1988 560SL. Engine Job 05-320. Questions about steps

[dmorrison]

In job 05-320 on the 88 560SL, Replacing timing chain. The second step is to "Remove rocker arm on right hand camshaft (05-230)"

Can't figure out why were removing the rocker arms. Nothing in the job description seems to require that they are removed.

Any ideas.

Dave

[joselu43]

Engine is easier to rotate that way. Probably helps in avoiding chain jumping. Don't need to do it. I did not do it.


Jl

[Strife]

There may be more to it than this. Without the tensioner and arm to hold the chain in place the cam can go back and forth in relation to the crank (and pistons, of course). It is my understanding that there is very, very little tolerance between the valve and piston during a rotation under NORMAL conditions when the chain is tight from the tensioner being in place pushing on the arm, etc. I don't think MB would have mentioned this in the manual for the heck of it, to give the mechanic something to do. It takes very little to bend a valve enough to cause it not to seal or to very prematurely wear out the guide (tolerances in this area are very, very tight).

My $0.02, this is extremely easy to do with the proper tool, it makes the rest of the job easier and less risky, and the only way to screw this up would be to put the followers back in different places than where they came from (easily avoided with an egg carton).

You will probably be lucky, but I know I have bad luck, I don't have a lot of experience doing this (I've done it on this type of engine exactly one time) but I did it apparently successfully.

I'd do it.

[ctaylor738]

I always thought you are more likely to get stuck than to do any damage. If you get stuck with a valve against a piston, then you would have to back up and re-tension the chain, which could get interesting.

[Tomguy]

I also did not do this, nor did I need to. I had a massive 12° of stretch too. If the valves didnt whap the pistons at startup or at 6k RPMs, they won't during chain replacement unless you skip a tooth, and even then you can easily back the engine off.

[Roncallo]

I dident do this on my 1988 560SL. But it is a good idea.

There are two reasones that I can think of that may be why they are asking us to do this:

1) It's safer in that valves cant hit pistons, except why would they only ask you to remove the rockers from the right hand side. Most likely because safety is not the reason they are asking this to be done.

2) In setting up the timing, the cam shafts want to rotate due to rocker arm pressure on the cam lobes. It is likely that with the engine at #1 TDC, looking at the cam from the front of the car, the left cam wants to rotated counter clockwise (not a problem as cam remains in time due to proper tension on the pulling side of the chain) and the right cam wants to rotate clockwise (this is a problem because the pulling side of the chain will slacken and the cam timing will be retarded as the tensioner gets pumped up and slack is removed from the pulling side of the chain).

Condition number 2 can be aliviated by checking your cam timing with the right cam held in counter clockwise tension and verifying a tight chain on the pulling side of the chain. A good way to double check cam timing is to rotate the engine about 5° - 10° past TDC using the crankshaft bolt. Then carefully using the right camshaft bolt pull the engine back to the TDC mark on the crank shaft and check timing on both cams while holding counter clockwise torque on the left cam. Be careful not to overshoot the crank timing mark or you will have to repeat the procedure. Also note that the came bolt may loosen doing this especially if you try it too fast. It is important to do a final torque check on the cam sprocket bolt after doing this procedure. This meanes pulling the bolt out adding Locktight and retorquing.

Note years ago when I was young and stupid, I used to roll in chains using the starter motor. This can be done with a very good understanding of how the system works, and a helper who also understands and knows how to hold back tension on the right side sprocket and a total disregaurd for risk of very expensive parts in very expensive locations. I never jumped a tooth in using this method, but that was probably because I was so scared of the process I held engadement for dear life.

John Roncallo