Is this another heat shield or just the prechamber? - PeachParts Mercedes-Benz Forum

rbtoj · #1 12-17-2017, 05:23 PM

I just finished cleaning and testing the injectors on my father's 81 300TD and was about to reinstall them, when I had a little surprise: one of the prechambers had a much bigger hole (where the injectors goes), than the others. I assumed at first that the previous owner had stacked two heat shields on some of the prechambers, but I couldn't get these "supposed" second heat shields out. I also noticed a difference in depth between the two holes (you can see it in the pictures).
So, are these heat shields or just a different type of prechamber?

EDIT: Deleted redundant pictures.
Just to clarify: cylinder 1 has the small hole, and cylinder 2 the larger.

marco5 · #2 12-17-2017, 06:22 PM

Hi there,

Pic 1 and 4 have no heat shield, 2 and 3 have heat shields that need to be removed. Clean up all of that crud as well. Shoot brake cleaner on them but don't spray directly into the chamber. Just enough so it soaks those stuck heat shields.

Heat shields can only be used once, clean all of those chambers and don't let any of that junk/dirt fall in. Use some brake cleaner on a cloth (don't spray it in the chamber) and clean it very nicely. Buy new heat shields, clean up nicely and torque to spec.

rbtoj · #3 12-17-2017, 07:03 PM

Thanks marco5. I tried to remove them again, but I'm starting to think that there are no heat shields there, here is why: I tried to jam a screw driver into the hole and turn, and all that I achieved was to dent the screw driver. I don't believe that a deformable heat shield would be made of a harder material than a tool.
I also tried turning the engine with the starter motor, and nothing.

Besides, this thread suggest that there are at least two types of prechambers.
85 300d prechamber difference - Mercedes-Benz Forum

I'm confused...

vstech · #4 12-17-2017, 07:09 PM

Both pictures have no shields in them.

marco5 · #5 12-17-2017, 07:12 PM

take a look again - the first one has a stuck/seized one I think. Perhaps I am incorrect though.

EDIT: I looked about 10-15 times, that first one has a heat shield. If I am incorrect (vstech may be right) and there are no heat shields, you simply have different 'prechambers' in the cylinders.

funola · #6 12-17-2017, 07:14 PM

The smaller hole one is a heat shield packed with carbon, that's why you can't get it out. The trick is to take a regular screw driver and a hammer, hit the perimeter of the heat shield all around to break the carbon bind, then use a hook to pull the heat shield out.

Diseasel300 · #7 12-17-2017, 07:46 PM

I sacrificed an old screwdriver to get the heatshields out of my engine. They were IN THERE. I folded over about 1/4" on the end so I could get it in the hole, then jerk it hard back out to break the shields loose. Another tip: Some Hoppe's #9 gun solvent works very well to break up the carbon. Drip it around the edge and let it soak for about 15 mins. Chances are, they'll come out with 1 good pop. Use more on a brush or long Q-tip to clean up the rest of the carbon. It also looks like the shield in the first picture was installed upside down too!

marco5 · #8 12-17-2017, 07:57 PM

Yeah - it's stuck hard in there. Whats that green monster ooze coming out of your valve cover gasket? LOL

Diesel911 · #9 12-17-2017, 08:07 PM

This pic is from someone elses thread along time ago. From what I remember they were different pre-chambers. There should be different the Numbers on the chambers rims.

Also in the 2 pictures posted by the OP it looks like the retaining rings are distorted because someone did not use the correct tool to install and remove them.

However as other said be sure the old heat shield is gone.

rbtoj · #10 12-17-2017, 09:56 PM

Thanks everyone for the tips. I'm going to make a new attempt tomorrow with a clean head.
Diseasel300: The sacrificial screw driver tip might just work...
Diesel911: That's the picture that made me think I have two different prechambers. I really don't wont to remove the collar nut to find out though...

SonnyMorrow · #11 12-18-2017, 12:06 AM

I had some pretty stuck heat shields once. I found a trick that worked for me. You're going to want to take some of these pliers (if you have some)
and jam them in the heat shied hole, and then open them as you pull the heat shield out of the pre-chamber. Maybe this will work for your situation,
if indeed that is a stuck heat shield.

Good luck

Maxbumpo · #12 12-18-2017, 09:11 AM

My opinion: two different types of pre-chamber. As noted, the locking ring on both looks deformed from an improper tool, and you mention a previous owner. If you've got maintenance and repair records, check to see if a pre-chamber was ever replaced or if the head was ever off for work.

If you want to be sure, you need to clean-clean-clean the pre-chamber with the smaller opening. Be careful to avoid contamination into the pre-chamber. Rig a vacuum cleaner to suck out debri, maybe rotate the engine until a valve is open so you can get air flow out of that hole. solvents like brake cleaner or Hoppes #9 may help you, focus on the outer edge to see if you can find a seam at the transition point from vertical to horizontal. I would not go prying around inside that hole until I was darn sure it really is a stuck heat shield.

ROLLGUY · #13 12-18-2017, 12:02 PM

Definitely different prechambers. The bottom of a heat shield is beveled, just like the mating surface you see in the two photos. The top surface of a heat shield is basically flat. Yes the groove can pack with carbon, and it appears like there is no shield there, but the screwdriver trick always gets the shield out. Do all the other PC's have the larger hole or the smaller?
EDIT: Disregard the last question, I just re-read that only one has a large hole.

vonsmog · #14 12-18-2017, 12:48 PM

My wagon has one small prechamber and the other four are large. Since the motor is not original and I know zero about the car before I got it, who knows what might have been done in the past 30 years! But it seems to run fine and I'm just too lazy to change it!

ROLLGUY · #15 12-18-2017, 08:34 PM

Quote:

Originally Posted by vonsmog

My wagon has one small prechamber and the other four are large. Since the motor is not original and I know zero about the car before I got it, who knows what might have been done in the past 30 years! But it seems to run fine and I'm just too lazy to change it!

Hey, maybe you two can get together and make a trade!