Replace Bent Valves

If i were to replace the bent valves on the head, would that be a case of simply replacing the valves, or would it require total disassembly, and reassembly of the head?


R&R the head is the heavy lifting part of this job and as you’re going to partially disassemble to replace the bent valves to my mind, unless the engine had a resent valve job, it would be foolish not to do a complete valve job while the head is off.


In my experience there is nothing simple about removing and replacing bent valves in a 4.2L XK engine but I have successfully done it.

The 4.2L EFI engine in my non-running 1985 XJ6 Vanden Plas parts car had two bent valves when I bought it from a junkyard. As I disassembled that car and engine I discovered that whoever worked on that engine last had just had the cylinder head machined, inadvertently swapped the cam shafts on reassembly and then bent the valves when they rotated the engine. The engine had never run after an expensive cylinder head job. The cam shaft on the intake side had “INTAKE” clearly written on it, but it was really the exhaust cam shaft. The cam shaft on the exhaust side had “EXHAUST” written on it but unfortunately it was really the intake cam shaft.

To make a long and somewhat complicated story short I removed the head, removed just the two bent valves and replaced them with two new ones that I got from one of the usual USA suppliers. I then installed that head on my 1969 E-Type which was having its own valve issues where it had great compression and continues to run just fine after several years of use.

So it’s not simple, it involves lots of complicated technical work, where there are plenty of opportunities for mistakes, but it can be done.


Bob, thanks for the advice, I assumed that was the answer but it was worth ask.



Big Jim on the XK forum has just posted a video of his head going through what you are asking about (sort of)

OK, I”m convinced. Back to the shop it goes. :slight_smile:


Thanks Paul:

If I do anything, I will have it done by a professional


I would check the valve guides and seats.
If all is well, then a simple valve replacement and just ‘lap’ the valves to the seats.

You can look at the seats and check the valves in the guides for ‘wobble’.


With head removed, Lou - you have to identify which valves are bent…

Which may be obvious, but in principle; all valves should be removed and ‘roll tested’. However, if the cams stayed put in the position set by the cam timing tool; #1 and #6 cylinders will be OK. If the cams moved at all during the rotation of the engine; all valves must be checked…

As Bob says, with the head successfully removed, the heavy part, replacing valves is tedious, but straight forward. In all cases; with the head removed it is prudent to do a ‘valve job’; lapping in the valves. And in the case of replaced valves; lapping the valves is essential to ensure proper sealing…

Also, remember that all parts that are to be reused must go back to their original places. So make careful records…

And again; it is absolutely essential to ensure the reason for the non-turning valves is identified to be rectified - and it should be done before you do anything else…

xj6 85 Sov Europe (UK/NZ)