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32 minutes ago, Wrinkley said:

Understand what you are suggesting but if two separate systems to measure revs that I'm using are roughly in line why would a third be different? 

 

I wasn't aware you had two separate means of measuring revs until now. What are these means?

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Both belts run from the engine pulley to the alternator pulley, they run in parallel. The cycle rev counter sensor is mounted on the inside of the engine pulley. The frequency counter is used on the one phase of the alternator stator winding. The engine to alternator pulley ratio is 3:1.

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36 minutes ago, Wrinkley said:

Thanks for the link. For a tenner it's got to be worth it. Just as an aside, how do you know the new one is accurate and your original one faulty?  ?

Try pointing it an mains powered led light it may just measure the mains frequency

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3 hours ago, Wrinkley said:

On full throttle there is still fuel running back to the tank indicating, to me, plenty of fuel available to the pump.

 

Is that really right?

 

The leak-off pipes should barely carry anything as I understand it. On my Kelvin I only get about half a litre in several hundred hours accumulating in the scotch bottle.   

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22 minutes ago, Mike the Boilerman said:

 

Is that really right?

 

The leak-off pipes should barely carry anything as I understand it. On my Kelvin I only get about half a litre in several hundred hours accumulating in the scotch bottle.   

It depends on the injection system, on our D3 there is a very significant flow and this comes from both the injection pump and the injectors, I have read that the flow through through the injectors in intended to provide some injector cooling.

 

Many years ago whilst getting the tank sucked out and refilled we attemped a very short cruise (boatyard to nearest VM) running on a 10 litre Jerry can as a makeshift fuel tank. The return still went to the main tank and after about 13 minutes the jerry can was empty

 

................Dave

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I have a Russell Newbery DM2 in my boat which is 18HP at 1200 RPM. I too have a 22 x 22 inch prop and a 2-1 reduction. It runs fine and clean, reving well. I would imagine that the OPs set up is more or less similar and should run OK. This was the prop that crowthers recommended and made for the boat when it was new. It was said that this would load the engine enough without over propping.

Edited by captain birdseye
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13 minutes ago, captain birdseye said:

I have a Russell Newbery DM2 in my boat which is 18HP at 1200 RPM. I too have a 22 x 22 inch prop and a 2-1 reduction. It runs fine and clean, reving well. I would imagine that the OPs set up is more or less similar and should run OK. This was the prop that crowthers recommended and made for the boat when it was new. It was said that this would load the engine enough without over propping.

Can you get right up to 1200 rpm on good deep water?

 

...............Dave

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2 hours ago, Wrinkley said:

Oooo that's a good idea. But then I'm not on mains at the moment. Could measure the hz of my mastervolt. 

You could, mine was spot on when I ran a synchronous timer for a week

1 hour ago, dmr said:

 

Many years ago whilst getting the tank sucked out and refilled we attemped a very short cruise (boatyard to nearest VM) running on a 10 litre Jerry can as a makeshift fuel tank. The return still went to the main tank and after about 13 minutes the jerry can was empty

 

................Dave

I keep the day dank for my Dickinson stove topped up with the return from the filters/injectors. Caught me out with 10 days in drydock last October

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22 minutes ago, captain birdseye said:

Never consciously tried, I'm not one to 'red line' engines but it revs OK and pushes me up the Trent and motors well on every waterway I've been on. 

Red Line is a rather dramatic term for getting a slow revver up to 1200, thats slower than the tickover of some petrol racing engines ?.

 

I've had mine running pretty much flat out a few times, once tied up in a lock. I wanted to know that the engine and cooling system were happy at those conditions and thought Id rather find out in a controlled test than in a real emergency. However we have the humble JD3 that revs to about 1300 whilst the base John Deere engine is good to at least 2400 so I knew there was little chance of breaking anything.

 

................Dave 

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whatever the maximum design speed is for an engine, that is the red line. For instance, my car red lines at 10000 RPM and my motorbike at 6500 RPM. I would run the car up to 6500 easily and be happy thrashing it up to 9000, but if I ran the bike all the time at 6500 I would soon wreck the engine, so for the same reason I wouldn't run an engine with a maximum design speed of 1200 RPM at that speed.

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4 hours ago, ditchcrawler said:

Try pointing it an mains powered led light it may just measure the mains frequency

If you’ve got a smart phone you can download a strobe light and use that against a mark on a pulley.  If you have a iPhone try “strobe light tachometer” app

Edited by Robbo
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On 18/10/2018 at 14:57, Loddon said:

 

I assume one of these would be more accurate than the free RPM app that I've downloaded onto my phone? I haven't tried it yet but I think it's supposed to be used in conjunction with the phone's proximity sensor (yes my phone has one).

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25 minutes ago, blackrose said:

 

I assume one of these would be more accurate than the free RPM app that I've downloaded onto my phone? I haven't tried it yet but I think it's supposed to be used in conjunction with the phone's proximity sensor (yes my phone has one).

The app uses the flash on your phone as a strobe, you manually adjust the rate of the strobe so the item in question looks stationary.  

 

The device will probably be more accurate.

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18 minutes ago, Robbo said:

The app uses the flash on your phone as a strobe, you manually adjust the rate of the strobe so the item in question looks stationary.  

 

The device will probably be more accurate.

 

I hope that app comes with a safety warning....I always have a great temptation to touch a strobed engine to see if it has really stopped.

 

................Dave

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Just for fun I down loaded rpm app that works on audio (apparently) and it worked! Would only measure 500rpm and above so no good for tick over but the readout was very close to the other two methods I have. This confirms, to me, that my engine will not turn the current prop above 950 engine rpm. But entertaining finding out. 

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4 minutes ago, Wrinkley said:

Just for fun I down loaded rpm app that works on audio (apparently) and it worked! Would only measure 500rpm and above so no good for tick over but the readout was very close to the other two methods I have. This confirms, to me, that my engine will not turn the current prop above 950 engine rpm. But entertaining finding out. 

 

If done correctly speed based on engine or exhaust noise can be very very accurate, and can get to well below 500rpm.  Writing such an app is on my list of things to do, but this list is now much longer than my likely life expectancy.

 

My figures do suggest you are over-propped (though I am only a beginner in this subject) but the comments from others on this forum suggest otherwise.  Is your boat speed at tickover ok or too fast?

 

................Dave 

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My understanding has always been that if you’re over-propped the exhaust will chuck out loads of black smoke (incomplete combustion) when it’s unable to rev any faster, which suggests that you’re not over-propped as your engine doesn’t do that. 

 

Or is my understanding incorrect?

Edited by WotEver
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Speed at tick over is OK. I don't get shouted at by folks or is that I only pass boats that are tied up correctly ? I have been in two minds for some years now. The boat behaves its self really well on the canals. Goes, stops, reverses all with out a fuss. In that wonderful, quiet, controlled way that a Gardner 2LW should. Its just that on the occasional times we venture out on the tidal bits I feel I could do with a bit more power. It's like going up a hill on a cycle in top gear, you drop it down one and go up easy. 

The engine never produces black smoke and never has done. You can wind it up from tick over to max quickly and not a hint of smoke. 

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