A recent need to remove a very defiant cylinder head from a 20/25 of mine resulted in the most frustrating and back-breaking experience imaginable. The defiance lasted some four days.

Snugly fitting steel rods and Stout Timber 'T' Piece in place

Since I bought this particular car some four years ago, the most irritating sight for me was a mongrel of a finned exhaust manifold with a badly welded ‘new’ 5 or 6 bolt flat-faced flange to match a corresponding flange at the top of the exhaust downpipe. It looked a mess and did the car no favours. For three years I had been waiting for a new finned manifold from Ristes of Nottingham. Sadly, some modern foundries have enormous difficulties in casting such good quality, complex components acceptable to the discerning enthusiast and also acceptable to Steve Lovatt at Ristes. In the end, my conclusion, based on advice given, was that an early 20/25 originally did not have the finned type and so the simpler, plain variety was not only more authentic but also cheaper.

In April, 2007 I bit the bullet and bought the non-finned type and planned a trip in the car to North Yorkshire to stay with a good friend, calling on Richard Lonsdale near Bedale for a new, compatible, stainless steel downpipe. My stop-off at Richard’s farmyard workshop took far longer than either of us realised; it was the often experienced revelation of unexpected related problems which had to be resolved there and then. The old manifold had not been off for donkey’s years and whilst Richard was making up the downpipe, I got on with its removal. About half the studs were in a very bad state and two of them had the rot at the inboard end and their respective holes in the head really needed ‘helicoiling’. Richard made up some ‘temporary’ studs and the new manifold was then fitted followed by the new downpipe. Time was running out but one of the studs on the rear port would not catch the virtually threadless hole in the head and in consequence leaked water  which dripped constantly on to the magneto en route to the undertray and beyond. Following my return home, at some point the bullet had to be bitten again and Helicoiling undertaken.

Steve Lovatt offered to loan me his Helicoil kit and with all necessary replacement manifold studs and gaskets by my side, the cooling system was drained and cylinder head was stripped of its two manifolds. The dodgy studs along with the temporary ones made by Richard Lonsdale were removed and binned. Next comes a warning to all prospective Helicoil supporters.

The relevant Helicoils for this particular job are 5/16ths compatible and the drill bit and tapered tap both relate to this and are engraved as such. Steve’s kit was missing its drill bit and so he found me a 5/16th bit to replace it. My discovery back at home was that this bit was too small in diameter and removed no metal from the stud holes at all. In consequence the Helicoil tapered tap would not engage. Back to Ristes for advice. The 5/16th drill is, in metric terms, 7.9mm in diameter and it was agreed that the Helicoil tap was indeed significantly wider. I was loaned an 8.1mm bit to try. This proved to be too small as well, so 8.3mm seemed a sensible, but final, step up and the stud holes were bored out at this. Trying to make the tap engage was extremely difficult. With one hole I was successful but it was very much a case of a tough, grinding process and the Helicoil did fit. The second one was far more frustrating and there was incredible resistance here. I was unlucky and the tap became well and truly jammed. To remove it, I was obliged to use a hammer on the spanner. The tap broke, leaving a substantial part of it in the stud hole. Tears were imminent.
In order to prevent further damage and for what appeared to be a case of very careful precision drilling to remove the offending tap, the cylinder head had to come off. In the meantime, I felt obliged to replace Steve’s Helicoil tap. Cromwell Machine Tools in Nottingham was the advised supplier. My visit there revealed the details of the Helicoiling system and the compatibility of all the components in the kits as follows:
        For a 5/16th Helicoil, a 5/16th Helicoil tap is needed and this is significantly wider than 5/16th and the drill in the kit is probably closer to 8.4mm. The lesson to be learned here is that the only 5/16th component is the manifold stud itself and by using an ordinary 5/16th or 7.9mm drill from your workshop will not do the trick.

The cylinder head was stripped of all its impedimentia, including manifolds, oil pipe unions, temperature sensor, Klaxon etc, the tedious job of ceremoniously removing the many nuts securing the rocker shaft to the head itself, strictly in accordance with the manual, was completed. Having removed and laid down the tappet push rods in their proper order, I removed the bonnet and straddled the engine bay ready for the big lift. I am not a weakly muscled person by any means and I am reasonably fit, but I simply could not make the head move at all. Several hours later and numerous telephone calls to Dennis Foster, John Eastwood and Steve Lovatt to seek advice, I had tried everything including rattling the sides of the head using a stout piece of timber and a hammer. John Eastwood relayed a story of a good friend of his with a similar problem on a Bentley R Type. The man resorted to suspending the head by block and tackle from an overhead beam in his garage, using the weight of the front end of the car as the separating force. The car remained suspended for 8 months. In the end, the head had to be cut into a number of pieces in situ in order to remove it. I dreaded the prospect of this method and I doubted the strength of my garage roof trusses to take the strain. I tried using liberal quantities of penetrating oil directed down the head stud holes (all 31 of them over a period of several hours but again without success. However, using the weight of the front end of the car appeared to be a useful approach.

Fortunately, the car was on my four-poster ramp and it does have a beam jack. I removed the nearside undertray (what a pain!), cut an appropriate length of 3”x 2”(7.5mm x 5mm) and jacked up the timber to meet the two studs emerging from the middle upper exhaust port making sure that it was completely vertical and as close to the manifold as possible. The real jacking up process then began. I kept a careful eye on the bottom edge of the nearside front tyre; all I needed was a fractional suspension. As I approached this critical point, I heard a crack from up above. However, my thoughts and hopes of success were soon dispelled when I observed the outcome. One stud had fractured and the other looked more like a hockey stick. Several hours with the thinking hat on allowed a variation on the same principle to surface. The inlet and exhaust ports are 1.25 inches in diameter and they have an internal cavity of approximately 3 inches (7.5cm). I needed three, 6 inch lengths of steel or aluminium exactly 1.25 inches in diameter to slot firmly into the middle port holes.
At around 06.30 hrs the following day, I thought of RREC member, Peter Boneham, now in his mid-80s. Peter is a retired precision engineer living, as the crow flies, some 1400 metres away from us. A mid-morning visit and an exploration of his shelves yielded three pieces of metal of the correct dimensions. Back home, the piece of timber was shortened and another piece screwed to one end to act as a platform on which the metal rods would rest. With the rods well into the port holes and the wooden ‘T’ in place, the front end of the car was jacked up once more. Silence prevailed and my anxiety levels were rising. As I looked at the engine from the side, suddenly there was a creak and the chassis fell back on to its tyres. Separation had been achieved and it took what must have been no longer than 4-5 minutes.

What hade caused the adhesion? The head gasket was intact and well lubricated and so it could only have been some corrosive binding between the block’s cylinder head locating dowels and the head itself. The problem had cost me three days of backache, head scratching, sweat and frustration, but at least I had found a method at little cost and a reasonably good cylinder head had been saved albeit with a few scars for history.

Steve Lovatt kindly offered to sort out the head, re-sleeve the offending stud holes and tap accordingly. He pressure tested the head (no problems here) before I collected it from him, bought a new head gasket and a pile of studs and with considerable help from John Eastwood the whole thing was put back together, tappets reset and engine fired up in the space of four hours.

Sincere gratitude to both John Eastwood and Steve Lovatt for their advice and practical help.