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Really hot dipstick


Roxylass
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30 minutes ago, Tony Brooks said:

I think the plate your two ducts are fitted to is/was a Lister part, except I have seen the crimped aluminium ducts used in place of your plastic ones. My guess is that the OP does not that the adaptor needed to fit either the ally, plastic or canvas ducts.

I think it almost certainly was. Of course, it draws air in from a big engine bay and a hefty slot in the other side of the hull, but still doesn't like really hot weather. Luckily  we don't get much of that here.

 

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6 hours ago, nicknorman said:

Bear in mind that the “throttle” isn’t really a throttle, it is an rpm selector for the governor. The governor will send in as much fuel as necessary to achieve the set rpm. So for example if the prop had some rubbish on it that created a lot of drag, the governor might be sending in nearly maximum fuel to achieve a middling rpm, and thus a lot more heat is created.

Everyone calls them throttles, as I am sure you know?

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Just now, Stilllearning said:

Everyone calls them throttles, as I am sure you know?

But it was a point well worth explaining to the OP and the fact the engine would not idle made it even more important for the OP to understand. From what we can tell it was not a fouled prop but a partial seizure doing exactly what Nick described.

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1 minute ago, Tony Brooks said:

But it was a point well worth explaining to the OP and the fact the engine would not idle made it even more important for the OP to understand. From what we can tell it was not a fouled prop but a partial seizure doing exactly what Nick described.

I take your point. Everyone does talk about the throttle lever though, no one ( I think) talks about operating the governor lever.

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2 hours ago, Tony Brooks said:

I think the gender you assume is from the boat name, the OP gives his sex as male.

Oops, foot in mouth time again, sorry 'fella' !

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2 hours ago, Stilllearning said:

I take your point. Everyone does talk about the throttle lever though, no one ( I think) talks about operating the governor lever.

Yes my point was not that the terminology was wrong, just that a function of a boat Diesel engine “throttle” is quite different from that of a car/petrol engine, eg that you can end up effectively on “full throttle” even when the lever is only half way.

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Quite right Tony

Quite right

Thinking of using a hole saw

Let some air into the box

I do have the fitting on mine

Like Arthur's for letting the hot air out

But sadly not one for letting air in

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22 minutes ago, Roxylass said:

Quite right Tony

Quite right

Thinking of using a hole saw

Let some air into the box

I do have the fitting on mine

Like Arthur's for letting the hot air out

But sadly not one for letting air in

 

As long as you discharge the hot air away from the cooling air inlet "hole" you only need a large hole to let the air in. I think the size is in the manual.

I can't stress it enough how important it is to duct the hot air out of the box and away from the cooling air intake. Used cooling air MUST be vented outside the engine case, otherwise it will be recirculated past the cylinders causing overheating and, as you found, partial seizure. While you work out the best  way of doing this can you run with no engine casing, so the engine is open to the air and there is lots of air around the engine.

 

What concerns me is that your boat is probably fairly small with a displacement hull, so 4 knots would be a reasonable speed, and that gives a solid hour's driving to and from the fishing ground. With a bit of wind and current, you may well be running at more than half throttle. I don't see that it is wise to risk overheating. You will need more than a few holes cut with a hole saw, I think.

 

 

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10 hours ago, nicknorman said:

Bear in mind that the “throttle” isn’t really a throttle, it is an rpm selector for the governor. The governor will send in as much fuel as necessary to achieve the set rpm. So for example if the prop had some rubbish on it that created a lot of drag, the governor might be sending in nearly maximum fuel to achieve a middling rpm, and thus a lot more heat is created.

I never knew that. Explains a lot.

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11 minutes ago, Arthur Marshall said:

I never knew that. Explains a lot.

You might have noticed Arthur after starting up and as your alternator completes it's initial high charge and falls back to low charge the engine speeds up a touch momentarily and then settles back to normal.

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17 hours ago, bizzard said:

You might have noticed Arthur after starting up and as your alternator completes it's initial high charge and falls back to low charge the engine speeds up a touch momentarily and then settles back to normal.

Not noticed  but I will... But doesn't that all imply that, other things being equal, I should always get the same revs and therefore the same speed out of the boat at the same lever position? And I'm fairly sure I don't.

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2 hours ago, Arthur Marshall said:

Not noticed  but I will... But doesn't that all imply that, other things being equal, I should always get the same revs and therefore the same speed out of the boat at the same lever position? And I'm fairly sure I don't.

 

Probably, but it uses a very crude governor system with lots of opportunity for friction, so lots of opportunity for it to "stick" a little.

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2 hours ago, Arthur Marshall said:

Not noticed  but I will... But doesn't that all imply that, other things being equal, I should always get the same revs and therefore the same speed out of the boat at the same lever position? And I'm fairly sure I don't.

As Tony says, stiction and slackness in the linkage, plus a governor characteristic ( of nearly all fairly simple mechanical governors) called 'governor droop' .  Nothing to do with brewers, it is that if you increase the load at any given speed setting the governor will eventually settle down at a different speed even though the speed setting has not been changed. Usually the new speed is lower, but some governors cause an increase.

It means you usyally get a higher frequency output from a mains  AC  generator at low load and a lower frequency at high load.

N

 

 

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3 hours ago, Arthur Marshall said:

Not noticed  but I will... But doesn't that all imply that, other things being equal, I should always get the same revs and therefore the same speed out of the boat at the same lever position? And I'm fairly sure I don't.

Well firstly same revs doesn't correspond to same speed out of the boat. Surely you know that! It would only be the case if all other things were equal, depth and width of water, whether prop clean, wind, currents etc

 

Secondly this type of governing system ( in fact pretty much any type of governing or regulation system pre-digital era) works on an error principle. In other words, in order for the governor to increase or decrease the fuel flow, there must be a difference between the rpm set by the "throttle" lever and the actual rpm (ie an error). So lets say the throttle is set for 1200rpm at no load. The fuel flow is a certain (fairly small) amount. Now a load is created, eg putting into gear. The load causes the rpm to decrease and the "error" to increase, so the governor adds more fuel to try to maintain the rpm and reduce the error. But there is a direct relationship between error and fuel flow, so if the load is sustained and there is a need for more fuel than under zero load, inevitably the error has to remain since it is the error that causes the increased fuel flow. So the rpm will settle at a bit less than the inital 1200, lets say 1100. So under normal cruise conditions that throttle position will always give 1100rpm.

 

But now we have some increased load eg rubbish on prop, engine friction increasing (starting to seize) etc. The rpm will decrease further and, without the operator doing anything, the fuel flow will correspondingly increase. So we might end up at 1000rpm and maximum fuel flow. And that maximum fuel flow obviously creates more heat / requires better cooling, than it did before the load increased.

 

So in summary there isn't a totally rigid relationship between lever position and rpm, but it is fairly close, AND the actual fuel flow doesn't necessarily bear any relation to the lever position.

 

If you are still readings it's worth considering WHY diesels have governors whilst petrol engines have throttles. It is because a throttle constricts the inlet for a petrol engine. If an idling engine rpm were to increase for some reason, the inlet air/petrol mix flow increases and the restriction of the throttle causes more drop in pressure thus reducing the available energy to the engine. The engine tends to slow back down again. In other words, it is a stable situation where for a given amount of throttle and no load, the engine tends to run steadily at certain rpm.

 

Things are different with a diesel since the fuel control unit specifies the amount of diesel injected into the cylinders at each compression cycle. And there is no throttle to restrict the air coming into the engine. So if an engine is idling and the fuel flow is just a tiny bit too much, the rpm starts to increase. The same amount of fuel is sent to the cylinders on each compression stroke but since the compression strokes are now coming faster, the fuel flow increases. The engine will continue to accelerate. 

 

The same applies if the fuel flow is just the tiniest bit too little, the engine will slow down and eventually stop. It is an unstable situation and a governor is needed to maintain a reasonably steady operating speed.

 

Edited by nicknorman
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47 minutes ago, BEngo said:

As Tony says, stiction and slackness in the linkage, plus a governor characteristic ( of nearly all fairly simple mechanical governors) called 'governor droop' .  Nothing to do with brewers, it is that if you increase the load at any given speed setting the governor will eventually settle down at a different speed even though the speed setting has not been changed. Usually the new speed is lower, but some governors cause an increase.

It means you usyally get a higher frequency output from a mains  AC  generator at low load and a lower frequency at high load.

N

 

 

Thanks to you,  Tony and Nick for the explanations. I knew diesels had governors, had no real concept of how they worked. I do like to know these things.

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3 minutes ago, Arthur Marshall said:

Thanks to you,  Tony and Nick for the explanations. I knew diesels had governors, had no real concept of how they worked. I do like to know these things.

There is a diagram very like your's in the FIE notes on my website.

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15 hours ago, BEngo said:

As Tony says, stiction and slackness in the linkage, plus a governor characteristic ( of nearly all fairly simple mechanical governors) called 'governor droop' .  Nothing to do with brewers, it is that if you increase the load at any given speed setting the governor will eventually settle down at a different speed even though the speed setting has not been changed. Usually the new speed is lower, but some governors cause an increase.

It means you usyally get a higher frequency output from a mains  AC  generator at low load and a lower frequency at high load.

N

 

 

 

Governor droop is very important when paralleling diesel engined generators with mechanical governors so that they share load. The lead generator always has a slightly higher speed than the others.

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On 26/07/2021 at 13:05, David Mack said:

This is a ST2, similar to your SR2. 

engine.jpg

Cooling air is drawn in through the grill between the engine and gearbox in the centre of the photo, and the hot air leaves the engine via the red metal duct and into the canvas trunking. You should have something similar to the red duct leading directly to the outside of the engine case.

Yes I have almost identical

Sue from primrose engineering

Is going to make me a length

Of canvas trunking up

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Pic of said engine lister sub forum

Page two titled fuel pipe

No space to make the box bigger

Does the rectangular frame look

 Complete

As this is how it was when I purchased it

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21 minutes ago, Roxylass said:

Pic of said engine lister sub forum

Page two titled fuel pipe

No space to make the box bigger

Does the rectangular frame look

 Complete

As this is how it was when I purchased it

This?

4C823C9A-B9B8-4E15-AE82-EA51C5D49A80.jpeg

 

You just need that rectangular frame extending to the engine case, with a similar sized opening in the engine case wall. Could be done with rectangular sheet metal trunking, circular ducts (with an adaptor plate), canvas trunking, or even in wood. A wooden duct could be attached to the case side panel with a foam gasket against the flange on the engine duct.

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57 minutes ago, Roxylass said:

Yes I have almost identical

Sue from primrose engineering

Is going to make me a length

Of canvas trunking up

If you have primrose engineering on the issue they should sort it 

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First, if that "bulkhead" against the flywheel housing is a good fit to the side panels and case top then as long as the outlet hole in the case is of adequate size then things are not as bad as I feared. Apart from  below engine bed height where there seems to be a free air flow.  With the cooling air intake grill open to the air, I don't think any hot air getting under the "bulkhead" will be significant.

 

I suspect we may be looking for something else here, like prolonged running with a fouled prop, possibly an oversized prop, or a tight/seizing stern gland, but much depends on the actual air temperature at the time.

 

Our SLs had a very similar metal cooling outlet duct with flange. The carpenters made a pair of rectangular frames from plywood. The canvas was trapped between the two and the lot was  bolted to the flange, However, looking  at the photo I think that as long as the hole in the case is as large or larger and in line with the engine outlet it should be adequate.

 

Edited to add: You seem to be drawing combustion air from inside the hot engine case. It would be better for engine efficiency and good combustion to draw air from outside the engine case.

Edited by Tony Brooks
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