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Learning how to build Lotus Seven replicas...together!
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PostPosted: Thu Jan 01, 2015 11:04 pm 
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Joined: Wed Apr 14, 2010 8:36 am
Posts: 11
I was nudged to get a build log started in the frame building section...so here goes.

I've been slowly collecting parts for about a year. I bought a house about 18 months ago and most of my free time went to remodeling the living room and insulating/sheathing the garage. Now that those projects are complete it was time to get going! I'm glad i finished the garage first as it's a lot more comfortable working in there on cold days with the insulation and a small 5500 watt heater.

I started with a pretty standard build table. Two sheets of 3/4 MDF over 20 ga steel studs. I wasn't thrilled with the grip strength of the steel studs but it's worked just fine so far. Next time I might lean toward just finding a few straight wood studs from the local lumber yard. The "table" is sitting on some very rigid steel sawhorses I found on sale at Menards. I've been comfortable setting the engine/trans on there for fit checks.

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After laying out the bottom rail marks I screwed in some small wood blocks which worked great.

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I've been using the HF 4x6 bandsaw which has worked surprisingly well. I cleanup each cut on the wire wheel and have been very happy with the joint fit so far.

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I have had to cut just a few by hand where the saw can't quite do the miter angle.

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Here's the bottom and front frame all tacked together.

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The 1'' box section I received was much cleaner than the 3/4 stuff. I've been painstakingly wire wheeling each piece of 3/4 and it's a chore.

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Finally all of the main tubes are tacked. This stage was so much fun as there were huge jumps in appearance each day. I was sure hoping the engine would fit without too much issue. I did check rough measurements but it seems hard to know for sure before you try it for real.

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Standard future driver's seat pose. That was a very genuine smile!

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Then came the diagonals and rear diff cage. It's crazy how much longer that took than the main chassis tubes.

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Then the rest of the rear tubes. I got a quote on having the two rear curved tubes mandrel bent locally. $200....each. After catching my breath I ordered some mandrel 90's online and picked up some DOM locally. Oddly it seems the local vendors only carry DOM for round tubing. Total price was about $50. Still steep but much more reasonable and you can't really see the difference. I also made some mods to fit the Jaz 8 gallon fuel cell (similar to Dave Struve's build).

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Then the moment I was most worried about. I dropped the engine in and to my surprise it actually fit quite well!! After playing with it for about half a day i settled on a final location. I ended up putting in the bottom tubes of the tunnel to help guide placement. I wanted to use the stock mounts if possible as I liked the flat mounting points and I'm sure a lot of engineering/analysis went into the NVH of those mounts. The pan sits just under 1.5'' below the frame rail which isn't ideal but I'm ok with it. The F20C is a tall engine so I knew there would have to be compromises and this is going to be a somewhat reasonable street car so I don't mind raising ride height a touch, if needed.

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Fabricating the engine mounts was very straightforward but certainly time consuming. I used the shear at work for many of the chassis plates but the office is closed for two weeks of the holiday season so these were fashioned with an angle grinder and bench grinder. That was a smelly day. The driver's side location ended up intersecting one of the frame rails but between welding in the insert and the plates sandwiched in, I think it will be ok. Getting the engine in and out is tight but I'm just happy it fits!

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Next is fitting the diff and fabricating a forward diff mount. The bottom tunnel tubes are per the Saturn plans but I'm wondering if I could actually make the driver's side a straight piece. It would give just a touch more room on that side where I plan to have a sliding seat. I guess in the UK it wouldn't be as important as the drive on the other side, but my backside would surely appreciate it. Anyone see a reason why that wouldn't work?

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PostPosted: Thu Jan 01, 2015 11:53 pm 
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Joined: Mon Feb 18, 2013 10:57 pm
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So if i was doing mine again, i wouldnt do the tunnel till after the diff and engine where installed. Cant remember if this is possible, but narrowing the tunnel will give you needed space.

Not sure what your plans are for seats, but there are not a lot of options that fit so the more space the better.

Things to worry about in that area.

Where are you putting the ebrake.
Where are you putting fuel and brake lines.
The driver side of the transmission reverse sensor will come in contact with the tunnel wall. You will need to dome the wall around the sensor.
Will any of this stuff interfere with moving parts if the tunnel is further narrowed.

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PostPosted: Fri Jan 02, 2015 12:15 am 
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That's kinda what i was thinking. Right now i just have the lower tunnel tubes tacked in. The front tubes look just about perfect. I forgot to mention that with the F20C there is a clutch slave cylinder and VSS on the driver's side and reverse switch on the passenger side. The VSS and reverse switch are very streamlined and shouldn't be a problem but the slave cylinder sticks out considerably. As a result the engine is pushed pretty far to the passenger side but the trans tail shaft still ends up in the center of the tunnel. The angle is really quite small so I think the driveshaft angle will be acceptable.

So I think i'm ok as-is with the engine side. I haven't bolted the diff in place yet, just set it in for the moment. But a quick glance left me thinking the driver's side of the rear tunnel section could be straight. In essence I would be moving toward the original book dimensions, making me think I should still have enough clearance for plumbing, electrical, etc. So many things to consider even at this early stage! I really appreciate the input.

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PostPosted: Fri Jan 02, 2015 9:29 am 
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Realized after i posted, that you wernt using the miata motor.

My next step would be to get that diff mounted up. If you still have the stock rubber bushings you need to ditch them for something much harder, there have been to many failures of the diff arms breaking. You want the diff having little to no movement.

Here are the suspension photos you requested. Could only get shots of the front. The rear is hidden from view.

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PostPosted: Mon Jan 05, 2015 1:13 pm 
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That is very helpful. Thank you!

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PostPosted: Sat Jan 24, 2015 5:43 pm 
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Please keep updating. Quality looks really good so far. I can't wait to see the finish product.

I've been debating buying a used birkin but they are so few and far between. Your build and Dave's build are very inspirational and starting to make me think I can tackle this all on my own. I was thinking similar setup as yours except k20 or k24 with s2k trans.


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PostPosted: Tue May 26, 2015 12:33 am 
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It had been a few months since I worked much on the car but finally had a productive weekend. I was making good progress but then got a new job and that slowed things down for a while. Then I decided I needed a mill and ended up buying an old Bridgeport. That took a couple weeks to get set up.

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After that I went to Europe with my girlfriend for a few weeks.

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Then when I got back we decided to buy some day old chicks and I had to build a chicken coop and shortly after I picked up a tig welder.

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Enough excuses...finally some car updates!

The first thing I worked on was a mounts for the differential. I replaced the two rubber mounts with polyurethane replacements. I also modified the lower one in the lathe so it's just a large flat poly washer. I then machined two steel disks for support from the bottom side. Much more rigid than the original rubber parts. Then I focused on the front diff mount. This one I had been picking away at for a while. I started with a 1.25'' sq bar and milled away what is essentially an adapter from the miata diff to a standard 1/2'' heim. There are also some "bushings" in there to keep everything centered. One is a machined hole so I could have a light press fit and the other was rough cast... JB Weld to the rescue. I'm really happy with how it turned out but it sure ended up taking longer than I thought.

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Next was the transmission mount. The S2000 trans is just huge. There's no other way to say it. Likewise, the trans bracket and mounts are huge and there's no way they would fit. I found a nice compact energy suspension mount that I think is for GMs. I did some major surgery on the factory bracket and then fabbed up a plate for the car. Like everything else, it took longer than expected but it works just like I hoped. I didn't grab a pic but I also bought new engine mounts. The originals had long studs going out the bottom. That required lifting the engine a few inches which made installation and removal a bear. The new ones have through bolts so I can just remove the engine and trans bolts, slide both forward a few inches and they come out with ease. I knew using this drivetrain would cause some frustration, but I'm happy to have this small piece finished. Plenty of clearance all around and having it finished is helping with my motivation to keep focused on the car.

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With the drivetrain components finally set, I was able to knock out the tunnel in relatively short order. I did end up changing the driver's side to the "book" straight tubes. I didn't see any need to keep the angled setup and I read it can cause issues with a seat slider. The passenger seat will be fixed so it's a non-issue on that side and it isn't optional there anyways.
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