With injectors removed the engine has no compression and can easily be turned by hand.

During a leak-down test, we always pressurized the cylinder, tested, and then did it again after putting a squirt of oil in the cylinder. If the squirt of oil reduces the leakdown a great deal then the problem is rings.

- Jeff Miller
190DT

MB FSM (factory service manual ) leak down test document says :

Warm up engine,
Unscrew glow plugs
on 615 and 616 wit pneumatic gov. pumps, detach rubber gaite on throttle body and set throttle to full delivery, on mechanical gov. pumps, detach air filter,
Remove oil cap
Top up coolant, leave cap off
Screw connector into glowplug hole 1
Set 1 at TDC
Connect leak tester to air system and calibrate
Screw tester hose to connector
Make sure engine no move
Note pressuer loss on tester
Listen to see whether pressure leaving form intake pipe, exhaust, oil filler cap, radiator cap, or glow plug hole of adjacent cylinder
Check all cylinders in firing order -- 1-3-4-2 for 615 and 616 and 1-2-4-5-3 for 617

I'm confused on where to listen at exhaust and what leakages out of adjacent glow plug hole tells you. Does that tell you you have valve leakage?

thanks

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What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

Can you you do leakdown test with valve cover off? To see TDC or cylinders you would not firing order and watch harmonic balancer pulley right? IE, Start at 1 and check valves are in V shape pointing up under oil cap and set balancer at 0. Then next time it goes around to 0 you know that the next cylinder in firing order is at TDC?


Also, you do the leakdown test in teh injector hole or glow plug hole right? I am going to do a compression and leak down test today. thanks

__________________
What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

Because the engine won't be turning fast enough to engage convertor. But you also should NOT rely on a manual transmission keeping the engine from turning when you apply pressure. The engine will still turn, but the car will move, possibly causing injury. Keep it in neutral (or park), and keep your hands clear of any moving parts during the test.

I think this is very wrong. If i remember from valve adjustment every 2 revolutions of crank shaft the #1 cyl. is TDC. I think those marking are only for #1 cylinder. Hmmmmm, how to check for TDC on cylinders with walve cover? just feel it? Look in fuel injector hole and feel it? hmmm. wondering and searching.

__________________
What Would Rudolph Do?
1975 300D, 1975 240D, 1985 300SD, 1997 300D, 2005 E320 , 2006 Toyota Prius

Are there marks possibly on the harmonic balancer for each cylinder on the 617? (mine's a little rusty and can barely even see the degree marks for cyl 1). Too bad the shop manual doesn't really give any detail about finding the other cylinders

What about a "TDC whistle"? I've seen these for gassers where you just listen for no sound as you crank. Never used one though. Maybe a hose could be used between an injector/glow plug adapter and a whistle.

__________________
Dave

2002 Audi S6 Avant
1983 300D
1984 300D (sold)
1990 560SEL (sold)

this post keeps coming up in my search results, and it sure seems it should have been answered/resolved. (i'd love to know how to do a leakdown test on my 617 3rd cylinder only, with the valve cover gasket on).

sdelasal's question:
biobenz617's question:

__________________
-lee
'83 300CDT (286k)

former proud owner of:
'85 mercedes euro 300TD
'80 mercedes 300TD
'77 mercedes 280e
'80 mercedes euro 250
'82 mercedes euro 250

On gas engines with no real timing marks whats usually done is to stick the wooden end of a pencil through the spark plug hole and use this trick too find TDC.

I doubt this would be possible on most diesel engine, but can you see the top of the piston through the injector hole?

If so it would work.

With a degree wheel on the crank, looking through the oil filler hole you could probably figure it out, but it would be easier too just take of the valve cover.

With a good light, you might be able to see the piston through the bottom port on the pre-chamber, but I couldn't swear to it.

__________________
-Josh
Testing the cheap Mercedes axiom, one bolt at a time...

Degree wheel installed on the damper. Calculate the other cylinders degree positions is one set up. Top dead centre for # 1 is marked on the damper already as a fixed refference for your calculations. So you can be deadly accurate this way. Fair to say it's a pain in the posterior though.
The only other way I can think on this engine is to set each cylinder to it's start of injector point for each cylinder in turn. I would dry out and use the point at which fuel starts to creep into the injection pumps exit port for that cylinder. By experimentation you then have to figure how many more degrees to turn the engine until top dead centre is found or close enough. I imagine about 14 degrees.
If you use # 1 cylinder you will get the physical distance measurement right plus a usable refference for the other cylinders. Just measure how much further the damper had to be moved to get to top dead centre past the injector pump fuel appearing on number one as it does indicate true top dead centre with a mark.
Mark the damper at the point of initial filling for the other cylinders in turn. Mark the distance to go on the damper that you aquired from your # 1 cylinder effort. Move the engine forward to your new mark will put you close enough to top dead centre for that cylinder.
You have a small degree of latitude here as you can be off a few degrees and the piston will not decend with air pressure. This way you do not need any special equipment.
I am not saying it is impossible to do it totally manually but insanity might develop over it.
Fortunatly I am concerned most the time with only one cylinders deficiency. For that injecting compressed air after fiddling around for awhile to put that piston at the top dead centre position so it does not move only takes a bit of effort.
On these indirect diesel engines I am probably still going to use the well up method on the pump to find it quickly though. I am only going to increase the air pressure until I hear where the air is going as well. Others will have better approaches perhaps.
For random home use I would use the initial fuel entering each exit port on the injection pump for simplicity and usable accuracy. Do not use kleenex to wick out existing fuel in the exit port on the pump. You do not want to add any contaminates at that point. A tiny blast of low pressure air might blow the fuel out instead for example.
It has to be dry to find when fuel first enters remember. Plus since there is no injector pop pressure to overcome even a worn pump is going to be fairly accurate at showing you when flow initiates into that cylinders element. Hope this is of some help as it's about the best I can do. It will work.

Leakage at adjacent cylinders glow plug hole. Bad head gasket or major head crack. Usually going to be the head gasket.
To listen for leaking exhaust valve go to the tailpipe at back of car. If you have a 300sdl it's a longer walk I imagine but dooable.