Help! Timing chain question!! 617 turbo

[rwthomas1]

Okay, preparing to pull the head on my 617 and I have two different manuals saying two different things. The Haynes manual states the timing chain must be supported, like hung from a bungee cord from the ceiling under tension, to keep the chain tight on the crank and IP sprockets when pulling the head and while its off. The MB manual (CD) states to rotate to TDC, pull the cam sprocket and pull the head. No mention of wiring the chain, etc. What to do? Does the MB have "guides" on the IP and crank sprockets that keep the chain from dropping off? I have worked on other engines where the chain must be kept tight but since I am working alone on this with no hoist for the head, just muscle, it would be a lot easier if I can just lay the chain on itself and pull the head. Need input fast on this one please. Thanks, RT

[Brian Carlton]

RWT:

You definitely need to make sure that the chain remains taut around the crankshaft. You can suspend the cam sprocket from the ceiling as I am thinking of doing. Alternately, you can lift the head, very slightly and jam a welding rod through the chain, beneath the head, so that the welding rod sits on the top of the block. This then prevents the chain from falling into the gallery when you pull the sprocket.

Note that I have not tried the welding rod approach, personally, so, it would be far better for someone else to chime in and provide you with the details.

I'm quite sure the suspension of the sprocket from a bungee cord attached to the ceiling is the least risky approach, however, it does compromise the capability of easily getting the head off the block, especially if you are by yourself.

One additional thought:

Use the bungee cord to suspend the cam sprocket until you can get the head up about 1 inch. Then use the welding wire to keep the chain from falling. Then you can remove the bungee cord to allow you to get the head out of the engine compartment.

[Breckman99]

I once had to pull this job by myself. Here is what I did: After I separated the chain I hung each side from a single point. I then suspended the head above the block with an engine jack (Getting that sucker off the block is sometimes tough) . I then moved the support around the outside and bottom of the head to keep the chain from moving while keeping tension on the chain above the head with my other hand. I then let the slack lay over the side of the block. Reversed the procedure to install. It was a bit tricky but not too bad if you are careful. It sounds like you aren't rolling in a new chain so you will only have to worry about one suspension point and not two. Good luck!

[Fisherman]

When I did the head on my old 240 I just took the chain and tied it off with some wire while I lifted the head and wedged in a 2 X 4. Then I took some tie wire and tied it off under teh head so that I could get the head clear. Reverse when reinstalling the head. I placed the head on a couple of 2 byes with the long side up and then moved the chain through the hole and dropped the head into place.

It's my understanding that there is nothing to fear except having the chain coil on itself down at the crank. Skipping a tooth or whatever does not affect the timing at this point, only when you are reinstalling and trying to get TDC with the cam lined up correctly.

In fact when putting it back on I seem to remember putting the chain on the sprocket with the tensioner removed and then remounting the sprocket to the cam shaft. Took a couple of shots to get the right tooth on the sprocket and get it aligned with the woodruff key but not too bad.

[TimFreeh]

It's a non issue since the important thing is the relationship between the IP and the crankshaft. Since the chain can't slip over the drive gears on the crank or the IP timer you can't really mess up the relationship between them.

Unhook the chain and drop it down into the crankcase, it will be easy to fish-out with a coat hanger when the head is off.

Be sure to remove the head with the engine at TDC, It will make re-assembly much easier.

If I were you I'd use a dial indicator to and the proper offset keys to get the valve timing spot-on, It's also a great time to use the drip method and set the IP timing right on the mark since it's very easy to turn the engine with the glow-plugs removed and it's easy to pivot the pump since the injection lines will not be installed.

[TimFreeh]

One other piece of advice - please reconsider removing the head by yourself.
Find somebody to give you a hand, unless you are built like the governor of California you are going to have a very tought time lifting it off the engine without some assistance.

[Brian Carlton]

Originally Posted by TimFreeh

It's a non issue since the important thing is the relationship between the IP and the crankshaft. Since the chain can't slip over the drive gears on the crank or the IP timer you can't really mess up the relationship between them.

Tim, could you explain this in more detail? I was under the assumption that the chain will fall off the IP sprocket and fall off the crankshaft sprocket if upward tension is not maintained? Not correct?

[TimFreeh]

Not correct based on my experiences - there are two main reasons for this.

1) the IP takes quite a bit of force to move, the weight of the chain will not provide nearly enough force to move it.

2) The chain runs very close to the crankcase at the point where it is meshed with the IP timer, there is not enough room for the chain to "jump a tooth" since it must lift off the gear far enough to disengage from the gear. The same situation exists on the crankshaft gear that drives the timing chain.

You can rotate the engine as long as you take up the slack in the chain by hold the chain clear while you turn the engine with a socket. Don't try to rotate the engine without supporting the chain - the chain will jam very quickly.

I must preface my comments by saying I'm pretty sure you would not change the timing using this method, but I would never re-assemble an engine without verifying the valve and IP timing using the correct factory methods.

[psfred]

Lift the head and run a peice of wire or brazing rod (it's flat) through the chain while holding the cam sproket or just the chain up so it won't fall down. It will NOT run off the crank or the timer unless you remove the retainer bolt from the side and monkey around with it, but it's a good idea to hold it up.

I managed to drop BOTH ends while rolling a new one in on the 220, and it's very close to correct (IP timing is 20, not 24, degrees at the moment).

Peter

[P.E.Haiges]

If you want to turn the engine like to R&R the rods while the head is off, the bungee cord idea works good. I thought of that a long time ago with out the help of a manual on my old 190D and I didn't lose the IP timing.

P E H

[Pete Burton]

Originally Posted by TimFreeh

It's a non issue since the important thing is the relationship between the IP and the crankshaft. Since the chain can't slip over the drive gears on the crank or the IP timer you can't really mess up the relationship between them.

Unhook the chain and drop it down into the crankcase, it will be easy to fish-out with a coat hanger when the head is off.

Be sure to remove the head with the engine at TDC, It will make re-assembly much easier.

If I were you I'd use a dial indicator to and the proper offset keys to get the valve timing spot-on, It's also a great time to use the drip method and set the IP timing right on the mark since it's very easy to turn the engine with the glow-plugs removed and it's easy to pivot the pump since the injection lines will not be installed.

I would not just drop the chain down into the crankcase. It easily get stuck and become a HUGE hassle. Just wire each end so you won't lose it. Don't worry about the tension, because you have to remove the tension anyway as the tensioner is in the head

[rwthomas1]

TimFreeh,
I guess I must be a little like Ahnold after all. I had no problem lifting the head out by myself.... Finally all those years of gym memberships paid off! RT