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PMac
USA
75 Posts |
 Posted - 06/05/2012 : 21:13:55
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All,
Save me from certain insanity. During a run around the local area a few weeks back, my J2 (J2517) started detonating and then stopped dead. For a couple of weekends I have worked to get the car back on the road but am now stuck and need help.
I have replaced spark plugs, coil, made up and fitted new ignition leads. This got the car running again albeit very poorly. I then worked over the distributor (type: Lucas DK4A) with NOS cap, NOS points, new condenser and NOS rotor button. I also replaced the distributor based plate with a NOS item and in doing so identified that the rotor cam sub assembly had spun free of the fly weights i.e. the small pins or toggles on the cam assembly had disengaged from the corresponding holes in the fly weights and although the cam was stuck, it was clearly way out of sync. All this corrected,I have re-set the ignition timing and now the car runs again. The engine idles very well and and runs very sweet at high revs. Unfortunately everything in between idle and high revs is nothing short of a trainwreck. The primary symptom is the expulsion of fuel vapor from the carbs. There is fuel visibly present (puddling) at the air inlets of the carbs and a blip of the throttle brings forth a signficant projection of fuel vapour out of the carb air inlets (there is no backfiring through the carbs). The car will drive but the constant stream of vapour from the right hand bonnet louvers is perhaps something you'd expect to see on Stanley Steamer and not an MG. The car is lacking in power and as you might expect, it drives very poorly - no power at all.
I have checked and re-checked the static timing. The physical position of No.1 piston at TDC matches the cam lobe position (No. 1 cylinder inlet and exhaust lobes are pointing at 10 and 2 oclock) and the 1/4 mark on the flywheel is at 12 o'clock. Also, the marks on the cam pinion gears match. The rotor button and points position all check out OK.
Armed with a timing light, I have checked and adjusted the running timing.
The valve clearances are fine and all valves cycle through OK (cranking over by hand, there are no valves that are visibly sticking).
Dist points and plug gaps have been properly set.
I have checked the compression with a screw in type gauge (suspecting a blown head gasket) but all cylinders are showing an even 8 bar.
I have worked over the SU's checking and fine tuning float and mixture setttings. Per the basic principles of setting up SU's, I can balance the carbs and run the car rich or lean. All seems to check out here with the exception of the fuel puddling and expulsion during running.
The real mystery is the vapour projecting from the carbs when the throttle is depressed and the engine is run up to speed (at idle or high revs there is no vapour).
Could this be a carb issue? Could the ignition be out by 180 deg? I note that the 1/4 mark on the flywheel also matches up with the TDC position for No.4 piston. Is it possible to install the distributor cam assemblly 180 deg out or is its fitment in the fly weights not specified? The rotor button rotates clockwise and can be advanced (rotated manually a few degrees)clockwise but not counter clockwise.
I am really hoping that there is something stupidly simple I have missed.
Value all thoughts or suggections.
Peter |
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DickMorbey
United Kingdom
3677 Posts |
Posted - 06/05/2012 : 21:54:09
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Peter
Have you checked the carb float valve settings? Maybe the fuel level in the carbs is too high?
Dick Morbey
PA/PB 0743
Henley-on-Thames, Oxon, UK |
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Robin Macmillan
United Kingdom
415 Posts |
Posted - 06/05/2012 : 22:04:51
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Well .... If it idles well then valve/ignition/cam/ timing are not likely to be much at fault, particularly as it was presumably running OK before it stopped !
You describe "detonating then stopping dead"... not really sure what this sounded or felt like.
I would suspect its a fuel carb problem. If fuel is pooling then float level and functioning of the float valves would be my major concerns. It seems that pooling in both carbs is occurring .. strange that a failing should occur in both carbs at the same time.
someone clever than me will no doubt contribute but when you find the answer I shall be most interested.
PB 0527 |
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leafrancis14
United Kingdom
323 Posts |
Posted - 06/05/2012 : 22:36:44
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Maybe the cam timing has somehow slipped. What about the dynamo fork or something like that? Might account for the sudden start of the problem.
Or head gasket is another possibility.
Barny Creaser
(Wellingborough) |
Edited by - leafrancis14 on 06/05/2012 22:44:44 |
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Allan Bentley
United Kingdom
257 Posts |
Posted - 07/05/2012 : 07:49:54
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Sounds as if the key in the vertical drive has sheared or is very loose. This will provide incontrolled VVC and in my experience with a J2 engine very varied performance including detonation, as the valve overlap may become excessive. Unbolt the coupling and check for movement.
Good luck. |
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PMac
USA
75 Posts |
Posted - 07/05/2012 : 16:41:48
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Thanks all for your feedback and advise. I will go over these potential issues again and see what I can find.
Peter |
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bahnisch
Australia
674 Posts |
Posted - 08/05/2012 : 09:31:59
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| I had a somewhat similar problem with my F2 Magna and (after all sorts of suspicions) it turned out to be air being sucked in from one of the petrol tank pipe connections. In my case it only happened on long(ish) hills, baffling at first! |
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PeterL
United Kingdom
1723 Posts |
Posted - 08/05/2012 : 09:44:47
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If we are into confessionals, I reconnected my dynamo 180 degrees out. You could tell the timing was spot on by the perfect explosion as the mixture erupted straight out of the open exhaust valve. Quite a shock, first time, had to be repeated to be believed! I still remember it, very clearly!
Cheers
P |
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JMH
United Kingdom
911 Posts |
Posted - 21/08/2012 : 21:12:35
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J2 troubles - it had to happen to me eventually. On Sunday for the first time in over 20 years (probably more), the J2 failed to make it home from an event...... After an enjoyable day at the SW Centre Mendip Trial (the sole MMM entry for a very good event) where the J saw off all bar a couple of midgets without missing a beat, having dropped my brother off, we stopped dead & failed to start. Still, the sun was still in the sky & we were on the drive way, so it could have been a lot worse. A few minutes of faffing around concluded no spark, not a sausage.
With a steady supply of tea & chips etc, further investigations showed 12 volts in all the right places (well, sparks anyway as I was a bit light on tools), but we could get nothing out of the HT side of things & suspicion fell on the condenser. So, with no spares brother was put to work washing all the mud off, whilst I pretended to ponder the problem further & drank more tea.
Help eventually arrived in the form of an understanding (but constantly bemused Sophie) with modern wheels & the J was trailered home (oh the shame of it).
A quick check with a multi-meter showed that the condenser was indeed leaking to earth like a sieve & fitting a replacement instantly cured the problem.
Whilst I'm sure that there's a morale in here somewhere, I've never known a condenser fail quite like this before - low revs, low load, no previous issues, it just died on the spot.
Still, as failures go, it could not have been more convenient!
JH
The SW Centre run another trial at the same venue in October (details on the SW web-site). Non damaging grass & not overly steep either, even a spectating Singer 9 has threatened to dip his toe in the water & enter. So, come on, it's only a bit of mud & grass, get your entries in!
one immobile J2! |
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