OM321 starting problems (1992 barge in france)
 

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.

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)
http://www.peachparts.com/shopforum/3222508-post5.html

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!

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.

http://www.peachparts.com/shopforum/...1&d=1392216682

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

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

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

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

...if not done already

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

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.

OM321 Engine
 

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.

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.

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!

Glow Plug Reamer
 

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?

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.

In the site I looked at it had Wires going from one Glow Plug to another but they appeared to be insulated.

On My Volvo the Pencil Type Glow Plugs were wired in Series Parallel. Meaning that all the terminal ends were connected in series to a Wire that has the Positive Voltage but the individual Glow Plugs are grounded in Parallel to the Cylinder Head.
(This is the same setup that people do when the install the Adapter Pencil Glow Plugs to replace the Filament/Loop type Glow Plugs.)

In that system one Plug can go bad and still not cut the electricity to the rest. But to test an individual Glow Plug you need to disconnect it from the Terminal Wire.

You would also need to know what size the reamer needs to be.

I don't see why Stainless Steel Rifle or Shot Gun Bore Brushes would not work.
On My own Engine after the Reaming is done you are supposed to tie or hold the Fuel Injection Pump Throttle Lever in the Shutoff Position and crank the Engine and it blows out any loose Carbon particles the fell into the Precombustion Chamber.
If you hold the Lever in the Shutoff Position and have someone else crank the Engine be sure to protect your Eyes; even if the minimun you do is to close your Eyes.

You would also need a section of Cleaning Rod to mount the Brush on.
SHOTGUN BRUSH SIZES; threaded end 5/16x24 inches in the USA.
Diameters of the Brushes.
10 gauge 0.775"
12 gauge 0.729"
16 gauge 0.662"
20 gauge 0.615"
28 gauge 0.550"
410 bore 0.410"

I thought the parts circled in the Pic were the Glow Plugs.

D911-
The OP has stated that the GPs are loop GPs, so they must be in series. The photo he posted also appears to have a ground wire from the last GP to the block. Also, I don't think the parallel pencil GP had been invented yet when his engine was made. So maybe that photo that you found is of an engine which has been retrofitted with pencil plugs.

To the OP-
Those pencil GPs were designed to retrofit into the same hole as the old loop GPs. So assuming your loop GPs are the same as later loop GPs (1960s), those pencil plugs would work just fine. But how many times per day do you start your engine? If it is only once or twice, I would say that upgrading to pencil plugs in parallel isn't really solving anything. Who cares if once or twice per day you save 20 seconds running the GPs?

If definitely sounds like you need to ream your holes. An earlier post of mine in this thread had a link to threads where I give the dimensions of the reamer. So if you are on a budget, get a drill bit of similar size and mark it to ensure you don't go in too deep. I will PM another option as well.

And adjusting the valves, as has been suggested, would be good use of your time. Good luck.

This is a bit of an assumption - the OM321 seems to originate from the 1950s and according to findpart.org the Bosch glow plugs of what we speak appeared in diesel vehicles from 1959 onwards =>

BOSCH 0 250 001 016 (0250001016) Glow Plug

They might be close cousins - they might be same - they might not. I can't find much information about the OM321 out there on the interweb.

The specifications for the glow plugs that MIGHT be the same are here =>

https://www.bosch-automotive-catalog.com/public/catalog/products?p_p_id=BoschWSRP&p_p_lifecycle=1&p_p_state=normal&p_p_mode=view&p_p_col_id=column-1&p_p_col_count=1&_BoschWSRP_wsrp-urlType=blockingAction&_BoschWSRP_wsrp-navigationalState=%2FWFS%2FAAGLOBAL-AA-Catalog-Site%2Fnl_NL%2F-%2FEUR%2FViewSearchProduct-Detail%3Bpgid%3DD41D8CD98F00B204E9800998ECF8IS7qrzXw%3Bsid%3Dul2b0DfTYl2TkWUtj8kXKjhYmvJYN_zt2Z0%3D& _BoschWSRP_proxyportlet-remoteInvocation=true

The OM321 was built with direct injection and indirect injection with prechambers.
Are you sure which version you have got?

How many hours are on the old nozzles? When was the pop pressure and spray pattern checked last time?

Gruß
Volker

That preheating.pdf document that I linked to in my second post describes how the older (1950s) GPs are different than our "modern" loop GPs. It describes how the oldest ones used some short of spiral filament (capable of handling 1.4 volts), versus the round wire loop that we are more familiar with (capable of handling 0.9V). It does not say that the threads were different, nor the overall dimensions being very different, which is why I made my assumption. So yes, it is a bit of a leap of faith since that document I found discusses only the om621 and om636, but the era is the same so it is not too unlikely that MB would re-use the same prechambers, gps, etc.

Well if the OP is so inclined the thread diameter and pitch is specified on the Bosch site I linked - may be he'll be so good as to tell us how he gets on?

I'm interested in where you got this information - I've been struggling to find out more (so I'm not being argumentative - just inquisitive). According to this link they all had pre-chambers

Mercedes-Benz OM 300 (klein)

It might be wrong though 'tis after all wikipedia(!)

As the thread starter said in post #10

http://www.peachparts.com/shopforum/3286276-post10.html

he has direct injection on his engine.

I did remember that on a research about the OM321V I found out that Mercedes tried several 100 engines with DI instead of IDI.
So I thought maybe the thread starter has an engine with direct injection that survived until now.
Although I think it is most likely a prechamber engine.

Here is some information about it with pictures.
The birth of a legend: the 300 engine series, first unveiled in 1949, is a major advancement | Daimler Global Media Site > Classic > Daimler AG > Technology

Gruß
Volker

But also from post 10:
"The glow plugs have a small wire loop that glows and once inside, resides in a small pre chamber."

That article discusses all of the 300 series engines, not just the 321. Based on a quick scan of that article, it appears that the DI engines got different numbers (om352). This is a line from the article which references the DI engines introduced around 1964 "The new units soon gained an excellent reputation and replaced the OM 312, OM 321 and OM 322 precombustion engines".

As you said, the OPs OM321 is likely an IDI engine.

Great link thanks - I've downloaded it for a bit of bed time reading!

The glow plugs for these engines will probably use an 18mm thread.

I know this because I measured the thread of four glow plugs I got that were wrapped in packaging dated 1939. Apparently, they were for a 260D Benz taxi (??).

There's a German company named Beru that makes glow plugs and spark plugs. They have this cage filament glow plug.

Don't know if they still make them, but I have seen these in the past two years, so they might be able to be procured in Europe, where people don't dispose of things as readily as here.