Wiring up a distributor cap

[mangocrazy]

Some time soon I want/need to set the static ignition timing on my rebuilt 2 litre Spider engine. The distributor cap and rotor arm are new and the distributor has been completely overhauled and reconditioned by HH Ignition. When I came to inspect the distributor cap, there were no marks or indication as to which lead should be connected to which cylinder. Is it simply a case of buying a cap that has indicative markings, or is there some way of working it out (I'm sure there must be)? The cap can only be fitted in one position on the body.

 

[jreacock]

When I was faced with this a few years ago, I think I just worked out which cylinder (1 or 4) was on the compression stroke at TDC, and you can then assume the rotor arm needs to be pointing to cylinder 1's HT lead. You might need to fit some temporary pointers to mark the rotor angle, which will be covered when you fit the cap. Rotate the dizzy so that one of the lead outputs match the angle of the rotor arm - this will then be #1. Then, follow the firing order around (1,3,4,2) making sure you get the rotation direction the right way. It's quite easy to push the car forward when in 4th gear (no spark plugs in) to move the rotor arm and to get TDC. I used a compression tester in #1 to see when it was on the compression stroke. #1 is the cylinder closest to the cam belt IIRC.

Let us know how it goes.

Cheers,
Justin.

[mangocrazy]

Hi Justin,

Thanks for that. I'll try out what you suggest next time I'm back where the engine is. I guess it's a question of where do you start? i.e. which take-off on the top of the dizzy do you nominate as cylinder 1? Is it as simple as getting the engine at 10 deg BTDC on cylinder one and seeing which terminal the rotor arm is pointing to? (I think I've just paraphrased your post there...) The engine is out of the car and on a dolly so everything is readily accessible.

Graham

[peteracs]

Hi Graham

You are just about there.

You need to know that the cyl 1 is on the compression stroke and then note where the rotor arm is pointing, that is the take off for cyl 1 on the dizzy cap. Then you need to understand the firing order which is 1 3 4 2. Looking down on the top of the cap, this is the order going clockwise. Piece of cake!

Peter

[Nigel]

Just to throw a few spanners about....

Mine is timed at firing No 4 on TDC, wasn't this the factory setting?
So firing order is more accurately stated as 4213.

Graham, check which valves are fully closed on TDC.

[peteracs]

Hi Nigel

Isn't TDC for cyls 1 and 4 the same thing as far as the crank pulley is concerned?

peter

[Nigel]

Hi Peter,

Yes, but only one of them is on Ignition, with cam lobes pointing up, that's #4.
You'll see that, at this moment #1 inlet valve is starting to open.
                                             
So at TDC:
Induction, Compression, Ignition, Exhaust 
      #1             #3             #4         #2

There you see the 'firing order' but in reality it starts at #4.
Confusing I know.

[mangocrazy]

Next time I'm back I'll whip the cam covers off, take the plugs out and rotate away. I'll take notes as to what state the cam lobes are in on cyls #1 and #4 when the crank pulley mark lines up with the mark on the cam cover at each full rotation. I presume the dizzy needs to be fitted on its spline so that the rotor arm points to my chosen terminal at 10 degrees BTDC on the firing stroke.

[Nigel]

That's it Graham.

One hint: the orientation of the dizzy doesn't matter, except that some have clips
like mine where one is longer that the other, and it helps future removal if you've
positioned the whole thing 'nicely' for ease of access.

I found one of the clips was preventing rotation clockwise as it was hitting the manifold!

Regards, Nigel

[mangocrazy]

Hi Nigel,

Yes, making sure that the clips are accessible and not fouling anything is definitely on my to do list. There's very little spare space in that area so it all needs careful planning. That's one of the reasons I relocated the dipstick holder.

Graham

[mangocrazy]

I've been giving this some more thought, and vaguly remembered a post by Ian (75coupe) regarding static ignition timing and eventually managed to track it down. It's here:

http://www.betaboyz.myzen.co.uk/forum/index.php?topic=2099.0

The important bit (to me) is copied here verbatim:

Static timing is set on no.4 cylinder on Betas. It is easy to get it 180 degrees out! I would recommend:

1. Take oil filler cap off so you can see No.1 cylinder (waterpump end) exhaust cam lobe
2. turn engine over until crank pulley marker lines up with static 10 deg before TDC mark (on cam cover usually)
3. Check exhaust lobe position on No.1. It should be pointing downwards at final stage of closing valve. This means No 1. is on the "overlap", exhaust closing inlet opening, and No.4 is nearly at top of compression stroke about to fire.
4. If No.1 exhaust cam lobe is pointing straight up, No.1 is on firing stroke, so keep turning engine over until you come back to 10 deg BTDC again on No.4
5. The rotor arm should now be directly pointing to No.4 lead on the cap. On most Bosch distributors there is also a line where the cap seats on the base in the same place that you can line up the rotor arm with.
6. Note position of dizzy in block, undo M8 nut and withdraw!
7. Note plug lead order before removing all leads! Firing rotation is clockwise and lead order is 1-3-4-2
8. When refitting line up rotor arm with line on dizzy first then insert, making sure rotor arm is held in place so it does not move.
9. When inserting make sure shaft splines engage in aux shaft driven gear. Don't forget gasket on base to block or you will have an oil leak....
10. Check static timing is 10 deg BTDC, rotor arm pointing to No.4 lead, refit clamp & just nip up bolt.
11. Re fit cap & leads, vacuum advance etc. Start & check timing with a strobe.

Easy.....

Which bears out what Nigel was saying earlier in this thread. So I followed the instructions and verified that exhaust cam lobe on #1 cylinder was facing down with the pointer lining up with one of the marks on the crank pulley. My only problem is that there are 3 marks on the crank pulley - two on the front face (ringed in red) and one on the back face (ringed in yellow). Which one is 10 deg BTDC and which one is TDC? And what is the third one for?

[Nigel]

Hi Graham,

Engine is rotating clockwise as viewed in pic, so first 2 reds are degrees Before TDC.
They look like 25 and 10 [which is at the pointer] but that would need verifying.

The last, in direction of rotation, is the yellow TDC mark.

Assuming there's no other marks.

Hope this helps

Nigel

[mangocrazy]

Hi Nigel,

Now you explain it, it all makes sense... 

Thanks for that, I'll take the next tentative steps in getting the timing sorted now...

Cheers,

Graham

[WestonE]

Hi Graham

A nice neat explanation from Nigel. If you want to know what those other marks represent and you are sure of TDC then it is time for a school boy clear plastic protractor and some blue tack. If you set the protractor with zero over TDC you can read off the degrees the marks represent.

FYI I use TDC with nice crisp white marking on both the crank pulley and pointer along with an adjustable strobe light. In this situation engine running and it set at 10 degrees before TDC the white marks will show steady lined up. This allows you to vary the timing in half degree increments with gentle distributor moves.

Enjoy.

Eric
PS Timing marks on the flywheel edge and gearbox casing are more accurate thanks to the diameter of the flywheel.     

[mangocrazy]

Hi Eric,

Yes, time to dig out my schoolboy protractors... 

I think it's also probably time to get some big boys degree gauges and start using them in earnest. I already have the Tippex...

Cheers,

Graham

[squiglyzigly]

I have a plastic timing wheel from a camshaft manufacturer that I have scanned. Then blow it up or down to print and laminate, to match whatever size pulley I need to mount it on using blue tack.

Just a 360 protractor essentially.


Ian

[mangocrazy]

I have a plastic timing wheel from a camshaft manufacturer that I have scanned. Then blow it up or down to print and laminate, to match whatever size pulley I need to mount it on using blue tack.

Just a 360 protractor essentially.


Ian

Thanks Ian. I stumbled across 'priintable degree wheels' on the web when I was searching for them, so I think that is the way forward. It provides enough precision for my needs. Laminating it/them is a smart move.

Cheers,

Graham

[mangocrazy]

I returned to the scene of the crime today, armed with a degree wheel and dial gauge with the intention of finding out what the marks on my crank pulley signify. What I found was not quite what I expected... The mark ringed in red and aligned with the pointer is in fact TDC. The dial gauge does not lie and it gave TDC as being smack bang in the middle of the mark. The other red ringed mark works out to 28 degrees before TDC, according to my degree wheel. That surprised me - I wasn't aware that 28 deg BTDC was a significant number, but it probably shows how little I know. Is that full advance? It does seem rather low.

[peteracs]

Hi

I think from memory on a different thread it was mentioned that 28 degrees is full advance.

Peter

[mangocrazy]

I have to report that I'm still no further forward than before. I've indexed the degree guage so that TDC (0 degrees) lines up precisely with the TDC mark on the crank pulley and Blu-tak'd it in place, then wound the pulley back so that the pointer is at precisely 10 degrees BTDC. All this has been done with cylinder #4 on the firing stroke. So far, so good.

It's the next step that I cannot fathom, moving the distributor to the exact point where the rotor arm makes contact with the post connected by the HT lead to cylinder #4. I must be missing something obvious, as I can find no way to determine that exact point accurately. What do I use as a datum point with the distributor cap off? The dizzy will rotate happily over a wide arc with the clamp undone, but where in that arc do I need to clamp it down?

I did try an experiment using a multimeter on continuity test setting with distributor cap fitted but without leads, one probe in the central (coil) connector and the other probe connected to where cylinder #4's HT lead would plug in, and than I rotated the distributor over the arc of movement. The theory was that the continuity tester would beep when the correct point was reached.

Except it didn't, as I'd forgotten that there is a small gap between rotor arm tip and distributor contact so the circuit would never complete. When HT current was flowing this would easily jump the gap, of course.

So how can I accurately determine the point where cylinder #4 is just about to fire within the available arc of movement of the distributor? Am I over-thinking this and trying for excessive accuracy, or am I missing something obvious?

Answers on a postcard addressed to Graham at Wit's End Close...