Strider93

OK, here's the situation: 1991 300E with 78K miles on it, running perfectly except: I had a hose split open, the one between the motor and the heater core on the driver's side. I never came close to overheating, and I thought it would be a simple fix. Turns out the split hose was just a symptom of the real problem, a blown head gasket and oil in the coolant.

So, being a mechanical engineer, and someone who's turned wrenches on just about everything for the last 25 years, I plan on doing all this work myself, I just need a good plan of attack, one that will be cost effective too.

For right now, I am just planning on R&R for the head gasket and valve seals. So my parts are going to be a hose, a valve stem seal kit, a head gasket kit, valve cover gasket, the new bolts and washers, and what else?? camshaft seal?? Anything else?

I don't want to do the valves now for these reasons: The car's history is one of a immaculate maintenance record, with frequent oil changes and the majority of the driving is commuting on the highway to work (14 miles one way). The car runs like an absolute top. Of course I'll do a compression test before I dissamble it (need a baseline), but I don't anticipate any surprises from that. Also, MB changed the material of the valves / guides in 1990, so my 91 is supposed to have longer lasting guides.

For similar reasons I don't want to do the timing chain now either. I've still got 22K miles until 100K.

Of course this depends on what my inspections find when I take it apart.

My other concern is flushing the oil out. I plan on flushing as best as I can or have patience for after reassembling the motor with this bit of work. Before summer (April or May), I was planning on replacing the radiator. I'm going to expand the scope of that job to include more flushing, replacing the expansion tank and all the other hoses and thermostat at that time. That way I can be more certain that I've gotton all the oil out before I put the new radiator, expansion tank, and hoses on.

The valves and timing chain I'll defer maintenance on until I reach 100K - 120K miles, just raise my awareness to the state of things, like perform a compression test every 7 - 10K miles from now until then.

Are there any holes in my plan? All opinions are gladly welcomed on this.

I'm figuring what, 6 - 8 hours time to R&R the head gasket, with inspections. Is that fair for a very experienced amatuer wrench?

Also, how much does the head weigh, both with and without the manifolds attached?

And finally, has anyone removed the head and left the intake manifold in place in the engine bay, just unbolted it in while in the car? If so, can you describe how?

Thanks everyone, all opinions, especially dissenting ones, gladly welcomed.

ashman

personally once the head is off, you might as well do the chain and upper chain guides. the upper chain guides can get brittle with age due tot he heat and them being a plastic material. it's just playing it safe.

As far as the rest, it sounds good, but if it were me as long as the head was off I would do the valves too and whatever else I could find, because since the head is already off you may as well.

As for the flushing, I would think the best thing to do would be to get a vacuum pump that can suckt he cooland out through the resevoir thats what my mechanic uses.

Replace the coolant with The coolant from the MB dealer. the pinkish stuff. The green stuff is known to cause corrosion.

Ashman

mhorn

I would agree with ashman, this is such a major undertaking to get the head off, why not go ahead and replace the timing chain? The money it will cost you for the parts is worth the aggravation of pulling the whole motor apart again 22k miles later.

124-Fan

I´ve replaced several headgaskets in the 103 motor and I always leave both the inlet- and exhaust mainfolds in place. Much less work, I believe.
-Apart from the bolts that attach the inlet manifold to the head, you must undo two or three bolts underneath it in order to free it slightly away from the cylinder head itself. -You gain better access to those bolts from underneath. And by all means, renew the short coolant hose between the cylinder head and the water pump. A slight amount of rubber grease in that hose makes reassembly a lot easier while fitting the head and getting the hose into place.
As for the timing chain, you can determine its condition by noting how many clicks, or how far the tensioner can go. You should be able to screw its inner part all the way in by hand and thus get zero slack at the chain. You can also note how well the timing marks align. Rotate the crankase clockwise(with the tensioner installed) and align its marks. If the camshaft marks aren´t completely aligned as well, the chain is beginning to stretch.
-But given the miles on your car, a chain replacement shouldn´t be necessary.
The cylinder head is slightly heavy, so having an assistant when removing and installing it eases the job considerably.
I would recommend replacing the valve stem seals. And while doing that, inspect the valves carefully. They sometimes take damage due to heat and age.
A very moderate grinding in shouldn´t hurt either.

Strider93

Thanks, I appreciate the reply.

Replace the chain: I considered this, yet decided against it depending upon what I find when I inspect. Ashman, consider that it is a relatively short, metal chain, with only two sprockets and a tensioner....very little alternating stresses from direction changes like a chain going around double cams has...by most accounts, the M103 chains last and last, 200K miles is not unheard of for them. I'll inspect for stretch by seeing how far the tensioner is adjusted out and then decide.

Then chain guides, on the other hand....yep, I think I'll consider that, as plastic doesn't just embrittle due to heat and stress, but from simple age as well, good call.

Other than a good inspection though, I really don't plan on doing the valves. I have worked several heads over the years, but I don't want to buy the metric reamers I'd need to do this head, and I don't want to pay someone else to do it until it is required.

I'm a mechanical engineer in nuclear power, where maintenance is everything. In the absense of a preventative maintenance schedule to follow, we have to go by the system's performace indicators and the system's history. The history and performance on this motor have been excellent. I would certainly not be pulling the head to do a valve job at 78K miles, with zero oil comsumption and and compression within specs. I don't want to do it now 'just because I'm in there and might as well'. In my industry we call that work scope or project creep. Besides, I enjoy turning wrenches. It is thereaputic for me...takes me away from the stresses of work

Coolant...suck it out of the resevoir? That is the system high point...OK, I understand, the majority of the oil will have gravitated to the high point. The car has never seen anything other than MB coolant...which to me looks more like a pale, clear yellow, not pink.

Thanks!

Strider93

Except that I'm a recreational wrench turner, and 22K miles for me is more than a years worth of driving, maybe 2 years, from now. I only drive this car about 30 miles a day to work and home, and I only drive it about 4-5 months out of the year. I ride my sport bike most of the time, and my bicycle the rest of the time....its nice living just 15 miles away from work.

Strider93

Excellent comments...

I replaced that short hose when I replaced the water pump in June, I think it will probably be OK, but I'll check it out. So long as I don't see any degradation from the oil in the coolant.

By grinding the valves, I assume you mean lapping the seats....Yeah, that's a given if I'm going to replace the valve seals. I was considering not replacing the valve seals though....again, zero oil consumption, even on the time I let the oil change interval go 5K miles it was not down at all. It's down about 1/4 quart now, which I'm assuming was lost to the coolant. We'll see when I get it off though...

By 'slightly heavy', what does that mean? 100lbs? 150? I don't have an engine hoist anymore, and was just planning on lifting it out, except it is a bit of a reach over the fender or grill, and safety comes first....I'll think of something. Maybe a comealong to my garage rafters or something...

Thanks.

ashman

My car did not need a new chain when I had the head done, there was minimal stretch, but since the head was off and getting redone, I told my mechanic roll in a new one and replace the guides.

The cost difference was negligable, and it gave me piece of mind. I also had him replace all the fluids.

He has a vacuum system he attaches to the radiator bottle, and it suckes every drop of fluid out through there. it builds up pressure and then whoosh it starts to pull the fluid out fast and easy. no mess. a lot easier than finding another way to drain it.

Just remmeber to use the MB Coolant, get it at the dealership. don;t use any green stuff or that orange stuff. the MB coolant is what is recommended and the only thing my mechanic uses in a benz and he has been working on them for over 40 years. His passion is rebuilding engines, and he knows them in and out.

Definately inspect the timing chain guides. they get brittle with heat and age, and if one breaks, its not good.

Ashman

mhorn

To drain the coolant, there is a pet **** drain at the bottom of the radiator. There are also drain plugs in the block of the eninge. You might be better off paying somebody to flush out the engine if you had all that oil sluding around inside your block. The guys are right, use only M.B. Coolant or you'll be turning wrenches on a new radiator instead of a new timing chain.

vinamg

Personally, at 78k I wouldn't touch anything. Just remove it and replace gasket. 103 heads are easier to remove with intake attached. This is a 2-3 hour job for an experienced mechanic, but since it is your first time 5-6 sounds about right. BTW, camshaft seal and top timing cover seal should be included with the head gasket kit.

Strider93

Hmmm.....The expansion tank is the high elevation point in the cooling system. Driving the coolant uphill with air pressure to remove all the coolant vs. opening the easily accesible drains on the engine block and radiator at the low points, and the block drain is designed to install a drain hose.....Having performed many venting and filling operations on large heat exchangers in the plant and other various pipe systems, I find that gravity usually works best for draining....interesting though.

As I said, I have never used anything other than MB coolant....preaching to the choir there. Except I'd like to point out that even with S&H charges, its cheaper to get it through MBSAUTOPARTS.COM than at the dealer. (Part Number Z8003-69600). I don't believe in supporting my local stealership.

Thanks

Strider93

Why easier with the intake attached? I have heard it both ways now. OK, maybe easier to remove, but more work overall?

Thanks for the info on the gasket set. I assumed that the top timing cover seal was included from the picture I saw of the kit, but looking at it again I see that you are correct about the camshaft seal as well.

Thanks,

ashman

I get my parts when I buy them from the dealer at wholesale so it doesn;t cost me much. Otherwise I order from my buddy online.

124-Fan

The head may not be very heavy to hold when out of the car. I´d say close to 10 or 15 kg., although I´ve never measured its weight. That is, without the inlet- and exhaust manifolds, camshaft and all the rocker arms… -The way I prefer removing it.
You should be able to remove it successfully alone although reinstalling it alone can be slightly more difficult. That is because you need to lower it slowly and smoothly onto the block without damaging anything and may have to arrange it a bit before it is properly set. And then there is also the previously mentioned coolant hose, which must be aligned properly. That´s where an assistant comes in handy.
I usually get a piece of wire or something similar and tie the inlet manifold as far away from the head as possible. Also the exhaust manifold. That way you get enough space to lift the head out. The exhaust is attached via a bracket to the rear of the transmission. Undo that as well as the exhaust manifold from the head.

The camshaft is retained by six “stools” as I call them, each retained by four bolts. Be advised when you undo each stool, that there is a tiny metal piece under each hydraulic tappet which becomes loose when you lift the stool. I usually bring them to safety using a small magnet. That way they won´t fall down into the engine. The tappets themselves can slide down as well from the rocker arms if you don´t convince them otherwise..

And BTW. I always have the head machined before reinstallation. Valve removal is not required for that on the 103 motor, but the camshaft should not be installed.
-This method has never let me down so far..

Cheers.

vinamg

On second thought, without some help or access to an engine hoist you are better off disconnecting intake. It will be easier to handle, especially when putting back together.

The reason I leave it on a 103 is that there are only a few things to remove in order to free it (wire harness, v brackets attached to block, and 2 fuel lines).

124-Fan

Well, there´s no right or wrong in this matter I think. It´s simply a matter of style, facilites and the amount of beer at hand. Isn´t it ?

vinamg

Another good thing about leaving the intake is that you don't have to worry about the intake gasket. Personally, I hate cleaning gasket residual.

However, 124-Fan hit right on the head. It's all about personal preference, facilities, and most importantly BEER.

Arnie

Don't forget the front crank shaft seal and the gasket between the upper and the lower chain covers. Since your radiator is going to be out, the front seal is a peice of cake. The cover gasket is a must, because that's where the oil always leaks out. And put a lot of silicone on theat gasket.