Injector body lapping

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1moley
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Injector body lapping

Post by 1moley »

Was listening in on an heated discussion between the Chief and Super today about the correct procedure for lapping in a injector body. Myself and C/E were new to vessel and unfortunately there was no dedicated injector overhauling kit available for use.

With relatively low experience in this area and two conflicting opinions to which is right I thought see what all you had to say from your experiences.

Of course sending ashore is sometimes best but in this situation this was not an option.

What would say would be the correct procedure for lapping in the injector body seat?

With the injector vertical in a vice.
a) Use a machined flat piece of cast iron the same diameter of the injector body, while using some jewellers rouge powder with a little MDO and moving it around. If necessary slowly increasing the course of the grit to remove imperfections and back up to jewellers rouge to provide a mirror finish as necessary.
b) As above but instead of a piece of machined flat cast iron. A piece of glass.
c) Something else entirely.

Part a) was attempted and successful. But the super insisted this was wrong and never attempted again. Where the C/E had potentially worn down the face of the injector body too much or unevenly and removed the hardened surface of the injector body seat.

Cheers all.
Moley
popeye62
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Re: Injector body lapping

Post by popeye62 »

Hello Moley. My short answer to the question 'What would say would be the correct procedure for lapping in the injector body seat?' is 'none'. The super is right. This is old school stuff and I have used a and b but neither are acceptable. Service letters from Wartsila and MAN advise against it. Why are you doing it? The injectors should be left alone unless they have reached their service limit (8000 hours) or there is something wrong (high/low exh. temp.) and then taken out of the engine and put straight on the test rig. If you are in the North Sea you are probably medium-speed on MGO? Have you seen any fuel leaking at the seating face through the nozzle nut? Presumably, you are fitting a new genuine nozzle which is flat, just fit it and see if it leaks (make sure the test rig gauge is certified calibrated). If they are leaking I would send them ashore and keep a full set as spare. The fuel must be as clean and free of water as possible. What make/type of injector are they? How many total hours do they have?
1moley
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Re: Injector body lapping

Post by 1moley »

Hi Popeye,

Thanks for your reply Popeye.

Decided between the two chiefs to replace them as last two times (3000hrs service interval) they were cleaned, checked and adjusted where necessary.

After fitting the spare set (with new nozzles).. yes we did have fuel leaking through the nozzle nut. So the decision was made to lap the bodies only.

Bergen/Rolls Royce is the engine manufacturer. I dont know if the injectors were made by a different manufacturer.

Cheers
Moley.
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The Dieselduck
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Re: Injector body lapping

Post by The Dieselduck »

Sounds like you have the service equipment already, and are planning to this frequently, I would suggest a proper lapping plate should be acquired. I haven't done it in decades, but if i remember it correctly, it was on a lapping plate, upside down, with the weight of the injector being enough downward pressure, motioning it in a figure eight pattern.
Martin Leduc
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Merlyn
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Re: Injector body lapping

Post by Merlyn »

Back to the sixties when I started a five year apprenticeship in Marine Engineering one of the first jobs you were taught was overhauling pumps and injectors.
This was interesting stuff but after twenty or so of doing them they became a bit of a ball ache to do as they became rather repetitive and you thanked your lucky stars that you were not destined to do just that for the rest of your career.
In the main these were often a stop gap job.
No outside work meant you were back to the pile to sort and after a few days outside work on a ship was most welcome to get away from the pile.
( this is how my article about using an injector and burning rag to demonstrate a flame thrower after the firms legendary Xmas booze up comes from )
The equipment used was Hartridge/Bosch/CAV and Merlin test equipment for overhauling/calibrating and sealing.
The Merlin injector grinder had a small chuck with a Morse one or two taper one end and a three jaw self centralising chuck the other end.
The tool head had a marked in degrees ( like a valve grinderM/C ) set up so you could set to the manufactures settings.
All pintles were ground and the body facings could be refaced as would the seats in the body using the cutters and tools supplied.
Every piece of kit ( Including pumps ) had a top and bottom limit so anything outside of those limits when cut / refaced would be scrap.
Springs checked, injector back together and psi/bar set to makers specification into the test rig and pump up by hand to check pressure settings and atomisations out of 3/4 whatever nozzle was installed.
Then reach for the next one.
Can’t remember what the limits were for the body or the pintles but I remember you could not take much off before the item was scrap.
A lot more importance was placed back then than today, exchange units not yet invented.
I remember refacing two/three fluted Poppet valves from inline pumps on the Merlin machine and recutting seats.
All of this was pre common rail as we are talking sixties here.
I remember the CAV/Hartridge /Lucas etc mobile kits of that era (still got one) but a lot of them were hard brass and when doing pintle valve seats they only cut out any deposits but would never ever remove any steps in the pintle.
We also had a huge sheet of hardened glass but this was used to reface Kinghorn valves and the like but I suppose if you are stuck maybe a flat mirror with fine grinding paste finishing off with jewellers rouge would get you out of trouble.
Like Martin remembers hand lapping was always done in the figure eight format.
Good old days from the past and with the price/availability of exchange units ( well, before covid anyway ) don’t do much of this anymore but at least it was all a good experience which can still stand you in good stead even today.
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.
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The Dieselduck
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Re: Injector body lapping

Post by The Dieselduck »

ehehehe, that does sound legendary.
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