V8i Pinging but timing ok??

Just set my timing on my diso 3.9 v8 to 6 deg btdc.
The engine is pinging and i have to retard it alot to get it to stop but then it 's lot lots of power.
Has an lpg convertion but does the same on petrol and gas.
Ive been told it could be the vacuum advance thats stuffed but surely if this wasn't working the timing would be even more retarded wouldn't it?

NO is the answer to that.

The whole ignition timing depends on the vacuum advance and retard being in working condition.

You will be able to set the static timing, but when the engine is running the timing will go skew-whiff.

Fix it. If you don't you may end up buying a few new pistons.

CharlesY

thanks for the advise i'll get a new one
cheers

just checked the vac advance by sucking on the pipe. No movement of the rotor arm so its u/s.

Replace it urgently will fook up the pistons if not

You might also want to check if your timing chain has stretched, this can cause the timing to wander a bit making it difficult to set the engine up properly.

Sucking on the pipe will NOT turn the rotor arm.

Sucking hard on the pipe SHOULD make the breaker plate turn a little. It is the rotation of the "static" breaker plate in relation to the rotating distributor cam lobes that alters the dynamic timing of the engine on the run.

Remember every degree the breaker plate moves is TWO degrees on the crankshaft.

There are various configurations of vacuum advance and retard mechanisms, but in a modern engine such as the Rover V-8 you can be pretty sure that it works along these lines ....

When there is NO vacuum on the pipe (wide open throttle) the ignition timing is RETARDED by quite a lot.

When there is HIGH vacuum (light throttle) on the pipe the ignition is ADVANCED quite a lot

and then infinite variations in between depending on throttle opening and engine speed.

The idea is to have the ignition timing ADVANCED as far as possible when cruising on light throttle (high vacuum) but to RETARD the ignition by an appropriate angle when you shove the throttle down to make the engine work harder.

If the vacuum system is jammed or disabled when you set the timing in the usual way, you can be sure there's going to be trouble as soon as you drive the car, ESPECIALLY when you try to apply power. PINKING (detonation of fuel-air mix) is a certainty and piston failure will occur sooner or later. It can happen very soon indeed.

Interestingly there is very little vacuum on the system when you start the engine so it starts on retarded ignition (= good) but as soon as it fires up to tickover speed it MAY advance the timing DEPENDING WHERE THE VACUUM PIPE TAKE-OFF NIPPLE IS LOCATED. Sometimes they are fitted right at the throttle butterfly to prevent this happening, and to make it work only at driving speeds when the throttle is more open than tickover. So, the vacuum pipe must be fitted to the correct nipple.
All very clever, IF IT WORKS!

CharlesY

Thanks.
I'll have another look at the plate with the cover removed.

Andy

av1adm said:

Thanks.
I'll have another look at the plate with the cover removed.

Andy

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With the strongest suck you can manage, you may just see the breaker plate try to move, and it should (usually) be in the opposite direction to the way the rotor turns.

Your strongest suck will be between 2 and 3 psi depression, whereas the engine will easily manage 10 - 12 psi depression, and in some cases even a bit more. A total vacuum is about 14.7 psi depression.

Do not apply PRESSURE to the pipe or diaphragm as that may jigger it pretty damn quick. Backfiring into the inlet manifold is one prime suspect for damaging vacuum advance and retard systems.

CharlesY

Just had a good suck but the brecker plate did not move.
the breaker plate was not seized as i could move it by hand but judging by how muck spring tention was on the plate i doubt i'd be able to suck enough to move anyway.
When sucking i also looked at the link rod from the diaphram to the plate to see if this moved a fraction but nothing. There was also no resistance to me sucking on the pipe. I checked the pipe it's self and that was fine.
So i think the diaphram is holed.
I've retarded my timing for now to reduce the pinging. i'll order a new one asap

av1adm said:

Just had a good suck but the brecker plate did not move.
the breaker plate was not seized as i could move it by hand but judging by how muck spring tention was on the plate i doubt i'd be able to suck enough to move anyway.
When sucking i also looked at the link rod from the diaphram to the plate to see if this moved a fraction but nothing. There was also no resistance to me sucking on the pipe. I checked the pipe it's self and that was fine.
So i think the diaphram is holed.
I've retarded my timing for now to reduce the pinging. i'll order a new one asap

Click to expand...

Well done!

Excellent diagnosis.

I suspect manifold backfiring has blasted the diaphragm and burst it.

Try BLOWING down the pipe to make sure the diaphragm is bust before spending money. If you are sure it's bust you can try rigging up a little funnel and pour water down the pipe and into the diaphragm capsule. Water will not flow down the little pipe unless air is escaping somewhere in the capsule. If it even flows in, let alone leaks out ANYWHERE, it's bust.

Once you are sure the diaphragm is burst get a replacement.

Then split the old one and let's have a picture of the thing.

LPG engines are especially prone to this.

CharlesY

Wow today Landyzone is a mine of great information...

I recently replaced my vacuum advance because it had no movement at all, but I expected the replacement to move a lot when I sucked hard, but it only moved a little. Now I understand why.

I also discovered not to cross ignition leads 5 and 7 and my landy is running much better today.

Definately get the Vacuum advance changed. When I was looking for one the shops kept asking if I had 2 wire or 3 wire? It seems there is a plug inside so check how many wires going into it. I took a guess because there was 2 wires going into my Dizzy body.

Hope this helps.

Brian S said:

Wow today Landyzone is a mine of great information...


I also discovered not to cross ignition leads 5 and 7 and my landy is running much better today.


Hope this helps.

Click to expand...

Oh yes, you can be quite sure that as a result of your discovery fewer LandyZoners will exchange leads 5 and 7 on their Vee-Eights!

The problem with so many cylinders is you don't notice if one or two don't work.

CharlesY

When I say crossed I did not mean they were swopped over, I mean they were touching each other. Has made a noticeable difference now I have clipped them up properly and they don't touch any more.

Brian S said:

When I say crossed I did not mean they were swopped over, I mean they were touching each other. Has made a noticeable difference now I have clipped them up properly and they don't touch any more.

Click to expand...

Got it.

I think that if the sparks were escaping THROUGH the HT lead insulation, it may be time to save up for a roll of new HT lead.

There are two sorts - resistor cable with a carbon string for a conductor, and real wire.

Real wire is far better but may cause TV interference. I can never see the problem there because people driving cars should not be watching TV anyway.

Best quality leads are always best, but how does one tell the good from the not so good? I don't know. I would always use the real wire HT leads myself.

CharlesY

My Astra has 8.5mm Magnecore leads. @ £100 for 4 leads I dread to think what V8 equivelents would cost.

I'll Just settle for making sure my current leads are run neatly and seperatly.

Just another thought ... keep in mind that it is a general fact in spark ignition engines that running with ignition RETARDED makes the innards of the engine run HOTTER.

Over an extended period, this can cause big time damage especially to the exhaust valves and seats, and the pistons.

Best plan is to get the ignition set up the way it should be.

CharlesY

I seem to remember (god that's 30 years ago) setting up my Rover V8 Escort timing (dynamic) with the vacuum pipe disconnected, this prevented fluctuations as the idle was a bit lumpy.....bloody high lift/long duration camshafts, there was never a lot of vacuum at idle anyway but it worked.

regards

Dave

Dave 2000 said:

I seem to remember (god that's 30 years ago) setting up my Rover V8 Escort timing (dynamic) with the vacuum pipe disconnected, this prevented fluctuations as the idle was a bit lumpy.....bloody high lift/long duration camshafts, there was never a lot of vacuum at idle anyway but it worked.

regards

Dave

Click to expand...

Yes indeed, and when I had my garage and was servicing cars, one of the first things we had to find out was if the vacuum pipe was to be ON or OFF when the timing was being set using the strobe on the running engine.

I still have that strobe. Lovely bit of kit. And the Snap-On cam dwell and RPM meter. Hey, I don't need them. How much would they be worth?

CharlesY

Hi
I've just fitted the new Vac Advance. The old one was definatly Knacked. However on revinng the enigne up quickly i still get the pinging type of noise as before. This time with my head under the bonnet it only seems to be coming from the nearside bank oil filler area ( i think it may have been all along and i just thought it was general pinging)
Rather that a definate ping it also has a churp or squeek to the noise??
I've heard the timing markings are supposed to be inaccurate on the crank pully should i just set it by ear / trial and error?
Any advise??
Again thanks for all the input..