Series 3 heads

[David Kemp]

The heads below are for sale, are they series 3 heads?
If not how do I spot series 3 heads when I see them?

received_996894625846990.jpeg

[David Morris]

Hi David, I expect others will come up with casting numbers that identify early and late heads? All I can offer is that the late heads won't have any sign of the rivets that secured the original tin plate covers that were to hold the bakelite plug covers on the top surface of the heads. Even though the tin plate covers might have been removed later, these early heads showed where the rivets used to be fitted around the edge. Also, the later heads were made even-handed, so that you could fit them on either side of the block. This meant that what was a waterway could have a frost blanking plug fitted, or the opposite. What was needed to enable this to work, was a tapped hole in the head on both the front and rear of the head, to take the stud to hold the water transfer casting. The later heads had both these tapped holes. Early heads would need work, to create the tapped holes.

The most important place to examine, before purchasing, is the narrow part of the casting between the exhaust and inlet valves. This is fagile and we have thrown away piles of heads that show evidence of small cracks here. You might be able to repair with replacement hardened valve seats, but this carries risks and is best avoided.

Hope this helps?

All the best, David

[Forumadmin]

Cracks across the narrow part between the valve ports are frequent but not terminal as inserts usually cure.

[David Kemp]

Heads have casting numbers below
301050
20950
Both have plates riveted to them for the bakelite plug covers.
Both have bathtub combustion chambers not the heart shaped chamber.
Are they better than the average style head?

[Keith Clements]

I used Members Services to search the archive using 'casting numbers', 'Head Casting' and various other combinations of search criteria, but I could not find any relevant documents. I have a faint recollection that someone at sometime did contribute on the subject but perhaps the OCR did not correctly interpret the scribblings. Anyway have a go yourself. My first search found over 1200 hits but that would be documents with both casting and numbers in the document. Using 'casting numbers head series ' reduces it to 417 hits.

I am working on a search engine with more intelligence on the ARCHIVE test server jowett.club. This server may OCR the documents again with hopefully better results.

[PJGD]

I am not aware that any Jowett head had what I would call the heart-shaped chamber, as is shown in the original Weslake patent as Figure 2, and was subsequently adopted by Austin/BMC in their engines. In place of the Vee of the heart, Jowett used a "squish shelf" to promote turbulence. Note that Figure 1 of the patent indicates its use with Siamese inlet ports, and there is even what I take to be the balance pipe port shown.

Note however that the early Jowett heads did use the scallop as described by Weslake in the chamber side wall adjacent to the inlet valve particularly, to minimize gas flow restriction as shown in Figure 3 and 5. Later heads were modified in various small ways as described in the JCL Competition Tuning Notes publication for the Jowett Javelin.

GB_637209_Harry Weslake_Jowett Chamber.pdf

[Keith Clements]

Interesting Philip that it was possible to patent such components of a design. Even more interesting that it was possible to police such a design and obtain patent fees from it.

[Srenner]

Most every discussion I have had on "better" heads focuses on who cast the head. I have seen 3: no identifier, Qualcast and Chromidium. Chamber shapes vary a bit even within manufacturer. Chromidium have an extra small ridge internally in the water jacket at the bottom, I think in all cases.
In my experience, early heads have rivet holes for the cover plate and very late ones do not.

I ASSUME later ones are better. Neil Moore opined there is really not much difference. Getting an equal volume in all the chambers is the goal.

I have run repaired cracked heads for decades. Most of the repairs were between the valves. The depth of the crack determines the likelyhood of a successful repair.

Also I have raced Sprites with A-series heads for over 30 years. The Heart shape is generally the least desirable chamber shape for power and any protuberance near the valves get removed.

[PJGD]

Keith; it is the claims section of the patent that is important, and in this case Weslake was only claiming the scalloped side walls and not any of the other aspects of the illustrated design. The scalloped design allows the largest possible valves within a given bore diameter and hence good gas flow in and out of the cylinder. It also redirects some of the flow towards the center of the cylinder which can assist turbulence, which is usually a good thing. However, as designed the scallop works for the standard factory valve lift, but a higher valve lift might start to restrict flow again.

The ridge that Scott mentions in the water jacket near the bottom is a strengthening web feature on the JCL cylinder head drawing, so it should appear in all heads, and can be seen in this photo:

Sectioned Qualcast Head.jpeg