Gearbox Whine

[pevil]

Hi All,

 

Wonder if anyone can help me with this, PRM80 gearbox whining in forward and reverse, attached to a Isuzu three cylinder 3LB1.

The story so far! Had a lot of gear rattle at low speeds, suspected drive plate deterioration so ordered a high deflection R&D. also clutch was slipping on first use, fine once oil warmed up, decided to change the oil to see if that would help, I'd always used engine oil as per the manual but discovered that PRM now advise using ATF so that's what I used, ATF seemed to help a little and we cruised on for another day and a half to pick up the drive plate, I changed the drive plate (on the cut) dropped her into gear and the whine started, first thought was drive plate tight and maybe it would wear in so we headed home, however five days later and the whining was still there. Once home I decided to remove the gearbox and check it out, I've changed the clutch cone, the input and output bearings (although they seemed fine, as did everything else in there)

The gearbox is now back on and still whining! I'm sure it's the box as I can hear it with a sound stick but why would changing the drive plate cause the gearbox to whine? or is it the ATF?

I've thought about putting the old drive plate back on but to be honest I'm sure it's not that making the noise, it's the box, I know that straight cut gears (as fitted in the PRM80) can whine but they never have before, well only slightly at high engine speeds on the river but nothing like this, anybody have any ideas because I'm stumped.

 

Thanks.

[bizzard]

I'm wondering if the new drive plates centre splined boss is slightly off centre putting side stress on the gearbox first motion shaft bearing. It might be worth re fitting the drive plate in a new position, 180 degs 1/2 turn from where it is now, if possible.

 

You may have waggled the gearbox about too much when fitting it and distorted the drive plate centre boss.

Edited October 1, 2016 by bizzard

[bigste]

I have been an engineer all my life and in your case I think we should be thinking oil. You have looked at the mechanical side and found nothing so oil change has to be next and it's the cheapest option.

[bizzard]

Could be. Whines are often bearing noise. The thicker engine oil could have been keeping it quiet. On the other hand you say that the whine only started after you changed the drive plate not after changing the type of oil.

Edited October 1, 2016 by bizzard

[bizzard]

Does it whine in neutral gear? The unit might be out of alignment with the propshaft causing the gearbox thrust bearing to whine if it only whines when in gear.

[pevil]

I'm wondering if the new drive plates centre splined boss is slightly off centre putting side stress on the gearbox first motion shaft bearing. It might be worth re fitting the drive plate in a new position, 180 degs 1/2 turn from where it is now, if possible.

 

You may have waggled the gearbox about too much when fitting it and distorted the drive plate centre boss.

 

Hi bizzard, the drive plate fits in a register on the flywheel and the gearbox is bolted to the bell housing end plate so everything should be in line, also the high deflection centre plate moves easily.

 

 

I have been an engineer all my life and in your case I think we should be thinking oil. You have looked at the mechanical side and found nothing so oil change has to be next and it's the cheapest option.

 

Thanks bigste, I was thinking that too, if I hadn't changed the oil and it whined after fitting the drive plate then I wouldn't be thinking oil at all but......

[pevil]

Does it whine in neutral gear? The unit might be out of alignment with the propshaft causing the gearbox thrust bearing to whine if it only whines when in gear.

 

Doesn't seem to whine in neutral and I have a Aquadrive fitted so no misalignment problems and no thrust to the gearbox.

[bizzard]

 

Doesn't seem to whine in neutral and I have a Aquadrive fitted so no misalignment problems and no thrust to the gearbox.

And your certain its not the aquadrive whining especially its thrust bearing, listening stick on it.

[sbillis]

I am not sure that PRM recommend a high deflection drive plate with a mechanical box.

 

Simon

nb Bulrush

[pevil]

And your certain its not the aquadrive whining especially its thrust bearing, listening stick on it.

 

Thrust bearing on the Aquadrive sounds fine, it's certainly a mystery.

I am not sure that PRM recommend a high deflection drive plate with a mechanical box.

 

Simon

nb Bulrush

 

Hi sbillis, I'm not sure they do either, may give them a call on Monday, R&D certainly do, I'd already spoken to them and they recommended a high deflection.

[sbillis]

I was told by both R and D and Lancing Marine that the stiff plate was required.

 

Simon

NB Bulrush

[pevil]

I was told by both R and D and Lancing Marine that the stiff plate was required.

 

Simon

NB Bulrush

 

We had the stiff (standard loop) plate on before this one and had a lot of gearbox chatter, what engine/gearbox do you run in Bulrush and do you have any such problems. Cheers.

[sbillis]

I have a Perkins 3 cylinder M30 engine driving a PRM 120 box and yes it rattles. So much so that in neutral it makes a sound that can best be described as hammering. The problem is the low mass of the flywheel on a 3 cylinder engine. This causes the flywheel to constantly speed up and slow down through the firing cycles and vibrate through through the gearbox.

 

I used to have a Hurth but that rattled. After that box expired I fitted the 120 with a stiff plate and that rattled. I tried a soft plate and that made all sorts of nasty noises when going into gear, hence my calls to PRM and Lancing Marine. I had a inertia plate made up by a local engineer with the aim of increasing the mass of the flywheel. I fitted a medium R and D plate. This has made a big difference and now the rattles and knocking are limited to a narrow rev range.

 

I am currently looking to fit a PRM 150 box and with that a soft plate. I will also increase further the mass of the flywheel by fitting a larger inertia plate. I am mindful that the increase in flywheels mass my put extra strain n the flywheel but as the engine was primarily fitted to machinery and vehicles the flywheel should be able to carry the mass equivalent to a clutch and a bit more

 

The engine though is superb. Always stars first time.

 

SImon

nb Bulrush

[pevil]

Hi Simon,

Seems you have experienced similar problems to myself with the 3 cylinder engine, they're not very well balanced as a rule, I've been through 3 sets of engine mounts in 12 years but back to the gearbox/drive plate, you say you had a medium plate fitted, was this the Hammer Head with 9 deg. of deflection, when I spoke to R & D that one wasn't mentioned.

[RLWP]

I can confirm Simon's engine and gearbox in Bulrush chatter away enough to frighten a poor engineer. Fortunately, it all seems to work just fine

 

Richard

 

Simon has the cleanest engine bay I have ever seen

[Dalslandia]

gear chatter come from TV, torsional vibrations, it is as said earler in this thread, when fly wheel speed up and down 2-4-6 times per turn, more fly wheel mass will help specially in the perferi.

destructive TV acure when the frequency equal the frequency of the driven parts, and load go way off the scale.

A long prop shaft will be a so called soft system, like a torsional spring, and will have a low critical Hz, a fly wheel and a propeller is a stiff spring, with a high critical Hz

A short and big diameter shaft will probably be a stiff system.

This is a very complicated thing to calculate, and impossible to eye ball,

if wrong a rubber damper will melt, a spring damper go in parts, gears go broken.

Not many that can calculate/simulate, and naturally very costy.

Edited October 2, 2016 by Dalslandia

[sbillis]

As I understand it there are several causes of torsional vibration on small marine engines.

 

1) Low mass of the flywheel

2) Misfiring of the engine

3) Engine mounts not fully supporting the engine.

 

I have sorted the last too as best as I can. This just leaves the first which is to increase the mass of the flywheel. I can also fit a high deflection drive plate but in order to accommodate this I will need to fit a hydraulic gearbox and not a mechanical one hence the PRM 150.

 

With cruising nearly over for the year I hope to start this project soon.

 

 

Simon

nb Bulrush

I can confirm Simon's engine and gearbox in Bulrush chatter away enough to frighten a poor engineer. Fortunately, it all seems to work just fine

Richard

Simon has the cleanest engine bay I have ever seen

Richard, thanks for your kind words. Just to let you know there area no longer any oil leaks and the engine performed superbly on our trip from Cropredy to Pyrford and back.

 

A great job.

 

Simon

[Tony Brooks]

I am afraid that you have missed the basic cause and that is the way the engine works. There is not much you can do about that though. I agree a heavier flywheel will help but I do not see how it can eliminate it without constantly twisting and untwisting the crankshaft. I go with your solution though.

[Dalslandia]

As I understand it there are several causes of torsional vibration on small marine engines.

 

1) Low mass of the flywheel

2) Misfiring of the engine

3) Engine mounts not fully supporting the engine.

 

I have sorted the last too as best as I can. This just leaves the first which is to increase the mass of the flywheel. I can also fit a high deflection drive plate but in order to accommodate this I will need to fit a hydraulic gearbox and not a mechanical one hence the PRM 150.

 

With cruising nearly over for the year I hope to start this project soon.

 

 

Simon

nb Bulrush

Richard, thanks for your kind words. Just to let you know there area no longer any oil leaks and the engine performed superbly on our trip from Cropredy to Pyrford and back.

 

A great job.

 

Simon

 

Right, there is always torsional vibrations from the engine, even from an electric motor, but we want the bad stuff to be outside the operational rpm range, below or above.

[sbillis]

 

I am afraid that you have missed the basic cause and that is the way the engine works. There is not much you can do about that though. I agree a heavier flywheel will help but I do not see how it can eliminate it without constantly twisting and untwisting the crankshaft. I go with your solution though.

 

Thanks Tony. What I am proposing is to increase the flywheel mass by approx. 25% of the weight of the outer 50mm of the flywheel. At present I have increased this by around 10% and it has made a significant difference and the engine no longer sounds like a clapped out taxi when it is idling. I still get a clatter at around 1000 to 1500 rpm and I am sure the increase in mass will, as before, reduce the clatter.

 

I understand that Beta fit additional mass to their flywheels "as standard". This allows the engine manufacturer to supply automotive weight flywheels and the extra mass is added at marinisation.

 

I appreciate all this adds additional load on to the crankshaft and bearings but the Perkins M30 (100 series) was developed to power small tractors etc. and so should be capable of carrying the mass of a clutch mechanisms as well as a flywheel.

 

I understand that BMC 1500 engines are sometimes fitted with additional mass on the flywheel.

 

The problems I have are common to a lot of three cylinder engines fitted with mechanical boxes.

 

An engine and set up similar to mine is on the you tube video. Taxi anyone! This is not my boat although the set up is similar; M30 engine and PRM 120 box.

 

https://www.youtube.com/watch?v=9RKc1FcFX7Q

 

 

Simon

nb Bulrush

[pevil]

Well in my case the High Deflection plate has totally eliminated the gearbox chatter, I just need to get to the bottom of this whining and I've cracked it!

[Dalslandia]

Well in my case the High Deflection plate has totally eliminated the gearbox chatter, I just need to get to the bottom of this whining and I've cracked it!

 

saw dust in the gearbox oil might help for some time :-)

 

go to the bottom with the problem, in a boat?

Edited October 2, 2016 by Dalslandia

[pevil]

Got in touch with PRM Monday but the lady I spoke to just told me to call Lancing Marine, spoke to Mark who seemed quiet knowledgeable but at the end of the day all he said was "it's got to be the drive plate, that's the only thing you've changed" well not exactly as the oil was changed to ATF, so still no closer.

I'm going to change the oil again for something like 15-40 and see if that helps, the box has been run on engine oil for 12 years with no adverse effects so can't see a problem, I don't think it will cure it straight away but if it quietens it down it'll be better.

Another ex Isuzu dealer I spoke to suggested changing the oil as well, he also said he thought the whine was preferable to the gears clattering as that could do more damage.

Right, off to the boat.

[sbillis]

Let us know how you get on.

 

Simon

nb Bulrush

[Machpoint005]

I have been an engineer all my life ...<<<.

 

How did you get the training in utero?