Bleed Screw ??

Caer Urfa

Caer Urfa

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We all undo the 'bleed screw' to bleed the engine but usualy never actualy take it out.
I am still trying to trace how after every 12/14 hrs my engine shuts down, as soon as I bleed it she runs for another 12/14 hrs, hence we think the engine fual system 'SOMEWHERE' is slowly 'sucking in' small amount of air over the time and builds up to a point the engine shuts down.
Both fuel tanks were removed and cleaned out, all new fual pipework and fittings also checked everything three times all jubilee clips,filter nuts/bolts,valves, tank connections etc etc.
However one thought is should there be a washer on a bleed screw? as what actualy seals it.
Any other suggestions 'very' welcome.
 
'If' a washer should be fitted what would others suggest Rubber or Copper or other?
Is it normal to have a washer fitted? is a bleed screw special and dedicated to the engine? or a standard bolt? as I have never actualy taken it out to look at it.
Mike
 
Lack of a washer could be your problem - had a similar prob on our last boat, cured by using a small fibre washer from a motor engineers shop. Think you can also use a soft copper washer..

Also have replaced a bleed screw with a standard bolt after re-cutting the hole to a slightly larger thread - & used a washer too!! Normal bleed screws have a slot cut up the thread to allow the air escape but, IMHO, not essential.
 
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should there be a washer on a bleed screw?

[/ QUOTE ]

Not always, it depends on the design of the bleed screw. A brake type bleed screw has a pointed end that seats in a tapered hole. This type does not need a washer. The other type seals under the heas of a screw and this type does require a copper washer.

If you think you have a leas of air into your fuel systen this is most likely between the tank and the lift pump as this us under suction. Between the lift pump and the injectors are under pressure which will cause fuel to leak out.

One of the ways to check for leaks is to disconnect the fuel pipe from the tank and pressurize the complete fuel line with a bicycle pump and check to air bubbles with a water/soap mix
 
The symptoms just don't seem to indicate a fuel system leak. I once had a cracked copper fuel pipe that took ages to locate but in that case the symptom was that the engine would never start from cold without bleeding - once running it would run forever.
It doesn't seem right that such a fault would be so predictably progressive - that sounds more like, perhaps, a blocked fuel tank vent or some other fault that leads to fuel starvation in a predictable period of time.
 
Quite correct Roger. Take the screw out and examine seating to see which type it is. DON'T use fibre washers. It should be copper if necessary at all. I am inclined to think that it might well be dirty or contaminated fuel blocking the small bore pipework somewhere though. Often the dreaded black bug gunge takes a while to build up, is cleared by bleeding, and then builds again. That's not to say it is not an air leak though. Check both. 12-14 hours trouble free running seems to indicate a progressive build up of gunge.
 
Many thanks Gents for the help so far.

All the existing Microbore copper pipe was removed and replaced with 3/8" LLoyds class rubber fuel pipe.
The primary/secondary filters were all replaced new with Glass bowl type,what I am saying is everything including cleaning out the tanks was done only 3 months ago.
Diesel is from our regular marina station.
There are no signs of fuel leakage anywhere
We therefore rightly or wrongly conclude 'Somewhere' we are 'sucking' air in and as said is building up over a time and shutting the engine down.
The one place I have not checked was the sealing of the bleed screw hence this post.
Some of you say you have had similar problems, where did you find the problem,was it air sucking in?
I will check the type of bleed screw the weekend and if necassary get a copper washer.
 
I always replace copper washers during my annual service. There is an informed opinion that by heating and annealing them they can be re-used. Personally for the cost don't think it's worth it.
 
It would help to know what type of pump you have. From the way you describe the motor shutting down, it is likely you have a distributor type pump.
Most DPA pumps should be able to cope with small air leaks as they generally self bleed while running; through the fuel return port.
The body bleed screws are at metering pressure when the engine is running and will therefore leak, not allow air in.

Some CAV rotary distributor pumps have a banjo bolt with a very small orifice drilled in it to allow self bleeding through the return port, whilst still allowing the metering pressure to be closely controlled.
If this orifice is blocked, then the pump cannot self bleed and will eventually stop injecting.
Other CAV types have a sprung ball valve in the banjo bolt to help control metering pressure, if this has stuck or the spring has broken.........

Other types have nothing but a plain banjo bolt or tube nut on the return port.

Filter heads. Is the return line from the connected to the return port on the filter head? I have known thiese to be wrongly connected and any air gets recirculated.
Likewise, is the return line from the top of the filter clear all the way back to the tank or thermostart fuel reservoir, then all the way back to the tank?
(I am assuming CAV system).


Just some simple things to check.
 
I spent months trying to cure a recurrent air problem, each time I found something suspect and fixed it, it popped up again. In the end I found the bleed screw seat on top of the filter was badly scored: coupled with fuel getting dirtier, when the filter nearest the injector pump got a bit jammed the pump sucked air in through the bleed screw which is between the final filter and the injector pump.

Normally the lift pump pressure would keep the air out, but only when there is a free flow through the filter.
 
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