OM321 starting problems (1992 barge in france) - PeachParts Mercedes-Benz Forum

Barginginfrance · #1 02-12-2014, 03:57 AM

I live aboard an old 1922 cargo barge in France with a Mercedes OM321 diesel. Over the last couple of years, the old girl has become increasingly difficult to start, resulting in my pre warming the air using a hair dryer stuck in the air intake on top of the rocker cover.

The problem is the glow plugs. I've checked the wiring, replaced the plugs but whatever I do, I think the plugs are 'shorting' by making contact with what I believe is carbon on the inside? Could this be right? If so, does anyone know how to get rid of it and would a reamer do the job? If so, any idea where I'd get one?

All help appreciated.

Shortsguy1 · #2 02-12-2014, 07:56 AM

Edit: Thanks for moving this vstech!

Original post:
Given the age of your engine, you should start a new thread. This thread deals with much newer glow plugs, so the expert you need may not ever see it. I just spent a few minutes trying to figure out if your engine is similar to the later om621 or om615, but was unsuccessful. Your engine is indirect injection and probably uses similar loop style glowplugs but perhaps it uses the even older wound filament gp. The post in this link has some links to other threads which may be useful (including reamer dimensions for the hopefully similar om615 engine)
w110 200d glow plug questions

and perhaps this document is relevant, but I am just not sure:
http://www.170v.de/yabbfiles/Attachments/Preheating.pdf

But like I said, your best bet is to start a new thread. Good luck!

vstech · #3 02-12-2014, 09:52 AM

more than likely, you have the loop style glow system that uses solid metal resistor wires and insulators between each subsequent glow plug, and a ground strap on the last plug in the circuit. I"d recommend upgrading to the pencil style plug. order the number of plugs your engine has, and install a set of Bosch 80035 plugs like pictured below, and throw away all the insulators, and disconnect the ground loop, then just use copper wire from the glow controller, to the plugs, and enjoy MUCH BETTER glow times.

mespe · #4 02-12-2014, 12:52 PM

First let me state, that I am not at all familar with that engine.
Secondly, if it's an older Mercedes Diesel, does it require valve adjustments?
Your problems sounds more like tight valves than GP

Shortsguy1 · #5 02-12-2014, 01:09 PM

Here is a MB manual that apparently addresses your engine. It is expensive and located in Australia, I think. But I wanted you to know it is out there.

MERCEDES L321 TRUCK LKW OMNIBUS BUS MANUAL L322 OM321 DIESEL 1959 | Truck Parts | Gumtree Australia Stirling Area - Trigg | 1038453638

Diesel911 · #6 02-12-2014, 06:32 PM

There is a pic of the side of the Engne that I think has the Glow Plugs (post#10). If so the Glow Plugs are in wired in series but there is no zig-zag resistance Wires.

300 Series Diesels; NA Pre-Chamber to Turbocharged Intercooled Direct Injection - Mercedes-Benz Forum

Stretch · #7 02-13-2014, 02:55 AM

Quote:

Originally Posted by mespe

First let me state, that I am not at all familar with that engine.
Secondly, if it's an older Mercedes Diesel, does it require valve adjustments?
Your problems sounds more like tight valves than GP

I agree - valves, new engine oil, check starter cranking speed, fuel filter and test for water in your fuel...

...if not done already

TnBob · #8 02-13-2014, 04:23 AM

On line search for : OM321 diesel comes up with lots of data too

TnBob · #9 02-13-2014, 04:28 AM

copied from an old post elsewhere

You can order a manual at Mercedes-Benz Classic-Nutzfahrzeug-Service Alfeld
They are selling copies of a manual containing all the "3" engines.

Barginginfrance · #10 02-13-2014, 08:24 AM

Thanks for your replies. A picture of an OM321 6 cylinder diesel can be seen here and you can clearly see the glow plugs below the direct injectors.

http://www.machinetrack.be/construction-machinery/parts/motors/1378220420951-36-2/mercedes-benz-om-321.jpg

Everything was working perfectly until a year ago. Started first turn every time. The wiring works fine, the plugs glow, but seem to 'short' when all bolted together again. Maybe that carbon build up?

The glow plugs have a small wire loop that glows and once inside, resides in a small pre chamber. I'm intrigued by the pencil glow plugs but wonder if I have the depth inside for them.

I'll try and get a reamer and see if that works.

Diesel911 · #11 02-13-2014, 09:28 AM

I am not sure if your Glow Plugs are Grounded through the Engine like Spark Plugs are or the Current goes through the Glow Plug with out grounding through the Engine. But, either way it is possible to check the individual Glow Plugs with an Ohm Meter (Volt/Ohm Meter/Multimeter) and see if there is an open circuit or the Resistance varies a lot from the rest of the Glow Plugs.

On the later Model Engines with the Filament/Loop Type Glow Plugs testing them on the Battery instantly burns them because on the Engine they are wired in a manner that reduces the overall Voltage to the Glow Plugs.
Also the above mentioned Glow Plugs do not ground through the Cylinder Head and are electrically insulated from the Cylinder Head. However, if enough Carbon bridges the insulated end of the of the Plug inside of the Engine it creates a ground there and shorts out another Glow Plug (burning the Filament creating an open circuit) closer to the Battery in the Circuit.
When the Series Curcit is broken like that none of the Plugs work.

vstech · #12 02-13-2014, 10:25 AM

Quote:

Originally Posted by Barginginfrance

Thanks for your replies. A picture of an OM321 6 cylinder diesel can be seen here and you can clearly see the glow plugs below the direct injectors.

http://www.machinetrack.be/construction-machinery/parts/motors/1378220420951-36-2/mercedes-benz-om-321.jpg

Everything was working perfectly until a year ago. Started first turn every time. The wiring works fine, the plugs glow, but seem to 'short' when all bolted together again. Maybe that carbon build up?

The glow plugs have a small wire loop that glows and once inside, resides in a small pre chamber. I'm intrigued by the pencil glow plugs but wonder if I have the depth inside for them.

I'll try and get a reamer and see if that works.

OP, the picture you linked to does show the metal resistor wires, so that engine has loop glow plugs.
a good glow plug reamer would help, but replacing them all with pencils would help more.
if the motor has not been tuned recently, the valves would certainly benefit from the attention!

Barginginfrance · #13 02-13-2014, 10:37 AM

Any suggestions as to where I might get a good quality reamer? I guess the thread has to be the same as the glow plugs?

jay_bob · #14 02-13-2014, 10:45 AM

Just to clarify what you have now for plugs

Battery -> glow system control (switch or relay) -> cyl 6 -> cyl 5 -> ... cyl 1 -> ground.

The current flows into and out of each glow plug top. There are two electrical connections on the top of each glow plug, an "out" and an "in". The current is not supposed to to get to ground except after it goes through cylinder 1's plug. The horizontal jumper wires carry the current from the "out" terminal to the "in" terminal on the next plug.

Inside the cylinder head the resistance element is just an open loop of wire. This loop can often break (which kills the current flow for the entire circuit) or the loop can short to the engine block (which removes the current from anything downstream of that point). Each plug is only rated to handle around 1.5 volts or so, the entire string of 6 in series absorbs the entire 12 volts along with the resistance built into the jumper bars. Kind of like the mini Christmas lights.

The newer replacement plugs are rated to accept the full 12 volts, so when you install them, you want to remove the jumper bars and use regular wire with ring terminals on the ends.

The easiest thing to do might be to go to a wrecking yard and find a glow relay from a late 80s or early 90s 6 cylinder car (i.e. 300D, 300TD, 300SD) and save the wiring harness as well. If you look online in startekinfo.com, workshop resources, 124 or 126 service info, you will find the wiring diagram for the car in question and should be able to figure out how to integrate the glow relay into your engine.

vstech · #15 02-13-2014, 11:04 AM

http://www.peachparts.com/shopforum/mercedes-benz-tools-reference-library/183783-glow-plug-reamers-917-0053-b606-0053-901-0053-a.html