Just pulled the head - '72 250

[Blue 72 250]

I would not rotate the bottom to inspect the #1 and #6. You can assume that they are fine based off of the compression check that you did before.

[250 Coupe]

Too many HTTP://s in a link will break it.

I too wouldn't bother cranking the engine over as it was the number 4 hole that had the worst readings. My impression is the the bottom end of a Mercedes motor is very stout and that the heads tend to require attention every few hundred thousand miles.

Michael

[Mr Basil]

I replaced a burnt valve a few weeks ago and rotated the engine so I could scrape the carbon off the piston tops with the piston at the top of its stroke. I tied the timing chain to the hood latch with a piece of string so it was taught and it rotated along with the engine. I wonder if anyone will cringe when I tell you I used brand new utility knife blades to scrape off the deposits? I hold them at 90 degrees to the piston top and am careful not to touch the bore. I also surrounded the whole area with paper and painters tape except for where I was working and frequently vacumed up the crud. I used a small tube and siphoned the coolant from the block so I could put small lint free rags in all thse holes and carefully scraped the gasket mating surface and went over the whole thing with a brass wirebrush on a flexshaft(piston tops included). I started at the front and kept moving my paper and tape and rags until I hit the rear of the block. I worked from the front of the car so I wouldn't damage the paint on either side of the hood. The whole thing looked great although I imagine my compression ratio dropped slightly due to the volume added by removing the deposits. The head was ready to go on before I did this. The last thing I did was a lint-free acetone wipe over the mating surface and I had #1 @ TDC so the timing chain would line up with the mark on the cam thrust washer. I also noted beforehand where the timing marks on the harmonic dampner were in relationship to the pointer and where the rotor was pointing in the distributor(#1 plug wire).
When I put the head and gasket on I set the timing chain into the well and retrieved it afterwards with one of those magnet-on-a-stick gizmos.

Judging from what others have written, I may seem overly thorough, but I have confidence in an excellent gasket installation.

I completely cleaned the inside of the intake manifold too, it was surprisingly dirty. That was slightly harder (although quicker) than cleaning the gasket area. No regrets!

Hope your installation goes well and you're soon back on the road!

Basil

[cth350]

definitely leave the bottom half alone, unless you've got about 3,000$ to devote to redoing it well.

Get a competent machinist that knows mercedes well to mill the head for straightness and to replace the guides. You're looking at 300$-500$ worth of work.

If both surfaces of the head require milling, strongly consider a different head.

-CTH

[MunichTaxi]

Had you ever posted how many degrees of stretch?

[rgnprof]

No to the chain stretch question - I have never measured it.

I did get a second opinion today from a local indy in OKC - he looked over my head very carefully and seems pretty confident the oil is leaking past the oil ring on the pistons. He is going to take the head apart and check everything closer, but he feels that the bulk of my problem is in the bottom end.

Question: Can I unbolt the pistons from below and push them up and out of the cylinders - without removing the engine? I know I would have to ream the top ridge of the cylinder wall some. Can I drop the pan(s) to get to the connecting rod bolts? If it is possible, what is involved in the process?

And, will replacing just the rings fix my problem, or just make things worse? Depending on the shape of the pistons and the cylinder walls, this guy thought that it would fix most of my problems.

He also looked over the new head and camshaft and towers and does not think they will work. Too much corrosion in several of the water passages and the camshaft was too rough and worn - where it rotates in the towers.

So, it looks like I'm back to using/reusing the old head! I'm beginning to wonder if someone is trying to tell me something! I definitely don't have $3000 to completely rebuild the block!

Ryan

[MunichTaxi]

Question: Can I unbolt the pistons from below and push them up and out of the cylinders - without removing the engine?

I remember a cross member on the W114 that would require pulling the engine. Probably also on the coupe series.

[t walgamuth]

Originally Posted by rgnprof

Tom,

This is my 250, not the 300D.

sorry, got lost for a bit there.

tom w

[rgnprof]

I talked to a very experienced indy last night for almost 40 minutes about my situation. He assures me that I can get the pistons out by pulling the pans, but he did say it wouldn't be easy! He said that I would have to disconnect the engine mounts (which I was going to replace anyway) and then lift the engine up and wedge in some 4x4 blocks of wood to keep the engine up to give me clearance to the lower oil pan.

Anyone ever done this?

Ryan

[Blue 72 250]

boy you are rapidly moving into the relm of engine swap in the name of a cost benefit analysis.

I agree with what cth said, the bottom half is a can o worm$.

[rgnprof]

I'm sure there is room for disagreement here - I have talked with at least 8 different, experienced mechanics - online, locally, by phone. Right now it is about 6-2 that the problems I'm having can be fixed simply by re-ringing the pistons.

The man I talked with last night has worked on Mercedes for over 30 years and has worrked on my specific model numerouos times and he almost guaranteed that the bores were fine and that I could fix my problem with new rings. He walked me thru the procedure, insisiting that I take notes and then bring my manuals down so he could help me further!

He also said that I would have to replace both the main bearings and the rod bearings.

I have thoroughly researched this topic and there are clearly divergent opinions here... makes it a little more interesting!

ryan

[MunichTaxi]

you want to work for a couple of dozen hours, under a 400 lb engine, still bolted to the tranny, and not replace the rear main seal?

Please question your mechanic, if you can properly torque all those caps, while lying on your back.

[rgnprof]

Both of those items were discussed actually - and I don't know for sure. The rear seal does not appear to be leaking but I am still weighing the pros and cons of pulling the engine (for one thing I don't have the necessary equipment to pull the engine and I don't have an engine stand either).

I have also specifically asked about torqueing the caps and getting everything back together properly - several have indicated that it is doable.

Again, I'm still weighing options.

ryan

[t walgamuth]

you need to pull the motor if you do all that.

imho. you cannot do it properly with it in the car. i dont know how you can replace main bearings with a motor in the car. the crank must come out. what you gonna do put in the bottom half only?

the crank cannot come out with the motor in the car.

tom w

[Chas H]

If the pan can be got off, the main bearings can be replaced without removing the crankshaft. The top half of the bearing can be slipped around and out and a new one slipped in. I've done it a few times.