I'm going to be getting the head gasket on my '89 300CE replaced. I've done some research on the M103 engine and its various faults, but I'm wondering if I need to do more extensive work when I have the head off. Firstly, i understand that valve guides and seals are a weak spot on the M103. Is it advisable to replace the valve guides, even if they are within factory specs? The car currently has 100k km (62 000 miles) and exhibits no significant amount of oil consumption besides the small amounts seeping from the leaking head gasket. Secondly, I understand that the timing chain and the timing chain cover are known to cause problems, I would imagine that the timing chain cover gasket would be replaced with the head off, but what about the chain. Is it advisable to change it at this time? Previous threads indicate that the relative ease of changing the chain while the head is off makes it all the more worthwhile to have replaced, but I'm wondering if this is overkill considering the car's low mileage. Is there anything else that should be considered when doing this job?

If you have the head off, get the valve guides and seals done. make sure the head is flat it's possible it needs machining.

Unless your mechanic has advised you that there is a problem with the timing chain and guides or if you have the current finances to do this, with only 62K miles this maybe not an issue.

I doubt it would need that extensive of a rebuild with only 62k on it....that's very low miles.

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Are you sure the head gasket is bad at 62k miles?
Are you losing compression?

But...if you do have the head off, I recommend (if you can afford it) doing the valve guides + seals, skim the head and replace coolant hoses (block to water pump).
Once the head is redone, you won't have to worry about it for at least 80k miles.

Also you must consider because the M103 does consume oil over time, the cats + precats eventually get clogged so you'll end up spending anywhere from $300-$1000 to get that fixed depending on your smog state + preference. So if you can prolong the original cat...it will save you money.

For the timing chain...it really depends on how frequent the oil changes were. Check for slack/play in the chain, then look at the plastic guide rails. If they look really worn then replace them as that usually causes premature life on the chain itself due to wearing guides. If you don't see much wear and the chain doesnt make any noises...I wouldn't worry about it. They tend to last anywhere from 100k-300k miles.

If you search my threads I have a complete M103 rebuild with a ton of pics. Might be helpful.

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If anyone ever used green coolant in the car, I would replace the water pump while you have improved access. I would definitely do the valve seals, since they harden with age and are cheap, but not the valve guides.

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Is it normal for a California version 1990 300E to have no pre-cats? Mine only has one large cat underneath with no-precats but it does have an EGR (which I disabled).

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

By all indications the head gasket appears to be bad. The rear of the block and undercarriage is covered with oil. Service records from the dealer indicate that the head gasket needed replacement, and this dates back around 5 years ago. Anyway you put it the head gasket is going to eventually need replacement. I'm going to do the guides and seals while the head is off. Water pump has already been replaced in the last several years at the dealer, however, the car is filled with green coolant. Is this any reason for concern? I understand that you need only use the MB Coolant, but what are the exact reasons for this? Will the green coolant cause excessive harm to the engine and cooling system?

Green coolant is for iron engines and will allow faster corrosion in other engines, causing leaks.

http://www.valvoline.com/zerex/automaker.asp

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