Ignition Timing

[dasadrew]

I don't know why just now, but I thought I'd look at my ignition timing to see if I can get the engine smoother at low & idle speeds. Went to the ROM to refersh my memory and read:

Dynamic Timing:

pull of vacuum advance pipe
run engine at 3400 rpm
strobe light should show 16 - 20 degrees of advance above the 14° BTDC of static timing, this means the strobe should show 30° - 34° advance, but the metal scale only goes up to 24°

In the table at the beginning of hte ROM chapter it states that centrifugal distributor advance at 3200 rpm should be 12° - 14° and crankshaft advance at 3400 rpm 16°-20°

I've set mine up to be 18° measured at the metal plate at 3400 rpm. Am I doing something wrong, or has the ROM tied itself in knots?

I'm sure this has been done to death in the forum, but I haven't been able to fathom out this conundrum from the posts I've dug up so far.

Can someone enlighten me?

[trunt]

Ideally What you need Drew is a better timing light!

Better ones have a dial that you set to an advance degrees and that will make it flash at the tdc mark so if it is actually running at 34 degrees you will see the TDC mark lined up to the 0 mark. That way you can go all the way to 40 degrees and avoid the inaccuracies of the marks. So you adjust it to show tdc and read off the advance figure on the timing light display..

On the centrifugal. normally Double the dizzy advance to find crank advance and add the static. But check static without vacuum, it may move a little when you disconnect. Also make sure the centrifugal is not already adding some advance in at idle, especially if it's a bit high, or the dizzy is worn.

I see the ROM shows Crank advance so then you are looking at eg (Im asssuming Mk2) 12-16 plus 14 static =26-30 TOTAL advance,

And yes that's low for the Mk2 with HC domed pistons, Mk1 runs at around 34-38 degrees.

[dasadrew]

So you confirm that the dynamic centrifugal timing should be 34° at 3400 rpm but Triumph only put a quadrant on the engine which goes to 24° ?

Not sure about the vacuum and static timing. Surely the vacuum plays no role when you're doing static timing?

If I double the dizzy advance (12° - 14° becomes 24°- 28°) and add the static (14°), then I get 38° - 42°?

Drew

[dasadrew]

....I see the ROM shows Crank advance so then you are looking at eg (Im asssuming Mk2) 12-16 plus 14 static =26-30 TOTAL advance,

can you point me to the ROM page where it quotes 12° - 16° as my ROm shows 16° - 20°? Maybe for US vehicles? Yes mine's a Mk2.

Drew

[trunt]

Engine tuning data -- page 05-2 or page-14 in my 1977 edition.
It states "Degrees Crankshaft advance" and I'm using the Mk2 dizzy part#219089

The ROW Mk2 has a lot less advance than Mk1 or Federals so 26-30 sounds good. Usually total advance for this type of head chamber (Wedge?) is around 34-36 but It was reduced ..maybe the domed pistons??

Yes vacuum plays no role but sometimes the advance is set "dynamic" i.e. with vacuum connected so when you disconnect it can change a bit, just saying to check it again with no vacuum. but if you are setting static by turning the engine by hand then all is good!

[dasadrew]

interesting, I was reading the ROM Section "Electrical" - "Ignition"

[trunt]

Probably instructions left over from the 71 edition. Mk1?

[Kithmo]

Unless something has changed, I always understood static timing as without the engine running and all the other figures were just checks done after setting the static timing and running up the engine to make sure the distributor was doing its job. Old school method, align the crankshaft pulley notch with the static timing marks, then with a test lamp connected to the -ve side of the coil from a live source, turn distributor until the test lamp goes out (points just opened), static timing set.
This doesn't always work with some electronic ignition set ups (no points), which makes it difficult to actually set the static timing and hence difficult to check if the distributor (or electronic ign) is advancing and retarding as it should.

[trunt]

Yes, hand crank is the best way.

I used to listen for the crack! of the spark.

[flying farmer]

If you have a mk2 distributor the advance weight stop will be marked 7 degrees, mark 1s are marked 13 degrees, no idea about USA spec distributors.

The advance marked is distributor degrees, it is doubled for crankshaft degrees, so 14 degrees for a mk2 and 26 degrees for a mk1 added to whatever static advance you start with.

The vacuum advance is disconnected for testing otherwise it will add a variable amount of extra timing.

I would suggest the ROM is wrong in this instance, you should have 28 degrees advance maximum on a mk2, but they often perform better with an extra couple of degrees. The MK1s will max out at 38 degrees with 12 degrees static timing but they have a lower compression ratio. I find my mk1 engined Estate doesn't like any extra timing since it is already getting plenty, it shows its protest by pinking with more than the standard static timing.

Neil

[Andes]

Apologies all......I’m completely confused over various methods of setting the timing that have been mentioned. I have electronic ignition on a mk2 and I’ve been using a timing light with the engine ticking over to set the mark on the pulley to approx 12 degrees on the metal plate, am I doing this right or is this the incorrect number to use with the engine running......the mention of dynamic and static has lost me, I sort of understand the principle but am still lost

[trunt]

You are fine! That’s how you set the timing.

Static is is the pre set advance of the ignition that is set without any influence from vacuum or centrifugal. The best way to set it is by turning the engine over by hand as that removes any of those influences.

But most cars are set dynamic, at idle speed with a timing light, sometimes with vacuum connected sometimes not, the tune up data tells you. If there is wear in the dizzy this can cause this to be slightly out, even though it looks ok.... (that’s where static check comes in)

The other checks sometimes done are seeing if the centrifugal advance is working ok, so that’s what you are seeing discussed here - the total advance, static plus centrifugal.

Then finally there is the vacuum advance which is harder to check but advances the ignition even more under low load conditions.

terry

[DJT]

This is all good stuff. I’m currently waiting for a fully refurbished dizzy c/w Pertronix ignition to come from the Distributor Doctor....

[Andes]

Thanks trunt that makes things clearer. I’m guessing if there’s any wear in the distributor that will show up in a reduction in power. Would it be in my interest to get the distributor assessed for wear or wait until there is an obvious problem with ignition then sort it?

[trunt]

You would probably only check this thoroughly if you thought had a problem, like low power or the timing wondering about at idle but it's nice to know how it works.

In most cases after you set the idle timing simply revving it up and making sure it advances smoothly and returns to the set point is usually enough.

Terry