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Cylinder Head-Aches !


The following series of six articles will explore the anatomy of the Daimler V8 saloon cylinder head, designed by Edward Turner. Everything from design, in service operation, corrosion, degeneration, repair, improvements and modifications will be covered.

As far as I am aware, never before has such a detailed comprehensive overview and examination been carried out on this cylinder head.

Before commencing, I would like to thank J&E Engineering Services for the detailed analysis and engineering interpretation, along with Robert Grinter for supplying the donor saloon cylinder head. Thank you both.


Richard Long, DLOC V8 250 Registrar

  • Richard Long

Cylinder Head-Aches !! Part 6

Updated: Aug 16, 2022

This is the concluding part of the Daimler V8 saloon cylinder head autopsy, which I hope you have enjoyed along with being informative. The rationale behind the series of articles is to give owners a better understanding as to the physical properties of this cylinder head, along with the potential issues that it can manifest, of which I am now certain you are more aware of. Thankfully, the vast majority of these cylinder heads can be recovered with the correct engineering application and expertise. In this part, we will take a look at what has been manufactured to negate the troublesome “oil in your tubes” situation along with additional modifications plus tools that have been designed and crafted for the benefit of those owing an Edward Turner Daimler V8 engine.

Spark Plug Tube Sealing:

The nature of the cylinder head design and central spark plug within the combustion chamber makes oil sealing a bit of a problem which was outlined in Part 3 of the series, see Fig.61(below).

Originally, the removable spark plug tube was sealed with the use of a copper washer at the base of the retaining thread around the spark plug. Note the small radius at the bottom of the threaded hole; this varies from head to head which limits sealing success when using the copper washer. Oil leaks from this area have plagued owners for many years and simply replacing the sealing ring has, in many cases, proved extremely unreliable.

A new state-of-the-art designed modified oil seal, see Fig.62(below), produced by “J&E Engineering Services” uses Viton O-rings within the plug tube and around the plug tube seat.

Fig.63(below) shows a plug tube with a section cut-away, showing the two seals being visible around the sealing ring.

Fig.64(below) shows, again, the cut-away cylinder head with the sealing ring and plug tube installed. The modification is highly effective and simple to fit, with these precision made items. The archaic Medieval days of the copper sealing ring are well and truly over, thank goodness, should you wish to venture into the 21st Century !!

Replacement Spark Plug Tubes:

It's not just the OE oil seals that can cause issue, but the actual spark plug tube. In some cases the tube thread that screws into the cylinder head is damaged as a result of incorrect installation or the tube has on removal incurred damage. The latter is usually the incorrect tool being used to extract the tube or decades of neglect that sees the tube no longer fit for purpose in respect of being able to assist in the sealing process.

Is there a solution ?? Yes there is, as you can buy second hand tubes from the usual outlets. However, a better cost effective common sense option is to purchase a spark plug tube - CNC machined from superior grade CDS tube (Cold drawn seamless) complete with the modified oil sealing end already machined and integrated. In essence two solutions rolled in to one !! See Fig.65(below).

Spark Plug Tube Removal / Install Tool:

The VL Churchill D.506 tool is no longer about and this has caused owners many an issue when trying to remove spark plug tubes. Make no mistake, these tubes can be nigh on difficult to remove on occasions without the correct extraction tool or a modern day designed removal tool to overcome the stubbornness of the tube.

Many of these tubes have suffered badly, see Fig.66(below), due to primitive attempts to extract them – in a lot of cases the tubes have been gripped by a wrench to assist in extraction.

The use of such tools compromises the integrity of the tube along with irreversible sidewall damage and / or thread damage. In essence the tube sustains a crushing injury which in a worst case scenario the tube can no longer be used.

Fig.67(below) shows a modern day designed spark plug tube removal tool that will remove even the most stubborn tube from the cylinder head, whilst protecting the integrity of the tube.

This is achieved by the complete length of the tube wall being uniformly supported, which allows significant torque to be applied to ensure a safe extraction. It's a precision engineered made tool and designed to exacting specifications; in fact the design is better than the original VL Churchill D.506 tool, which relied upon gripping the upper (rocker cover nut) thread to extract the tube. Needless to say, such a system is not ideal as threads should be protected as much as possible when a removal / install process is being undertaken. The good news is that all of the above modifications and tools are available to purchase; you can even hire the spark plug tube removal/install tool if so required and when available.

Before signing off, I would like to extend my grateful appreciation and thanks to J&E Engineering Services, Robert Grinter and Kevin Bennett. Without their assistance, these series of articles would not have been possible.

Should you wish to enquire about any aspects of the six-part series, please contact me.

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