Timing

[Duncan Grimmond]

I can't find the device I had when I was a young motorcyclist in the 1960s. A handy TDC indicator which screwed into the plug hole and hex.rod marked in 1/16ths with a circlip to stop it falling in.
I know I have it somewhere, it just vaporised when I put it down on the bench...
However, I do know where the thread adapter for the plug hole is!

[Charles P]

Throw all the precision of "degrees" in the bin, especially if you applying them to the cam pulley which isn't keyed to anything. Use some old fashioned judgement.
Put any manual advance retard mechanism to a middling position, slightly slacken the distributor clamp (but only a little), put on a robust glove, start the engine and manually swing the distributor until you get it running nicely. If you don't think that you know what that will be, if you possess a scintilla of mechanical sympathy, you will.
When it's running OK switch off, tighten the clamp bolt and drive it. The manual advance retard will tell you how to fine tune it. If you are unfortunate enough to be lacking manual advance, I'm sorry for you. What appeared to be improvements aren't always useful.

When it's running as desired lift the flywheel cover/starter motor and make some repeatable measurements/marks/count teeth and note them down somewhere safe.

[Howard Wright]

Hi All

I’ve always had trouble finding the compression stroke.  Seems my thumb is totally insensitive to compression (or the rings in my engine are shot  )

So I screw in the tail of my compression tester with the cut off finger off a nitrile glove rubber banded around the end.  Easy to see the end of the finger acting like a balloon. Don’t crank too fast or it goes pop!

Cheers

Howard

+1 for Charles method.

[Roger]

I too have just constructed a TDC indicator plus timing mark. In my two wheeler days I used a dial test indicator to measure the firing point, I may even modify this device to suit a dti.
I have also added a manual timing adjuster so that I can fine tune the timing on the road, it is easy to feel the best spot, then just lock the distributor in that position.
A Rubber finger stretched over the top of the top of this indicator plug also shows the firing stroke before inserting the steel rod.

Roger

   

[Charles P]

I have a similar device, but with the plunger off-centre - useful at times

   

[Peter Clayton]

Roger, with your TDC/Timing dipstick, what distance on the rod  before TDC do you set the static timing to? I also used to time my 500 single motor cycle this way.

[Hedd_Jones]

How do you guys use the TDC measuring implements?. Ive always found that they dwell considerably at the top, that is they stop moving and you can turn the crank significantly before they move again. Getting an accurate TDC involves either skill or luck.

On any engine (including when setting the valves on my steam roller) I effectivley measure the same piston displacement each side of TDC, mark the flywheel (each side) then split the difference on the circumference of the flywheel with some dividers.  And bobs your uncle. A pretty accurate TDC mark.

Just the job if someone has turned the marks off your flywheel, and/or it has some non factory markings. 

I have to admit, to get an engine to start an approximate TDC is probably all that is nerded and I time by ear in anycase. So its a bit irrelevant to be, but all you whallas using timing guns should really be quoting degrees before an accurate TDC mark. Not a guessdimate of where it is.

[Charles P]

How do you guys use the TDC measuring implements?. Ive always found that they dwell considerably at the top, that is they stop moving and you can turn the crank significantly before they move again. Getting an accurate TDC involves either skill or luck.

Spot on. 
The only way that you can find TDC with one is to interpolate from two equal levels of lift either side of TDC measured with a dial gauge on the top of the rod. It is however useful as a crude TDC finder for the "swing the dizzy" approach to timing.

[Roger]

Peter,

It turns out that my static firing point appears to be at TDC, I then marked the “dipstick” and turned a distinct groove with the lathe to show TDC. I Assume the auto advance weights do the rest.
Having set my timing to “Near enough” I go for a drive to fine tune using the manual control for this purpose. My reason for using the “dipstick” is if I need to change to my spare distributor that I carry it is easier to confirm the correct settings, although now I know it is at TDC I don’t need it.

Roger

[Hedd_Jones]

How do you guys use the TDC measuring implements?. Ive always found that they dwell considerably at the top, that is they stop moving and you can turn the crank significantly before they move again. Getting an accurate TDC involves either skill or luck.

Spot on. 
The only way that you can find TDC with one is to interpolate from two equal levels of lift either side of TDC measured with a dial gauge on the top of the rod. It is however useful as a crude TDC finder for the "swing the dizzy" approach to timing.

I compared 2 approaches on my steam roller. I have the benefit of a crosshead to use for measurement.

I put some tape on the circumference of the flywheel, made a pointer and used a sharp pencil to mark.

I did similar on the crosshead and and guide, basically a pencil mark on each. Ligned them up and marked up the flywheel in 2 spots.

I then tried the DTI. I didn't need to draw any new marks, they were spot on. And this is on a flywheel approx 2 1/2 foot diameter. Any error would be less on a '7' sized flywheel. My conclusion was DTI not required.