250 SL - injection pump cylinder moving with piston

[Mqueretin]

Hi there,

my 205  SL was not running on all its cylinders. I removed all fuel pipes on top of the injection pump and the pressure valves and found that three pistons were blocked. I unblocked them however only to realise that cylinder 5 and 6 are  moving up and down with their piston,  which does not sound like a good news to me. I have taken a video which is too big to post, but I'm posting two pictures taken at 1 second interval or so from each other, which show the different positions of the cylinder.

Is there any fix to this ?

[Cees Klumper]

Have you tried soaking in penetrant to free the pistons? I hear vinegar can also work.

[ja17]

Flood the problem cylinders with penetrant. Install the valves and fittings so that the IP cylinders stay down. Thread a machine screw into the end of the rack and exercise the rack back and fourth. The IP pistons (plungers) in addition to moving up and down, also rotate. The rack rotates the IP pistons (plungers). Once the rack becomes free, the IP pistons become free and you IP cylinders will be un-stuck. Occasionally you may need to remove the fittings and valves so you can tap down on the stuck pistons. Rotate the engine to move the cam under the iP pistons as needed. Keep us up to date.

[Mqueretin]

Thanks for the replies.

I had used WD 40 and let it rest a while.

Then I tapped gently the cylinders with a stick and a mallet while cranking and the two plungers (piston) came loose. The cylinders were still moving but the plungers were moving independently from the cylinders. I put everything back and after cranking a while to get fuel back in the IP, and the 250 SL worked very well again on all six cylinders. I torqued the connectors over the IP at 35 Nm as advised by Haynes

I don't know where to locate the end of the rack to fit a screw and  move it but I will find out. Would that be a quicker way to unlock pistons if there get blocked again ? (this is the second time this happens to my SL, and each time after not running for a long while).

I noticed that the ball pressure valves were very easy to put back whilst they were pretty hard to remove, so i suggest the plastic rings dried during the 3-4 days they were out. When the engine is cold, it takes quite some time before the engine runs, so may be the pressure valves are not tight enough anymore and the fuel in the injectors pipes does not stay ?

Thanks a lot again.

[mrfatboy]

Check out this thread on where to locate the rack screw.

https://www.sl113.org/forums/index.php?topic=28596.0

[Mqueretin]

Thank you for flagging this interesting info thread.

I think I can locate the rack screw on Alexander's pictures attached to his response.