Smokey Exhaust

[RobMcC]

My S1 4.2 has always burnt a bit of oil (approximately 1 litre per 750 miles), and this did not change after a bottom-end rebuild 3000 miles ago. The rebuild comprised a crank regrind, rebore and new pistons. Top end work was limited to 3 new valves, re-lapping of the valves, and new rubber oil seals on the inlet stems. The rebuilder told me the valve guides were not excessively worn, but I did not check this myself. Though I do not think it is relevant, the crankcase breather is vented to atmosphere rather than to the carburetor breather box. The engine was carefully run-in.

While idling the car for 2 1/2 hours, waiting to get into Silverstone the car would smoke a lot from the exhaust when revved to move on as the queue moved (sorry folks in the OTS behind). I had not noticed this problem before, but then I have never sat with the car idling for so long before. When I arrived, the car had used almost a litre of oil on the 100 mile run. Once in free traffic, the smoke disappeared, and on the drive home, I could not see any smoke in the headlights of the cars behind.

My question is: Is smoke on revving after prolonged idling a sign of worn valve guides as I suspect ? If so, any tips on rebuilding the head ?

Thanks and regards,

Rob McClarence

[christopher storey]

These engines were designed now some 66 years ago, and the material specifications , and the resultant tolerances ,are not what we are now accustomed to. Of the XK engines that I have had, all have used oil , usually at a rate of about 300 miles per pint at best, and 150 miles per pint at worst , and anecdotally much of this has been from oil being sucked down the guides under high vacuum conditions, to judge from the remarks about a puff of blue on gearchanges - or indeed after a prolonged idle for say 2 minutes . I have also found from fairly lengthy experience that these engines are peculiarly susceptible to oil level : even a very modest degree of overfilling, of the order of 1 to 2 pints , ( such as many of us indulge in as an insurance when setting out on a long single sector journey) leads to a marked degree of increased consumption . The long and the short of it is that I would not worry about your recent experience