V8 Running On

[Spearos]

Hi forum, forgive my ignorance - I need help once again!

My '87 V8 90 has developed an annoying problem, when I switch it off it gives a few little 'rattles'. It only does this when hot, I believe it could be pre-ignition?

Am I right in thinking that this is not to do with the timing as when the pre ignition happens the ignition is switched off? I have not heard any pinking during normal operating.

I have recently set the timing to 8 degrees BTDC and the CO2 to about 2.5% using a Gunsons Gastester.

[Hybrid_From_Hell]

8 degrees ???

Why 8 ???

What the engine spec / dizzy number ?

Without looking it up thats feels wrong

Nige

[Spearos]

It's a standard 1987, 3.5 running SU carbs and LPG. I think the distributor is a 35DLM8 (it has the little black box mounted on the side - amp?). Will try and confirm this tomorrow.

I set it at 8 degrees as from the various different opinions I've read, I thought somewhere between 6 and 8 degrees would be ok for dual fuel usage (petrol/LPG).

Again, please forgive my ignorance but is it possible that ignition timing can cause this problem? I only ask as surely when the ignition is switched off, there is no spark? I may well be talking carp and be totally wrong but my knowledge is basic and I'm just trying to learn more as well as sorting this problem out.

Thanks,

Mark

[101sean]

Do a google on Rover V8, there's heaps of advice inc running on. Hopefully you get it sorted here first though.

AFAIK timing can affect running on, I presume your setting is a compromise between petrol/lpg?

Another problem can be the overun poppet valves in the throttle butterflies, most owners solder them shut (make sure you do it properly, my engine just ate one, no ill effects apart from v fast idle after )

[pat_pending]

Most running on problems are caused simply by too high an idle speed. 750rpm I think, check that first before you get carried away. Altering the timing will effect the idle. Also timing should be checked with the vacumn advance disconnected and the pipe to the manifold blanked off to stop it drawing air and the idle creeping up whilst checking.

Also I'd recommend getting it running properly on petrol first before you start altering anything for gas. Too many people make the mistake of randomly tweaking things and end up with an engine that wont run right on either.

A 3.5 on SUs properly set up is a smooth runner, IF.....

Engine mechanically sound.

Breather system clear.

Ignition system good and timing set correctly.

Carbs set and balanced correctly, CO set.

In that order.

Once all this is done and it runs right on petrol...then try gas and see if you think anything needs altering.

If you think, say the timing needs a bit more advance, Switch to petrol, try an extra 2 degrees, adjust idle to suit. Road test on petrol and if it's OK, THEN switch back to gas and see if you have an improvement there. And so on.

If your adjustments to get it right on gas start having a negative effect on petrol running, STOP. Either you have past the point of "the best it's going to be" or you have a fault in the gas system.

[oakesy]

If the engine is running high, this maybe to do with petrol mix screws vibrating loose on each su carb. Some reason while using the lpg for a spate of time pushes up the revs by 200 odd on mine. Also never try to start on lpg the old girl become crabby for ten minutes. Mine is a open system so run the engine up warm on petrol then drain those lovely su's till a struggle then flick the switch to gas.

[Spearos]

AFAIK timing can affect running on, I presume your setting is a compromise between petrol/lpg?

Another problem can be the overun poppet valves in the throttle butterflies, most owners solder them shut (make sure you do it properly, my engine just ate one, no ill effects apart from v fast idle after )

Thank you for clearing that up Sean. And yes that was the idea - that 8 degrees would be a compromise between petrol and LPG.

Also, I'm sure the poppet valves have already been soldered shut.

Most running on problems are caused simply by too high an idle speed. 750rpm I think, check that first before you get carried away. Altering the timing will effect the idle. Also timing should be checked with the vacumn advance disconnected and the pipe to the manifold blanked off to stop it drawing air and the idle creeping up whilst checking.

Also I'd recommend getting it running properly on petrol first before you start altering anything for gas. Too many people make the mistake of randomly tweaking things and end up with an engine that wont run right on either.

A 3.5 on SUs properly set up is a smooth runner, IF.....

Engine mechanically sound.

Breather system clear.

Ignition system good and timing set correctly.

Carbs set and balanced correctly, CO set.

In that order.

Once all this is done and it runs right on petrol...then try gas and see if you think anything needs altering.

If you think, say the timing needs a bit more advance, Switch to petrol, try an extra 2 degrees, adjust idle to suit. Road test on petrol and if it's OK, THEN switch back to gas and see if you have an improvement there. And so on.

If your adjustments to get it right on gas start having a negative effect on petrol running, STOP. Either you have past the point of "the best it's going to be" or you have a fault in the gas system.

Spot on pat_pending, there's a lot there for me to go on. Looks like I need to get it running sweet on petrol first then. Any one know what I should set the timing to for petrol?

Thanks for the replies guys.

[pat_pending]

6 degrees BTDC @ 700rpm no vacumn, is the factory setting. This was with leaded fuel though, so 4 may be a better start point.

Make sure both the mechanical and vac advance is working.

[Spearos]

Great! Thanks once again. I will get chance to adjust the timing on my next day off, probably Tuesday.

Make sure both the mechanical and vac advance is working.

I'm confused here, did you mean mechanical or vacuum advance?

[Pete Attryde]

Both. There are weights and springs inside the body of the distributor that change the timing using centrifugal force. This is in addition to the vacuum advance.

Pete.

[pat_pending]

Both. There are weights and springs inside the body of the distributor that change the timing using centrifugal force. This is in addition to the vacuum advance.

Pete.

Correct. Once you've set the timing rev the engine up to 2000rpm or so with the vac disconnected. You should see the timing advance if the mechanical system is working. Whilst holding at 2000, reconnect the vac pipe and it should advance up a bit further if the vacs OK. That's a rough guide, there are specific figures in the manual.

You can also check both statically, remove the dist cap and twist the rotor arm, it should move against spring pressure in one direction and return. Connect a pipe to the vac capsule and suck hard, you should feel resistance and see the dist base plate move.

[Spearos]

Both. There are weights and springs inside the body of the distributor that change the timing using centrifugal force. This is in addition to the vacuum advance.

I thought you had one or the other! Learnt something already

Once you've set the timing rev the engine up to 2000rpm or so with the vac disconnected. You should see the timing advance if the mechanical system is working. Whilst holding at 2000, reconnect the vac pipe and it should advance up a bit further if the vacs OK. That's a rough guide, there are specific figures in the manual.

You can also check both statically, remove the dist cap and twist the rotor arm, it should move against spring pressure in one direction and return. Connect a pipe to the vac capsule and suck hard, you should feel resistance and see the dist base plate move.

Will check this after doing the timing and report back. Great advice guys, much appreciated.

[Spearos]

What the engine spec / dizzy number ?

Nige

Had a quick look outside with a torch, found part number ETC6876 on the distributor. Quick search on Google confirms what thought - it is an 35DLM8 distributor.

You can also check both statically, remove the dist cap and twist the rotor arm, it should move against spring pressure in one direction and return.

I checked the rotor arm movement while I was out there too, it moved a few degrees, but didn't want to spring back

Might be worth mentioning that when I changed the rotor arm last summer, the old one was seized and whilst trying to get it off by pulling upwards I remember the shaft it is attached to rising slightly. At which point my pants turned brown I tried a different approach - breaking the rotor arm up, which worked. My point is I'm thinking maybe I've dis-lodged something or, even broken something?!!

[Quagmire]

With the lucas dizzy you can dislodge the springs on the bobweights if you pull the rotor arm up too hard, i've never been unlucky enough for this to happen so have no idea whats involved in taking the dizzy apart to sort it out. Hopefully someone will be along soon to enlighten us, as i am sure its fairly common. If you get no luck here then try looking here for v8 (mostly Rover) related stuff - V8 forum There are a few LR4x4ers on there i think...

[Spearos]

Sorted! Well, one bit anyway - Retarded the timing, re-set the idle speed and CO2 and balanced the carbs. She now runs sweet, better than it ever did! And no running on! Thanks to all that replied, especially pat pending for your instructions.

Just need to do a bit of road testing and see how the LPG likes the 'tweeks'...

I also managed to have a look and a play regarding the distributor - I think the vacuum advance is working fine, tried the sucking trick and I see the arm move. Also with the engine revs increased the timing does move, but seems a little slow to react. Could this be because of the vacuum delay valve in the vacuum line? I guess this is what it's supposed to do, hence the name but what is it's purpose?

However, the centrifugal advance definitely isn't working - with the vacuum advance disconnected there is no change in the timing at higher revs. With the dizzy cap off the rotor arm only 'twists' about 5 degrees but does not spring back, during these 5 degrees of movement there is a noise that I can only describe as a rattle.

So, further investigation is required - does any one know (or have a link) how to dismantle the distributor so I can see what's happened to the centrifugal advance?

Thanks for the site recommendation Quagmire, I will be looking on there tonight.

[pat_pending]

Often the mechanical advance seizes where the inner/outer shafts meet. Remove the rotor arm and put a few drops of light oil or penetrating fluid into the cavity below, there may be a little felt pad in there, so pop that out first. Refit the arm and work it backwards and forwards. It should free up. Keep trying, add another few drops of oil, leave overnight to soak in. If it still wont go then it looks like a dizzy strip.

Even when it's OK you wont find masses of movement, there is a bit of slack before you feel the spring but it should turn against resistance and want to return.

If you do this every service and keep the felt pad(if it's still there)wet with oil, it stops this from happening.

[Spearos]

Often the mechanical advance seizes where the inner/outer shafts meet.

Not sure where you mean, there's two shafts? Will have a look tomorrow and see if it becomes clear.

Thanks,

Mark

[pat_pending]

Not sure where you mean, there's two shafts? Will have a look tomorrow and see if it becomes clear.

Thanks,

Mark

There is an inner shaft, the main dist' drive, and an outer shaft at the top that carries the coil trigger and rotor arm.

They are connected together via the centrifugal/mechanical advance. This allows the outer shaft to rotate in relation to the inner and advance the ignition.

Sorry it's not easy to describe in text, you should be able to find a diagram of a dizzy on the net or in a manual somewhere and all will become apparent.

[Spearos]

There is an inner shaft, the main dist' drive, and an outer shaft at the top that carries the coil trigger and rotor arm.

They are connected together via the centrifugal/mechanical advance. This allows the outer shaft to rotate in relation to the inner and advance the ignition.

Sorry it's not easy to describe in text, you should be able to find a diagram of a dizzy on the net or in a manual somewhere and all will become apparent.

Thanks pat pending all is apparant now after stripping the dizzy today and found the springs not connected! Connected them up and re-built it, I now have centrifugal advance!

Here is the link to the page that tells you how to strip the distributor, should any one want a gander:

http://how-to-build-a-pilgrim-sumo.wikidot...cles-by-members

Thanks to everyone who took the time to reply.

All the best,

Mark