The 'E' Type Forum

OK, I hold my hand up and I should have checked the most obvious thing, but the signs were there to prevent me and I was blinded my the offer of a potential "big valve" head going begging.

Many of you followed my fun wet weekend in November 2014 when I removed a cylinder head from a relatively low mileage, (61,808 miles), 1984 Series III fuel injected 4.2 Sovereign. The full story was in the Technical topic under "Removing Cylinder Head studs in situ" in November 2014 as I sought advice on the best way to tackle the challenge. As a relaxing winter workshop job, I removed the cams and valve gear and then had the head glass blasted - followed by some welding done to fill the two unwanted rear water ways and to plug some minor corrosion. I then took the head to my local machine shop friend Fred to be skimmed and the valve seats cut to accept my new inlet and exhaust valves. Fred skimmed the head and confirmed the valve guides were fine and set about cutting the seats, but I got a call from him tonight to say the exhaust seats were done, but the inlet valves I supplied were too big.

Having checked my old inlet valves for the first time - big red face now !!! - I found these were the "normal" 1 3/4 inch and not the "big valve" 1 7/8 inch size. So how come I was blinded by the fuel injection, the low mileage car and no apparent later work to the car, the "PI" cast in the head - which I assumed meant fuel injection, all the inlet valves had the later valve seals which I thought were only on these Series III heads - and the head had the smaller valve seats, spring retainers and collets.

So, either this car has had a modified earlier head fitted with inlet valve seals which would make that were there three types of inlet valve for the 4.2 engine ? An early larger collet 1 3/4 inch dia, a smaller collet 1 3/4 inch dia and a smaller collet 1 7/8 inch dia ?

Either way, I still have a spare head, but I will need to order the 2nd of these valves to rebuild this head, if someone can confirm the two types of 1 3/4 inch valves and just for fun speculate on the history of this fuel injected car.

Photo of the head being removed with the fuel injection:-



Things were looking so good then !!!



After blasting. The head was blasted with the cam covers on and the pipe insulation is only there to protect the cam bucket surfaces :-



What really threw me - the "PI" casting - what is this all about ???



This does not normally happen to me, but I hold my hand up as an example of always checking the obvious !!

Cheers,

Dave

If its any consolation we did the exact same thing a few weeks ago with a 4.2 head I was utterly convinced it was a big valve head,... and like you only when I actually compared and measured the inlet valves did I realise they were not 1 7/8" as I thought but 1 3/4". Still decided to keep it as bigger valves can still be machined in.

Hmm, the P & I must have blind-sided you. One of my heads just has an 8 and another has nothing. Fuel injection came in 78.5 for US 4.2 Series 2 cars and those had normal valves afaik. The seals came around 69 - much earlier than S3 XJ and are no guide ('scuse pun) to anything much. You can still fit the big valves if things are properly concentric, as they just about sit on the outer rim of the insert. However, that does mean the insert has to be opened out to get the full benefit and you can't go to the max on undersize seats. The port needs opening out a little too if you want full big-valve spec.

3.4s kept the small valves to the end of XK production but were carbed cars. I guess your car got the head off a 4.2 S2 or a 3.4 S3 at some point? The fact that the heads weren't numbered by that stage means things get a bit murky.

Pete