Isuzu 55 tick over speed

[Mike Adams]

Does anyone know the correct or best speed to set the tick over on this engine? I can't find any reference to it in any of the paperwork I have. I can set it to run slow but it hunts when cold, runs smooth as it heats up but slows down and hunts again when it is fully hot to a point when its almost stalling. I think I must have it set too slow at about 600rpm. It was originally set at about 800rpm when I got the engine which seems a bit high and results in a bit too much progress at tickover speed. Setting it anywhere between 600 and 800 causes the engine to vibrate more than I would like.

[Drayke]

I have the Isuzu 70 engine in my boat and is set to tick over at 750.

[Boater Sam]

800 is about right. Remember your tacho may well not be at all accurate.

Engine mounts? Prop clean? Is the alternator slowing it due to the load charging batteries?

[Mike Adams]

I will leave at 800 for now I set the speed with my optical tachometer -the panel tacho, that is about 50 feet away, seems to be quite inaccurate and reads way too low.

[bizzard]

If that engine is in a narrowboat and is propped correctly for it and the gear ratio the boat will never go nice and slow unless its well underpropped.

[Mike Adams]

As it is hydraulic drive I maybe able to introduce a flow diverter at tick over to reduce the prop speed. Maybe a bypass valve to take 50% of the flow from the motor operated by an electrical switch?  It's such a pain to have to drop in and out of gear all the time.

[Boater Sam]

46 minutes ago, Mike Adams said:

As it is hydraulic drive I maybe able to introduce a flow diverter at tick over to reduce the prop speed. Maybe a bypass valve to take 50% of the flow from the motor operated by an electrical switch?  It's such a pain to have to drop in and out of gear all the time.

That bit of information may explain the problem!

Is there not a shunt bypass from the pump outlet back to the oil header tank? A simple hand valve would allow you to reduce the pump flow in this manner.

[Tony Brooks]

4 hours ago, Boater Sam said:

That bit of information may explain the problem!

Is there not a shunt bypass from the pump outlet back to the oil header tank? A simple hand valve would allow you to reduce the pump flow in this manner.

I would be very surprised if it did not have a PRV somewhere.

 

A less bodgy answer would be to fit a larger capacity motor or a smaller capacity pump but changing the prop would be easier.

 

[Mike Adams]

The system is great apart from being a little too quick on tick over so I want to stick with it. The control valve and prv are integrated to the side of the reservoir tank all next to the engine at the front of the boat with just two pipes going to the stern to the hydraulic motor. As the motor is fixed displacement as well it is effectively a 2:1 reduction system (19cc/rev pump and 39 cc/rev motor). What I need is the hydraulic equivalent of a 'trolling valve' which fishing boats use. I think I need a flow control valve (electrically operated?) to take say 50% of the motor flow when engaged and the engine running at tick over. At 800rpm tick over the flow rate would be 19cc x 800  = 15200cc/min so if half that say is diverted through the valve, the flow rate to the motor will be halved and the prop speed reduced by half. This might make a two speed gearbox? I remember visiting Venice where the Vaporetto Ferries seem to have two speed gearboxes which give them higher torque when starting and stopping and then 'change up when under way'.

I know that more modern hydraulic drives use a variable displacement  pump which I guess gives infinite control of the flow and hence the prop speed regardless of engine speed but mine isn't in that league.

I will  see if I can find a suitable valve.

[dor]

800 rpm tickover is about normal for modern marine diesel engines.  Any slower and they tend to shake about, especially when under load.  I wouldn't be looking to lower the tickover.  A trolling-type valve is what you need, or a smaller prop.

[blackrose]

On 25/02/2019 at 09:40, bizzard said:

If that engine is in a narrowboat and is propped correctly for it and the gear ratio the boat will never go nice and slow unless its well underpropped.

 

My boat has an Isuzu 55. It's correctly propped and it does go nice and slow. It used to be over-propped and it still went nice and slow, but I had the prop pitch reduced. It's slightly shower at tickover now. It's a widebeam though, not a narrowboat.

 

My recounter wasn't calibrated properly. I thought it was ticking over in neutral at about 600rpm but I've found its actually about 700rpm 

Edited February 27, 2019 by blackrose

[bizzard]

7 minutes ago, blackrose said:

 

My boat has an Isuzu 55. It's correctly propped and it does go nice and slow. It used to be over-propped and it still went nice and slow, but I had the prop pitch reduced. It's slightly shower at tickover now. It's a widebeam though, not a narrowboat.

 

My recounter wasn't calibrated properly. I thought it was ticking over in neutral at about 600rpm but I've found its actually about 700rpm 

I inquired if the 55 hp engine was in a narrow boat, therefore way over powered really and would be pushing a much less wall of water along in front of it, less forward resistance so would be too fast on tick over with that size of engine.  Rather than it being in a wide beam 10' 6'' plus boat pushing a higher resistance  larger wall of water ahead of it,  or like yours Mike 12' wide, the size of boats which those engine are intended for.  He didn't reply to me so we still don't know whether narrow or wide beam.

[Mike Adams]

This boat is rather unusual for a 'narrow' boat being only about 6' 6" width of hull 62 feet long and quite slippery. It is a good copy of a Bridgewater Canal little packet from 1875 with a fine bow and long swim so as long as it isn't dragging the bottom it's good.  It soon gets up to a good speed and takes a long time to slow down even on the shallow Basingstoke Canal so 55Hp is really not normally needed but at just over tick over at about 1000 rpm everything goes nicely. I am yet to try it on a river but it should go well enough.

I have seen a widebeam brick (12ft beam x 2'8" draft) try to push its way along the Basingstoke - very hard on the canal and its banks due to the backflow around the boat. Isn't that why they gave up with wide beamed powered working boats on the GU? I am not anti-wide beam by the way but I lot of their modern hull designs (do they have any?) are not sympathetic to the waterways they are being sold to be used on unless they go at a snail’s pace or get a horse(or is that not allowed anymore because of upsetting continuous moorers). Apologies for rant.

[Boater Sam]

You have to have permission for a horse/mule on the towing path now, but not a bike. Such is progress.

 

I have noticed that the square stern on many wider hulls seems to produce considerable turbulence across the canal to the banks, very noticable when being moored up and they go past.

[bizzard]

1 hour ago, Mike Adams said:

This boat is rather unusual for a 'narrow' boat being only about 6' 6" width of hull 62 feet long and quite slippery. It is a good copy of a Bridgewater Canal little packet from 1875 with a fine bow and long swim so as long as it isn't dragging the bottom it's good.  It soon gets up to a good speed and takes a long time to slow down even on the shallow Basingstoke Canal so 55Hp is really not normally needed but at just over tick over at about 1000 rpm everything goes nicely. I am yet to try it on a river but it should go well enough.

 

I have seen a widebeam brick (12ft beam x 2'8" draft) try to push its way along the Basingstoke - very hard on the canal and its banks due to the backflow around the boat. Isn't that why they gave up with wide beamed powered working boats on the GU? I am not anti-wide beam by the way but I lot of their modern hull designs (do they have any?) are not sympathetic to the waterways they are being sold to be used on unless they go at a snail’s pace or get a horse(or is that not allowed anymore because of upsetting continuous moorers). Apologies for rant.

 

Ah, fine in the bow too, I bet it bombs along.  Harborough marine boats had fairly fine bows and long swims and could fly along even with a 13hp Lister SR2 in a 45' or so boat or a 70' one with an 18hp SR3.  I reckon about 90% of modern wide beam boats never go anywhere, are just live aboards and only move to go to top up with water or to pump the toilet out. We have five of them around here and is all the ever move for.   And yes modern square stern wide beams at speed can really cause a huge dwell disturbance in their wake,

Edited February 27, 2019 by bizzard