a question of timing....

[dubstar]

Hi gang.

I'm running a 6n dizzy on my PY lump, for the improved hall sensor. So far, I've not driven it but it idles up to temp and the fan kicks in & out. It hunts a bit when stone cold, but soon evens out (as I hear they often do). It's a happy engine, as it'll sit at 820rpm (ish) and when I pull the blue temp sensor it goes up to 1000 rpm - all good. AFR is showing 14.6 at idle when warm.

So as I just plonked the dizzy on and although it's running nicely I need to set the base timing before winding the boost up on't road.

Here's how my 6n dizzy looks (mainly so you can note the position on the adjusting slots.)



So I borrowed a snap-on strobe (which is how I know the RPM so accurately). Warmed her up & pulled the blue temp, revs raised. I set the scope to 5 degrees advance and the timing mark looks like this - RED arrow represents the mark, so you can see it. Small BLUE arrow represents roughly where the mark was at 5 degrees advanced with it running.



At this point, the car is running champion. If I start to move the dizzy round to force the mark to line up with the TDC indicator it starts off ok but by the time I get it to line up, the revs drop and it stalls. Summat ain't right.

I don't want to damage the engine on the road. I reckon either my TDC marker is wrong, or i've got a gash single bottom pulley but both look ok. The pulley can only go on one way. Anyway, i'm struggling to set the ignition timing meaningfully.

Is there another way to do it?
Am I doing something wrong?
What am I missing?
Does your 6n dizzy sit in the same orientation as mine at 5°?

Any help appreciated.


Ross.

[Yoof]

I can't remember if the trigger wheel on a 6n dizzy is the same as a G40 one - worth checking.

I'd also ensure the mark on the crank pulley is actually TDC (you've got a dial in gun, so one mark will suffice) stick a dti down plug hole no. 1 and check, given the slop in the pulley and the bendy timing markers, a stock setup can be a fair way out.

No surprise you'll need to tweak the idle speed when setting the timing, especially if you're retarding it 

[hayesey]

I don't think the timing marks can be relied on if you have a G40 pointer with a non-g40 pulley wheel (as I also do).  I used a DTI gauge to measure TDC on mine and made new marks on the pulley.  I also have a 6n dizzy too (and have for years).

[dubstar]

Thanks guys, that's great 

[dubstar]

Just to complete this thread, in the absence of having a DTI (or anyone who I could easily call on easily friend or work wise having one..) I made an adjustable plug-stop and did it like that (over TDC on a known compression stroke so as not to damage any valves...)

Got a TDC mark then used my borrowed gun to time it up. Spot on now.  If I had to guess I'd say the difference between the new and original mark (on the non-PY pulley) was around 3°.

Enough to warrant the dicking about to get it spot on, and to make it stall on setting it up originally.

Cheers.