1098 Frustration

[cyrilsmoggie]

Dear Collective, can you help! We have a 1971 1098cc 2 door saloon which isn't used that frequently these days. Recently it hasn't been running well, losing power and producing a little white smoke on overrun and the engine continues to run on after the ignition is turned off. The engine has done around 20k miles. Removing the head recently I noticed the exhaust valve on No 4 cylinder was burned away on one side and the guide badly worn (it was a unleaded head by the way). The crown of No 4 piston was also much cleaner than the other 3 suggesting the cyclinder hadn't been running properly - problem diagnosed we thought. Well after fitting a reconditioned head, it does run a liottle better than before, on the first test run everything appeared OK, still a little white smoke on overrun but hey maybe that'll clear. checking the oil, level it was slightly above max so we drained some off. The next day on its first journey out, two miles down the road - no power, white smoke on overrun and running for as long as 30 seconds after the ignition is turned off, finishing with a huge sigh and discharge of white smoke back through the air filter. It still starts OK and idles beautifully and picks up well when revved up under no load with just awhiff of white smoke on overrun.

Can anyone help to diagnose this issue - I did wonder if we had defective/stuck piston rings - looking at the bores - all appear in excellent condition. Thanks in anticipation, Father-in-law's Chief Mechanic.

[lambrettalad]

Preignition can be caused by ,timing issues, also loss of power,white smoke is usually water ,so suggesting head gasket,did you re tighten the head after a heat cycle?,what do your plugs look like?

[bmcecosse]

Any chance diesel was put in the fuel tank by mistake?

[cyrilsmoggie]

Thank for the feedback thus far, to respond to the various points:
- The white smoke has a bluish tinge, is quite dense and lingers so probably not water vapour, almost certainly oil
- Head gasket is new and the head has been retorqued after running so fairly sure it's good
- Don't think diesel has been put in the tank, to be honest it runs too well. However the running on is undoubtedly compression ignition, I removed the HT lead from the coil to be sure and it continued to run on.
- We did have some trouble with the timing. It has a new dizzy fitted and the timing had to be quite advanced to get it to idle off choke. When the engine was warm I set the timing to 3deg BTDC, checking the mixture it was very weak, so I enriched it to soemthing more normal using the lift pin on the carb and then it would idle properly at the correct timing and also start much better.

again many thanks for your help, all further suggestion welcomed!

[bmcecosse]

It's not compression ignition! You need ~ 20:1 for that to work... It is something glowing hot inside the combustion chambers and igniting the fuel...... Either drastic over-rich mix leaving carbon behind or very retarded ignition. I still suspect diesel (or some other strange fuel addition) I've never heard of an engine running on for 30 seconds !!

[lambrettalad]

Try using a strobe to see what the actual timing is

[cyrilsmoggie]

Thanks for your comments, I will check the fuel but no one has admited to dropping some diesel in the tank by mistake! Regarding the ignition timing I have set it by strobe. I'll have another go this weekend to see if anything else comes to light - it is a really wierd one - both the overrun smoke and the running one hence why I've come in search of advice. When I inspected the cylinders they were all good and piston crowns were carefully cleaned - I'm not sure what could be hot enough to cause ignition but I know where you are coming from. I'm coming to the conclusion that the car just likes my garage...

[bmcecosse]

Throw away the strobe and advance the timing till it kicks against the starter. That's too far of course, but gives a point of reference - so then take it back very slightly and road test it to check for any pinking and/or reduction in smoke etc.