Mercedes 240 D loop glow plug problem?

Question

I am looking at a low-mileage 78 240d that supposedly had the wire loop from the glow plug come loose and stick in the exhaust valve. It seems a likely story but I have no experience with this engine. I have rebuilt an M110 inline 6 with good results, so am no stranger to Mercedes in general. Is it possible that this is as simple as it seems? Pull head, grind exhaust valve and seat, install head, add new glow plug? Or is there something else that you think might be happening that will make this a difficult repair?

Answer 1

When those loop-type glow plugs melt, they generally disintegrate and flow through the engine and out the exhaust. Since yours seems to have gotten stuck between the seat and valve, you likely bent that exhaust valve. Even if you think it's straight, replace it. They're cheap compared to taking the head off again.

Since those heads were pretty much bullet-proof, I would think you could replace that one valve and lapp it back into the seat. Probably wouldn't be a bad idea to cut all the seats and valves, check for excess play between the valve stems and guides, and replace the guide seals. And if that one glow plug failed, you should replace all of them.

Hope this helps, good luck.

Answer 2

You'll find it easier to work on the head if you have the special wrenches for the valve tappets. You need to work two wrenches and a feeler gauge at once: the correct tools have bent handles so that you can work two of the wrenches with one hand. There's also a special wrench for removing the valve spring. Here's a set I spotted on e-bay: http://cgi.ebay.com/ebaymotors/Hazet-Mercedes-Valve-Wrenches-Repair-Parts-Tools-3_W0QQcmdZViewItemQQcategoryZ63703QQihZ008QQitemZ180016568123QQrdZ1QQsspagenameZWD1V

Are you sure the valve is bad? The tip of the glow plug is pretty rugged. It may be a cracked prechamber. If so, you can probably repair it without pulling the head. You will also need tools to remove the offending prechamber: http://cgi.ebay.com/Prechamber-Cylinder-Head-Repair-Tools-2-for-Mercedes_W0QQitemZ170009548906QQihZ007QQcategoryZ42337QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

I should add that if a prechamber has broken up, the pieces would have done more than wreck a valve.

Here are some photos of what's inside a typical Mercedes Diesel motor:
http://www.dieselgiant.com/mercedes617engineinternals.htm

Answer 3

Since it's a diesel motor if the valve stuck open it most likely has at least one bent valve and maybe a damaged piston. Still its an easy fix. At worst you may need to buy a new head.

Answer 4

This sounds correct. How long did the owner run it this way? May have to replace the valve(bent). I would also have you consider cylinder wall scoring from metallic bits of the glow plug bursting. Good Luck! ;-)=