Misfire - most likely culprit?

[Pete Lewis]

at 3.5ohms  you are running at 12v not ballasted ???

on the delco make sure rotor sprung sweeper is in contact with the fixed brush in the cap 

Pete

 

 

[Chris A]

40 minutes ago, 1969Mk3Spitfire said:

Choke returning fully (why only 1 sooty plug).

That points to the problem being specific to that cylinder rather than a general problem.

Moving the plug to another cylinder, does the problem follow the plug or stay at the original cylinder, the answer to that either proves or disproves the theory of the plug being the weak link.

Swapping an HT lead in the same way would do the same for the HT lead.

You seem to be dealing with the problem very coolly, well done. By now I would have resorted to drastic measures, 'gros mots' and hitting the car with a 'clé anglaise'.

[1969Mk3Spitfire]

57 minutes ago, Pete Lewis said:

at 3.5ohms  you are running at 12v not ballasted ???

on the delco make sure rotor sprung sweeper is in contact with the fixed brush in the cap 

Pete

 

 

I believe the original spec is 3.1 to 3.5 ohm with 12v so it’s ok, n’est ce pas?

Sweeper is in contact with the cap fixed brush.

57 minutes ago, Chris A said:

That points to the problem being specific to that cylinder rather than a general problem.

Moving the plug to another cylinder, does the problem follow the plug or stay at the original cylinder, the answer to that either proves or disproves the theory of the plug being the weak link.

Swapping an HT lead in the same way would do the same for the HT lead.

You seem to be dealing with the problem very coolly, well done. By now I would have resorted to drastic measures, 'gros mots' and hitting the car with a 'clé anglaise'.

Yes, Chris, I’ve been through all of the swaps and I’m 100% sure that the issue is specific to No2 cylinder only.

I was turning the front crank nut earlier today to measure points gap on each lobe. At one point, I managed to get my sleeve stuck between fan belt and dynamo pulley. I was not very cool at that moment. Normally, I’m quite chilled and enjoy tinkering with the 50 year old technology. Nonetheless, I’d really like to have all 4 cylinders working in unison. All offers of help or advice on this is gratefully received. 

[Wagger]

2 minutes ago, 1969Mk3Spitfire said:

I believe the original spec is 3.1 to 3.5 ohm with 12v so it’s ok, n’est ce pas?

Sweeper is in contact with the cap fixed brush.

Yes, Chris, I’ve been through all of the swaps and I’m 100% sure that the issue is specific to No2 cylinder only.

I was turning the front crank nut earlier today to measure points gap on each lobe. At one point, I managed to get my sleeve stuck between fan belt and dynamo pulley. I was not very cool at that moment. Normally, I’m quite chilled and enjoy tinkering with the 50 year old technology. Nonetheless, I’d really like to have all 4 cylinders working in unison. All offers of help or advice on this is gratefully received. 

My brother started his 1957 Ford 100E with the handbook laying open near the fan. The blades turned the pages over one at a time slashing each one as they went. Language was intolerable.

The advice has all been sensible. Only thing that I can add is that a worn valve guide would allow more oil to be sucked in via the inlet valve if the seal was missing or worn. On a motor-cycle of  mine, the guide was moving in the head allowing a large volume of oil to soot it up in 5 miles. I have not seen that in a car 'Yet' but there is always a first time.

[NonMember]

52 minutes ago, Wagger said:

inlet valve if the seal was missing or worn

Seal? What seal? This is a Spitfire engine we're talking about. No valve stem seals, just careful oil metering to the rocker area.

[Pete Lewis]

its worth having a look inside the rocker cover at the breather outlet  many have a gauze flame filter trapped under a bit of simple metalwork

its worth prise this open and remove the gauze for a clean in some petrol  as poor breathing can force oil down the valve guides

and if the problem on No2 is rings  then a soak of redex in the bores overnight might free any gooey rings 

Pete

 

 

 

[Wagger]

1 hour ago, NonMember said:

Seal? What seal? This is a Spitfire engine we're talking about. No valve stem seals, just careful oil metering to the rocker area.

Sorry, I have a Vitesse so overlooked that even though I rebuilt my 1500cc Dolly engine.

[Wagger]

16 hours ago, Mathew said:

You could move the position of the distributor so the plugs are 90 deg round and see if the position of the fouling moves. That will either eliminate the distributor or the cylinder.

Yes, I agree with Mathew here. Good reasoning and would identify what to do next.

[1969Mk3Spitfire]

Thanks again to you all, appreciate your help in trying to solve the sooty plug issue.

Rocker case breather is clear

I’ve injected just 10ml of Redex into the No2 cylinder. With plug removed and using a torch, the top of the piston is nice and clean, not soot blackened, which is heartening. That said, the cylinder held pressure during CR test (which I did more than 6 months ago).

I’m interested in the idea of rotating the distributor. This resonates also in that access to No3 plug is difficult. Picture attached. What is the factory orientation? 

How is this accomplished? Presumably, set crank position using light bulb on points, rotate distributor 90 degrees and move all HT leads?

I’ve fitted the Sparkrite plug testers (only 3 because no access to No 3 cylinder) and, subjectively, all cylinders have healthy sparks

 

 

[johny]

I think youve already got the usual dizzy position and rotating 90º will put the vac unit in the way of lead 2☹️

[johny]

I see, also it cant go clockwise cos of the dynamo but dont think it'll go anticlockwise either...

[NonMember]

11 minutes ago, johny said:

I think youve already got the usual dizzy position

I think it looks a little out but not 90deg - more like 45. That would need the drive gear to be rotated, though.

[Wagger]

Looks like this may be impossible on a 4 cylinder. On a 6 cylinder it requires only 60 degrees of rotation, quite easy by comparison. You will have to remove the Dizzy and 'Faff' around with inserting it at different angles, then re-timing. This may also prove difficult or impossible due the the offsett slot in the drive shaft. Pete will know.

Following is my experience of a plug oiling up. If I drove gently, it oiled up and fouled the plug in five miles. Driving hard it lasted ten miles. This was because so much oil was getting into one cylinder via a inlet valve and guide that it was not being burned off unless I used heavy throttle opening. The soot completely shorted the plug out.

There is a chance that your problem will just go away with more use of the car. I would do just that until it recurrs. Hopefully, it won't.

 

[1969Mk3Spitfire]

I replied earlier and for the second time within thread it has vanished into the ether.

I've looked again and I don't think it will rotate.  Clockwise, likely the vacuum advance will foul the dynamo.  Counter clockwise, likely it will obscure access to No 3 plug lead.

With your help, much appreciated, I think we've exhausted all of the easy checks.  I don't think it's ignition, I'm leaning towards valve guides as it's the only scenario that makes reasonable sense.  I have no (current) intention to remove and work on the head so I'll live with it and adopt a regime of regular plug cleaning.

More use of the car and at higher engine loads sounds like a good plan, too.

A pal (owned his Elan Sprint for more than 50 years) is visiting tomorrow and we hope to fit pesky seals and mount my newly refurbished hardtop.  I still don't have a rear glass but that's another thread entirely.  As I'm sure is true for all Triumphs, there's always plenty of tinkering jobs to do without looking for more.

 

 

[daverclasper]

Just something that I noticed on my 6. A couple of plugs (same 2 plugs, though at different times), often looked a bit oily if I took plugs out. I think this was after some slow/traffic running. I did notice a petrol smell from the plugs and put it down to petrol soaked soot?, so assumed that the cylinders for those plugs were sealed in the combustion chamber on ignition cut off and the fuel that was spurted in did not evaporate quickly?. just an off the wall theory?