Lotus Twin-Cam Cylinder Head Development Version History

[rgh0]

To aid in identification of various versions of the cylinder head I have started this thread and attached the development history as I understand it. I will update it with photos when I get a chance and also any other information that comes to light when people find interesting old heads

cheers
Rohan

Lotus Twin-Cam Cylinder Head Version History
Rohan Hodges 17/7/14
This is the best I can do based on all the usual reference sources (e.g. Miles Wilkins book on Twin-Cams) and posts of photos and histories by various people over the years. I will add photos to illustrate the various versions when I have a chance.

1.First prototype and development heads were sand cast by Birmid and also it appears Williams and Mills and had many variations including some having a centre rib in the plug well and some not, different length intake runners, the addition of the breather vent oil knockout chamber, only 4 rather 5 bearings per cam and the thermostat housing on the inlet side and bolt on inlet manifold. First prototype ran October 1961 and versions were developed for racing and as part of Elan and Cortina development programs

2. Type 1 Heads ? First production heads, by now the same for the Elan and Cortina were die cast by Williams and Mills and machined by JAP and introduced February 1963. They had half- moons down the centre well and square reinforcing blocks on the inlets and a centre rib in the spark plug well between cylinders 2 and 3, not known number of these produced. At some stage Lotus changed to back to sand casting but it is not clear if this occurred with the change to the type 2 heads at around engine LP 6075 in 1966 (earliest engine number type 2 head located?) or prior to that time within the types 1 head production run.

3.Type 2A heads- Earliest versions of type 2 Heads had no reinforcing webs on 1 and 2 inlets, when these webs were introduced is not clear. All type 2 heads did not have the half- moons down the centre well and had larger diameter intake runners than the Type 1 heads.

4. Type 2B heads The next version added the reinforcing webs on the inlets, (not known when) and added the cross drilling behind no 4 exhaust port for oil drainage and / or sand removal from castings (not sure if these changes occurred separately or the same time). Both these changes appear to have been in place at latest by around 1968 and the 6 bolt crank engines introduction.

5. Final versions were variations on the type 2B heads with the Stromberg version in 1968 and machining changes for the Big Valve engine in 1971 and modification for Twin-cam Europa with the extended inlet cam installation driving the alternator in 1971

[trw99]

Well done Rohan, excellent effort.

Engine blocks next?

Tim

[rgh0]

Hi Tim you read my mind. We have a good collection of engine block version history here also that greatly expands upon the write up on the Lotus Cortina site that has been the definitive summary for many years.

One day I will get around to it if some other anorak does not beat me to it

cheers
Rohan

[rgh0]

I have converted my history to a pdf document and added photos of the various versions. Any extra information to add to the story always appreciated.

I want to add few more sections covering competition modifications and developments since the end of Lotus production but that will take a little while to do.

cheers
Rohan

Lotus Twin Cam Head version History.pdf

(562.67 KiB) Downloaded 3857 times

[englishmaninwales]

Rohan
One of the Type 1 CHs, as described in your very helpful text with the inlet side thermostat housing and variable length inlets, appeared on eBay UK last winter, being auctioned as a 'standard TC cylinder head'. I sent a message (as did other people) to the seller advising that it was an early prototype, and the description was changed. I recall the auction ran and it was sold. Maybe someone on here bought it?

Thank you for collating this interesting information.
Malcolm

[LCRJ]

Hi Rohan,
It?s great work, very nice information and quite interesting for me.
I?ve seen the very early prototype head in Lotus 23 here. Yes, It?s still alive! Also you can see with Later preproduction head on Road & Track Sept.,1962 or a book?The history of the Lotus 23?.
I think the key identification feature of the early type 1 head have two holes between inlet rib 2 and 3 for bracket(Accelerator shaft support to Maniforld:parts#26S026 Maybe until 1963?). Also the early type 1 head must be date stamp on bottom face.
I?m interested in the picture of the another early type 1 head with a boss in front of the No1 spark plug. I've never seen this type before. It's looks like has two holes between inlet rib 2 and 3. So it must be early one.
Ordinary type 1 head have a brass negative screw in front of the No1 spark plug? My type 1 head has one.
Please keep up the good work, Rohan.
Thank you again for the information.
Hiro

[Elanintheforest]

Great job, Rohan. Here are a couple of additional bits for consideration.

Firstly, LP008, cast on 15th Feb 1963. A production head, but it doesn't have the front half-moon casting.

It also has no cast-in manufacturing details on the back of the head , but 'LM+6' stamped on. Was this a case of using what was essentially a prototype head as a production unit? Will we ever know??!!

Next is LP189, cast on 9th March 1963. I found this on my S4 Elan a couple of weeks ago, and it was converted from Strombergs to Webers in the early 1970s. The owner ran a Lotus garage in Yorkshire, so I guess had this head hanging around, left over from a dead and quite early Lotus Cortina.

As Hero points out, it has the date of casting , and the two holes on the inlet manifold web. It also has a cast in manufacturers mark, showing '26E 311', then underneath 'WM', and underneath that 'LM8 WP'

Last thought....probably worth mentioning the 'N' stamped on the big valve head.

Malcolm, I went to have a look at that pre-production head and took many photos of it...Rohan has a couple in his write up, and I can post more if you're interested. The vendor deals in some very exotic classic racers, and had this head with a job lot of spares that came with a Lotus 23 a few years earlier. It sold for very little money!

When this is complete, or as complete as can be, I'll pop in on the Lotus Cortina Information website as well, if that's OK with you Rohan.....full credits of course!

Mark

[LCRJ]

Hi Mark,
Thank you for the information.
Now I understand the early type 1 head with a boss in front of the No1 spark plug is very early one.
I would like to see your pictures of pre-production head. Include cam cover?
Have you seen a pictures of pre-production head on early Lotus Elan?
Kind regards,
Hiro

[Elanintheforest]

Hi Hiro
Here are some photos of the early head. It didn't have a cam cover unfortunately.

I've also put on a cutaway drawing of the Twincam dated in June 1962 with the thermostat housing on the 'production' side, which put this prototype head earlier than that.

Mark

[englishmaninwales]

Mark
Thanks for posting the remaining pictures. If it went for very little money at eBay auction I wish I'd bought it, purely to admire it!

Malcolm

[SJ Lambert]

It would be fantastic to see it nestled in an early 23!!

From the earliest development type head to what I presume is one of the last 1971 ? Type 2B head castings.

Here's a few of a Stromberg Europa head with John McCoy's stage 4 Weber four port modification.





Oops, sorry about the Cosworth reference there!!

[KevJ+2]

I did think of posting this as a separate question but maybe it's relevant to the head development.
Today I filled my rebuilt engine with oil and gave the cams a bathing at the same time. I noticed that number 4 inlet and exhaust 'wells' overflowed and did not drain away. My head is an early half moon (LP 1916) and wondered if this has any relevance?
It's been about 24 years since my last twincam rebuild but can't remember if the same thing occurred.
Regards,
Kev.

[trw99]

LP1916 would have been from Mar-May 1964. Not in my records for an Elan so perhaps ex LoCort.

Tim

[billwill]

Comment deleted as irrelevant.

[rgh0]

I did think of posting this as a separate question but maybe it's relevant to the head development.
Today I filled my rebuilt engine with oil and gave the cams a bathing at the same time. I noticed that number 4 inlet and exhaust 'wells' overflowed and did not drain away. My head is an early half moon (LP 1916) and wondered if this has any relevance?
It's been about 24 years since my last twincam rebuild but can't remember if the same thing occurred.
Regards,
Kev.

I have never examined the drainage of a type 1 head in detail as I don't have one but the cross drilling at the back in the later type 2B heads that I show in my pdf file enables the rear of the head on both sides to drain oil. My understanding is this was done to either aid removal of sand from the rear of the casting and / or to aid oil drainage so that you did not get oil leaking down the valve stems and producing blue smoke of start-up.

cheers
Rohan