The V8 Owners Forum -

Hi again..I just run my trike engine,a 3.5 v8...With DLMN8 Dizzy,with box on side .I was to put a timing light to set timing..It was running like a bag of nails and started to knock,so I switched it off...I reset the timing statically...IE no 1 cylinder..The rotor arm wasnt facing no 1 pot...So I set no 1 lead where the rotor was pointing...I started it,but still it ran rough..I noticed that NO 1,and No 7 weren't firing,the exhaust pipe at them cylinders was cooler than the rest....I had replaced the head gasket,and had heads skimmed before hand..What causes tha to happen? Any help would be appreciated..Regards..Kev

And i forgot to say,that the plugs and leads are all new,and all are sparking.

Worth double checking the order of the leads on the distributor cap is right?, i.e. you've not got a couple swapped around?

Chris.

I've done that a couple f times to makesure....Gonna check if there is an air leak on inlet manifold,and try and retime it again,see what happens..Thanx for your reply...

This might help - also shows the best layout to prevent cross firing:-

Thanks Dave.Gonna Move rotor arm on dizzy ,so it faces no 1 pot,and then make sure I have timed it to that one....And see how it goes then...Dave ,I have heard of crossfiring,what is this..??As you can polly tell,I dont know much about V8's.More of a motorbike engine,or 4 cylinders..

I think cross-firing is basically when the leads are close enough to allow electrical energy to pass from one to another and therefore trigger a spark in the wrong pot at the wrong time.

Not usually a problem if you are triggering a spark at totally the wrong time, like the exhaust stroke - then its the same as wasted spark.

However this is a problem with pots 5 and 7 on the Rover V8 as they fire consecutively. This means the spark happens at the wrong time, but not wrong enough- and so the effect is like having the timing well out of whack on that cylinder.

A grown up will come along shortly and give you the right answer I'm sure...

Pete? Where are you?

Retimed the engine,rotor facing 1....Start it,and still 1,and 7,not firing....All plugs new,leads new,new dizzy cap...Checked that all leads in correct order.....No air leak on inlet manifold...Don't know what else to do....All pots have compression...

I've had brand new plugs not fire, got me scratching my head on a 6cyl Zephyr some years back.

Try swapping plugs around , and leads too if you can, to see if problem moves or stays with the same cylinders.

Chances are if you've been running the engine that those plugs that weren't firing are now saturated, try with two older plugs.

Thing is ,they are sparking...The pipes on 1 and 7,are colder than 3and 5,which are very hot...I will have to do a compression test on it over the next few days....It ran the other day,all be it a bit rough..And every now and then,the revs picked up on that side of the engine....

Any chance the camshaft is very badly worn? Do the valves on the non firing cylinders open and close obviously?

haystax wrote:Thing is ,they are sparking...The pipes on 1 and 7,are colder than 3and 5,which are very hot...I will have to do a compression test on it over the next few days....It ran the other day,all be it a bit rough..And every now and then,the revs picked up on that side of the engine....

I gather you tried the plugs sparking outside the engine, they may not be when under compression. I'd still move the plugs around and see if the fault moves with them, or even try a couple of 'new' plugs just to make sure. But to have 2 faulty plugs out of 8 new ones is a bit rare. But even so, running the engine for a while with 2 plugs not sparking yet still getting doused in petrol won't do them much good.


Did you use a good cap as I've also read on this forum about caps where the rotor doesn't line up properly with the cap contact at the moment of firing.