12- Testing and Diagnostics
             12.1 Compression testing
             12.2 Leak down testing
             12.3 Bench test of rebuilt engine

             12.4 Test results
             12.5 Injector testing

             Table of contents

12.1 Compression Testing


12.2 Leak down testing

There is a lot of info on the net about building and using a leak down tester, Harbour freight sells units as do many other automotive supply centers.

Living on a small Island access to stores is limited so I tend to do it yourself, searching the net I found a few designs of which I show you the basic how it works here and a photo of my finished unit. This unit seems to work fine and I have added a link to a youtube video that I have created to show folks how this simple test works. I created this video as there seemed to be a lot or poor instructions trhat come with commercial units and misunderstanding on the part of the home mechanics on how to get meaningful results. so here ya go.

leakdown testerPretty simple really, from the right a pressure gauge screwed into a side port of a standard compressor pressure regulator, you connect your air supply to the quick connector on the front. The knob on the top is for adjusting the pressure, the gauge on the right shows you what the pressure regulator is set at (not really all that relevant). Continuing on from the left of the regulator a pipe runs out to a small brass fitting that I filled with solder then drilled a 1mm hole in the center of. This is the restrictor or orifice that allows you to obtain a pressure differential. Next is a "T" with a pressure gauge, followed by a gate valve and finally a quick connector that you hook your hose and head adapter to. I stripped down and welded up an old injector, some folks use a compression tester adaptor with the check valve removed on gas engines you can adapt an old spark plug. You could even use an old glow plug I bet. You want to set the regulator to get a 100 psi reading with the gate valve closed, when you open the gate valve and pressurize the piston the pressure drop is the percentage of leak down. See the video below.


Your basic schematic of a leak down tester as built above.
This drawing conveniently snagged off the internet, I would normally give credit to the author but a number of people have used this drawing and not given credit to the original source, my apologise.

12.3 Bench test of rebuilt engine


12.4 Test Results

To put all this testing into context below are the results of the engines that I have tested with the above tools.

Cold or warm indicates whether I had warmed up the engine prior to testing.

  ENGINE 1 N/A DIESEL 540KM (cold) ENGINE 2 TURBO DIESEL UNKNOWN KM (warm) ENGINE 3 TURBO DIESEL 200 KM on rebuild ENGINE 4 TURBO DIESEL  Low KM on rebuild (cold)
CYL #1 500 PSI 15% 540 PSI 10%  STAY TUNED     450  25%
CYL # 2 500 PSI 15% 520 PSI 12%     490 15%
CYL #3 500 PSI 15% 540 PSI 10%     450 20%
CYL #4 500 PSI 15% 540PSI 10%     490 10%
COMMENT A little tired burns oil, runs good Runs good, smokes a little Rebuilt recently, runs nice Rebuilt recently, runs good
Diagnostics Over all not bad, perhaps oil seals need replacing to solve the burning oil issue.
UPDATE: Replaced the seals and indeed the blowing blue is gone.
Clearly a little low on one cylinder.
It sounds from the air escaping out the air intake like not a good seal on the an intake valve on that cylinder. Not serious enough to do anything at this time, will monitor over time.
  Whoa Nelly, two cylinders down, and air coming out the exhaust valves, perhaps carbon build up or cracks. You could actually hear the air coming out of the other cylinders injector holes, due to there exhaust valves being open.
Very revealing.

12.5 Injector testing