Replacing welsh plugs, OM617

fig

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Just before Christmas my 1982 300GD blew a welsh plug on the engine. It started leaking from the front right plug (FIF), under the manifolds.

I see there are 6 plugs on the block: 3 on the left, with the rearmost one being a screw-in type to allow for a coolant heater to be fitted; 2 on the right, and one on the rear in front of the flywheel.

I assume it would be prudent to replace all of them if one has corroded through.

Are there any tips or tricks to make this easier? Can it be done without removing the manifolds and the injector pump? Can I just remove the injector pump and then replace it, or will it need recalibration/timing reset? Would it be too risky to not replace the rear plug? The thought of removing gearbox and flywheel depresses me.

Any advice welcome. We've started removing the manifolds, which also means removing the aircon bracket and compressor.
 
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Pete460332

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No need to recalibrate IP. Its the first time I have ever heard of the plugs failing , what antifreeze has been in the coolant. I guess check if another one ( thaats easy to remove ) is suspect - perhaps is just a material weakness in the one
 

fig

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No need to recalibrate IP. Its the first time I have ever heard of the plugs failing , what antifreeze has been in the coolant. I guess check if another one ( thaats easy to remove ) is suspect - perhaps is just a material weakness in the one
Thanks Peter. It looks like the engine ran for a long time with no antifreeze. We've removed the failed one and it's heavily corroded on the inside, so I'm guessing they all look the same.
 

JJVDMZN

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What's the possibility of moving the engine and gearbox (forward as a whole) forward in the engine compartment so that you can get to the rear welsh plug?
Just off my head I would think you would have to remove the radiator to create space, the hoses, fuel line, and exhaust. Gearbox side, the short prop shaft and gear linkages and maybe loosen the clutch slave.

J.J.
 

Pete460332

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What's the possibility of moving the engine and gearbox (forward as a whole) forward in the engine compartment so that you can get to the rear welsh plug?
Just off my head I would think you would have to remove the radiator to create space, the hoses, fuel line, and exhaust. Gearbox side, the short prop shaft and gear linkages and maybe loosen the clutch slave.

J.J.
There is also one behind flywheel!
 

JJVDMZN

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Ai, ja jai ja jai.

That changes it completely, that means clutch alignment as well when putting it all back together.
IMO I would do all the w plugs, you can't risk not doing the rear w plug that's a water leak that you won't see until it's to late.

J.J.
 
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fig

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Thanks all.

Yes, we're replacing all of them. We've removed the 5 on the sides of the engine already; not too much work to remove aircon compressor, manifolds, oil filter housing and injector pump. Although all were badly corroded on the inside, the welsh plugs all came out easily once we had access.

We got the gearbox loose yesterday, so it's coming out now and we can remove the last plug. I struggled to find 34mm welsh plugs in Vanderbijlpark yesterday. Eventually had Midas order me a set, which should arrive today.

Having the gearbox out will also give me an opportunity to inspect the clutch.

Removing all the engine ancillaries exposed a few other issues that were brewing, so the welsh plug failure was a blessing in disguise, and I can pre-empt some future failures.
 

fig

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Can anyone tell me what brand of antifreeze I should use? I know I should use Mercedes antifreeze, but life is too short to spend it in the parts department, with their mostly ignorant staff and ridiculous processes that show total disregard for my time.
 

fig

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What's the possibility of moving the engine and gearbox (forward as a whole) forward in the engine compartment so that you can get to the rear welsh plug?
Just off my head I would think you would have to remove the radiator to create space, the hoses, fuel line, and exhaust. Gearbox side, the short prop shaft and gear linkages and maybe loosen the clutch slave.

J.J.
Once we got into it, it didn't take long to remove all the ancillaries and extract 5 of the 6 welsh plugs. Probably a lot less work than removing the radiators, etc.

We got the gearbox loose yesterday as well, and we're removing it now.

Can I just remove the flywheel and bolt it back up, or must one set crank end float or anything like that? I also have a new crank rope seal, but I'm not sure whether it's a good idea to interfere with the existing one, since it's not leaking.
 

fig

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I see the manual mentions coating the new welsh plugs with sealant before installation, part number 002 989 94 71.

What kind of sealant is required? Will red permatex do?

Update: gearbox is out and we've removed all the old plugs. Clutch looks good, so it's going back in. Now I'm busy rigging up a plug installation tool from an old socket.
 

Dawie Louw

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Last time I checked, the Mercedes Anti-Freeze was cheaper than anything else I could buy. Otherwise, I would stick to a well known brand such as Castrol. Buy undiluited and do your own 50:50 dilution.
 
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fig

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I got new cadmium plated welsh plugs from Midas. They're marked 34mm and they have a very slightly bigger circumference when compared to the old ones, which makes sense.

What doesn't make sense is the new ones easily slide into the holes, no interference fit.

I suppose I'd best order new plugs from Mercedes.
 

Alan

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Hi Fig, you could also try Alert Engine spares. They seem to stock quite a bit of spares for Merc engines.
 
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Dawie Louw

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I had to buy 5 liters of MA000 989 09 25 100% anti-freeze today. Plastic coolant header tank on my 2004 W203 give up and I suffered some loss. R73,66 per liter from MB The Glen. They did not have the 5 liter bottles in stock, which may be a little cheaper.
 
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Gerhard van Rooyen

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Once we got into it, it didn't take long to remove all the ancillaries and extract 5 of the 6 welsh plugs. Probably a lot less work than removing the radiators, etc.

We got the gearbox loose yesterday as well, and we're removing it now.

Can I just remove the flywheel and bolt it back up, or must one set crank end float or anything like that? I also have a new crank rope seal, but I'm not sure whether it's a good idea to interfere with the existing one, since it's not leaking.
Helo Fig, just check in the manual that the flywheel bolts are not stretch bolts. I am not sure about the 617, but the 605 has stretch bolts. quite painful at around R65 per bolt.

I agree with Dawie - MB antifreeze is the cheapest I could find, and if I am not mistaken they only use one type now.
 

fig

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Thanks for the tip Gerhard. Unfortunately the flywheel is on and the gearbox back in place. Manual describes "necked down" bolts, and specifies a minimum width for the neck of the bolt. Not sure if that counts as a stretch bolt, which I understand are one use only.

Thanks for all the advice G team. I ditched the Midas plugs and bought stainless steel ones from Alert. They were 5x the price, but were same thickness as original and were a proper snug fit.

We haven't quite finished reassembly, but it's just the oil filter housing, manifolds and aircon compressor bracket still to go back on.
 

Gerhard van Rooyen

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Ja, I might be wrong, and hopefully some of the more knowledgeable folk will chime in, but the 'necked down' bolts are stretch bolts - we measured mine compared with the new ones before installing and there were a 0,2mm difference if I remember correctly. One can also feel them stretching when applying the specified torque procedure.
 
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