Leaky Injectors

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. Pipe lengths are supposed to be the same length to keep the injection timing the same on each cylinder.

First iv heard about this...be interested to know a bit more !.....

[/ QUOTE ]Me too! new one on me that the length of the injector feed pipe controlled the injrctor timing /forums/images/graemlins/wink.gif
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"Artificial intelligence is no match for natural stupidity"
 
Internal diameter of the injector pipe is important - too small and insufficient fuel is delivered, too large and insufficient pressure is developed to fire the injector precisely on time. I had not heard that length matters, but if the quantity of fuel in the pipe between the pump and the injector is important, then incorrect length would alter the time the pressure pulse reaches the injector to fire it, and also could alter the opening time of the injector, changing the amount of fuel delivered into the cylinder. It is quite surprising how much difference an incorrectly sized high pressure pipe will make to an engine.
 
So that’s it John
You may not want to change the pipes but unless you particularly like the smell of diesel you will have to, no seal or repair will stand that pressure that’s why it`s a metal to metal joint to start with. So you must bite the bullet and put your hand in your pocket.

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all quite simple really.
 
If you mean the pipe between the injector pump and the injectors then neither length or diameter makes any difference. As it is a hydraulic action (ie. you can’t compress a liquid) the pipe could be a meter in length and as long as there was no air in it any pressure supplied at one end would be the same at the other.
So a high pressure is delivered to the injector which is set to burst open at a preset pressure and any access is led away down the weep line back to the fuel tank.
On the new single rail diesels there is only one pipe supplying the injectors and the burst timing in the injector is controlled by computer.
So they have taken a good basic design and made it extremely complicated, still that’s progress I suppose.


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what a pl***er!
i cant believe anybody would show their ignorance so publicly and seriously think they are right!
stu
 
oh deary me, what a load of cobblers, in essence, diesel is not compressible, pressure applied one end comes out the other end so it doesnt matter how big the internal diameter is when it is filled. the reason injector pipe is very small internally is because the smaller it is the less surface area is exposed to the the v hi pressure ( 200 bar approx or 3000 psi)
 
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Pipe lengths are supposed to be the same length to keep the injection timing the same on each cylinder.


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/forums/images/graemlins/ooo.gifSorry but I disagree with that statement!!!!!

When I first started my apprenticeship it was in Aussie working for the NSW Gov railways and I worked on both steam and diesel engines. In the case of the diesels they were V12 cyl Detroit diesels and I can tell you that the difference in pipe lengths between No 6 cyl and No 12 was about 6 feet!!!!!

You can't compress diesel so once the line is bled as soon as the distrubutor pump fired so did the injector.

So on small marine diesels it wouldn't matter a hoot if the pipe was a couple of inches longer/shorter.
 
johnneale,
am I misunderstanding your question? The union between the delivery pipe from the injector to the injector pump is normally the same type of metal-to-metal (normally steel-to-steel) joint as the union between the delivery pipe and the injector, therefore you need copper washers there too. A steel-to-steel union will leak without maleable metal washers.
 
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If you mean the pipe between the injector pump and the injectors then neither length or diameter makes any difference. As it is a hydraulic action (ie. you can’t compress a liquid) the pipe could be a meter in length and as long as there was no air in it any pressure supplied at one end would be the same at the other.
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[/ QUOTE ] In practice, replacing a fractured pipe with one of a different size makes the engine run rough. Also diesel is slightly compressible, unlike water, which is why water in the fuel instantly wrecks many injector pumps. I was taught that when the pump opens a hydraulic shock wave travels up the injector pipe causing a tiny but measurable delay before the injector reaches pressure to open. Pipe length was therefore regarded as critical. The actual designed length of the pipe was allowed for in setting the injection timing, so will be altered if the pipe length is changed appreciably so a 6 foot delivery pipe length would be allowed for by the designer when setting the timing.

As I understand it the new common rail injection system was developed to get round these delay problems, to ensure smoother more precise delivery to the injectors and to reduce the level of hydraulic shock loading which is one of the causes of delivery pipe failure. It also apparently improves the quality of the fuel burn by controlling the precise moment of injection/ignition which in turn improves fuel efficiency and reduces particulate emission. So I am told.

The diameter of the pipe is also critical, as it affects the amount of fuel that reaches the injector during the pressure pulse. If the bore is too small, it prevents sufficient fuel being delivered while the injection pump valve remains open to deliver the charge. Again a problem entirely resolved by the common rail system.

Even a tiny amount of air in the system is highly compressible and will absorb most of the pressure, which is why bubble free fuel is so important.
 
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Replace the pipes, a diesel mist is a fire hazzard.

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But it does stop the engine from rusting /forums/images/graemlins/smile.gif

To be serious - change the pipes, can't believe they will cost that much if made up by an injection specialist. The spray is only going to get worse and eventually some air or crud will get in when the engine is switched off, risking an air lock or a blocked injector.
 
If I was wrong to say "Cliff says it doesn't make any difference to hardness if you quench or not.", what does "Subsequent quenching will not harden the copper again" mean?

Making another comment based on my experience, I am sure that there is no need to have injection pipes the same length otherwise millions of engines would not work.

What sometimes causes this leaking is if the high pressure line is not properly aligned with the injector. If the cone on the end of the pipe is canted there can be a leakage past the joint. Loosen off the anti-vibration clamping and the high pressure joints to the injector. Ensure that the pipe is lined up with the injector and tighten union. When all unions have been pinched up, retighten the anti vibration clamps. You may find that this solves your problem. If not, it sounds like new piping is required.
 
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, I am sure that there is no need to have injection pipes the same length otherwise millions of engines would not work.

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I dont think I said the pipes had to be all the same length - just that when replacing them, they new ones need to match the originals both for length and internal diameter to ensure fuel delivery is unaffected.
 
Oldharry

I believe you, well I`m willing to give you the benefit of the doubt, but then does it really matter as surely it would not be cost effective to make up your own pipes, unless of course the engine is an antique and spares are not available.
Johnny has kept his engine make secret but he has a Husky 24 so the engine will be quite small and so new pipes relatively inexpensive, I don’t think there’s any doubt that’s the only way to cure the leak.

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Steel is elastic. The pipe expands in diameter and length when the pressure is applied. This increases the volume of the pipe. The volume of fuel pumped into the injector pipe in small engines particularly, is very small. The wall thickness of injector tubing is very high in order to limit the volume increase rather than to withstand the pressure which is much the same as hydraulic equipment pressure. A flexible hydraulic hose as fitted to mobile plant etc. would withstand the pressure involved but the tiny pulse of fuel being pumped into the pipe would merely cause the hose to expand and nothing would come out of the other end.

This is an extreme illustration and many an engine would continue to run even with unbalanced pipe lengths. I have welded up broken pipes on occasion and used whatever pipe was to hand temporarily, but if you examine most multi cylinder engines you will find that the pipe lengths have been made the same even though the runs from the pump to the various injectors could have been made shorter for some of the cylinders.

More modern engines with common rail systems have become more fuel efficient and quieter due to the more accurate control possible with electronics and multi-stage injection - injecting a small amount of the fuel to ignite and then the remainder once the flame is established. The pressures have increased ten fold from around 2,000psi to 20,000 psi which better atomises the fuel and produces a cleaner more efficient engine.
 
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Oldharry

I believe you, well I`m willing to give you the benefit of the doubt.....

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Hmmm - shouldnt do too much of that if I were you!

Most of what I know was picked up from practical experience running a fleet of commercial passenger boats, and with the inshore fishing fleet. (not a lot small boat fishermen dont know about their engines - and significant how rarely they came up in RNLI figures with engine failures, compared to us yotties...?)
 
Re: Leaky Injectors - Another point

Thanks all --- I think we've got that cleared up now & I need to renew all the pipes - The engine is a 4 cylinder BMC Captain with Hydraulic pump. Pipes are all the same length and I should be able to get them made up here in the UK. ........

However ..... The boat is in Greece & I wont be going there until April ----- has anyone any experience of bending these pipes to fit???? or can I get them pre-formed for my engine ????

If they are not identical to the originals (not here) then the timing will be out.
 
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