V8 Engine running problems

[Aragorn]

Cool. Excuse my ignorance with the "old skool" here but if i want to "check the timing" how exactly do i do it, and how do i ensure the vacuum and mechanical advance is working correctly on the distributor?

[Quagmire]

To check mech advance take off dizzy cap and see f you can twist the rotor arm. It should feel sprung and Allow you to rotate it a few degrees, when you let go it should snap back into position. Mine currently doesn't and although I have had a minor drop in mpg, performance doesn't seem to be too bad. My vacuum is still working though

As for timing, have a look at the crank pulley, there should be some marks on there. Clean them up and highlight them with some white paint. Stick a timing light on it, connected to cylinder 1. Fire it up and see where your White marks align with the pointer. I tend to just paint the book figure on the pulley as you only have one line to look for then.

Witht he carbs, read the manual I posted up and all will (hopefully) become clear.

good luck!

[Aragorn]

Hmm i dont have such a thing as a timing light so i'll need to pick one up.

What exactly do the marks on the pulley represent, and how do i use these marks to get the timing?

Not 100% sure what you mean by "paint the book figure"?

I think what you mean is that the pulley has a number of marks which represent various timing values, and when you point the timing strobe at the marks, the mark will line up with the pointer at the point at which the strobe fires?

Is it obvious from looking at the pulley which mark i want? I dont have a book for the truck, so i've no idea what i should be ensuring its set to.

Also if i suck on the vac advance pipe, will that make the arm inside the dizzy move? or is there some other method of knowing the vac advance is working?

Cheers

[Boothy]

Not the best answer in the world for you this, but I really do think your one of the people who would benefit from a Halfords workshop mannual, just to give you some basic ideas of how things work, before you do something or, spend something not so wisely, not knowing how to check timing sort of tells me that you don't have a fundemental knowledge of the internal combustion engine and its quirks, and a good read of the Halfords for your vehicle may enlighten you somewhat.

Best of luck.

[Bowie69]

Not 100% sure what you mean by "paint the book figure"?

Book figure will be around 6 degrees before top dead centre, the pulley (I think) is marked in both direction, one indeicated with 'BTDC', which is what you want. It goes 12 degrees either from the middle '0' or TDC mark, so half way between that and the end of the scale is probably where you want to be. Painting the 6 degree mark with tippex or similar is what is suggested above.

I think what you mean is that the pulley has a number of marks which represent various timing values, and when you point the timing strobe at the marks, the mark will line up with the pointer at the point at which the strobe fires?

Is it obvious from looking at the pulley which mark i want? I dont have a book for the truck, so i've no idea what i should be ensuring its set to.

Exactly, the mark you want should be obvious from the the above description.

Also if i suck on the vac advance pipe, will that make the arm inside the dizzy move? or is there some other method of knowing the vac advance is working?

You'll see the base plate of the dizzy move, as it's a Disco, you should have electronic ignition which means you probably need to remove the clear (or yellowed clear) plastic cover under the rotor arm to see this.

Hope that helps a bit

A Haynes would help with all the above I am sure

[Aragorn]

Cheers guys.

I understand how an engine works, and i've rebuilt a few in the past, but they've mostly all been modern things with EFI and either coilpack or fixed dizzy systems, which dont really need the timing touched.

The vauxhall motors i've worked on a lot only have one mark on the pulley, which when lined up with the pointer means the timing is correct. I never needed to check it however as the dizzy simply lines up with a mark on the cam box and cant really be adjusted. Its better to ensure i know what i'm looking at before i go setting it to the wrong value!

If you look at my last post you'll see i have a rough idea of what is involved in checking the timing, ive just never actually done it. I'd rather clarify the fine details on here, than waste time at the weekend scratching my head with the timing light!

The other issue is i can only get to the truck at weekends until its MOT'd, taxed etc, as its parked off the road at a mates farm. So its better going out there armed with as much info as possible, than trying one thing and still being stumped if that doesn't work!

I will try to pick up a haynes manual, but moneys tight just now as the missus has just finished uni and hasnt started work yet, so saving £20 on a manual can make the difference between buying a set of plugs or not!

Cheers

[steve_d]

Some 'Old School' bits for you then.

An EFI age engine is going to do all the timing from a map so the sensor has only one position to be in.

In a dizzy there are two timing advance mechanisms.

Mechanical...this is archived by a set of weights down in the bowels of the dizzy that are flung outwards as the revs increase. In doing so they rotate the upper section relative to the lower section of the shaft.

Vacuum....this is connected (by a tube) to the inlet to sense engine load. At the dizzy a diaphragm pulls on, and rotates, the base plate which carries the timing sensor or points if you go really old school.

As you can imagine over time this whole arrangement wears which is why it has to be adjusted. Adjustment is by way of loosening and rotating the dizzy.

The timing marks are a fixed pointer on the timing cover beside the front pulley and the timing marks on the pulley itself. You will need to know the setting you are aiming for but the 6 degrees before TDC sounds about right. Mark both these lines with a thin line of tipex or white paint.

With a timing light connected to spark lead one, engine running at about 800 revs and the vacuum pipe disconnected you should see both marks lit up by the light and in line with each other.

If you rev the engine you should see the mechanical system advancing the spark. If you suck on the vac pipe you should again see the spark advance but it needs a good hearty suck (I use a syringe).

HTH

Steve

ETA Don't forget the fan. It will make a nasty mess of a timing light and body parts too so go careful.