Volvo Penta MD1 Injector (again)

ferrispeterchris

ferrispeterchris

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I posted previously asking for help in removing the injector.I followed the advice given and out she popped! Now a follow-up.My knowledge of all things diesel is ziltch and some how i always imagined the injector to be the size and shape of a spark plug spraying the fuel into the combustion chamber.What I have is a tube about 9" long. How does that supply a spray from that far down in the block? /forums/images/graemlins/confused.gif Peter.
 
The injector passages are full of fuel when running supplied through the pipe with the big nut. At the bottom of the injector is a dimple in which there are 5 0r 6 minute holes. Every time the fuel pump delivers this results in fuel being discharged through these holes as a very fine spray which ignites inside the combustion space above the piston due to the heat in the compressed air.

Inside the injector there is a needle valve with a very strong spring which the injection pressure has to overcome.

The tolerances inside an injector are so fine and the spring has to be set using calibrated equipment so not wise to try and fix yourself. About all you can do is to carefully brush the dimple with a brass brush to remove carbon.

The internal parts are lubricated by a minute leakage and this leakage comes out of the injector through the spill connection.

Always take fuel injectors and fuel pumps to an authorised fuel injection service centre where the correct equipment is available to service them correctly.
 
I still can't understand where physically the injector is spraying.The nozzle appears nowhere near the combustion chamber. Peter.
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Ahhhhhhhhhhhhhhhhhhhhhhhhh........

Some engines have the injector spraying directly into the combustion space above the piston. However some engines have the injector spraying into a separate combustion space which is connected to the space above the piston by a passageway. MAybe you have the latter which is not so usual on small engines.

However if you really have an MD1 then the injector does poke into the combustion space above the piston through that copper hole though only the tip is visible and the spray is shaped to fill the space. I am puzzled why you can t see this???????
 
[ QUOTE ]
some engines have the injector spraying into a separate combustion space which is connected to the space above the piston by a passageway. MAybe you have the latter which is not so usual on small engines.


[/ QUOTE ] No the MD1 is a direct injection engine.

The combustion chamber is the small space left between the crown of the piston and the underside of the cylinder head. The injector will just reach that space.

Unfortunately apart from the pretty picture in the brochure in the above link I cannot find any diagrams of the MD1
THIS, however is a diagram of the injector in an MD1B. Similar but maybe not the same
 
The bits in the diagram are what you should have removed as one unit. Take it as it is to get it serviced. It needs specialist facilities from here on in.

Handle it with some care, especially when you get it back as you do not want to damage the tip.
 
if you look at the tip with a magnifing glass you will see the spray holes which are easily damaged,
so try not to bang the tip, the injector is set to such a high pressure the diesel spray is so fine it would pierce
your skin like a hypodermic needle, hence the need
to take it to the pro.s for proper servicing.
 
The more I look at it the clearer it becomes.I was not allowing for the thickness of the head I believe so the nozzle tip looks to be where it should.By the way where can you get hold of a compression tester that will be able to be held on as opposed to screwed in?
 
The w/shop manual (for the MD1) describes carrying out a compression test (Done warm BTW) so obviously you can get a compression tester to fit. But where you would be able to hire/borrow one from is another matter.

I forget what started you delving into the diesel system but another thing that it might be worth checking/getting checked is the injection pump pressure. Adequate pressure is crucial to correct atomisation of the fuel.
 
be carefull if you decide to try the injector out of the engine as the spray can penetrate skin and cause big problems


do not fit any washers under the injector!!!!!!!
 
Just a brief update.Took the injector to a recommended diesel injector doctor a couple of hours ago.He kindly connected it up to a test rig and showed me how pathetically it was operating.Diesel was coming out in jets instead of a fine spray.He said he would order me a new (Bosch) nozzle to cost around £30,so I agreed happily.Unfortunately he has since phoned me to tell me Bosch UK and Bosch Germany have none in stock and will not have one until mid June.What a bummer! However he is try to "fiddle" with mine to try to get an temporary improvement until the new one arrives.Fingers crossed! Peter.
 
I hope you took the HP pump with the injector, nothing is designed to piss you off more than fixing the injector and discovering the pump can'r cut the mustard and you have to do the whole job over again. I last did something like this back inthe swinging sixties, but we always did the pumps and injectors together so we had the right fuel pressure to activate the injector. The pump stroke determined how much deisel was introduced and hence how much (or rather how little) power was developed....~ 6HP on the MD1 if I remember.
 
What a bummer! However he is try to "fiddle" with mine to try to get an temporary improvement until the new one arrives.Fingers crossed! Peter.

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If he has the right lapping equipment then he would be able to restore it to as good as new at a cost/time.
 
1/
I dont think that it is all that easy to lap in these nozzles as the have a double chamfer
2/ if you remove the pump watch out as the gasket is in fact a number of shims that determine the timing so require to be measured exactly and watch out for the slug on the rack peg they be missed out in the removal process

try vp for a nozzle
 
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