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Old 04-11-2007, 08:23 PM
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Join Date: Apr 2007
Location: UK
Posts: 357
OM606 Inlet Valve Seats & IP Timing

Hello All,

Please forgive the naive questions of a newbie!

If all goes to plan, I should be able to pick my cylinder head up from the machine shop tomorrow. After replacing the 'o' ring seals on the fuel pipes, I started the engine. This was when I found that the inlet valves on No. 6 weren't doing a great job of keeping the combustion gases in the cylinder!!

Has anyone else seen inlet valve seat recession on an OM606? Allegedly, mine has 125k on the clock. The valves had sunk by getting on for 3/16", and I suspect the hydraulic tappets were towards the end of their range.

Anyway, some new inlet valves and valve seats later, I hope to put the engine back together tomorrow. I have read with great interest about the milli-volt IP timing method. Has anyone tried this on an OM606? How many mV should I be expecting to read on this engine? I am fitting a new set of BERU glow plugs, and I've had new nozzles put in the injectors, so all should be fairly well balanced.

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Old 04-11-2007, 09:00 PM
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Join Date: Nov 2004
Location: Nova Scotia, Canada.
Posts: 6,510
The 606s time so nicely with the proper specific tool it is really the way to go if the timing needs checked. Interesting how much those intake seats recessed into the head. If only one or two I wonder why.
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Old 04-12-2007, 07:40 AM
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Join Date: Apr 2007
Location: UK
Posts: 357
Hi Barry,

Thanks for your reply.

The valve seats which had sunk were numbers 11 and 12. The valve seat in number 10 was also showing some signs of discolouration, so I have had the seats in numbers 9, 10, 11, and 12 replaced.

When I ran the engine with all of the manifolds connected, it ran OK, and there was no indication that anything was wrong. It was only when running the engine without the manifold on that I saw anything wrong.

I suppose there was a clue there - the inlet ports for 11 and 12 were sooted up rather than being just oily like all the others - as mine is a naturally aspirated 606, there are connections between the cranckase ventialtion system and each runner of the manifold, so I would expect to see some oil in each port. I'm going to check that this isn't blocked up for ports 11 and 12, because perhaps the small amount of blowby oil is enough to lubricate these valves and seats?

Thanks for your views about the injection pump timing - having read your posts on the subject, I'm really impressed with the work and the investigations you did.

When you suggest that timing using the correct tool is the way to go, which tool do you mean - sorry, I don't have any real MB experience or knowledge.

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Old 04-12-2007, 11:44 AM
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Join Date: Nov 2004
Location: Nova Scotia, Canada.
Posts: 6,510
Thanks for your detailed response. Others are better informed yet I think you borrow a rv timing device for your engine. Or find someone with one. I have no experience with your engine type.
I would check the archives under rv tool and the tool rental program for specifics. The tool has indicator lights on it to set your timing. Seems fairly easy and accurate to use.
That also sounded like a good investigation you performed on your engine. I wonder too if those valve seats were runing perhaps hotter than the others? Or just not lubricated as well. Or perhaps a combination of things.
Sometimes there will be recessed seats because the valves are not adjusted regularily and the adjusters were weak on certian cylinders and moved easier than the others. So repeat failure or burning of the same valve and seat required many heavy grindings of the individual seat. As the substandard adjuster was not dealt with.
This was not your case as you have hydralic lifters but that senario did apply to some of their earlier gas engines. You may have also stumbled on a possible additional contributing cause of the dreaded head failures on that type engine. Much hotter individual cylinder temperatures for whatever reason. Causing unequal stresses in the head castings.
This is an area where the milli volt method can shine. The next time you change glow plugs you could hot calibrate them off the car. Install them and read their milli volt output. That would definatly indicate if you had a cyinder or two running hotter than the others.
On your engine the position and difficulty of swapping glowplugs makes this check far harder than on the older 616 and 617 engines. In my opinion and remember it is only an opinion.
If any one cylinder had a two millivolt or higher reading than the others I would first swap injectors. If the higher reading transits with the injector you have your problem. The other approach that may be cheap and effective is just to have that one cylinders injector checked out for leakage, pop pressure, etc.
Again in my opinion it was a good ideal of yours to look around for any obvious cause. This way the knowledge base continually increases on those heads.

Last edited by barry123400; 04-12-2007 at 12:05 PM.
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Old 04-12-2007, 07:24 PM
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Join Date: Apr 2007
Location: UK
Posts: 357
Hi Barry,

Thanks again for your thoughts and inputs - much appreciated!

I haven't put my new glow plugs in yet - I'm thinking of leaving them out for the moment to allow the engine to spin over easily, and bleed fuel through without having to struggle against the compression. So, I can do a calibration of my new glow plugs - I was thinking of measuring them at room temperature, and again with the tips in boiling water, although, perhaps I should be doing the cold test using an ice/water mix, which would give me a change in milli-volts over a known change in temperature.

I think your suggestion of cylinder temperature is a really strong possibility. No 6 is furthest from the water pump, and radiator, so I would expect it to run hotter. Using the glow plugs to test for this is a good plan - I'll give it a go.

I don't have easy access to the electronic tool to set the pump timing, so, I was thinking of doing it the slow way, using something like the 601-589-05-21-00 plug tool mentioned in the thread below.

Specialized Indicator for IP Timing

Does anyone know the dimensions of the tip? Particularly the diameter of the plug, and the width of the slot? With that info, I could probably make one up in 10 minutes, using some scrap steel bar. Otherwise, I'll have to order one up, from MB, and I'm an impatient type!


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