Checked the oil and coolant tonight in my 77 240d and found the dreaded milkshake coolant. I drained the radiator and it was a nice Jamocha shake color. My question is how involved is it to change the headgasket? I did a quick search and couldn't find a write up. TIA

Never mind found a write up on this site using Google. Should be good to go.

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1977 240D
1981 300SD

In addition to the write up that you found, check the link below for our site's DIY procedure guide.

https://www.pelicanparts.com/techarticles/Mercedes-W123/51-ENGINE-Head_Gasket_Replacement/51-ENGINE-Head_Gasket_Replacement.htm

Got the head off today and will get it to a shop tomorrow. Block looks like the definition of a bad head gasket. Forty one years, 271k miles, many at wide open throttle, I'd say the gasket did its job.

Attached Thumbnails

 

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1977 240D
1981 300SD

Double and triple check the head for cracking, especially around the valve recesses and injector areas.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

If the timing chain is original consider replacing it...seen more than one break on 240's.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Check the head for straightness/warpage and the block as well.

Cover up the Fuel Injection Pump to Injector outlests (the glue on tape came be messy but does a fari job keeping curd out; a piece of dirt from that area moves on into the Injectors).

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84 300D, 82 Volvo 244Gl Diesel

Could also remove the Vacuum Pump and check the actuating arm and bearing for pending failure and look at the ramp on the Timer.

Then there is the in and out play of the Timer Bushing.

My question What in particular causes vacuum pump failure?
What in particular causes vacuum pump failure?

2 Vacuum Pumps destroyed timer Bushing Identified as the problem
http://www.mbca.org/forum/2013-12-29/why-are-these-vacuum-pumps-being-destroyed

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84 300D, 82 Volvo 244Gl Diesel

Ahhh, nothing like good old mission creep!

ALWAYS happens to me. Start out doing something straight forward and the next thing I know, "Ya know, while I'm right here anyway....".

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

But, I know from experience that it is awful to finish one job and then get the vehicle down the road a bit and something else fails and you need to go back into the same area you just put together.

Since that Timer Intermediate Shaft Bushing and the Vacuum Pump are potential engine killers it seems worth while to check them.

Also with the Head off it is a good idea to take a look at the Timing Chain Tensioner Rail and the Tensioner itself.

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84 300D, 82 Volvo 244Gl Diesel

Yup, I agree. This sort of thing(s) is why it is so difficult to give a repair price quote on the older cars.

If you pull the vacuum pump to check it you might as well replace the pump's roller bearings (depending on the type of pump) with new caged ones, might be a good time to replace the diaphragm also.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now