Sixto -

Probably a stupid question, but trying to run through the scenarios in my mind before I do it.

I am thinking that the only way to be sure the pistons are at their crown (other than #1), is that you turn until you see it dip and then know you have turned to far.

You say not to turn the IP CCW, but I'm thinking that it is going to have to be necessary to turn the engine CCW with the cam sprocket off in order to get each piston at it very top height.

Also, you say measure front to back on the piston, but wouldn't the rod bend so that the measurements would be different left to right rather than front to back? Guess I could take all four measurements.

Is there a tolerance spec for a difference?

Don't turn the engine a lot CCW. A couple of degrees to make sure the piston is at its zenith is okay. Two reasons I can think of are you might hydrolock the IP turning it backwards and it's difficult to keep tension on the chain turning it CCW since the crank lags the IP in that direction. Essentially you have to pull on the chain with enough force to turn the IP timer and simultaneously turn the crank to keep up. It's not a problem CW since the crank leads the IP. Nor is it a problem to turn the crank CCW a couple of degrees since there won't be enough slack to fold the chain in an unfoldable way.

An unfortunate nature of geometry is that there isn't a lot y-axis motion in response to x-axis motion at the top and bottom of a circle. It's really hard to find TDC with your eyes. Get a cheap dial gauge and stand at harborfreight.com to be sure you're measuring at TDC. You can also confirm that the crank damper indicator is calibrated since it's adjustable and who knows who touched it before you. I suppose it's okay to eyeball TDC since you're more concerned about protrusion difference fore and aft for a piston than comparing protrusion across pistons.

The wrist pin runs fore-aft so the piston naturally rocks left to right in the block. You'd be measuring a moving target if you compare left and right protrusion. It might be useful to compare those measurements across cylinders but it tells you nothing about the rod in the way rods typically bend in a 3.5. You're more concerned about the rod bending forward - check my avatar - as if paying homage to the radiator. But yes, rods bend the other way too.

If you're so inclined, you can measure each cylinder for ovalness since a bent rod will cause uneven wear. Compare the longitudinal and transverse diameters halfway up the piston travel or top, bottom and halfway up for good... umm... measure. This assumes you understand normal wear, which I don't. A rod bent forward will generally accelerate wear in the longitudinal direction. You can also or instead inspect crosshatch patterns. The [hopefully] factory crosshatching of the cylinders should be uniform top to bottom and around the circumference. Areas of smoothed crosshatching indicate more wear in those areas.

And all this assumes you'd do anything about it. IMO, there's no ROI in refurbishing a 3.5 block. Nor is it imperative to toss a block with a bent rod or two. If it runs well and doesn't burn more oil and/or blow more smoke than you can tolerate, slap on a new head gasket and keep going. A 3.5 isn't going to leave you stranded because the rods are bent. You're just going to get sick and tired of driving it enough to do something about it.

Sixto
87 300D

My gaskets have not arrived yet but I thought I would do a compression check to see what I was dealing with.

I believe that I am looking at a textbook example of how the rods bend in these engines.

The engine has almost 200,000 miles on it, but it was a very sweet running car. The turbo vacuum hose was cracked and it caused an overboost situation that caused the car to go into fuel cut-off mode.

Shortly thereafter, the car started to create a great white smokescreen. I am thinking of seeing if the military will take this off my hands for a few million as I think it produces enough smoke to mask an invasion of Syria. Although once we invade, we won't be able to see what to shoot...

I looked at the dipstick last week and saw no coolant, which was a good sign. I also started the car to move it and saw no real smoke being made and viewed this as a second good sign.

Today my wife moved the car into the garage for me. Being as she had to back it in, she had it running for longer than I did. It started making smoke. Lots of it.

In doing a compression test, I found the following:

When I was testing the compression for cylinder #1, (I took out all of the injectors so it would crank easier) cylinder #2 started blowing out oil. I could not see any coolant - only oil, but the car has used a little coolant so I think I have some coolant leakage also. Oil SPRAYING out of a cylinder is not good because the cylinder would fill with oil and hydro-lock and bend the rod. Which is probably what has happened. I am anxious to pull the head and take some measurements. If by some miracle the rod isn't bent, I need to figure out where the oil is coming from

Here are my measurements:

#1 475
#2 700 (as oil continued to build - it may even have gone further, but I stopped cranking)
#3 475
#4 475
#5 475
#6 475


Has anyone seen this in action before? And if so, please let me know what ended up happening. If you guys have any thoughts as to what I'll see when I take the head off, I'd be interested in that too.

Thanks

Just drained my coolant - it had just been flushed recently and it was pristine. Definitely no contamination in the coolant. The FSM says to pull the radiator to change the head. Seems like a lot of work for nothing. I see no reason that the radiator would be in the way when taking off the head.

That's because the FSM expects you to use a slide hammer to remove the chain rail pins, which may require more space. And/or the radiator may need to come out if you are removing the fan clutch without the special tools. I don't think you'll need to pull the radiator if you don't want to. You may want get the fan clutch out of the way so you can easily access the front crank bolt for rotating the engine.

Pics of my cylinder head R&R on my 87 300D OM603 are at this link.

I see you took off your cam. I was going to leave mine on so I didn't have to worry about putting it back on correctly.

Also, I see you took off all the exhaust manifold. Was it necessary to remove it all? I'm trying to take off as little as possible to get the head off.

It depends what you're going to do with the head. I'm deathly scared of handling a head with valves open. I also don't have a long enough XZN bit to remove the head bolts covered by the cam towers. That's why the cam is the first thing I remove.

Next is a suitable place to work on the head. The block makes an excellent work bench to remove the turbo and exhaust manifold. I'd have to fabricate a jig to hold the head with valves open to a work bench otherwise. The nuts and bolts holding the turbo to the manifold are on there but good. You'd flip the engine on an engine stand levering the fasteners you can't get to with an impact wrench.

A personal reason is I have two skinny arms and no hoist. I have to work within the limits of what I can lift. Dave has German elves who work on his cars and keep everything clean while he sleeps so I don't know his motivations but I suspect the cam came off for access to the valve stem seals.

If all you're going to do is give the head mating surface a cursory cleaning, I suppose you can leave the manifold and turbo attached. Then you have to worry about head gasket debris getting into the ports through open valves. That's not for me.

Sixto
87 300D

Didn't have much time tonight so all I did was take the air cleaner off and the big hose off between the airflow sensor and the turbo. The hose has quite a bit of oil in it. I'm really not sure if it was being sucked out of the engine and moving through the turbocharger, or that the turbocharger seals were out. In other words, was the oil from the engine leak I saw in cylinder #2 or was it a seperate oil leak from the turbo seals which also probably need replacing.

Clean the hose and turbo inlet, direct the vent hose into any old bottle, cap the fitting in the big hose, go for a spirited drive. See if there's any/more oil in the turbo inlet or in the bottle.

Before anything else, takes lots of pictures of the engine bay as it is. Take close-ups of wiring harnesses and connectors, the fuel supply and return lines by the big filter, etc.

Sixto
87 300D

I managed to get the turbo and exhaust manifold off tonight. So I've got the right side cleared out. I'll try and go after the intake tomorrow.

Early night tonight (at least as far as the car goes.) Got the intake off and that's about it for tonight. My goal is to figure out what is wrong with it by the end of the weekend.

Not a very productive night tonight. The glow plugs are normally easy to take off once the intake is off, but the wires were spinning with the nuts and I didn't want to cause any damage. In any case, I had a hard time grabbing onto them so that the nut could be broken loose. All I accomplished tonight was to get the engine to TDC and get the glow plugs out.

I started to try and take off the rear water connection to the head, but it does not seem to want to move and I think I will have to unbolt it in a few places as it goes around the oil filter. All I got done there was to remove the retaining clip.

I did this once before on my other car, but it's been too long to remember. Anyone done this recently that has some good shortcuts?

I still need to get that off, the head temp sensor, the fuel filter and the front housing that holds the two temp sensors that connects to the radiator. Then I need to make a decision as to whether or not to remove the cam before taking off the head.

You have to remove the cam in order to get to the head bolts under the cam towers.

__________________
Chief

1991 350SD

The cam towers have holes and enough air gap so you can loosen the head bolts with a really long XZN bit. I don't understand the point if you have to measure the head bolts before installation.

Sixto
87 300D

The cam towers have holes and enough air gap so you can loosen the head bolts with a really long XZN bit. I don't understand the point if you have to measure the head bolts before installation.

Sixto
87 300D