Selami Kumru

Articles by Selami Kumru on the RSS Kumru Automotive blog.

Drawing: four injectors side by side on top of an engine; a clear hose runs down from the return port on top of each injector into one of four clear chambers hanging side by side in front of the engine; in three chambers the fuel stands at the same level, in one it is clearly higher, and that chamber and its injector are marked in red; the magnifier shows the push-fit return connector on top of an injector with its clip and O-ring, and diesel seeping from the joint and dripping down the side of the injector

September 8, 2026Injection and fuel lines

Injector leak-off line: what it does, why it leaks, and when the injector is to blame

When a common-rail leak-off line leaks, check the clip and O-ring first. How a leak-off test is done, how to read it, and where the sources disagree.

Drawing: four fitting ends in section, side by side: banjo, tapered thread, flat face with O-ring, flared cone; on each one the place where it seals is marked in the same blue: the two washers on the banjo, the thread itself on the tapered thread, the O-ring in the face on the flat-face end, the cone faces on the flare; the magnifier shows two cones whose threads engage but whose angles differ, with a thin gap left between them

August 11, 2026Fittings and selection

Hydraulic fitting types: JIC, ORFS, BSP, NPT, metric, and 37° versus 45° flare

A fitting is identified by where it seals, not by its thread. JIC, ORFS, BSP, NPT and metric ends, why 37° and 45° flares do not mix, how to measure.

Drawing: a fuel pipe running over the hot exhaust manifold on the side of an engine; diesel leaking from the fitting in the middle of the pipe drips onto the manifold, which is drawn in red and gives off heat; in the corner an inspection sheet with one line marked with a cross; the magnifier shows the drop hanging under the fitting and a piece of cardboard held beneath it to find the leak, with a wet patch on it

June 30, 2026Injection and fuel lines

Is a diesel leak dangerous, and will it pass inspection?

A diesel leak can ignite on hot parts and, under pressure, penetrate skin. How the MOT manual and Turkey’s defect table class it, and what to do.

Drawing: a banjo joint in section; a hollow banjo bolt passes through the ring end of the pipe and screws into the housing, with a washer on each face of the ring, and the oil comes from the engine along the pipe and through the bolt into the housing; the magnifier shows a new washer above an old one that took the imprint of the faces when it was tightened

June 16, 2026Fittings and selection

Banjo bolts, washers and gaskets: copper or aluminium, reuse, and sealant

Banjo bolt washers are renewed every time, in the specified material, with no sealant. Copper versus aluminium, annealing, and why no general torque exists.

Drawing: two lengths of hydraulic hose of the same type, one above the other, one thin and one thick; a line of print, drawn as small boxes, runs along each of them; the pressure gauge beside the thin hose reads high and the one beside the thick hose reads low; the magnifier shows the four boxes of the layline: type, size, working pressure marked in red, and date of manufacture

June 2, 2026Fittings and selection

How to read a hydraulic hose pressure rating: what the layline tells you

The layline gives type, size and working pressure. What 1SN, 2SN and 4SP mean, how pressure changes with size, and whether a 3000 psi hose will do.

Drawing: the path of the fuel on a diesel engine, left to right: tank, filter with a bleed screw on top, high-pressure pump, fuel rail and injector; the low-pressure side from the tank to the pump is marked, and the nut of the high-pressure line running from the fuel rail down to the injector is marked in red; the magnifier shows fuel with bubbles coming out around the loosened bleed screw

December 4, 2025Injection and fuel lines

How to bleed a diesel fuel system after a filter or line change

Mechanical pump: bleed screw, hand primer, then the line nuts. Common rail: the electric pump fills the system and the high-pressure lines stay tight.

Drawing: two hoses taking the same turn, one inside the other, each with a fitting at both ends; the upper one, a steel-braided PTFE hose, passes a hot part that gives off heat and takes the turn in a wide bend, while the rubber hose below takes the same turn more tightly; the magnifier shows a PTFE hose bent too sharply, in section: the liner has collapsed inwards at the bend and narrowed the passage

November 4, 2025Fittings and selection

PTFE hose or rubber hose? Temperature, fluid, bending and service life

What temperature a PTFE hose takes, why it kinks, why fuel needs a conductive liner and how long it keeps on the shelf, set against rubber hose.

Drawing: the suction side of a fuel system, left to right: tank, the pipe leaving the tank, a rubber hose with two clamps, filter, a clear hose and the pump; the loose clamp, the crack in the hose and the filter seal are marked in red, blue arrows show air getting in at those points, and bubbles travel along the clear hose towards the pump; the magnifier shows air being drawn in through a hairline crack in the wall of the hose, with bubbles in the fuel

October 30, 2025Injection and fuel lines

Air in a diesel fuel line: hard starting caused by pipes and hoses

When air keeps coming back, look for a leak: hoses, clamps, filter seals or the return line. The symptoms, and four ways to find where it gets in.

Drawing: a high-pressure pump on the left, an injector on the right and, between them, a jacketed fuel pipe that looks like one thick pipe; a window opened in the pipe shows the thin high-pressure pipe inside it and a crack in that pipe; a thin leak-off line runs from the lower end of the pipe down to a small collecting tank, and a red alarm lamp is lit beside the tank; the magnifier shows the cracked high-pressure pipe, the outer pipe around it and the fuel from the crack staying inside the outer pipe

August 26, 2025Injection and fuel lines

Jacketed (double-wall) fuel injection pipes on marine diesel engines: what SOLAS requires

SOLAS wants the high-pressure fuel pipes between pump and injector jacketed. The rule’s wording, which ships it covers, the 375 kW exception and upkeep.

Drawing: an injection pump on the left and four injectors in a row on the right; one line runs from the pump to each injector, the line to the near injector loops around on its way and the line to the far injector goes straight there; below, the same four lines are drawn straight with their ends level, all four the same length; the magnifier shows a shortened line that does not reach its seat, leaving a gap

July 15, 2025Injection and fuel lines

Why are injector lines the same length? Can they be shortened or bent?

Why injector lines are made the same length, and why they are not shortened or bent: Bosch’s rule on line dimensions and Perkins’ advice on fitting.

Drawing: a cracked injector line running from the fuel rail to the injector, patched with a sleeve, yet diesel keeps dripping from under the patch; below it a new line bent to the same shape waits to take its place; the magnifier shows the patch in section: the crack runs through the wall of the line from the inner wall to the outside, and the patch stays on the outside

May 6, 2025Injection and fuel lines

Can a cracked fuel or hydraulic line be repaired?

A cracked injector line is replaced, not repaired. Why welding, brazing and unions fail, and what changes on supply, return and hydraulic lines.

Drawing: a bent injector line running from the fuel rail to the injector, with a clamp at mid length; the magnifier shows a crack starting right behind the nut

March 11, 2025Injection and fuel lines

Why do injector lines crack?

Not from pressure but from fatigue: vibration, assembly strain and material. What the clamps do, the right fitting order, and why a cracked line is never repaired.

Drawing: a single hydraulic hose in side view, gently curved, with a fitting at each end; three signs of damage are marked in red along it, from left to right: a section where the cover is worn away and the wire braid shows, a blister, and fine cracks; the magnifier shows the right-hand end: the hose has slipped out of the ferrule, leaving its old seat exposed, and a drop of oil hangs at the end of the ferrule

February 11, 2025Fittings and selection

When to replace a hydraulic hose: the failure signs

The signs that a hydraulic hose must be replaced and what causes them, DGUV’s 6-year guide value, and why a leak is never traced by hand.

Drawing: an injector line running from the fuel rail to the injector, with diesel dripping from behind the nut at the injector end; the magnifier shows the inside of the nut: the cone on the line sits in its seat metal to metal, with no gasket, and a scratch on the sealing face lets the fuel out

January 15, 2025Injection and fuel lines

Injector line leaking at the nut: tighten, clean or replace?

More torque is not the fix. Check the torque once, then the sealing faces and the alignment; on common rail fit a new line. The order of work.

Drawing: the same steel tube in four states from top to bottom, with arrows between the steps: a straight tube cut to length; the tube with its nuts on and a cone pressed on each end; the tube bent; the finished line with a cap on each end. The magnifier shows the end of the tube in section: the pressed cone, the nut behind it and the bore left open inside

August 13, 2024Injection and fuel lines

How a diesel injection line is made: from steel tube to finished part

How a diesel injection line is made: seamless steel tube, cutting, cone forming, bending, autofrettage, coating and cleaning, with the reason for each step.

Drawing: an injector line removed from the injector and pulled back, its cone facing the empty seat in the injector; the magnifier shows a new cone above a used cone: the used one is marked and its bore has narrowed

June 13, 2024Injection and fuel lines

Can injector lines be reused once they have been removed?

On common rail most makers want a new pipe every time; on older mechanical engines a sound pipe goes back. How to judge the cone and when to scrap the pipe.

Drawing: a fuel rail on top of the engine with steel high-pressure pipes running down to three injectors; the union of one pipe is wet, diesel has pooled at the foot of that injector, and a fine mist and a smell rise above the union; the diagnostic tool beside the engine shows no fault code; the magnifier shows a hairline crack in the pipe right next to the union, with diesel seeping from it

February 20, 2024Injection and fuel lines

Common-rail pipe leak: symptoms and what to do

A leaking common-rail pipe shows as diesel smell, wet fuel or mist, sometimes with no fault code. Symptoms, risk and the order of work from maker documents.

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