Gearboxes and heads

[Barry20383]

I have 2 spare Meadows gearboxes will these fit directly onto my 1953 Javelin.
Also i have 3 spare heads will these also fit on my Javelin or did they vary over production time.
Thanks Barry

[Keith Clements]

Yes and yes.

[David Morris]

Hi Barry,

Keith is basically correct, with a couple of provisos over the heads. Jowett's initially supplied heads that had a metal tin lid ( for want of a better description ) over the sparking plug holes and under the carburetor inlets. This was to accommodate their unique sparking plug caps that had a rather clever bayonet type of fitting that used a rubber sealing ring. There cannot be many of these left now, as the Bakelite gets cracked due to the heat from the heads and the bayonet 'ears' eventually snapped off.

Many owners have reverted to conventional plug lead connectors, rendering the tin lids on the early heads redundant and these can be popped off. They are held on with blind rivets. I use motorcycle plug lead connectors fitted through a disc of rubber sheet about 8cm in dia. over the sparking plug holes. These keep the water out, unless you plunge through a ford. Jowett's deleted these tin lids themselves later on in production.

The other change that Jowett's made to the heads was to make them possible to fit to either bank of cylinders, ie, to remove the situation where they would be 'handed'. This involved the tapping of holes in the factory for the studs that hold the water transfer cast pipes at the front of the heads. Later heads have tappings on both sides of the heads, with a bolt fitted to the unused side of the head and a conventional core plug to fill the water port. You can, if needed, tap out an early head, where there is a flat 'land' on the head to take the tapped hole, although you need to make careful measurements.

My advice when thinking about fitting a different head is to examine very carefully the narrow gap between the inlet and exhaust valves inside the combustion chamber. You will, unfortunately, often find this is cracked through, rendering the head scrap. Apart from a visual check, I would then recommend fitting the valves and springs, plus a plug. Invert the head and fill the combustion chamber with some paraffin, or similar and leave overnight. If she holds the liquid overnight, then you have a good chance that the head is usable.

It might also be useful to do some measurements on the height of the head, compared with others. We have seen some heads that have been ground down, presumably to increase the compression ratio? Remember you are dealing with a component that is some 60 years old and has been through several, maybe not too careful, hands. On the worst examples we found, the grinding had opened up the hidden waterways within the head, obviously making the head scrap.

Do hope this helps?

All the best and take care,

David

[Nick Webster]

And I will add that later heads benefitted from Jowett's own recommendations on tuning the engine for competition which were later put into standard production. The combustion chamber space is much more rounded and shaped without sharp edges, particularly in the area of the spark plug. Of course earlier heads may have been modified, which was the original objective, so it can be difficult to tell without having a couple for comparison. In modern times for the average car these differences will probably be difficult to detect when driving so the older heads are still useful. It follows though that for balance sake the two heads should be the same spec.

Nick