Unleaded Experience

Drama with Col Murray's "S" Type

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Background

When I rebuilt my 3.4 litre engine in 1997 I had to have a fair amount of work performed by specialists.  The cylinder head, being aluminum, required work as could be expected for a 32 years old engine.  Typically, the valves were replaced, seats re-cut, corroded waterways welded and the head refaced.  The valve guides were knurled and fitted with K Line phosphor bronze inserts, this being a common way to retrieve valve guides without actually having to replace them. I asked about having hardened valve seats fitted and was advised that it was un-necessary as "all Jaguars had hardened valve seats". How wrong was that?

After the rebuild, the engine always sounded noisy around the inlet camshaft area (the previous owner felt the same), and knowing that the clearances were correct I was always been a little concerned. In the winter of 2001/2 I replaced all camshaft buckets and re-shimmed the valve clearances. The result was that the noise, which had been heavier then a tappet noise, had reduced dramatically. Success? No, because as the year wore on the noise returned and appeared to be louder than ever.  After being asked, at the Selkirk Show, what diesel engine I was running I decided something had to be done and more investigation required.

In October 2002 I spoke at length to VSE engine specialists in Wales who confirmed that valve tappet bucket/guide wear was a common occurrence and that it could easily be rectified by honing out the guides and fitting oversize buckets.  Acting on this advice I removed and dismantled the head and took it to their premises in Llanbister in mid Wales. I was given great service by Neil who cleaned and measured all bucket guides and pronounced that they could be recovered by using 3 thou oversize buckets however worse was to follow.

When dismantling and cleaning the head prior to getting it to VSE it was obvious that the exhaust valve seats were badly pitted and in fact looked as though they had been hit with a ball peen hammer.  I also noticed a significant amount of wear on the valve stems.  Measurement and inspection at VSE showed that all valve seats, inlet and exhaust, were beyond repair as were the valves and valve guides.  To put it bluntly, the head wanted a complete rebuild at a cost of £620.  Shocked? Yes, particularly as the car has only traveled some 7000 miles since the last rebuild.

Conclusion.

Neil at VSE was also convinced that the cause of the severe valve seat wear was down to the use of un-leaded petrol.  He advised that all XK engines manufactured prior to 1969 were only fitted with a soft valve seat material, this being un-suitable for use with un-leaded petrol.  I had also read that Jaguar engines could be run on un-leaded provided the engine was in good mechanical condition, the cooling system was functioning as it should, the ignition timing was correct and that the engine revs should not exceed 3000 RPM for sustained periods.  After ensuring all of this, I now find that severe damage has occurred.  In addition, numerous motor magazine articles have indicated that the "lead memory effect" should stay with the car for many miles, maybe this was destroyed when I had the valves and seats refurbished in 1996.

Anyway the results are now obvious and a warning to anyone running an un-modified pre 1969 XK engine on un-leaded petrol. I was mislead by good performance and good economy; and bad advice. If it had not been that I was concerned about the noisy cam followers then a severe engine failure may have resulted.

Cost?

£620 - expensive I guess but the head has been completely rebuilt and equipped  to run on un-leaded petrol. The front part of the head has been polished and the rest painted the correct colour.  All inlet and exhaust studs and all core plugs replaced.  This should now give me peace of mind when filling up with the Worlds answer to pollution -- UN-LEADED.

Col Murray