Valve Timing + Dizzie set-up - quick reality check!

[dasadrew]

It's been a long day, and my cerebral capacity is exhausted, so here's a quick question ..... help!

I built the engine and set up the chains so that the crankshaft is at TDC, both cams have the grooove lined up with the bearing cap indentation, and even the scribed line on jackshaft sprocket is in that half sloping down position like it says in the book.

Question 1) Does this mean that cylinder n° 2 (LH bank) now has valves closed at the top of the compression stroke on n° 2 piston?

Question 2) The crankshaft sprocket has 20 teeth, the camshaft sprockets have 40 teeth and the jackshaft has 30 teeth. So, that position as described above will occur every 6 turns of the crankshaft, yes? (although that is just to have the jackshaft aligned which is not absolutely necessary just to get the engine running)

Question 3) Fitting the distributor, it only ever mentions that the crankshaft should be at 14° BTDC etc. but this could have the distributor 180° out or am I nuts?

Question 4) My distributor cap from the PO has N°2 lead coming off the cap at the lowest position next to the front LH wing, but surely the N°2 lead has to be where the rotor arm is pointing - i.e. towards the coil and RH wing?

I know that you can rotate the dizzie more or less where you want and fit the leads accordingly but I'm after fitting it in the "book" position so I have a refernce if I need to replace it at any time.

Last question: when I'm setting up the dizzie, can I rotate the engine slightly back and forth or do the chains jump of the tensioners or whatever?

Thanks in advance!

Drew

[MLCstag]

Just a quick reply (about to go off to work) as I've just been through the chain replacement and had the jack shaft out, dizzy overhaul etc (no expert though)
1 TDC is top of compression stroke ready to fire and rotor should be pointing to no2 lead normally towards coil mounting bolt.
2 my maths says the cogs line up every 6 crank shaft revolutions
3 so long as tdc is set up on crank and cams with rotor pointing to no2, all should be well. Sounds like your rotor may be 180 degrees out
4 see above, yes point at no.2 but check and double check firing order. I changed the dizzy cap and leads after setting the timing and wondered why is started to run rough. Timing was 90 degrees advanced!!! Until firing order was restored to normal.

Hope this helps. No doubt more replies will be along shortly.

[Stagdad]

Hi Drew
1 yes
2 sounds about right but I've never had an issue lining up the dissy
3 correct
4 Again I just line up the rotor arm with no 2 contact as I lower the dizzy in but it may not be to manual spec
I wouldn't turn the engine backwards if I were you.
cheers Steve

[dasadrew]

Thanks for the quick replies chaps!

I'm getting there on the "mechanical" side of things but .... I've just been playing around with the static basic timing set up. I'm sure there's a bug in the manuals because it must be different for a twin-points dizzie? With the test lamp method, you turn the dizzie until the lamp just extinguishes = points are just opening and a spark is just being produced. Hey presto, everything lines up and the rotor points at one of the dizzie cap contacts which is then your N°1 plug on any engine (and N°2 on the Stag). My rotor arm points between two dizzie cap contacts when the test lamp extinguishes becaus it only goes out when the second set of points has also opened. This is after the first set opened as the rotor was pointing at a contact. Puzzled

[flying farmer]

As Steve says for the first three, but I have never caused any mischief by turning the engine backwards a little when trying to get TDC, it does put all the chain tension on the chain tensioners, but unless the ratchet mechanism inside them is knackered it shouldn't do any harm. You do however have to make sure the last movement of the crank before any setting up is done in the correct direction of rotation to ensure the tension is on the correct side of the chains.

Of course if I break anything in the future Steve can have the pleasure of saying Told you so!

Neil

[Stagdad]

Not saying it will break something but it's easy to go the right way isn't it.i suppose I've backed it by a few degrees in the past when I have overshot the intended timing mark.
Cheers Steve

[mike@thenook]

Hi Drew,

if you have all the marks lined up as you say you have, ensure the rotor is pointing at the outer coil mounting bolt point and that this also coincides with no 2 lead. When I re-built my engine last I set the distributor on static to tdc (it fired up first time) then adjusted to 14btdc with a timing light afterwards.
I must admit that I only ever turned the engine "clockwise" before I ran it for fear of upsetting the tensioners before they had been oiled up but, as Neil says, that should not be a problem.
Good luck and hope its all up and running soon

Cheers

[flying farmer]

If the rotor arm is central between two distributor contacts at the time the spark occurs you definitely have a problem. it could simply be that you are one tooth out when you dropped the distributor into place (IIRC 12 teeth on the dizzy drive gear ie one and a half teeth per cylinder)
I had this problem once and it was due to a dodgy vacuum advance capsule with the wrong length arm, but it was years ago and it might have been one from another engine out of a scrapyard.

Don't forget the static timing has to be about 14 degrees not TDC, and also that the mechanical advance will give either another 7 degrees advance with a mk2 distributor and 13 degrees with a mk1. I don't think the vacuum advance alters the relationship between the rotor arm and the distributor cap, but you have to allow for the difference in mechanical advance which sees the rotor arm move in relation to the distributor cap as the ignition advances.

If the rotor arm is slightly past its centre point on the cap contact measured statically, it can move too far away from the contact at maximum advance for the spark to jump!

I had the opposite problem on my engine with the dodgy vacuum advance capsule in that it would run perfectly with any revs or any part throttle application but misfire very badly at low revs when full throttle was applied. In this situation with no mechanical or vacuum advance the rotor arm was too far from the cap contact for the spark to jump and I had to remedy the situation by putting a washer between the distributor body and the vacuum advance capsule to pull the distributor baseplate round a few degrees.

When I fitted the Megasquirt to the TR's engine this Winter I had a hell of a job to find a rotor arm position that could cope with the amount of advance required and had to modify the base plate so I could get the rotor arm to sweep its full width across the cap contact over its full range of advance.

I have actually got an old distributor cap that I have cut the top off so I can look inside to ensure the rotor arm points the right direction all the way through the advance range.

Neil

[dasadrew]

Thanks guys again! I really must call it a day as I'm getting things mixed up! There was no way tonight that I could get the rotor arm to point at the outermost coil fixing bolt; it points at the inboard one. However, I've just realised that I'm setting it up with crank at 14° BTDC as I was checking the timing. If I move it tomorrow to TDC, then the rotor arm will swing further around 9° (ratio of aux shaft cog to carnkshaft cog) so that it will point even further away from the outer fixing bolt. I imagine that I will then be able to turn back one tooth on the dizzie (12 teeth as Neil says = 30° per tooth) and the rotor arm should point more or less to the outer bolt I think. Hopefully the rotor arm will then align to a contact in the distributor cap.

I'd never realised that the dual points dizzie is to have a longer dwell and that there are two contact breaker openings each firing sequence, and there are thus 16 per revolution of the dizzie. I previously thought it was a set-up to only have four sparks per contact set to reduce wear and erosion.

I seem to recall that everyone is quite laid back about the jackshaft sprocket position and that scribed line when assembling the engine. I realise now that, as the jackshaft cog has 30 teeth and the distributor drive has 12 teeth, there's lots of opportunity to fit the jackshaft so that the rotor arm doesn't point to that dammed outer bolt!