Idle Chatter

[MWhit50]

Hello everyone.

New to the Forum but not new to Boat Building.

I finished off boat building by building my own Wide Beam to live on and apart from a big learning curve on fitting out, the Engine and train gear has given me a head Ache!!

The boat is 60'x13.5', Dutch Style, 35Tons approx.

My set up is : Gardner 5LW (not originally a marine set up) 95Hp @ 1700RPM, Spider driven to a MG-506 Twin Disc 1.5:1 Gear box, then a 1.8m UJ propeller shaft to a  18" long 1 3/4"  stainless shaft, Supported by a SKF Thrust bearing, and finally a 4 Blade 24"x14" propeller. 

The issue is on idle 450RPM there is a loud chatter coming from the gear box, but once off idle this goes away. The gear engages good and the strainer is not blocked, oil level as should be. 

An interesting test I did do was disconnect the propeller shaft from the output shaft of the gear box and when I put in drive it is smooth and without noise. 

So given when I take torsional force away from the output it is quiet, I have come to the conclusion that the Propeller could be over propped???

On idle the boat can get up to 3mph/2.8knots.

I have a friend with the same 5LW , spider Drive MG-506 Twin Disc Box , but 2:1, 3 Blade propeller 26"x22" and direct shaft drive, but he has not chatter on idle.

On this forum I have seen a thread with this comment " I bought a steel river boat, 54' x 12', with a Gardner 6LW engine driving a 25 x 11 3-blade prop through a PRM 2:1 gearbox."

This boat had a larger Gardner than mine with a PRM 2:1 Box and 3 Blade Prop.

So at the moment I am looking at taking my prop off and getting it pitched from 24x14 to 24x11.

I am open to all comments and has anyone else had this issue with chatter with there new set ups.

[David Mack]

10 hours ago, MWhit50 said:

On idle the boat can get up to 3mph/2.8knots.

So is this the slowest you can go? With slower travel necessitating dropping into and out of gear?

[Bee]

I don't know much about the engine or the gearbox but is the gearbox new? If not it might have wear in it that becomes apparent when the load from the prop comes in. Presumably it is OK in neutral? Re pitching could help but 24x14 is not hugely coarse. My guess for what it's worth is that a 4 bladed 24 inch prop is not heavy enough to be it's own flywheel at lower revs but has enough resistance to magnify any wear in the box

[MWhit50]

1 hour ago, David Mack said:

So is this the slowest you can go? With slower travel necessitating dropping into and out of gear?

Yes, and I do have to pop in and out gear when mooring up. 

[MWhit50]

54 minutes ago, Bee said:

I don't know much about the engine or the gearbox but is the gearbox new? If not it might have wear in it that becomes apparent when the load from the prop comes in. Presumably it is OK in neutral? Re pitching could help but 24x14 is not hugely coarse. My guess for what it's worth is that a 4 bladed 24 inch prop is not heavy enough to be it's own flywheel at lower revs but has enough resistance to magnify any wear in the box

Hi, the Twin Disc is no longer in production, but on checking the oil is still clean, no blockage in the strainer, and goes in neutral and gear spot on. When I do put it in gear as it is, the engine revs at its 450 idle do not dip, unlike a friends Twin potter. I have considered changing for my old Velvet Drive Borge Warner which is a 2:1 and I did have that on a Perkins T3654.

[Tony Brooks]

Not much help as I do not have the experience needed for these engines but:

 

Google AI (which can not be trusted) says:

 

The recommended idle speed for a Gardner 5LW engine depends on whether it is configured for

automotive or marine use. 

• For an automotive Gardner 5LW engine, the stated idle speed is typically around 420 rpm.
• For a marine Gardner 5LW engine (commonly used in narrowboats), the idle speed is often set lower, around 330 rpm. 

The low idle speed is a characteristic feature of Gardner engines, and they are designed to run smoothly at these very slow revolutions per minute (RPM). 

 

So that looks as if your idle speed is too high and that might explain the high boat speed at idle, but I don't see that it in any way explains the chatter.

 

An online manual I found, that did not distinguish between automotive, rail, and marine LW engines, gave the idle speed as 420 rpm.

 

I don't see how a 5-cylinder engine can ever be totally balanced, so vibrations and torsional oscillation are likely to be greater than for a four or six cylinder. Audi had to use liquid filled engine mounts for their 5 cylinder petrol engine, bit I suspect that was more to do with engine vibrations than torsional oscillation.

 

I know that the marinisation of smaller marine diesels involved fitting a heaver flywheel or a bulk ring to the automotive flywheel to give a smother idle when in gear, but the Gardner manual I found said that the whole flywheel assembly (I add including the clutch and drive plate) should be a slight as possible.

 

I don't know exactly what you mean by being spider driven because Google gives several options, but the two main ones that seem to be spring/rubber/plastic drive plate replacements do not seem likely candidates to cause chatter unless worn and old, but chatter at idle is a known symptom of a worn/failing drive plate, but without seeing your "spider" I can not comment on how likely that is to be the cause. What i ca say is that my little 3 pot Bukh had a rubber spider drive, and replacing the old hardened rubber section made it smoother at idle in gear.

 

I am having difficulty seeing how the prop size could cause chatter unless there is wear somewhere in the drive line, so I think I am with Bee on the possible cause. Have you had the opportunity to drive the boat flat out, if you have and the exhaust did not make black smoke then the prop is probably roughly correct.  

 

Maybe your fiends boat's drive line is less worn than yours.

[MtB]

13 hours ago, MWhit50 said:

The issue is on idle 450RPM there is a loud chatter coming from the gear box, but once off idle this goes away. The gear engages good and the strainer is not blocked, oil level as should be. 

An interesting test I did do was disconnect the propeller shaft from the output shaft of the gear box and when I put in drive it is smooth and without noise. 

 

It's not clear to me when this chatter is present and when not. 

 

Does it chatter at idle out of gear?

Does it chatter at idle when in gear?

 

All I can really work out is the chatter stops when you unbolt the prop shaft, then put it in gear. Maybe you've said but I can't spot it! 

 

 

 

 

 

[MWhit50]

1 hour ago, Tony Brooks said:

Not much help as I do not have the experience needed for these engines but:

 

Google AI (which can not be trusted) says:

 

The recommended idle speed for a Gardner 5LW engine depends on whether it is configured for

automotive or marine use. 

• For an automotive Gardner 5LW engine, the stated idle speed is typically around 420 rpm.
• For a marine Gardner 5LW engine (commonly used in narrowboats), the idle speed is often set lower, around 330 rpm. 

The low idle speed is a characteristic feature of Gardner engines, and they are designed to run smoothly at these very slow revolutions per minute (RPM). 

 

So that looks as if your idle speed is too high and that might explain the high boat speed at idle, but I don't see that it in any way explains the chatter.

 

An online manual I found, that did not distinguish between automotive, rail, and marine LW engines, gave the idle speed as 420 rpm.

 

I don't see how a 5-cylinder engine can ever be totally balanced, so vibrations and torsional oscillation are likely to be greater than for a four or six cylinder. Audi had to use liquid filled engine mounts for their 5 cylinder petrol engine, bit I suspect that was more to do with engine vibrations than torsional oscillation.

 

I know that the marinisation of smaller marine diesels involved fitting a heaver flywheel or a bulk ring to the automotive flywheel to give a smother idle when in gear, but the Gardner manual I found said that the whole flywheel assembly (I add including the clutch and drive plate) should be a slight as possible.

 

I don't know exactly what you mean by being spider driven because Google gives several options, but the two main ones that seem to be spring/rubber/plastic drive plate replacements do not seem likely candidates to cause chatter unless worn and old, but chatter at idle is a known symptom of a worn/failing drive plate, but without seeing your "spider" I can not comment on how likely that is to be the cause. What i ca say is that my little 3 pot Bukh had a rubber spider drive, and replacing the old hardened rubber section made it smoother at idle in gear.

 

I am having difficulty seeing how the prop size could cause chatter unless there is wear somewhere in the drive line, so I think I am with Bee on the possible cause. Have you had the opportunity to drive the boat flat out, if you have and the exhaust did not make black smoke then the prop is probably roughly correct.  

 

Maybe your fiends boat's drive line is less worn than yours.

Dropping the RPM to the 300 ish I have never tried but will give it a go. The Spider drive has 20 rubbers on the end of a the male part on the input of the gearbox. According to Twin disc web site the Spider is meant for Generators, Forklifts, Plant equipment , and a Flexi CF I think it was is for Marine use with an Engine that runs on low RPM, But that conflicts with a friends same set up that does not create noise ( But he is 2:1 Twin Disc). R&D do a Flexi Drive but not one that would fit a Key Shaft only Splined, so I cant buy that to try. The reason for taking pitch off was because when no prop shaft is bolted to the output flange then there is no noise smooth as butter (less pitch less resistance), but soon as I link up the train gear the idle noise is back. The boat handles and cruises just fine and off tick over no noise just the sweet sound of the Gardner. As for a 5 pot engine running smooth, these Gardners are very smooth, can even do the pound coin trick on the rocker cover. 

Just good to get other peoples results or opinions. 

[David Mack]

2 hours ago, MWhit50 said:

Yes, and I do have to pop in and out gear when mooring up. 

In which case you don't have the right setup for a canal boat. Might be a good match for travelling at speed on open water, but for canal use a finer pitch would give you more control.

[MWhit50]

8 minutes ago, MtB said:

 

It's not clear to me when this chatter is present and when not. 

 

Does it chatter at idle out of gear?

Does it chatter at idle when in gear?

 

All I can really work out is the chatter stops when you unbolt the prop shaft, then put it in gear. Maybe you've said but I can't spot it! 

 

 

 

 

 

Only chatters when in gear forward or reverse . No chatter once off idle around 600rpm, no noise in Neutral. No diss colour in the oil (30wt) 

17 minutes ago, David Mack said:

In which case you don't have the right setup for a canal boat. Might be a good match for travelling at speed on open water, but for canal use a finer pitch would give you more control.

Yes I've realised this but the idle noise is the main push to get it sorted and that out of 1700rpm max revs it will only do 1250 in gear on full throttle.

Also the cost of having the pitch taken out is not something that I can see would need putting back even if I changed the Gear Box in the future.

Most of the time I am on wide Canals and the Trent one day.

 

This is a link to my Chatty Gear Box.....

[Tony Brooks]

43 minutes ago, MWhit50 said:

Yes I've realised this but the idle noise is the main push to get it sorted and that out of 1700rpm max revs it will only do 1250 in gear on full throttle.

 

That suggest that you may be over propped, so reducing the prop a bit should not do any harm

 

48 minutes ago, MWhit50 said:

The Spider drive has 20 rubbers on the end of a the male part on the input of the gearbox. According to Twin disc web site the Spider is meant for Generators, Forklifts, Plant equipment , and a Flexi CF I think it was is for Marine use with an Engine that runs on low RPM, But that conflicts with a friends same set up that does not create noise ( But he is 2:1 Twin Disc).

 

That is what I suspected you meant, how soft are those rubbers, they can harden with age.

 

If the noise is coming from the gearbox, then what part of the gearbox, that makes it sound more like gearbox wear with chattering in splines or between teeth. 

 

52 minutes ago, MWhit50 said:

As for a 5 pot engine running smooth, these Gardners are very smooth, can even do the pound coin trick on the rocker cover. 

 

You need to differentiate between torsional oscillation in the driveline and out of balance vibration. The chatter is likely to be caused by torsional oscillation and may well not affect engine vibration.

 

[MWhit50]

10 minutes ago, Tony Brooks said:

 

That suggest that you may be over propped, so reducing the prop a bit should not do any harm

 

 

That is what I suspected you meant, how soft are those rubbers, they can harden with age.

 

If the noise is coming from the gearbox, then what part of the gearbox, that makes it sound more like gearbox wear with chattering in splines or between teeth. 

 

 

You need to differentiate between torsional oscillation in the driveline and out of balance vibration. The chatter is likely to be caused by torsional oscillation and may well not affect engine vibration.

 

I did put a lump of wood under the prop shaft and lifted it to see if it made a sound difference and it made no difference, but as you might know I can not take away the torsional forces. 

 

 

[MWhit50]

Just tried the Gear Box on lower revs and apart from the Engine protesting it actually made the noise just as bad.

[Tony Brooks]

1 hour ago, MWhit50 said:

I did put a lump of wood under the prop shaft and lifted it to see if it made a sound difference and it made no difference, but as you might know I can not take away the torsional forces. 

 

 

 

It can not take away torsional oscillation between the crankshaft and prop shaft, and I doubt that it would take it out of the prop shaft, except in so far as it puts resistance to rotation on the shaft so any flexibility in the shaft coupling or drive plate damps the oscillations. Have you tried a listening stick or stethoscope on various ares of the gearbox case and flywheel housing? That may help localise the chatter.

5 minutes ago, MWhit50 said:

Just tried the Gear Box on lower revs and apart from the Engine protesting it actually made the noise just as bad.

 

If the spider rubbers are in good condition, then that still suggests gearbox wear to me. If your gearbox input shaft uses splines in the drive plate, then I have known those to develop significant wear and become noisy. On one occasion, becoming so badly worn and stepped, it was a struggle to get the gearbox off the engine.

[MWhit50]

7 minutes ago, Tony Brooks said:

 

It can not take away torsional oscillation between the crankshaft and prop shaft, and I doubt that it would take it out of the prop shaft, except in so far as it puts resistance to rotation on the shaft so any flexibility in the shaft coupling or drive plate damps the oscillations. Have you tried a listening stick or stethoscope on various ares of the gearbox case and flywheel housing? That may help localise the chatter.

 

If the spider rubbers are in good condition, then that still suggests gearbox wear to me. If your gearbox input shaft uses splines in the drive plate, then I have known those to develop significant wear and become noisy. On one occasion, becoming so badly worn and stepped, it was a struggle to get the gearbox off the engine.

Yes I get that as I work in Maintenance so fully aware of mechanical things. And Ive checked the Gearbox input shaft and it had a Keyway shaft with zero play. If I had a splined shaft I would be looking at an R&D Damper drive. I will be giving them a ring on Monday to see if they could do anything or like I've said on another thread might look at putting a Borge Warner 2:1 Box on it, just means engineering a new adapter ring.

[Mike Adams]

You have my sympathy. I was in a similar situation years ago with an MG506 (1.93:1) coupled to 2 different engines a Dorman 3LB and a 6cylinder Toyota which I believe is still in the boat. Neither engine vibrated but there was always a bit of chatter usually just beyond tick over and then disappearing at about 800 revs. Trouble was the speed that was just right for canals was exactly where the chatter occurred.   I tried all sorts of things including increasing the flywheel mass and different couplings, engine mounts but I never managed to solve it completely. I am not sure these gearboxes are designed to run so slowly, I think it is in line so you are going through 3 gears which doesn't help with the chatter. Most people seem to use prm boxes on old engines but then the prop-shaft will be  shaft be lower than the crank.