Big questions that don't necessarily have concrete answers. I won't really know what I need until the mechanic opens it up. But, I'm trying to set up a tentative parts budget.

Compression is 350/350/350/250 wet. Harbor Freight gauge read 290 across the board dry before #4 went. Also has a leaky rear main seal. Oil consumption not checked after the sudden drop in #4 but was 1 quart per 800 miles. I suspect most wasn't burnt, rather leaked from the rear of the engine. Still fires up first crank with 30-45 seconds of glowing on cold days.

The car has ~ 190,000 miles.

The long block was replaced ~ 130,000 miles ago. Head was not resurfaced or rebuilt at that time. So, 190,000 on the head.

New timing chain and injection pump rebuilt 12,000 miles ago. Injectors about the same time.

Water pump replaced 2,000 miles ago.

I figure that I'm out a complete head build. Possibly a new sleeve in #4, maybe all. I'm hoping that pistons and valves can be salvaged. Cam and rockers look ok to my shadetree eyes.


I figure that I'll need at least the following:

Complete gasket kit (with valve seals and front main and rear rope seal)
Piston rings
Valve guides
Main bearings
Rod bearings
Head bolts
Connecting rod bolts and nuts
Piston sleeves
Valve springs?


Possibly - new pistons (includes rings and wrist pin), new intake and exhaust valves (sodium exhaust valves still?)


Should I consider a new timing chain kit even though the old one is fairly fresh? Reinstall the water pump instead of replacing?

What else? What little things am I overlooking (precombustion chamber shims, etc.)

__________________
1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.

Try putting air in the cylinder to see where the leak is before disassembling. It may just be a valve and the rings are fine. On number 4 do a dry test and then a wet test. If little to no increase wet then it is a valve.

Good luck and keep us posted.

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

It's already in the shop. Engine should be removed and tore down this week.

I neglected to mention that I overheated the car when the alternator pulley froze.

__________________
1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.

Ouch! Good luck with the diagnosis.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

The bottom end on these cars are pretty stout and especially your longblock is fairly new and barely broken in.. What kind of overheating are we talking? To the point the car had steam coming out of the hood? Dave, most likely you may have damaged the liner at MOST and can replace that and do a top end and be ok. Pistons are probably fine and take a LOT of heat and consistent overheating to damage and burn up a piston. I don't even think your liner is damaged. Are you dumping coolant out the exhaust? The timing chain would be a waste. It's a double row chain, they can last 300k miles with regular 5k oil change intervals.

__________________
Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k

Diagnose before taking the engine apart otherwise you are going to end up with a mess, needless repairs or a For Sale ad on cragislist.

"Dry" compression tests are quick to do but don't identify the exact source of the problem.

"Wet" compression tests are meaningless, introducing a non compressible liquid into the cylinder will raise static compression ratio regardless if the piston rings are good and it won't identify a slightly leaking valve.

Do a leak down test, this is where you have both valves closed, piston at TDC and about 100 PSI air is pumped into the cylinder after removing the injector / glow plug or spark plug on gas engines. You then look to see where air is leaking out. Some past the rings is normal as miles pile on, some from the exhaust is normal at high miles but not optimal , some from the intake needs to be addressed. Any leaking into the radiator needs fixed.

Only after this testing can you determine what to fix.

Yup. Boiling over. No coolant from the exhaust.

Temp gauge worked, but I was trying to limp home to avoid a tow.

I was guessing worst case in my original post. Optimistically, and perhaps realistically, was thinking gaskets, rings, bearings and redo the top end.

Regardless, the parts cost on this old beast isn't too bad considering. Based on what I've found so far, even if I need pistons and valves I'd only be adding $600 or in parts cost. That's not too bad considering the age and relative obscurity of these W115s.

__________________
1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.

I'm not exactly sure what tests the independent Mercedes mechanic performed to isolate it. But, last summer, said that I was probably looking at a rebuild. So, I've been saving my pennies.

As I mentioned in a previous post, I'm cautiously optimistic that it won't require four new sleeves and pistons. But I've already committed to tearing it down if, for no other reason, to replace that darned rope seal. At that point you might as well replace anything that needs it.

However, it has a "miss" that can't be attributed to fuel, injection timing, or valves. The obvious place to start is #4 piston/rings.

__________________
1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.

If you just need one sleeve then change it. If all four cylinders need work, first repair size pistons may be a good option. I went that route on a 240 and it worked. In short, it's new oversize pistons with the existing sleeves bored to fit. The first cylinder piston clearance is different than two through four. Discuss this with the builder.
Good luck!!!

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

You may be able to salvage a lot of cylinder head parts.


is the mechanic just replacing everything or is he checking items using data from the Factory Service Manual (FSM)?


If mechanic's measurements or test results give you at least 50% margin on certain items (like spring strength) and the item is the same across the board, consider leaving it and not replacing.


Check if new cylinder head bolts are required.
Above all, invest in a GOOD cylinder head gasket and make sure your mechanic properly torques these items in the correct order.




Good luck!

__________________
Strelnik
Invest in America: Buy a Congressman!

1950 170SD
1951 Citroen 11BN
1953 Citroen 11BNF limo
1953 220a project
1959 180D
1960 190D
1960 Borgward Isabella TS 2dr
1983 240D daily driver
1983 380SL
1990 350SDL daily driver alt
3 x Citroen DS21M, down from 5
3 x Citroen 2CV, down from 6

Without doing a leakdown test, a leaking valve can't be ruled out.

True.

But at 120-130k on the long block, rebuilding only the head is a job half done especially, as I mentioned above, I'm losing a great deal of oil from the rear rope seal which requires a lower end disassembly in order to replace.

If I plan on driving it for another 30 years, IMO it's better to get a rebuild out of the way now while the parts and expertise are still available.

Since I've already mentally prepared myself to go this route, even if it's just a few valves, the entire engine will get a going through...hence my original question.

__________________
1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.

Yes, I'm all for freshening up an engine but I'm also for proper diagnosis before dissassembly. Many of my posts through out this site speak to that. I've got 40+ years in and around the auto repair business and have "rebuilt to 100 % of new" / "patched up to get a few more miles" countless engines.

120 K isn't super high miles for a bottom end, if ring seal is super good no use changing them.

I haven't had to go into these engines but have watched the threads over the years where a "mechanic" stated "engine rebuild time" and a machine shop did the work as if he had a standard 350 Chevy in the shop.

Your most difficult task will be getting the shop and the mechanic to RTFM (and follow it). Most think they know all that is necessary. They do have what is necessary IF they add the FSM data and follow it - without short cuts.

Many of the threads were dealing with how to fix the short cutted screw up without starting over.

Edit: do the suspension and clean the engine bay when the engine is out. What about the trans?

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

The shop has the FSM. I left my copies of both the chassis and the engine manuals just in case.

The transmission seems to be doing good. Shifts are a bit harsh when it's cold, but when up to temperature it smooths out. It did lose passing gear on me, but the same shop troubleshot the problem to a faulty kick down solenoid and it's been fine since.

__________________
1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.