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1973 W115 timing and starting

10004 Views 3 Replies 4 Participants Last post by  IPTV HD
I have been struggling with a W115's timing for some time. After having the carb set, the tappets and timing set by a professional qualified mechanic she would start first and every time at the turn of the key, sound and run beautifully.
Then after running her for 2 or 3 days she won't start, I reset the timing to get her started but she then runs badly pinging and knocking.
I have been through this about three or four times... Any advise would be very very welcome, have any of you had this problem? I really am not sure where to turn next as it seems the mechanics (specialised classic car and merc mechanics) are having trouble with this.
Thanks in advance for any replies.
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Hey DMon,
The problem you have could come from a number of issues. Please confirm that the primary issue began before you had the carburettor cleaned/set. i am also presuming you have the M115 motor - either a 200 or 230 4 cylinder.
Start with the easier problems. 1) Check your vacuum system carefully. The vacuum advance/retard hoses could be loose, leaking or possibly incorrectly fitted. There is a also a vacuum non-return valve on the primary hose between the Inlet manifold and the Brake booster housing, this could be faulty and contributing to faulty ignition advance/retard.
2) The ignition distributor shaft could be worn around the area of interface with ignition contact points, a visual inspection can show this.
3) I presume you are setting the timing using a strobe/timing light. If indeed you are seeing a significant variation of timing readings, then you probably have a major timing system fault. This can be caused by a sticking timing chain tensioner. This has to be removed and inspected manually, and invariably replaced if it is not operating freely. A faulty tensioner can cause damage to the chain system itself, so avoid over-revving the engine until this is resolved.
4) By removing the top/valve cover, you can inspect the camshaft gear for wear or any damage, but the more plausible suspect would be the intermediate gear which drives the ignition distributor and rotor. This could also be worn and introduce significant play which causes your timing to 'jump'.

I hope this helps,

Good luck
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