Finally time to replace the head - PeachParts Mercedes-Benz Forum

psfred · #1 03-31-2007, 02:40 AM

Finally had to break down and replace the head on my 87 300D. I suspect it's been weak for a long time (always had some oil in the coolant tank), but this winter it suddenly got really smoky on starting and left a white trail until it warmed up a couple times.

I pulled the head of the off-chance it was just a gasket (it was also leaking oil at the front below the chain tensioner), and the head gasket was indeed bad -- blown between #3 and #4, blown out the back right side on #6, and leaking both oil and coolant around. Broke a head bolt (the hole was full of carbon from the blown gasket), bent the oil feed line to to the turbo all to h... and back, found a broken exhaust stud late on a Sunday afternoon, all in all quite a project.

Ran a lot better, much less vibration, but clattered a lot more than I wanted, and got pressure in the cooling system too fast. Yup, sure enough, cold pressure and white smoke...

I did do a visual inspection of the head and didn't see anything, but I didn't have it tested, I was in a hurry to get the car back on the road (the 280 SE gets 14 mpg....). Went back on OK, but its either badly warped or cracked (I vote for cracked...).

I got a replacement head with valves, nothing else except the cam bearings, so tomorrow I have to go out and see if the shop that did the valves screwed up the guide clearance -- no springs, and the valves are taped in, making be think they are WAY too loose. Probably end up having new guides put in before I install. Valves are new, but I'm afraid someone put them in with "Chevy" clearance and they will allow oil into the combustion chambers. Not the first time I've seen this, by the way.

So in the next couple of weeks I get to do the job again. Should have followed my initial instincts and snagged that head off eBay I saw while I was in the middle of the job last time, I'd be done by now and it was a bit less, although I'd probably have bought new valves rather than use the ones with 260,000 miles on them!

A nice project for my vacation!

Peter

mespe · #2 03-31-2007, 08:56 AM

I can't recall a single time that I've tried to take a short cut and things worked out OK. My dad used to say, if you're gonna do something, do it right the first time.

jfikentscher · #3 03-31-2007, 09:10 AM

AHHH, the old customer service slogan, "Do it right the first time, on time, every time".

Mine exhibits the same smoking in the cold weather, but when warm out the smoking goes away quickly or does not exist. I do, however, lose coolant and have the pressure in the system even when cold in the morning.

Looks like I will be doing my head sometime soon also.

Joe

Brian Carlton · #4 03-31-2007, 09:55 AM

Quote:

Originally Posted by mespe

I can't recall a single time that I've tried to take a short cut and things worked out OK. My dad used to say, if you're gonna do something, do it right the first time.

I agree.

On these vehicles, every time you go forward, in a hurry, with the attitude "should be OK.........", you pay for it with twice the work.

I now work without a timetable. The vehicle sets the timetable. If the parts are not available, or there is a technical question...........it just sits until it's resolved. I took nearly five months to finally get the head done on the SD............long story...........but, nothing was done as "good enough" and the engine continues to impress me to this day.

psfred · #5 03-31-2007, 11:13 AM

Yeah, my mechanic friend thought it was just the head gasket, says he's not seen any that cracked (and he probably hasn't --he retired a couple years ago). I got a good deal on the car because we thought the head was bad and/or the head gasket was bad at the time (heavy knock, shaking at idle, low compression in a couple cylinders but no oil consumption), so I got 100,000 miles for free.

I'll check out the head this weekend and if it needs new guides will get that done before I tangle with it.

It sure helps to have done a couple, the job shrinks amazingly with practice!

And the head gasket WAS blown, completely separate from the cracks, those were a new thing. I suspect that it was installed badly OR the head itself "went bad" as the gasket was the original type without re-inforcement at the front oil passage.

Peter

psfred · #6 04-01-2007, 11:04 PM

Inspected the head this afternoon -- sure did break a chain, there are the expected scars in the chain case.

Valves are sloppy, too, so I'm going to get new guides put in and check the valves for correct size. I no longer trust machine shops I don't know, too many chances for sloppy work like this. Pull the valve down and push side to side and you can HEAR the click! Must be 0.010" clearance in there on the exhaust valves. No way it's not gonna burn oil like crazy!

Peter