450 SL in Denmark

Hi there,

I have been looking at ignition timing and have arrived at these values after some adjusting.

Timing at idle: 5-6 degrees BTDC (a long way from spec of 5 degrees ATDC
1500 rpm: 12.5 degrees BTDC (within spec)
3000 rpm: 20 degrees BTDC (within spec)

That seems OK, although the static timing seems a bit too advanced. I later discovered that most likely my vacuum box on the distributor is not impacted by vaccum. The box itself holds vacuum so either there could be a fault in the change-over valve or a leak in the vacuum lines. Will check this tomorrow.

Anything to be worried about with the static timing? It has been raining heavily in DK so I haven’t had the chance to drive the car with the adjusted timing.

Best, Peter

Hi Peter,

it is correct that your timing at idle is wrong. It should be 5° AFTER TDC. You measured before TDC. It seems that your vacuum box does either not work or distibutor is badly moving. That should be corrected.

Hi Volker,I have changed the vacuum hose and now I get 5 degrees ATDC at idle. Went for a ride and things are slightly better. Still judders at low rpm, but not as much as before. Still puffing randomly from the exhaust in idle. Mixture screw all the way counter-clockwise. I adjusted the timing to TDC at idle and around 15-16 degrees BTDC at 1500 rpm and around 22-23 degrees BTDC at 3000 rpm. (should be OK compared to spec, although in the high end) and went for a ride. That improved the low rpm driving (below ca. 1200-1500 rpm) even more, but there is still some juddering when pulling away from a red light, etc. and it still puffs from the exhaust randomly. I'm of course now over-sensitive and maybe expecting too much from an engine that regardless of good compression, etc. still has around 450.000 km on the clock.  

Best, Peter

Hi Peter,

what I have seen with old ignition distributors is that they tend to hang as grease and dirt is sticky. In such cases I take them apart, clean and test everything and adjust on test stand after new grease and reassembly.

Puffing in exhaust is typically wrong ignition timing or wrong valve timing.

Thanks, Volker! Considering that the engine behaves totally normal with no puffing during warm-up and only starts to puff when it reaches operating temp., does that provide a pointer to where I should begin? Valves or distributor?

Best, Peter

Hi Peter,

check both: Valve clearance on hot engine and distributpr timing on cold and hot engine.