Uh-oh...I think I've got big problems here - 73 220D - PeachParts Mercedes-Benz Forum

kalpol · #1 03-07-2009, 10:26 AM

After getting my cylinder head rebuilt, I installed it and had trouble setting the timing (see my earlier thread). Well to facilitate getting it right I removed the cam followers again (so all the valves stay closed and I can easily rotate the camshaft) and the engine is still hitting something at both TDC no.1, and if i turn it halfway around it jams at TDC No. 2. With all the valves closed, the only thing I can think of is that they milled the head too much and / or didn't reseat the valves sufficiently. The machine shop was recommended by the Mercedes shop I usually go to, so they ought to know what they are doing. But I can't think of any other reason for this interference.

Even if this problem were fixed, what about the prechambers? will they hit the top of the piston? (they're the old flat kind).

jt20 · #2 03-07-2009, 11:03 AM

if they milled the head and did not compensate on the PC height with some kind of spacer of stacked washer it certainly could be an issue as well.

All of the limits for milling the head should have been available to them. It seems like a really stupid mess-up. Both of your theories are spot-on.

I can only guess that maybe the head gaskets are not the same thickness as the FSM numbers were once based on.

you can test to see what is hitting by returning the engine to where it binds up and then pressing down on the valves to search for the piston head.

jt20 · #3 03-07-2009, 11:04 AM

also.. make sure it isn't something else that is binding... like a vacuum pump or chain rail.

I would think you would know the difference... just keep it in mind

Diesel911 · #4 03-07-2009, 11:22 AM

When you sent the Head to them were the Pre-Combustion chambers still in the head.
If not the Rebuilder would have had no way to check the protrusion.
If the other things suggested do not free up the Engine you may have to pull the Chambers to see if it frees up the Engine.

kalpol · #5 03-07-2009, 11:35 AM

I turned the engine (backwards) to the first lock, which is about TDC +5-7 degrees, and the No. 1 and No. 4 valves all depressed about a quarter inch (just guessing) before they hit the piston. I turned it forward around 180 degrees to the other lock (just before the BDC mark on the crank) and Nos. 2 and 3 did the same. So I am slightly encouraged since the pistons aren't pinning the valves closed, but mightily puzzled.

The engine cranked fine before I took the head off (albeit without compression due to blown gasket).

It locks hard too, just like a contact lock, with freedom to move back (although I haven't made a huge effort to lock it). I can't see how a chain rail would cause any trouble, and surely it's not the vacuum pump suddenly failing while sitting still. I can't think of any other projections in the head that would be contacting anything (nothing is installed). The camshaft is free, and the accessories turn just fine. I guess I can remove the vacuum pump and try it, if that's my only other option other than taking the head off again.

kalpol · #6 03-07-2009, 11:36 AM

Quote:

Originally Posted by Diesel911

When you sent the Head to them were the Pre-Combustion chambers still in the head.
If not the Rebuilder would have had no way to check the protrusion.
If the other things suggested do not free up the Engine you may have to pull the Chambers to see if it frees up the Engine.

Prechambers aren't installed at the moment, but yeah I may have a small problem there since I didn't have the chambers in the head when I sent it. But I'll cross that bridge when I come to it.

#7 03-07-2009, 12:47 PM

I had a similar problem with my 98 Land Rover, I had purchased it for a low price knowing it had a blown head gasket. I took the heads off, made sure all the cylender liners were flat with the deck (all aluminum V8) and sent the heads in to be re-surfaced. The guy then calls me and says "Well... I found about .009 of warpage in your heads, so I milled of .010
I was furious, The max spec for a land rover is .008, and that is MAX. But I didnt have time to fool around so I paid the guy, and bit the bullet, got home, tried installing them, and like yours, contact lock, I then took them off. I then did some searching and found some head gaskets called composite head gaskets, that were stated to be designed for engines milled from .010-.015, They are a little thicker, to compensate for an accidental, or even intentional over sized resurface. I put it back together with the new gaskets, no more contact lock. Finished putting it back together, started her up and ran fine, no knocks, pings, or any noises for that matter. That was a year ago. It is still kicking ass, you know, I even feel that it has more power than before, maybe because the elimination of the blown head gasket, or a slightly increase compression ratio, I dunno. But that is what fixed my LR

kalpol · #8 03-07-2009, 12:59 PM

Quote:

Originally Posted by 83240D

I had a similar problem with my 98 Land Rover, I had purchased it for a low price knowing it had a blown head gasket. I took the heads off, made sure all the cylender liners were flat with the deck (all aluminum V8) and sent the heads in to be re-surfaced. The guy then calls me and says "Well... I found about .009 of warpage in your heads, so I milled of .010
I was furious, The max spec for a land rover is .008, and that is MAX. But I didnt have time to fool around so I paid the guy, and bit the bullet, got home, tried installing them, and like yours, contact lock, I then took them off. I then did some searching and found some head gaskets called composite head gaskets, that were stated to be designed for engines milled from .010-.015, They are a little thicker, to compensate for an accidental, or even intentional over sized resurface. I put it back together with the new gaskets, no more contact lock. Finished putting it back together, started her up and ran fine, no knocks, pings, or any noises for that matter. That was a year ago. It is still kicking ass, you know, I even feel that it has more power than before, maybe because the elimination of the blown head gasket, or a slightly increase compression ratio, I dunno. But that is what fixed my LR

I guess I'm gonna have to bite the bullet and take the head back off and see what is hitting what...hopefully there will be witness marks.

kalpol · #9 03-07-2009, 03:26 PM

I took the head back off and examined things - I had looked at the head of course before I put it on, and all still looks OK there. What I did notice this time was that (since i ignored timing this go-around) the nos 2 and 3 pistons rise slightly above the cylinder head at the BDC mark, while the Nos. 1 and 4 never quite reach that level at TDC. I can't figure out why the lock occurs at No. 1 TDC but it's pretty obvious that the lock just before the BDC mark occurs as the pistons are hitting the head as they try to rise above the deck.

So it looks to me like I'm screwed with bent rods or something. I never turned the engine over till now with the head off for fear of losing timing, and while I noticed No.1 was slightly below the deck I attributed that to the chain stretch.

The head was just fine when I took it off - no evidence of contact and the valves are all OK (the stems were coked heavily and they were sticking open just a tad, so no compression for starting, plus the head gasket was blown). I can't figure out, if something bent rods, how it happened, and how it's so uniform with 1 and 4 matching and 2 and 3 matching.

leathermang · #10 03-07-2009, 03:37 PM

I would not suspect bent rods as the first thing to look at.
Chain stretch would not affect the height the piston achieves in the block.
As far as all the reading I have done in the FSM... it is not acceptable to turn the crank backwards as far as you indicated you did. So would suggest not doing that again after you get everything back together.

kerry · #11 03-07-2009, 03:59 PM

Bent rods are going to be shorter, not longer. Was the engine running ok prior to head removal? Never heard of a piston rising above the block. Any chance the engine has the wrong rods in it? 616 rods in a 615 engine? Why did the head gasket blow?

leathermang · #12 03-07-2009, 04:06 PM

This might be a good time to mention that MB changed out the design of the head gaskets a couple or three times... and may have sealed or drilled some holes differently later on to improve cooling...
so a careful reading of the 615,616,na617 manual would be in order when putting the engine back together ( this is in response to the mention of the head gasket having been blown )....

kalpol · #13 03-07-2009, 04:36 PM

Quote:

Originally Posted by kerry

Bent rods are going to be shorter, not longer. Was the engine running ok prior to head removal? Never heard of a piston rising above the block. Any chance the engine has the wrong rods in it? 616 rods in a 615 engine? Why did the head gasket blow?

I got the car non-running, i figured i'd have a look at the engine and if it was beyond repair, I'd either part it or put a 240 engine in it. It cranked, but had no compression on a couple of cylinders and was pressurizing the radiator. I took the head off and found a gouge in the head gasket between the water jacket and No.3 (which was full of coolant, green of course) and also found that the valve stems were all coked up and the valves were sticking open a bit. The head looked fine though, and so did the cylinder bores, so I had new guides and seals installed and reused the old valves, which looked fine and the shop said they were all right. Put it back on, present dilemma.

The 2 and 3 pistons rise just a hair above the block, but they're defiinitely above (and as far as I can tell running my finger around it, even), and 1 and 4 don't quite make it.

The engine does have a number starting with "616" cast into the side but someone (mercedes parts supplier who shall rename nameless at the moment) said that's just a casting number and it's still a 615. The new head gasket fit without any problems, all the passages were open.

sO i don't know what's going on and i'm about to start looking for a good 240 engine for it. It probably would have been less work to swap engines at this point.