What is too hot for these cars to run? In the summer I run higher than 80 and at max the 100 mark. Most of the time it is in between the two. My 300sdl runs a similar temp to the 350sdl, maybe a tad cooler. Is 100 too high? Will that cause a crack over time in the 300sdl? Now getting paranoid about 300sdl head. Thanks

Were those compression readings performed when cold? If so, not bad. A 30psi loss on one cylinder is close to a 10% loss, but could be something not so $$$, such as a stuck ring, cracked head, etc. I am amazed to see the cross hatch still in the cylinder walls. What does the wall look like for the #4 cylinder with all the coolant in it?

An observation in pic 1 of 14 of your Dropbox acct. --Pic 1 shows coolant sitting on top of your #4 intake valve (air side, valve closed) and the glow plug is removed. I am not sure how coolant could end up on the valve, unless coolant is being bypassed by coming in the intake before combustion chamber and entering the cylinder when the intake valve opens.

Also, my thoughts are that given the design of the exhaust manifold, and the fact that the runners go downward to the ports, coupled with the downward slope of the engine as it sits in the engine bay, if #4 leaked coolant (exhaust valve opened while sitting) and overflowed out of the exhaust, it would eventually fill #5 and then #6 exhaust ports, due to gravity. If #5 and #6 exhaust valves were closed (most likely, since 2 or more cylinders are not on the same stroke) coolant would not be detected in the cylinders. So, #4 would still be isolated.

I would think if a bent rod, would be lower compression than that, depending on the severity of the bend. I too would measure TDC height of each piston to see if there is much variation. If within specs, throw a head on 'er and call it a day.

Can anyone chime in on if there is a coolant jacket around the area between the intake and exhaust valve guide area or perhaps an oil passage in these heads?

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Thanks,
Mark in NC

"Spark plugs?...We don't need no stinking spark plugs!"
1985 300SD "Der Silberne Schlitten" 420,000 mi


Wish these were diesel:
2003 Ford Club Wagon 130,000 mi

I thought that MB's spec for comp on the 603 was approx. 375 - 450? When testing my 3.5 603, I found most cyl's around 450, and the worst bent rod at 360.

Operating temps of 100 are fine as long as your cooling system is ok- Good belt, hoses, radiator, etc. Make sure you have a good 1.4 cap on the expansion tank.

My system is 100% new. At ambient temps below 85f, it runs at approx. 90. Temps here in the 90's now, and it will climb to 100 for short periods depending on conditions.

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Chief

1991 350SD

Good point, Chief. I wonder if the OP performed the compression test was with all injectors/glow plugs removed for proper compression readings with max. cranking speed...

__________________
Thanks,
Mark in NC

"Spark plugs?...We don't need no stinking spark plugs!"
1985 300SD "Der Silberne Schlitten" 420,000 mi


Wish these were diesel:
2003 Ford Club Wagon 130,000 mi

Mach:

The compression test was done early on after I purchased the vehicle. I was new to MB and diesels. After I found oil in the coolant I began to search. I did the compression test through the glow plug holes and left all the injectors in place. I let the "pressure" sit for less than a minute to see if it will hold pressure. Everything seemed to be good to go. I did a coolant flush thinking that the previous owner may have had a bad head gasket changed out but didnt replace the hoses.

I have only put about 5k miles on the vehicle since ownership. I replaced: injectors, tensioners, springs, diesel purge, belt, alternator, hydraulic tappets, glow plugs, new thermostat, and many other small items.

Since changing the coolant I would also squeeze the top radiator hose regularly to try and get any air out of the system. My obsession finally lead to a cracked hose that I didnt realize for a little while. Could that have lead to this? (would the thermostat still have been accurate?)

I will have pictures of #4 cylinder shortly.....

Looking from Passenger side of vehicle:

Number 5 is on the LEFT and #4 which had coolant filled is on the RIGHT. Cleaned with brake cleaner (all I had around-Hope it doesnt eat the rest of it,ha).



#4 up close. Some visible wear on cylinder?



#5 up close. Different wear pattern than #4

Looking from DRIVERS side:

#4 up close: Visible wear pattern.



#4 looking down. Would this be the visual symptom of a bent rod?



From left to right: #2,3,4,5 : Definite change in wear pattern across the cylinders.

I simple compression tester will not usually show a leak down, b/c it has a schrader valve that holds pressure in the hose and/or gauge. A leak down tester, however will show a % loss over time, but has to be checked at TDC and both valves closed. At this point, measuring piston height in each of the bores would be the next step in determining which way to take it next. If it checks out, then I would pull #4 out and look at the piston and rings/ ring lands, then reassess. It may not be worth fixing depending on what you find next.

__________________
Thanks,
Mark in NC

"Spark plugs?...We don't need no stinking spark plugs!"
1985 300SD "Der Silberne Schlitten" 420,000 mi


Wish these were diesel:
2003 Ford Club Wagon 130,000 mi

After you get everything lined up at TDC and go to take off the head, how do you make sure that you don't lose chain timing? Do you clamp the chain to the sprocket and unbolt the spocket from the cam while at TDC?

Even if you did that, you would have to keep tension on the chain to be sure it didn't come off the teeth on the bottom sprockets. Seems like this would be difficult.

Then, if you took the head off and wanted to measure the height of the pistons, you would have to rotate the crank anyway, and you would loose the timing anyway.

Probably making this more complex than it needs to be, but any guidance would be good.

The chain won't come off the crank or IP sprocket while the head is off. There are enough guides that you don't have to worry about it. You might index the chain to the cam sprocket before removing the cam sprocket but even that's hard to mess up during installation.

The tendency is for #1 and #6 to bend and they're at TDC when the indicator shows TDC. There's enough slack in the chain to rock the crank a couple of degrees both ways to make sure the piston is at its apex. Use a dial gauge to be sure. To check the rest, keep hand tension on the chain as it rises against the tensioner rail as you turn the engine CW, and slowly feed the chain towards the IP so it doesn't bunch. The IP will follow the crank and stay in time. Turn the crank an even number of revolutions back to TDC to keep cam and IP phasing.

If you turn the crank, all bets are off for any index marks between the chain and the cam sprocket.

Sixto
87 300D

sixto -- thanks!

That's exactly what I was referring to. In order to measure the piston crown measurement on all 6 cylinders, I am going to have to rotate the crank with the head off.

You say that will eliminate any indexing to the cam.

and additionally, as you say, I have to be worried about the IP timing

So, what is the best way to take the head off and take measurements of the pistons in order to determine any bent rods while maintaining chain timing? I will be right there and seems a shame not to do that.

Do I absolutely have to take the chain apart or can I take the whole cam sprocket off to eliminate that step on assembly? I don't have the chain link tool, so that would be a big help.

If you turn the crank with the head off, you'll forfeit the accuracy of indexing marks you made between the chain and cam sprocket. No big deal. It's relatively easy to establish cam timing if you keep track of how many full rotations you turned the crank. If you lose track, you can use the IP to re-establish #1 TDC.

You have to worry about IP phasing if you turn the crank with the head off. The crank turns at twice the speed of the cam and IP and since the IP remains tied to the crank, you have to be sure the IP is at #1 TDC when you install the head. You can't just go by the crank since there's a 50-50 chance the crank at TDC is at #1 TDC.

You don't want to take the chain apart! If you're an arachnid you can hold the cam sprocket on the chain while you turn the engine to raise the other pistons. Or just remove the cam sprocket and keep track of the crank. Put a dab of paint on the IP timer (sprocket) to indicate TDC. No point in indexing the chain since you shouldn't turn the IP CCW. That means pulling the vacuum pump which you otherwise don't have to do when replacing the head gasket. When the crank is at TDC, the paint mark on the IP timer will either be where you made it or 180* off. If it's off, give the crank one turn to set the paint mark where you made it. Now install the head.

Sixto
87 300D

Sixto - ok. Makes sense. One thing I had read though that is different from what you mentioned. Some post I had read in the past talked about the chain tension being lost and the chain dropping off the lower sprockets. That, along with the chain coming off the IP timing assembly are my two worries. I guess the tension was lost (because the chain was off the cam sprocket?) and it allowed the chain to miss the teeth as the engine rotated.

You indicated that this could not happen though.

The rest doesn't seem too bad. Do you HAVE to machine the head? Also, I was not planning to get the head pressure tested since I have access to being able to detect cracks in it.

If the pistons do not all come up to the same height, I would guess this means bent rods. If they are bent, should I scrap the rest of the job, or go ahead and reassemble and keep running it? It was running great before.

Maybe that's advice for a 617. If this picture makes sense to you, you'll see that there's nowhere for the chain to fall off any sprocket -



Don't turn the engine without some sort of tension on the chain. You don't want the chain to bunch up and you might damage something of turn the engine against a bunched up chain. Hold the chain as it feeds into the upper guide and you'll be fine.

Measuring piston protrusion is more scientific. With the piston at TDC, measure protrusion at the forward end and aft end of the piston. It should be same value of about 0.7mm. Check the FSM for the spec. If the measurements aren't the same for any piston, the rod is bent. I've only seen and hear of cases in which the forward end was lower - protruded less - than the aft end.

I don't know that you have to machine the head but you should check it for flatness particularly if the engine ran hot. It's an opportunity to replace the valve stem seals (use MB brand only) and check if any valve guides are worn.

Thanks. No It's never run hot for as long as I've owned it. - going on four years now.