91 350 SDL Head R & R - PeachParts Mercedes-Benz Forum

GregMN · #1 08-25-2009, 08:08 PM

Moving over from the buying thread (http://www.peachparts.com/shopforum/showthread.php?t=257294) to the Tech forum.

1991 350SDL 188k, one owner, dealer serviced since new. (The service manager said he had 158 service records for that car, too many to print out for me.)
Lost the drive belt and overheated enough to melt the core of the temp sending unit. It starts and runs fine, it just blows the coolant out the overflow bottle as soon as it starts. No oil in water, or water in oil. No smoke out the tail pipe. Leads me to think head gasket and/or warped head.

I am getting ready to pull the head. I have never done that on this type motor. My biggest concern is maintaining the timing of the crank, injection pump, and cam. I will not be removing the cam from the head. I will zip tie the chain to the cam gear once I get the crank to TDC.

From what I have read I will:
remove the whole chain tensioner assembly from the lower passenger's side.
remove the upper chain guide by pulling the pin (advice on how best to do this?)

I assume the cam gear and chain will pass out the bottom of the chain passageway as the head comes off.

Is it necessary to lock the cam and the injection pump? if so, how?

What is the order for loosening the head bolts?

What else do I need to know to get the head off safely?

Once the head is off I can see if it is worth fixing. I bought it assuming that the motor would need to be replaced with a 603.961 or 617, but I will at least take one run at fixing it before I pull it out.

I already have the intake manifold, fuel lines, and valve cover off.

Thanks,
Greg

kmaysob · #2 08-25-2009, 09:13 PM

i may be wrong, but from what i gather, your plan is to remove the gear as it is keyed and cannot be installed wrong, right? im not sure that you will even get the head off this way. you would be better off to set the timing to the proper mark, mark it again just in case and remove it completely. you should be fine removing them without a sequence. just break them loose and then skip around. be sure that you socket is a tight fit.

NJ300sdl · #3 08-25-2009, 10:36 PM

Guide pins have a internal thread, can be removed by screwing in a bolt that has a nut run up enough to push against a stack of washers when tightened. Pin will be drawn out. Cam gear will pass thru head when on chain. I like leaving it on. The gear could come off on its own instead. No need to lock cam or injection pump. Cam and lifters are easy to remove, makes head lighter for removal. Vac pump pulls on chain, easy to remove. There are two small bolts that secure the head to timing cover.

sixto · #4 08-26-2009, 12:56 AM

Get youself a copy of the factory service manual!

There's a sequence for removing the cam towers which cover some head bolts. Get it wrong and you'll have a two-piece cam. The 126 FSM on CD has verbiage and diagram which contradict. The verbiage is correct, the color of the arrows in the diagram is wrong. The 124 FSM has it correct. But get an FSM anyway

Aside from the 2 small bolts into the front cover NJ300sdl mentioned, there's a bolt off by the fuel filter.

Set the crank to #1 TDC. Don't worry about the IP but don't touch it either. Index the chain to the cam sprocket, remove the cam sprocket (IIRC there's a semi circular thrust bearing to watch out for), remove the tensioner, remove the upper chain guide. Don't worry about the chain. It can only fall so far into the front cover and won't come off anything else. You can retrieve it with a hook or magnet.

For removing the upper chain guide, this tool is worth the price -

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=370249177688

There is a pin in the head and a pin in the block. The pin in the head will be covered by the upper belt idler if your engine has such a beast. Note how the upper chain guide is installed. One of the holes the pin goes through is round, the other is elongated. It fits either way but I don't remember which way is right. The FSM drawing vaguely shows one more elongated than the other.

Sixto
87 300D

GregMN · #5 08-26-2009, 10:11 AM

Thanks for your replies.

I have ordered the FSM on CD.

I will keep you updated on the progress (or lack there of).

Thanks,
Greg

GregMN · #6 08-26-2009, 04:52 PM

This engine got hot. Notice the plastic shrouds around the first 2 injectors are gone and the others are brittle and will flake off by hand. The close up is of #2 & #3.

I used a socket for a spacer, some washers, and one of the valve cover bolts to pull the pin. Seemed to work easy.

I will pull the head later, or tomorrow.

Knowledge is the most valuable tool in the toolbox. Thanks for your advice so far.

GregMN · #7 08-28-2009, 04:33 PM

Searching through the forum for information on how to remove the head everyone said "be sure to remove the cam towers in the proper order, using the proper procedure, or you will end up with a broken cam shaft". Ok, but they didn't mentioned what the proper order and procedure is. So for anyone reading this thread in the future, looking for just that type of information, here is what I did eventually find, and use, successfully:
With cam at TDC remove 1,5,6
Slacken the bolts on 2,3,4,7 one turn at a time on each bolt until loose. This will take about 5 or 6 repetitions until all the tension is removed.

The head is off.

No steam cleaned cylinders.
No cracks visible to my naked eye.

All of the exhaust side head bolts were tight.
All of the head bolts under the cam towers were tight.
1/2 of the head bolts under the injectors were not tight.
1/2 of the intake side head bolts were finger loose!!!

At first look, using a carpenter's square as a flat edge, the head seems to be warped. Sitting right side up, the center is arched up.

My thinking is that the loose bolts were stretched when the head was overheated and warped. Once the head cooled and relaxed a little, the bolts were then loose.

In the photos: The head was wiped clean with a little degreaser. The block has not been cleaned yet.

michakaveli · #8 08-28-2009, 06:30 PM

Good Luck. Subscribed.

sixto · #9 08-28-2009, 07:46 PM

Quote:

Originally Posted by GregMN

This engine got hot. Notice the plastic shrouds around the first 2 injectors are gone and the others are brittle and will flake off by hand.

The shrouds are no longer available from MB but it's no problem to do without.

Sixto
87 300D

sixto · #10 08-28-2009, 07:50 PM

On the #14 casting the cracks are typically seen between valve seats.

Sixto
87 300D

babymog · #11 08-28-2009, 08:39 PM

And from valve seat to pre-chamber.

Photo shows a #17 head, it'll be interesting to see if there is a failure or just warpage.

From what I remember, not much machining can be done to the head before it's not useable, check into that before putting down your money for machining.

GregMN · #12 08-28-2009, 08:56 PM

#17 head

I am taking it to the machine shop on Monday. If they say it's good, I will order the gaskets, bolts, and a temp sender.

I will make sure they check the specs before they start doing anything.

GregMN · #13 08-31-2009, 02:36 PM

The head is at the machine shop.
No cracks.
The amount of material needed to be removed to straighten the head is within the specs of what is allowable.
A valve job will be done at the same time. I have ordered valve guide seals from Mercedes.
I have sent "billybob" a deposit on the rental of the tools needed to remove the pre-chambers.

So now it is just wait, wait, wait...

GregMN · #14 09-19-2009, 03:06 PM

The head is back on.

As I was cranking the motor, waiting for the air in the lines to bleed out, I noticed a spray from the #4 injector. I stopped cranking, cracked open the fuel fitting and re-tightened it. Then I started the engine. There was still a leak from the #4 injector, but it was air blowing by on compression. I re-torqued the injector, no change. I removed the injector and the heat shield. I noticed that the new heat shield was thinner than the old ones, so I reinstalled the injector with one of the old heat shields. It is still blowing out around the base of the injector. I can hear and feel air above it. I noticed that #2 injector is doing the same thing, but much less than #4.

I did notice that the leak was coming from between the injector and the pre-chamber, not between the pre-chamber and the head.

Any ideas?

Thanks,
Greg

babymog · #15 09-19-2009, 06:07 PM

The heat-shield has to seal to the bottom of the hole, was it clean and free from scratches/damage?

And it almost pains me to ask as you sound like you know what you're doing, but did you install the heat-shields right-side-up?