Engine Rebuild
 

I have a 1989 300SE which I want to rebuild the engine. It needs motor mounts, 2 lower oil gaskets because it leaks quite a lot, amongst some other minor issues. I have rebuilt in the past - way past - about 25 years ago, but I can handle. My question is - is there a good shop manual that I can get that will guide me through? The engine looks like the engine I worked on, not the new ones where you can't get your hand in anything. May be a silly question, but I will ask anyway. Given that the engine is "simple" to a degree, is it possible to do a tear down from within the engine compartment, or is complete removal intact the best way? Any other comments, suggestions would be helpful. I'm in the northeast & will not begin until the weather warms up. Thank you.

What are you considering a rebuild?

The M103 typically does not need an "engine rebuild". Usually just a head refresh and seals.
The bottom end is pretty bulletproof.

Engine Rebuild
 

Given that several of the oil gaskets that I know of leak like crazy and I suspect head gasket issues too, I figured if I'm planning to keep the car long term, why not do a complete clean up? I'm 4th owner and I suspect it had been through a rough time with the previous owner before me.

Don't touch the bottom end. Just pull the head, have the valve guides and seals replaced, then have it LIGHTLY skimmed and pressure tested.

Use MB head gasket rather than Victor Reinz based on my experience (twice). Yes it is twice the price, but its not worth pulling the head again prematurely.

Leave the intake manifold in the engine. Just unbolt and pull head and exhaust manifolds off as one.

Engine Rebuild
 

Thanks Ps2cho for the helpful advise.

These are very, very durable engines.

Do a compression test before pulling it apart so you have an idea of what to look for, if anything. Look for cylinder wall problems/scratches/glaze when the head is off. If compression is good and the walls look good I would stop and only do as suggested, the cylinder head. Use all new head bolts.

Learn and understand the timing chain tensioner before putting it back together, this is critical. It will only ratchet tighter, to get it looser it has to be taken apart. Install the body of the tensioner by itself to the head and then install the plunger, spring and plug into the body of the tensioner after the timing chain is in place. The spring has alot of tension and the plug is not easy to install wear safety glasses when working with the spring. If the chain is too tight due to the tensioner being installed incorrectly the job will not last long at all.

The camshafts are hollow and easy to crack, be careful and follow the manual.

The rocker arm bolt hole threads in the head tend to strip and then the rocker assembly pulls off the head. Longer bolts are sometimes substituted, I would consider thread inserts on them. Does anyone have any comments on the best way to repair the rocker arm bolt situation?