Ignition Timing

[MaestroMatt]

Has anyone got any tips for getting this spot on?

I have started running my 1893 VP on Optimax (I will get the valves done before they burn out, promise!) and needed to retard the ignition timing by about three degrees to get it running smoothly. I did this last night with the aid of a rather temperamental timing light and, although it is running a bit smoother, I think I have gone too far as she now feels too far retarded (a bit lumpy on acceleration but pretty smooth at constant speeds). :banghead:

Does anyone have any tips on how to get it spot on, or is it just a matter of trial and error? It doesn't help that the Haynes manual gives timing settings at 1500RPM, twice the idle speed! Jolly awkward.

[E_T_V]

1893!! Wow now that is an old one! :) :laugh:

Seriously though, to get the timing spot on, get/borrow/steal a timing light that works, highlight the line on the pully with tipex, and the arrow marker that you are trying to get it near it makes it so much easier to see. Then tweak up the idle screw to the specified 1500 rpm. Then you can twiddle to your hearts content. you'll soon tell if it is pinking especially under harsh acceleration. The usual rule of thumb for converting to unleaded is to change the timing by 4 degrees, (can't for the life of me remember which way!) You want it to just not pinking under full acceleration and load, otherwise you'll soon need a new set of valves! ;)

The timing changes with revs, (you might want to check that the relavent bits are working correctly), and of course vacuum. I believe on mine you have to disconnect and plug the vacuum tube to the dissy before starting to tune it.

Otherwise it is just a fiddly but straightforward.

Hope you get it sorted

Dan

[MGTurbo]

If your using Optimax why are you retarding the timing? Just set it at the correct figure with Optimax/SUL and if you use unleaded, unless you hear any pinking under load at low revs i wouldnt bother retarding the timing at all.

Gareth

[MGTurbo]

ETV why would pinking causes damaged valves? Far more likely if the pinking is chronic there would be a big hole in a piston or two..

Gareth

[MaestroMatt]

Thanks for the advice E_T_V. I have retarded it about 4 degrees but think I have gone too far, but otherwise I have - reassuringly - done things as you suggest.

To answer your question, Gareth, I am changing it because the timing doesn't feel right now I have switched to unleaded. Left as it was (too far advanced) it accelerated like a dream but was lumpy when cruising at a steady speed which was annoying. I have read that the R series engine needs retarding three degrees to run properly on unleaded and avoid pinking.

I guess I'll have to give it a few more twiddles until it performs pretty well at all revs!

[MGTurbo]

What was the timing set at before? If it was correct then it might not have been the timing at fault (assuming 97/98.6 octane was used)and more likely the mixture setting.

Gareth

[MaestroMatt]

It was spot on 16 degrees BTDC at 1500 RPM - as the Haynes advises for leaded fuel. The idle speed is about 850 RPM when warm which seems about right. What do you think?

I got the advice to retard it three degrees from here:
http://tinyurl.com/bxbl

But on reading it again, it suggests that for 98 RON fuel, only a slight reduction is necessary. I shall try again tonight!

[E_T_V]

I always thought pinking resulted in hotter valve temperatures which caused valves to burn out, the same sort of effect too lean a mixture has. Knocking (Detonation as it is sometimes called) now that'll blow a hole in your piston, as the ignition point occurs at a random position, not your spark plug and sends shock waves through it usually knocking the hell out of it.

I could well be wrong though as it is years since I understood fully what it was all about - some guy at rover research explained it all to me as we tested a prototype engine. All that drinking at uni has since dulled my memory. I always remember pinking as pre-ignition (igniting too early in the cycle before TDC) and knocking as too late so that the mixture explodes spontaneously like in a diesel. I'd like to know if I'm wrong there before I give any duff advice.

Cheers

Dan

[J199 HHG]

Pinking is when the spark is too early, so the flame front hits the piston and causes the noise you hear. In a direct injection diesel, the flame front also hits the piston, hence the noise (indirect injection diesels have a precombustion chamber so that exhaust gases push the piston down, that's why they are quieter).

When the flame front hits the piston, it will heat it more than it's supposed to, and also the mechanical loading is higher. A diesel is built more substantially to cater for this.

Pre-ignition is when some part of your engine is so hot inside (carbon deposits usually), that when you cut the spark, the engine continues to run on for a bit. A good decoke should fix it, unless it's caused by the effects of pinking.

Knocking is when you have a failed big end - bad news!

Running lean also causes the engine to run at elevated temperatures, which can cause pre-ignition, but I'm not sure that you can hear it though. In the old days of leaded petrol you could tell from the colour of the deposits on the inside of the exhaust pipe. A nice grey colour was good. Now it's always black.

I optimise my timing by driving it, and fiddling with the timing so it's just on the cusp of pinking at high load / low engine speed.

[MaestroMatt]

That's interesting. I did notice that when my car was too far advanced, it had the most astounding performance - it would absolutely shoot forwards in the lower gears, and only start pinking (or, at elast, only start making the noise) under hard acceleration in 3rd, 4th and 5th. I retarded it a fair whack, in line with the Haynes manual minus a bit for using unleaded and it certainly doesn't pink any more, but doesn't perform either. Looks like I will have to have another look at it. This is a new area for me - I have never st up timing or carb fuel mix before. On the subect of the latter - anyone got any tips?

[F690OTF(RIP)]

I thought pinking was the common name for pre-ignition, because it sounds like the noise pre-ignition causes. Knocking is the common name for auto-ignition, i.e., in a spark-ignition engine when for some reason the fuel ignites before the spark by the heat caused by the compression process. That's what I thought, anyway. Rather a lot of websites seem to think they're the same thing.

Looking elsewhere on the web, it would appear that Americans refer to pinking as pinging, and pinking to them is an alternative term for what they normally refer to as dieseling, which is when the engine continues to run after you've turned the ignition off. Just to confuse everyone!

Anyway, I've got a lecture to go to. One which will, unfortunately, shed absolutely no light on this subject. So much for mechanical engineering.

[J199 HHG]

Originally posted by MaestroMatt
That's interesting. I did notice that when my car was too far advanced, it had the most astounding performance - it would absolutely shoot forwards in the lower gears, and only start pinking (or, at elast, only start making the noise) under hard acceleration in 3rd, 4th and 5th. I retarded it a fair whack, in line with the Haynes manual minus a bit for using unleaded and it certainly doesn't pink any more, but doesn't perform either.

I have found that doing the timing as per manufacturers spec to be impossible. Nomatter how hard I try, I can't seem to get decent performance. I suspect it's something to do with the fact that you are supposed to disconnect the vacuum connection, but that has other effects.

That's the reason I do it by the seat of my pants, to good effect.