Lotus Excel 912 Stripping the cylinder head

Removal of exhaust manifold. 
A few nuts were missing but the manifold came off relatively easily, two nuts coming out with their studs attached, but separated easily once out.

I cleaned the manifold and resprayed it with aluminium effect VHT paint.

The first thing I noticed about this 1984 head was that there was a line of 8 Allen screws along the exhaust manifold side

The head before dis-assembly, note row of Allen screws.

2 Allen screws per combustion chamber... what are they for

 I stripped the head by removing all of the studs using a thread-grabbing stud extractor- this worked really well and allowed me to clean around the stud bases where there was a lot of excess sealant or corrosion.

Most studs came out easily, blunt end inserted into the block first

Only one stud was actually damaged- this one had previously been repaired with a helicoil insert, but the repair unscrewed with the stud and will need doing again.

Used a motorcycle valve compressor

 I had a Sykes Pickavant valve compressor, but this turned out to be too small. I was lucky in that my Laser motorcycle valve compressor fitted well.

Compression released, collets easily removed with a magnet

Removed valve

 Here I was in for a surprise... amazingly the valves were in excellent condition! There was hardly any wear to them and most were really clean. Its as if the motor had just been reconditioned before something went wrong soon or immediately after the refit. This is hopeful and perhaps the motor had been well cared for before it had some traumatic outcome following reconditioning and then started to sink through misuse before ending up in the hands of the LBPO. Some hope perhaps?
However, all exhaust valves were very tight; All but one needed a mallet to remove them, 2 in fact were very badly bent.

Bent exhaust valve

No 1 exhaust valve spring seat was distorted (visible here at 5 O'clock position) and the seat wouldn't come out of the head. It was eventually pulled out with pliers but the head will need attention here and a new spring seat is needed.

  No 7 exhaust valve was difficult, the collets wouldn't release easily although they came out eventually, the valve guide was actually fractured across the line of the mounting circlip, half of the guide remaining in the head.

Broken Valve guide

I stored all the components in a head rack- I could have used holes-in-cardboard but this seemed nicer! It keeps all the components in the correct order and as long as I don't drop it or kick it over then all should be well.

In contrast to the exhausts, all inlet valves were perfect, nice and clean, no slop in guides and all slid in and out smoothly and easily!

Valves, springs and tappet buckets stored in head rack

I cleaned up the head with degreasant prior to measuring its thickness. However the line of screws/bolts is mystifying and given the catastrophic turn of events shortly after this head was fitted, I suppose I do have to consider that this is somehow unsuitable for the block. I really need to know more about it, so I posted a question to the Lotus excel forum... currently awaiting info. However as regards identifying this head it does have some marks...

On one end it has the lotus number: C907E0311Y on the left and a second number LN(or M)25WP above the core plug. The large number 21351 is inscribed towards the bottom of the head.

On the other end:

... a large number 83 and in a much smaller font 19KDB19 with a large letter "B" stamped at an oblique angle.

I think the Lotus No "C ...etc." is  a part number and these were numbered from the first time that the part was used... so this is a 907 head. However the part number is slightly different from that given in the manual (C907E0703J). I don't know if this is significant. Presumably 21351 is just a casting number and the large "B" a size range spec (?). That leaves me confused about the LN(M?)25WP and the 19KDB19!

Well thanks to all on the forum who helped with this. It seems these screws are blocking a line of ports used for an emission control system not fitted in the UK. They were apparently standard on all US motors and introduced to all heads sold as replacement stand alone units  and  later motors in the UK. My car is an early car so this must imply that the head at least isn't original to the car. Replacement heads sold as "stand-alones" wouldn't usually have the large casting number so this looks like a head swapped from a later UK motor. I need to check and see whether the whole motor was actually swapped at some time in the past or if it was simply the head. The  LN... number specifies a grade of aluminium for the casting. The 19K... number remains a mystery!