Diesel Injector pipe leak

[eastlaked]

Hi Guys,

I noticed a leak where the pipe meets the injector. I didn't look too close as I didn't want to risk getting squirted with high pressure diesel. But it looked like the leak was at the pipe-nut join rather than a obvious split or hole in the pipe. I tried tightening, but no luck it still leaked.

All the other injector pipes look newer, so I guess this one has had its day. Its a Thornycroft T80 (D), so has had 20 years of vibration. I recently ran it hard to catch the marina lock, so that may have been the final straw!

I guess the options are:
(A) buy a new pipe, but I tried the usual web sites but none in stock at ASAP and the parts not mentioned on the Thornycroft site.

(B) Do I have to buy a Thornycoft specific part, or is it something that a garage / workshop just makes (ie bending a bit of new pipe to the correct shape)?

(c) Should I dismantle the joint, remove the copper washers and replace them or heat cherry red (are there copper washers? Hang on, it must be an Olive ????) ???

Some guidance welcome!

Thanks,
David.

 

[rob2]

Not familiar with the Thorneycroft, but most older design engines have a banjo union on the injector so it may well be that the copper washers will need reannealing to make a good seal.

Rob.
P.S. Sorry, it's normally the return lines that use banjo bolts!

 

[david_bagshaw]

Hi Guys,

I noticed a leak where the pipe meets the injector. I didn't look too close as I didn't want to risk getting squirted with high pressure diesel. But it looked like the leak was at the pipe-nut join rather than a obvious split or hole in the pipe. I tried tightening, but no luck it still leaked.

All the other injector pipes look newer, so I guess this one has had its day. Its a Thornycroft T80 (D), so has had 20 years of vibration. I recently ran it hard to catch the marina lock, so that may have been the final straw!

I guess the options are:
(A) buy a new pipe, but I tried the usual web sites but none in stock at ASAP and the parts not mentioned on the Thornycroft site.

(B) Do I have to buy a Thornycoft specific part, or is it something that a garage / workshop just makes (ie bending a bit of new pipe to the correct shape)?

(c) Should I dismantle the joint, remove the copper washers and replace them or heat cherry red (are there copper washers? Hang on, it must be an Olive ????) ???

Some guidance welcome!

Thanks,
David.

The high pressure pipes to the injector are not normally repairable.

the thorny croft, probably is based on the BMC 1.5 or 1.8ltr and readymade pipes are available, asap being a good supplier,(he bought a no2 cylinder pipe about 16 notes about a week ago, so give them a call. ). A common repair item on this engine. Just did one on a pals canal boat at the weekend, along with a water pump, which finally gave up from a couple of hours use on 3 cyl.

the split in all cases i have seen are directly at the bit where the pipe goes into the end fitting.

 

[The Dogs Pollacks Brother]

As above.......we had to replace one of ours on the old BMC last autumn (self inflicted damage!) and we just took the pipe to a local diesel fitter who made us one for a tenner!........job done.
It wont be a nightmare job to do so no worrys mate!

 

[savageseadog]

As above.......we had to replace one of ours on the old BMC last autumn (self inflicted damage!) and we just took the pipe to a local diesel fitter who made us one for a tenner!........job done.
It wont be a nightmare job to do so no worrys mate!

That's good advice.

I would suggest you check that the injector pipes are supported/clipped to prevent vibration which can fracture them. I don't know if it's done on those engines but it's often the case that they are lost over time if they are.

 

[The Dogs Pollacks Brother]

Our particular BMC does indeed have a couple of clips/brackets at various points to stop vibration savageseadog.
Another problem we solved easily was a very very slow drip of fuel from one of the pipe outlets on the injector pump.....not from the top end of the nut where the pipe clamps in, but from the threaded part of the nut. I can only assume it was old age as we had never touched the thing, but a very carefully applied bit of ptfe tape has done the trick!

 

[PaulJS]

One or two condescending but helpful hints

I realise that I'm probably stating the obvious here:-


When fitting new or used high pressure fuel injector pipes it's always advisable to judiciously bend them into place so that the connections are in the correct alignment and position with no tendency to spring away before tightening the unions. This simply reduces the stress on the pipe and helps mitigate against fatigue failure exacerbated by vibration.
The clamps are often used to damp out resonant vibrations rather than actually support the pipes.

Again probably stating the obvious, but when working on injector lines cleanliness is about 3 steps beyond godliness, a smear of carbon or fibre of matial on an injector or fuel pump union land can ensure that it will never seal. If it's spotlessly clean, undamaged, and has been flushed/blown through it will seal easily... And don't overtighten them!!! if it hasn't sealed at the correct torque, it probably never will.

Paul

 

[Halo]

Agree is should be do-able without too much stress. It is also advisable to match the overall length and inside diameter of the pipes if you can. On some engines injector pipe length is an important factor in timing the injection to match the piston stroke. It takes a very short time for the pressure pulse to pass through the pipe but a longer pipe delay the injection very very slightly.
Best advice I have seen on diesel fuel injection was in an old handbook
"the fuel injection systems of a good quality diesel should be left SEVERELY alone"

 

[theoldsalt]

Thornycroft T80 is not based on a BMC engine but is a marinised Mitsubishi K4 plant engine.

 

[The Dogs Pollacks Brother]

...well I never!!!!............I always thought Thorneycraft were just a company/firm that marinised various engines!

I am sure I have read about Thorneycraft BMC engines on the tinternet somewhere?.....canal junction perhaps?

May be wrong though.....

 

[SimonA]

Thornycroft T90 is the same as a BMC 1.5.

 

[eastlaked]

Thanks guys for all the hints and advice. Especially glad to have the comments about it (a) not being too costly, (b) not being too difficult and (c) I do have the option of getting a diesel workshop to make me a pipe up relatively cheaply if I can't buy one off the shelf !!

As stated, the T80 is a Mitsubushi K4 and the T90 a BMC unit.

Thanks again guys!
David.

 

[Heckler]

Agree is should be do-able without too much stress. It is also advisable to match the overall length and inside diameter of the pipes if you can. On some engines injector pipe length is an important factor in timing the injection to match the piston stroke. It takes a very short time for the pressure pulse to pass through the pipe but a longer pipe delay the injection very very slightly.
Best advice I have seen on diesel fuel injection was in an old handbook
"the fuel injection systems of a good quality diesel should be left SEVERELY alone"

Ive been a maintenance man all my life, diesels a speciality. The bit about the length of diesel injector pipe. Diesel for all intents and purposes is not compressible, therefore the "column" of diesel fuel in the pipe pushes on the injector whether it is an inch away or a mile away. Fords, old Fords, used to go to great lengths to make the pipes all the same size, others didnt. I never saw the point to be honest. Think about it!
Stu

 

[cimo]

Ive been a maintenance man all my life, diesels a speciality. The bit about the length of diesel injector pipe. Diesel for all intents and purposes is not compressible, therefore the "column" of diesel fuel in the pipe pushes on the injector whether it is an inch away or a mile away. Fords, old Fords, used to go to great lengths to make the pipes all the same size, others didnt. I never saw the point to be honest. Think about it!
Stu

thats what I was thinking. Common rail systems wouldn't work if lenght mattered?

 

[david_bagshaw]

thats what I was thinking. Common rail systems wouldn't work if lenght mattered?

different, injection electronically controlled at the injector, so length behind it is immaterial. the common rail becomes a type of resevoir, hence why the rail is larger.

all in line small engine pumps i have dealt with have same length,pipes bosch, mercedes benz, mitsubushi & kubota, also dpa pumps as fitted to peugot, bmc etc

 

[oldharry]

Common rail works very differently to the old mechanical rotary pumps: in common rail the injectors are all fed from a reservoir, kept under a constant pressure. The injectors are opened and shut electronically, providing very much more precise control of timing and quantity of fuel injected.

The old mechanical pumps operated by increasing the pressure in the injector feed pipe, against a spring in the injector. When the pressure reached a pre-set level the spring was forced open to allow the injector to work. The timing and duration of the pressure pulse was critical, and much research was undertaken to try to make the timing and metering of the mechanical system more precise, so the debate about the length, diameter and material of injector pipes was intense.

 

[cimo]

ah! could have thought about that a little longer . thanks.

so what is the general concensus on pipe lenght for older mechanical systems.
what sort of tolerances are we talking about? (bukh 20 owner).

 

[PaulJS]

Ive been a maintenance man all my life, diesels a speciality. The bit about the length of diesel injector pipe. Diesel for all intents and purposes is not compressible, therefore the "column" of diesel fuel in the pipe pushes on the injector whether it is an inch away or a mile away. Fords, old Fords, used to go to great lengths to make the pipes all the same size, others didnt. I never saw the point to be honest. Think about it!
Stu

I've been a marine engineer all of my working life and until recently would have agreed 100% with this, but I've recently been studying hydraulics and have found that fluids are appreciably compressable at high pressures - about 4% at 400 bar. I appreciate that 4% isn't much, but in a 1800rpm 4-stroke there are 15 accurately metered injections every second per cylinder, so maybe that 4% is important...

 

[savageseadog]

I've been a marine engineer all of my working life and until recently would have agreed 100% with this, but I've recently been studying hydraulics and have found that fluids are appreciably compressable at high pressures - about 4% at 400 bar. I appreciate that 4% isn't much, but in a 1800rpm 4-stroke there are 15 accurately metered injections every second per cylinder, so maybe that 4% is important...

There's also the elasticity of the pipework

 

[Heckler]

I've been a marine engineer all of my working life and until recently would have agreed 100% with this, but I've recently been studying hydraulics and have found that fluids are appreciably compressable at high pressures - about 4% at 400 bar. I appreciate that 4% isn't much, but in a 1800rpm 4-stroke there are 15 accurately metered injections every second per cylinder, so maybe that 4% is important...

Im talking 4108 perkins, rolls royce eagles, the old straight six fords, cat 3306 (see here http://www.youtube.com/watch?v=T8TfYXJE-uY ) engines of that ilk and era, the fords were the only ones that bothered. The vast majority of our yacht engines are old tech as well and i would be surprised to see any serious efforts made to make sure the pipes are of the same length.
Stu
PS I set up 3 of those cats in Angola in the late 70s as the camp gennies, used to run them a month at a time in rotation. The turbos used to run red hot and the glow used to light up the gennie shed at night, We had 8 Porta kabins, a double PK kitchen unit with a walk in fridge and a walk in freezer. All electric range and full AC in all cabins. They were 135 kva each, I adjusted them to run at 1800 revs rather than the std 1500 rpm, this to up the voltage and cycles. The ware house man had orderd thinking the camp was going to be 50 Hz. It wasnt! Plus we had to adjust the windings to give 110v phase neutral and 208 (upped to about 215 by the increase in speed) phase to phase for some of the UK stuff