Group Build: Lotus S3 Twin Cam

[MPWR]

Finally I get started! There's just about 4 1/2 months left until we plan to wrap up the group build- so time to get going. Fortunately, it's a small kit. (Hopefully that will help.)

I thought I had a good idea what I wanted to do with this build when I first suggested this kit for the group build. I'd been thinking something crazy and modernized, big wheels and BMW engine up front. I originally got this kit as an excuse to do something other that the factory stock builds I tend to stick with. But of course the more I got into researching this one, the more facinated I got with actual Lotus and Caterham Sevens. Well OK , maybe I'll eventually get to doing a crazy hypothetical Seven- but for now, this one is going to keep to a good measure of authenticity.

I got this book

used cheap on Amazon, and it's helped me get sorted out as to the histories of these cars, their engines, and what the real difference between a Lotus 7 and a Caterham is. Good stuff, if real Sevens are your interest I can definately recommend it.

After lots of consideration, I decided that my Seven is going to get built up as a Lotus Series 3 with a Lotus Twin Cam engine. The Series 3 is the definitive version of the 7. It's the version that Caterham continues to make today. The Twin Cam was a Lotus developed and manufactured upgrade of the Ford Kent- the engine that went into nearly every 7 (in some form or other) until Ford stopped making it and Caterham had to switch to Vauxhall powerplants in the early 90's. During the years that it could be had, the Twin Cam was considerd to be the engine to have in your 7, be it an S3 or S4, Lotus or Caterham. The Twin Cam was eclipsed only by the rare Cosworth BDR as the ultimate version of the Kent powered 7. But, more on the engine as I get to it.

Lately I've managed to get my hands on the kit I'll be copying the engine from, and HLJ has just notified me they've finally got my wheels in and are sending them out to me (so I should have them sometime in early February )- so now I can really get to work.

On to the the kit itself.



Here it is, Tamiya's modest yet terrific little 1/24 Lotus 7 kit. As depicted in the kit, it's a Lotus Series 2 with a Cosworth tuned 1300/1500cc Ford Kent 'Sidevalve' engine. The sidevalve (also called the pre-crossflow) had the intake and exhaust manifolds on the same side of the cylander head. Lotus made about 1300 of the Series 2 during the 1960's. In '68, a few S2's were made with the new Crossflow configuration of the Kent. Lotus then began production of the Series three, and the Crossflow was availible in the Series 3 up until 1998.



Any rumours of me skipping buying the kit and machining the whole thing out of aluminum are as you can see exaggerated. As a number of you have already discovered, the kit is tiny- but nicely detailed. Part of the reason the kit is so inexpensive is that the body/chassis part is attached to one of the conventional parts trees- no expensive specialised slide mold needed. Not alot of parts, but what's there is good.

To start off, I'm removing the wing fenders. Crazy Modeler's thin PE saws are perfect for this.



Sevens were made with either wing fenders (as depicted in the kit) or cycle fenders. A factory Lotus S3 would likely have wing fenders, but cycle fenders have been a popular conversion- the wing fenders appearently generate alot of lift. These days it's hard to get anything other than cycle fenders on a Caterham 7. I'm converting mine to cycle because I like the look, and it will make the 'painting' process I have in mind for later easier.



Hack, cut, saw.

The rear fenders also come off (they will have to be widened for the S3 configuration), but first some locator holes are drilled.



This will (hopefully) help me locate the widened fenders on the body when they will get reattached.

The bump on the side of the bonnet gets taken off.



This is supposed to be an intake scoop for the carburators. But as my engine will have its carbs on the right side, there won't be an intake on the left.

Even the battery gets removed.



This will make room for the heater installation.



There. As anyone who's built a Fujimi enthu kit knows, more parts = better kit = more fun, right? I'm going to squeeze every dime of building enjoyment I can out of this little $10 kit! But I guess that means that sooner or later I'm going to have to get to actually putting this mess together....

[Martin S]

Looks like a good start there MPWR.
I'm really looking forward to see the work of the group build starter himself.
But the fact that it's only 4,5 months left makes me a bit stressed to finish mine..

[OrangeR]

Nice!
Great start, I have started mine and also taken the wing fenders off with the help of my kotobukiya saws but wasn't brave enough to cut the rear fenders... you have shown me the way!
Thanks for sharing.

[MPWR]

Yeah, March seems long enough away now, but I expect it will approach with frightening rapidity. So on that note, I can stand it no longer- time to start the engine!

The Lotus Twin Cam engine originally powered Lotus's Elan. Lotus didn't at first offer it in the 7, and insisted it couldn't be fit into the engine bay. However this was disproved by a customer who installed one himself, and Lotus quickly realized the potential this engine offered the 7. Unfortunately, the production span of the Lotus S3 was just about over. Lotus made just thirteen of the Twin Cam powered S3 in 1969 before they killed the S3 for the new S4. The Twin Cam was also a popular choice in the S4- but the S4 itself was never particularly popular. Lotus soon dropped the Seven all together. Caterham then stepped forward and aquired the rights to build the Seven. They produced a few dozen of the S4, and then reverted back to the S3 which they've been making since. The first engine Caterham offered in their 'new' S3 was the Twin Cam- and they made more than 300 until Lotus stopped producing the engine.



One of the reasons the Twin Cam remained in production after Lotus stopped the 7 was that it was being used in the later models of the Lotus Europa. As it turns out, Tamiya thoughtfully enough produces a rather nice kit of the Europa- and it happens to include a decent Twin Cam to go in it!



So I had an excuse to get another cool old Lotus kit.

Here are the kit engines-



Twin Cam (with overly shiney valve cover) on the left, Sidevalve on the right.

The big difference is the cylander head, but the engine block itself is the same.



Remove the heads and transmissions along the grid lines on the cutout mat and you can see the family resemblance.

Here's the Sidevalve mounted up,



and here's the Twin Cam in it's place.



Looks simple enough, right? That would probably be the logical way of going about it. Granted the mid-engine transmission on the Europa engine would have to be replaced, but I have sharp little saws so I could probably do a transplant- and even have a mid-engine Crossflow left over to put in the Europa (if ever such a thing was done ). I'm sure if I had any sense, this is how I would go about it. But instead, I have machine tools.

I used to make my living in aerospace engineering- so I'm quite accustomed to the $5000 answer to the $50 problem. I think it was best summed up by John F. Kennedy, when he famously said "We choose to go to the moon... not because [it is] easy, but because [it will be COOL!]". (Well, we all know that's what he was thinking. )

The first step is the valve cover. It needs to look the part pretty well as it will certainly be easily visible. Fortunately, the Tamiya Europa part is excellent (aside from being covered in that ghastly chrome!).



After studying it with calipers and noting its dimensions I was ready to start. I began with a 1x.5x.25" block of aluminum, and shaped it to general dimensions with a fly cutter. Sure an end mill would work fine, but for this kind of work I love using the fly cutter- faster, easier, and a much better finish.



The blue on the raised area is just layout fluid. Often when designing and making a part like this a good way to do it is to start with your block of material, paint the top with colored layout fluid and scribe the design of the part you're going to cut. I painted the top blue, drew the line I was going to cut to, and removed everthing up to it.

The next step was done with end mills.



The center slot (where the spark plugs go) was cut with a 1/8" dia end mill. Happily it was exactly the diameter I needed to make the nice radiused end of the slot. I then switched to a 1/16" dia end mill for the radiused cuts along the sides, and to cut all the bottom edge flanges (which made this a very complicated little part! ) The edge flange on the center slot was cut under radius with the 1/16, and was corrected later with a small rat tail file.

Then the holes for the hold down bolts and oil filler were drilled, the edges were rounded with files, and the part was brushed to give a good paintable surface.



Seems to look the part pretty well! Some Twin Cams had ridges running the length of the cam covers, and some (like in the first pic above) did not. I kinda like it without (I think it has a nice unadorned, purposeful look about it), and it simplified the machining a bit.



Next will come the engine head itself.

[rsxse240]

damnit, not another blue seven? you guys make me SICK with envy!!! that is a fabulous valve cover, I can't wait to see the rest.

[Layla's Keeper]

You're doing some excellent work, as always, on this kit, but it really wasn't necessary to buy a whole Tamiya Lotus Europa kit to get the Twin-Cam....

http://www.rndunique.com/rnd_displayitem.cfm?pk=108


The Lotus 1600cc Twin-Cam, by Mini Exotics.

[auw12]

ill always follow your thread Mr.MPWR~~

[robrex]

Awesome work on that head!
I just got the go-ahead from my wife to buy a milling machine and seeing this thread just excites me even more!

[deltableh]

Gorgeous...

[rsxse240]

Originally Posted by robrex

Awesome work on that head!
I just got the go-ahead from my wife to buy a milling machine and seeing this thread just excites me even more!

yeah, I've had the "go ahead" for about 5 years now, but I'm just to responsible, and look out for the family to much, so guess what? I still don't have a mill/lathe.

[eph2]

Wonderfull Detailing!!!

[Ferrari TR]

Nice!
Looking fwd to more of this insanity.
I mean that in the nicest way.

[klutz_100]

Whoa! Nearly missed this!

Bring it on!

[willimo]

Woah!

[gionc]

Missed! Me too!

I start to hate you buddy as usual stunning machined stuff.