding top edge fair with the casting surface.
Machine the ID to the same size as the original bore less ~ 0.001"

The fit to the shaft when assembled needs to be a really close clearance fit. I would use a flex hone to adjust the fit

Rebuild the shafts with the shimming correctly set for the taper bearings required pre-load (as per Twin Disc instructions).

Re-assemble the box and go boating.

 

[vas]

Re: port gearbox works only on reverse

thanks SH,

that's more or less what the machinist is contemplating, only he'd rather use a bronze alloy rather than cast iron. I wonder if that is going to be a problem!

BTW, I need new specs!!!

was at the boat today doing something else and went down to the engine bay with clean hands and no gloves to get a spanner. Since I was down there and the light was just right, I moved my fingers over the axles.
There ARE steel rings on both grooves on both axles!!!
When working on them with lower lighting and gloves I couldn't feel the groove, very odd.
Anyway, need to bring along a decent vernier and my trusty old mircometer and measure the axle and the rings. They rotate smoothly on the axle, doesn't seem there's any play along the axle and they are definitely a bit proud of the axle.
pics from post 70 that show the rings (pressed in so protruding on the rear non-visible side)

NU and KevB, apologies for missing 4 bleeding rings around 3mm wide, FFS!!!
Going to the optician on Monday morning

Now, new Q, when the whole assembly is in place, what does the ring do:

• rotate with the axle
• stay put pressed against the diverter valve casing, while the axle rotates round it, all lubricated by the presurised oil.

BTW, the analysis of the whole event is plausible now, only last minute detail I'm missing is WHY it just went from proper engaging to nothing in a split second?

• Something gave in?
• A final fraction of a mm on the casing grooves that dropped oil pressure under the minimum pressure capable to keep the disks engaged?
• Something else?

TBH, wont change the actions taking by machinist, just curious. I should have the diverter repaired by midweek. I wonder what dia these rings should be and, how easy are they to remove and where can I get replacements (assuming they are worn!)
An x-ray sketch of such a ring would be welcomed!

cheers

V.

 

[superheat6k]

Re: port gearbox works only on reverse

My only concern with using bronze would be the expansion. These boxes run quite warm, so you do not want the sleeve to come loose.

As you have piston rings to form the seal I would suggest increasing the clearance to around 0.004", but worth checking the stbd box to see what the clearance on that one is.

I would expect the ring rotates.

 

[NorthUp]

Re: port gearbox works only on reverse

Good news, you are making progress! Don't bother trying to machine replacement sleeves in a different material, different expansion rates with heat and hardness of materials will beat you. New parts is the way ahead- I have always had very good service from Marine and Industrial Transmissions at Queenborough in Kent. No doubt they can send parts overseas- they always managed for me! No connection just a satisfied customer of many years

 

[vas]

Re: port gearbox works only on reverse

Good news, you are making progress! Don't bother trying to machine replacement sleeves in a different material, different expansion rates with heat and hardness of materials will beat you. New parts is the way ahead- I have always had very good service from Marine and Industrial Transmissions at Queenborough in Kent. No doubt they can send parts overseas- they always managed for me! No connection just a satisfied customer of many years

I'll have a go at repairing the part and ordering as well. Since ordering and fitting can take some time and since my machinist is reasonably cheap, I'd rather have the repaired one as spare in the future

Emailed and sent a few pics to these MIT ppl, will see what they come up with. I'll also make a few phonecalls and see if someone in Greece stocks parts for Technomarine boxes.

My only concern with using bronze would be the expansion. These boxes run quite warm, so you do not want the sleeve to come loose.

As you have piston rings to form the seal I would suggest increasing the clearance to around 0.004", but worth checking the stbd box to see what the clearance on that one is.

I would expect the ring rotates.

SH, from memory and experience, I'd say that boxes run rather cool, so doubt at 70-90C it's going to make much of a difference. However I'll ask him if he can get it from same material and do the freeze / heat bit.
Valid point re removing the stbrd box, but I'm slightly worried as boat is in the water and in an emergency I need to have control over it wont happen with both boxes out of order

Any of you guys able to explain HOW to remove these metal rings off the axles?
Before getting new specs or a magnifying lens I cannot see any gap or groove or someway to split them!

cheers

V.

 

[superheat6k]

Re: port gearbox works only on reverse

I would assume these are the same as a small piston ring, so these should be a joint somewhere around its periphery.
To remove simply pry the ends apart at the joint gently with your finger nails opening until the inner diameter is just bigger than the journal, then slide it off.

Do not over stretch it as it might snap.

You might need to use a small screwdriver to initially pry the ends apart.

I have the advantage of having fitted and removed literally 1,000's of piston rings, and rarely have snapped any.

 

[MapisM]

Re: port gearbox works only on reverse

Agreed, that's what I thought when looking at the drawings in post #70, where the joint is somewhat visible.
I would just suggest to put some extra care vs. a piston ring, because the much smaller diameter could make them more prone to be snapped...

 

[NorthUp]

Re: port gearbox works only on reverse

I have a PRM type here, but cannot upload a photo.....
Anyway this one has a stepped joint which opens under its own springiness if that makes any sense.
It's a while since I last opened a twindisc, but I think I remember its rings were a hook arrangement to keep them closed, needed a vertical or radial movement to separate the ends.
Buy two, yes they are brittle!

 

[vas]

Re: port gearbox works only on reverse

I would assume these are the same as a small piston ring, so these should be a joint somewhere around its periphery.
To remove simply pry the ends apart at the joint gently with your finger nails opening until the inner diameter is just bigger than the journal, then slide it off.

Do not over stretch it as it might snap.

You might need to use a small screwdriver to initially pry the ends apart.

I have the advantage of having fitted and removed literally 1,000's of piston rings, and rarely have snapped any.

yep, screwdriver for sure, tried today, no luck will be back with my minute screwdrivers

Agreed, that's what I thought when looking at the drawings in post #70, where the joint is somewhat visible.

you have a great imagination figuring out a cut on this awful scanned wireframe P.
but you're right

I have a PRM type here, but cannot upload a photo.....
Anyway this one has a stepped joint which opens under its own springiness if that makes any sense.
It's a while since I last opened a twindisc, but I think I remember its rings were a hook arrangement to keep them closed, needed a vertical or radial movement to separate the ends.
Buy two, yes they are brittle!

thanks for the email and pic, much appreciated.

Actually you are right they do have a hook arrangement.

Now, Q time yet again

got quoted 150euro +VAT for the metal diverter valve casing and a bleeding 100+VAT for a set of rings, is that a steal or not???

Now, measured the axle is 30mm sharp.
measured the casing hole and I think it's 30.1mm (hadn't enough light nor specs to be more accurate...)

Also measured these rings on both axles and they seem to be 30.3mm at 90deg from the hook and in a relaxed state, ie NOT compressed.

the 123euro Q is do I get new rings as well?

fwiw, the UK quote is much higher (guess getting something from IT, shipped to UK to be shipped again back down next door to IT doesn't help...) at 277gbp net for the casing and a seal ring kit for 84gbp net. Courier 35gbp.

Anyway, I'm in Athens tomorrow, will go and order it on Thursday unless I find something better.

cheers

V.

 

[vas]

Re: port gearbox works only on reverse

a quick update to say that spares arrived yesterday and I did get new rings.
Starting shifting bolts and diverter valve and the filter from the old to the new piece that ofcourse came unpainted.
so i'm now halfway changing over, painting in sections and changing o-rings.

New piece has a neutral valve hole which I don't have so I'm trying to source a temp M14 bolt to blank it (not with great luck but should find something eventually at the boat)

Checking again the manual I found why there's no pressure registering on the gauges, it was really simple and the installer was really an arsehole!
By the drawing you'll see three pickup points for oil pressure, pump f/wd and reverse. Guess where the sensor was?

On the plain return pipe from the heat exchanger where the temp sensor should have been placed!!!

Will get a 200mm long flex hose with M8X1 thread to the sensor thread for test purposes and figure out a rigid piece for permanent installation of the two sensors.
Q, since there are three pickup points (and they are the wrong way round on my port engine which has the problem) do I get the gauge on the pump one?
Makes more sense.

cheers

V.

 

[rafiki_]

Re: port gearbox works only on reverse

Sounds like you are getting it together Vas. You will certainly know your boat top to bottom, including the mechanicals and electronics when you are done. Great stuff!

 

[vas]

Re: port gearbox works only on reverse

Sounds like you are getting it together Vas. You will certainly know your boat top to bottom, including the mechanicals and electronics when you are done. Great stuff!

I could live without knowing MiToS that intimately Paul...

took me just over an hour to reassemble everything on port gbox the new painted diverter, and the pump on top

started engine, astern works fine (as always did), ahead sort of wants to do it, but unless I rev up to 800-900rpm doesn't do anything. Once I let revs drop to idle axle stops turning...

Result is that box is still sick.
Courses of action are limited to removing the box and having a look in it, or sending it off to someone to have a look in it

Undoing the 4 bolts that hold the propshaft and pushing it back say 60-80mm is not an issue. Stuffing box will still do it's thing and seal
Undoing the dozen or so M10 (iirc) screws that hold the box on the engine is also not a big deal.
Disengaging the box to the engine is a thing I'm not sure about and I'll probably need a small portable winch with a block of wood on the salon floor and a chain to hold it and avoid making a nice big hole on the bottom of the boat as it disengages.

Is there something I have to take care of whilst doing this?

Not yet sure if I'll tackle it myself, just testing.

Also curious what the actual deal is considering that box is at 600h. and there was no bronze grindings in the filter or oil, just metal which matches the casting missing off the ahead axle diverter casing.
How plausible is that the wrong pre-loading of the ahead axle, made all this mess on the casting which led to reduced pressure on the ahead plates which then worn them badly?

and if so, shouldn't I be able to see the grindings somewhere?
Is there any change that some metal grindings from the diverter case found their way on the ahead axle and blocked the oil route (too far fetched?)

any other ideas most welcomed!

cheers

V.

 

[TK Blue MAX]

Re: port gearbox works only on reverse

Hi vas , I don't suppose you have had time to rig up a pressure gauge to see whether you get the same pressure forward and reverse? Regarding removing the box you may find you have to lift the rear of the engine, if this is the case, try not to disturb the bottom adjuster nut on the engine mounts, it make realignment much easier, don't ask me how I know !!!!
Great rebuild project by the way.

Regards Tony

 

[P4Paul]

Re: port gearbox works only on reverse

Hi Vas,

As TKBlueMax suggests I would rig the pressure gauge and see what the pressure is doing when in forward on tick-over and then what happens as you gradually increase engine speed.

Being honest, it sounds to me like the forward clutch pack piston seal is leaking.

 

[rafiki_]

Re: port gearbox works only on reverse

Vas, I think you should always revert back to what changed and when. When you relaunched, she was fine. Pretty soon after, you found this problem with the port gearbox. So, what could have happened while she was standing for so long? It still feels like a seal has hardened then failed.

 

[superheat6k]

Re: port gearbox works only on reverse

Vas

Assuming the box is essentially the same as the Twin Disc MG502, I found removing it quite straightforward.

I made a lifting strop from several shackles linked together and attached these to two of the bolts joining the central casings. This was lifted with a lever hoist, which can be bought from Ebay for around £50. 1/4 tonne is more than enough.

Once the output coupling is released and pulled clear by at least 75mm take the weight of the box gently onto the hoist, undo all the bolts holding it to the engine, then 'persuade' it to pull back the 70mm or so required to disengage the splined input shaft, then haul it straight up.

Not massively heavy, but do not try and lift it without a tackle as it is simply too awkward to hold onto. I made a lifting beam from a couple of lengths of 40 x 60 timber screwed one onto the other to form a tee, then you need something firm to rest this on each end so it spans over & above the gearbox.

 

[vas]

Re: port gearbox works only on reverse

Hi vas , I don't suppose you have had time to rig up a pressure gauge to see whether you get the same pressure forward and reverse? Regarding removing the box you may find you have to lift the rear of the engine, if this is the case, try not to disturb the bottom adjuster nut on the engine mounts, it make realignment much easier, don't ask me how I know !!!!
Great rebuild project by the way.

Regards Tony

Hi Vas,

As TKBlueMax suggests I would rig the pressure gauge and see what the pressure is doing when in forward on tick-over and then what happens as you gradually increase engine speed.

Being honest, it sounds to me like the forward clutch pack piston seal is leaking.

Tony and Paul,

had a hell of a time trying to find a way to rig my WIKA 500psi gauge on this as the pump pickup is in a v.tight spot and I wanted a universal solution that can easily move from point to point...
Will have the banjo (or something like that) assembly tomorrow and will test it for sure and compare to stbrd engine on all 3 ports (pump, astern/ahead)
Will report ASAP.

Vas, I think you should always revert back to what changed and when. When you relaunched, she was fine. Pretty soon after, you found this problem with the port gearbox. So, what could have happened while she was standing for so long? It still feels like a seal has hardened then failed.

P&P,

although I've very much like this scenario cannot see WHAT has hardened and stopped sealing as there aren't really many rubber things in this assembly. Will have another detailed look on the manual and if ahead pressure is indeed low, I'll start investigating.

Vas

Assuming the box is essentially the same as the Twin Disc MG502, I found removing it quite straightforward.

I made a lifting strop from several shackles linked together and attached these to two of the bolts joining the central casings. This was lifted with a lever hoist, which can be bought from Ebay for around £50. 1/4 tonne is more than enough.

Once the output coupling is released and pulled clear by at least 75mm take the weight of the box gently onto the hoist, undo all the bolts holding it to the engine, then 'persuade' it to pull back the 70mm or so required to disengage the splined input shaft, then haul it straight up.

Not massively heavy, but do not try and lift it without a tackle as it is simply too awkward to hold onto. I made a lifting beam from a couple of lengths of 40 x 60 timber screwed one onto the other to form a tee, then you need something firm to rest this on each end so it spans over & above the gearbox.

Trevor,

thanks for the info, you recon I need 75+70mm to clear the engine? that's a hell of a spline!!!
I'll keep the info handy (and most likely come back with more Qs) once I do my homework.
Still hoping that it will magically heal itself or only need a rubber o-ring (I think I saw one on the axle in front of the needle bearing)

Let's wait for the pressure tests and we'll know for sure if it's removal time

cheers

V.

 

[vas]

Re: port gearbox works only on reverse

me again, waiting for comments on the following:

WIKA connected to the pump output, shows 330psi on idle and a hair more at 1500rpm
reverse axle output shows 360psi on idle
forward axle output shows 70-80psi on idle and 100psi or so at 1500rpm

recommended pressures from the twin disk manual are:
290-335 idle
275-335 ahead or astern at idle
idle is around 600rpm.
Mind, recommended values are for hot oil, my tests were with nice cold fresh oil, so should drop a bit when hot but well within the limits.

Now before replying one more fact:

The two rings I bought for the axle to replace the existing ones were wrong (40euro wasted) they are 40odd mm in dia and I wanted 30mm
I'll complain, but that's another story.

further these buggers are REALLY sensitive, tried to check how it hooks up one side to the other and I broke the one without anyforce whatsoever and with me just testing it on my hands (specs not on though). Rather peculiar!

Therefore the 1000euro Q is:
could the change from axle not turning at all (with the old worn diverter casing) to sort of thinking about turning and when revved up to 1000rpm slowly turning (with the new diverter casing) be sorted with new rings on the diverter casing?
I know I'll order a few as it's only going to be an hours work to replace and test, and avoid removing the box, but just wondering...

If the answer is "yes could be", wonder what really happened when it started slipping that day in October. Doesn't quite make (engineering) sense to me, glad to be corrected though.

looking forward to your replies.

cheers

V.

PS. NMEA0183 sentences intercepting coding finally worked late last night, so not everything went wrong yesterday after all...

 

[david_bagshaw]

Re: port gearbox works only on reverse

Hi Vas

Been following this thread.

From my limited experience with Borg warner marine and AP vehicle transmissions, the low oil pressure indicates a large leak, most probably caused bt the forward clutch piston seal having failed.

it would be interesting if you could pressurise the appropriate oil gallery o n the shafts with air and work out if the wear on the housing is serious. Cant see how the casing wear would lead the drive to fail in one go, if it had gradually got worse, yes.

On one gearbox I had the forward clutch plate container ring failed,(item 40 in your diagram above) no drive forward, no noises etc as the bits stayed nearly in place , but the piston moved sufficiently for the resulting oil leak to cause the pressure to drop to near zero. Reverse only worked as well.

That was an instant failure as well.