Setting Engine Timing AFTER Top Dead Centre (WTF!)

[Andrew353w]

Hi there! I've been having great fun with my Daf 33 since I drove it home from Yorkshire in December & have done a fair bit of fettling to it, although the car is basically very sound. 

 

 

It has suffered from a persistent problem of hesitancy when moving off. The previous owner assured me the car had been given new points, condenser & plugs, and had had the timing properly set. Although I had no reason to doubt him this hesitancy proved embarrassing at traffic lights, so I thought I'd check things.

1/ The points may well have been new, but were hardly opening; I reset them & things improved dramatically! 

2/ I invested in a strobe timing light and checked the Daf's timing; The dwell was correct and the timing has to be set at 5 degrees AFTER for this car, to comply with emissions legislation post 1972. 

Does anyone out there know why setting the timing AFTER T.D.C. makes the emissions different? Also, would not the engine's (already limited!) power be reduced? I have always thought ignition systems were set for BEFORE T.D.C. to gain extra power.

 

Any thoughts? 

[Skizzer]

It's a Daf. All bets are off.

[Dave_Q]

Sounds like madness, I would expect ignition before tdc at all times, it is a 4 stroke yes?

 

The only thing i can think is that maybe the timing mark on the crank doesn't correspond to actual tdc for some reason, and 5 degrees after the mark is actually 10btdc or whatever.

[Captain Furious]

I would have thought it would be well down on power setting it after TDC, the 'bang' is happening too late and the flame front is just chasing the piston down the cylinder instead of all of the energy being used to force it down.

 

TBH though with old cars I've always used the 'by ear' method, keep advancing it until it starts to pink and back it off slightly.

[Andrew353w]

It's a Daf. All bets are off.

 

 

I read this too quickly and thought you'd typed "all BELTS are off".... Dafs, eh?

[Andrew353w]

Sounds like madness, I would expect ignition before tdc at all times, it is a 4 stroke yes?

 

The only thing i can think is that maybe the timing mark on the crank doesn't correspond to actual tdc for some reason, and 5 degrees after the mark is actually 10btdc or whatever.

 

 

It's an air-cooled twin cylinder (horizontally opposed) 4 stroke engine; a bit like half a VW Beetle engine! It has an electrical cut-off solenoid on the carb that stops the fuel supply when the ignition's turned off. Maybe this has something to do with the emissions, too.

[dave21478]

Sounds strange to me.

Personally, I would mark the current distributor position and go for a drive with a spanner, trying the dizzy in various positions to get best on the road results.

[Bren]

Factory marks incorrect? Some rover V8 crank pulleys are miles out.

[Andrew353w]

Thanks for all your thoughts! I'll investigate things & report back soon......

[spike60]

Autodata say 4 degrees static, 10/2500rpm and 16-20/3600  all before tdc with vacuum disconnected for a 1973/4 Daf 33.

[spike60]

Where did the 5 degree after figure come from? Could you be mistaken with the engines direction of rotation or something?

[fordperv]

I read this too quickly and thought you'd typed "all BELTS are off".... Dafs, eh?

 

I also did the same thing

[Station]

Loads of cars have slightly advanced timing, that's why people fit vernier cam pulleys. It affects power delivery, but it's well more complex than I can understand ( explosion and flame fronts in the cylinder etc ??? )

The k10 micra is 5 degrees advanced I think, which translates to a couple of mm of travel in the piston. 5 degrees / 360 degrees x length of stroke will give the position of the piston, which isn't a lot considering pi/circumference covered by crank rotation compared to 50mm stroke or whatever.

 

It is related to vacuum operated distributor, the dizzy rotates and retards or advances the ignition timing as vacuum builds as the power delivery 'needs' alter, so your timing is constantly changing as you go faster, probably going to 0 degrees at some point.

[Sigmund Fraud]

ATDC timing is correct for those, and it is indeed due to emissions.

 

The earlier engines were timed 4 degrees BTDC. I suspect there's no reason you can't time a later engine like that (in terms of camshaft grind and carburettor), but can't be sure.

 

If there's one person who can tell for sure, it's Mr.E.Honda of this parish, who I suspect will be joining the conversation soon...

[seth]

You set ignition timing ATDC on cars you drive mostly in reverse.

[RayMK]

My only thought on this was that perhaps something has been lost in translation when unleaded came on the scene.  For cars which had valves and seats which could stand the stuff, retarding the ignition was often advised in order to prevent pinking.  Popping the fuel air mix after TDC will cause incomplete combustion, reduced performance and an increase in unburnt hydrocarbons in most engines.  I can't see why the DAF unit would be an exception, and in any case, a DAF of this age should not be subject to such stringent emissions requirements.  I would definitely re-time it by ear and performance as others have suggested.

 

PS: Another cause of hesitation could be a vacuum leak somewhere - hopefully just a pipe, but possibly a transmission  diaphragm, assuming the 33 is the same as later Variomatics.

[uk_senator]

Good to see it back in action! Is that your beige ADO16 I`ve seen up the road?

 

I need to speak to you actually Andrew, could you DM your number again, I seem to have lost it (Paolo that had the red Reggie 5 Campus you looked at).

 

Ta!

[lisbon_road]

I just wonder if the reason for setting the static timing to after dead centre is that this is a way of getting the timing correct at higher operational engine speeds.  Why they couldn't get it correct at static and correct at higher engine speeds, I don't know, after all, everyone else did, so I'm not even convincing myself let alone you all.