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Learning how to build Lotus Seven replicas...together!
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PostPosted: Thu Nov 01, 2007 6:50 pm 
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Posts: 91
Location: Central MA
I've been watching around here for ideas and info once I decided to build a 7. I took the leap this October and purchased a partially built kit from a fellow forum member who decided to go another direction with cars. At this point, my build will consist of the following components. I will continue to update things as progress continues - this will probably be a very slow build though.

The chassis is a book build, originally designed for a Suzuki Swift motor, Samarui tranny, and solid rear axle design. I considered moving forward with this build but after researching the power potential of the engine provided, I decided it wouldn't work for me so its up for sale.

After finding an M42 relatively close by for $100, my decision to sell the swift engine was done - I was thrilled to find that the tranny was attached and it didn't cost anything more :lol: .

So my build components will be as follows:

Book build chassis
BMW M42 engine
Getrag tranny
BMW 4.10lsd differential
BMW rear axles
Custom uprights designed around E39 bearings since they bolt into place rather than being pressed - also allows for a bit more flexibility when designing the suspension
E30 steering components
I'll wire the car from new wiring and universal fuse boxes with the exception of the core engine harness components

I am currently parting a BMW E30 track car which is the source of my steering components and a few miscellaneous parts. As a result, my cost for the project currently breaks down as follows:

$1000 chassis - included nose cone and scuttle
$100 drivetrain
$50 M3 pistons

-$300? existing engine/tranny and rear end componets

Net would then be $850 I may make a run for the Grassroots Motorsports $2009 challenge series if I can continue with good $ luck.

My suspension setup will consistent of a bellcrank design using double adjustable coilovers - my preference at least. I suspect and hope that my most expensive components are in the suspension and safety devices.

The other area of some expense will be the engine rebuild. The M42 is known as a relatively lively little engine in the E30 and can be modified relatively quick to produce a bit more ponies. Rather than simply rebuilding using the existing components, I'll be boring the engine from 84mm to 86mm using M3 pistons from the E36. I'll also install a later version M44 crank to increase stroke slightly. The intake is a 2 piece design which allows for easy adaption of individual throttle bodies since you already have the manifold with injector bungs in place. These changes along with an SMT6 piggy back ecu unit will allow me to better tune the engine. In the end, I'm thinking the engine will be around 170-185hp if I'm lucky.

I'll be lightening up the entire drivetrain where possible to get as close to 350lbs as I can - this might be a stretch for the engine/tranny setup, but we'll see.

Haven't decided on wheels yet, but I'm a fan of 15" wheels so I'll likely target a 15x8 wheel size as the basis of my suspension designs. I'll post pics of all the parts later but figured I'd start the log now since I'm so syked about how things are coming along with parts acquisition.


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PostPosted: Sat Dec 29, 2007 3:09 pm 
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Location: Atlanta, GA
Hey, no one else has posted so I guess I may as well.. I'm very interested in your build as I have an m42 e30, and was considering between an e30 donor or a miata donor.

Good luck!


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PostPosted: Sun Dec 30, 2007 11:15 pm 
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Location: Central MA
I'll be posting more soon as I've just finished parting the E30 to the point of removal from the garage. A new addition to the build is a mini supercharger. It'll be a good little screamer with that added.


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PostPosted: Wed Apr 30, 2008 7:07 pm 
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Location: Clemson SC
hows the build going? :wink:

if i may pick your mind for some ideas, how are things going with the E39 idea going? i think this idea has a lot of potential, but the one problem i see is the different diameter of E39 hubs vs. most other BMWs (~74mm vs. ~72mm)

my theory is ot use E39 front hubs with E36 rear hubs get a set of wheels for the E39 and use hub-centric rings for the rear



Thanks for the help and good luck :wink:


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PostPosted: Sat Jan 17, 2009 2:52 pm 
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I too drive an M42 powered e30 and have been interested in adapting an M42 into my future Locost build. I'm currently looking into running all of the e30 running gear with custom axles mated to miata uprights. My chassis design is based on a +442 with more triangulation. I look forward to seeing your progress on the build as it seems similar to what I want to do.


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PostPosted: Mon Mar 21, 2011 7:54 pm 
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Joined: Sat Sep 08, 2007 8:45 pm
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Location: Central MA
So this thread is now back from the dead after a long pause in my ability to work on the project. I've been doing a lot of contemplating (selling the project) research (what to buy or build), planning (what will my suspension look like), and purchasing (tools and books). After having all that time I decided to keep the project, and build the car as I had originally intended. I've purchased several missing components for the build, including both parts and tools, and will likely be able to start posting pics in a couple weeks of the frame in my garage for the first time in over a year. I dug it out from under cover, and was shocked to find it looked almost new - that POR compound used originally worked very well.

I will begin to post here as I get moving for those interested in a BMW based build.


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PostPosted: Wed Apr 13, 2011 8:33 am 
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Location: Central MA
Work has started. I'll post some pics soon. I've been spending most of my time on getting my engine design down. This car will be a true mongrel of sorts.

Since I had originally planned to build a BMW engined locost, I targeted the lighter 4 cylinder engine used in the early 3 series. In naturally aspirated format, it puts out about 130hp, and is relatively compact. I was able to mate this to my 6 cylinder LSD diff from an M3, which is geared well for the 4 cylinder. However, I wanted a little more power, so I decided to add a supercharger. I knew this would require a reduction of compression since my engine was a 10:1 CR, so my engine building became somewhat a priority so I could make sure everything fit with the added bulk of a roots style blower (from a Mini Cooper).

So my mongrel engine is almost finished in design. BMW's are interesting in that they use a wide variety of strokes, but rarely seem to vary in rod length and piston bore size (although compression volumes vary as well as shape). Fortunately, most BMW's also use Mahle pistons, and this company produces excellent specs on their website. After about an hour of surfing their site for data, I was able to find the right combination of parts to make the compression much more reasonable without having to machine a single part. The end result is the following:

The original M42 block (84mm bore)
The M44 crank (increases stroke from 81mm to 83.5mm)
The M42 rods (these are forged, M44 are cast - both are 140mm)
The M54 pistons (similar compression volume shape, but come from a 6 cylinder and sit a little lower in the block)

When all is said and done, I increased my stroke by 2.5mm, and lowered the compression to around 9:1 - 9.6:1 depending on head gasket thickness. I'm estimating that I can get the engine to reach approximately 200hp pretty easily with the right boost level and engine management tweaks.

Also, my welder came in, my protective gear, rear trailing arms to cut up for the uprights, axle shafts, and drive shaft. I should be able to begin chassis modifications to fit the engine and rebuild my front/rear suspension in the coming weeks. I doubt I'll be posting much, but as things develop, I'll try to get the updates out with pics as time permits.


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PostPosted: Wed Apr 13, 2011 7:24 pm 
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Congrats on the engine build progress...That's pretty cool that you can mix-n-match BMW engine components like that. :cheers:

So does your earlier reference imply that the E30 and E39 use the same splined section (diameter, count, and length) on the hubs/axles such that they E30 axles will slide/bolt right up to the E39 hubs? It's always great for crazy project building when the manufacturers are kind enough to maintain commonality of part design between multiple generations...Unfortunately it's not often able to be a more common practice.

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Also follow my build on blogspot, tumblr, or instagram and twitter (GarageOdyssey)


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PostPosted: Wed Apr 13, 2011 9:54 pm 
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Location: Central MA
Driven5 wrote:
Congrats on the engine build progress...That's pretty cool that you can mix-n-match BMW engine components like that. :cheers:

So does your earlier reference imply that the E30 and E39 use the same splined section (diameter, count, and length) on the hubs/axles such that they E30 axles will slide/bolt right up to the E39 hubs? It's always great for crazy project building when the manufacturers are kind enough to maintain commonality of part design between multiple generations...Unfortunately it's not often able to be a more common practice.



Never got that far - just decided I'd stick to the e30 rear and make my own uprights using the hubs at both ends. I may still look to see if the splines will work, but at this point I'm inclined to stick with the e30 for cost purposes (they're cheaper to maintain and my base cost was only $60 - which is more than one bearing on the E39).

Daniel


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PostPosted: Thu Apr 28, 2011 7:49 am 
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Location: Central MA
So I was able to get the pistons installed into the block and validated my measurements. Below is a pic of the M54 piston in the M42 block, with the M44 crank. The piston sits approximately 2.08mm lower in the block than a stock piston, but it has no dish in the piston, so the compression actually won't change significantly, but increases stroke slightly and will allow me to lower compression to a more reasonable level for boosting with a supercharger. Now I can start to rebuild the engine temporarily so that I can fit it into the chassis and continue with that process while the engine is begin rebuilt and cleaned up a bit.

Image


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PostPosted: Thu Apr 28, 2011 10:55 am 
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Now I'm not one to advise you either way but. ..
I've seen debates on "squish zone" and piston ring loading when changing to flat tops.
I would think that a flat top would load the rings a bit more since theres a larger contiguous area between the rings and the head, what true effect that would have is probably minimal in a pleasure use vehicle.
Whether or not having a squish zone is a big difference is a matter of opinion it seems.
I don't see many engines without them anymore. ..

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For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett


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PostPosted: Thu Apr 28, 2011 1:23 pm 
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Location: Central MA
oldejack wrote:
Now I'm not one to advise you either way but. ..
I've seen debates on "squish zone" and piston ring loading when changing to flat tops.
I would think that a flat top would load the rings a bit more since theres a larger contiguous area between the rings and the head, what true effect that would have is probably minimal in a pleasure use vehicle.
Whether or not having a squish zone is a big difference is a matter of opinion it seems.
I don't see many engines without them anymore. ..



These are from the BMW roadsters and 3 series cars that were made into the year 2006, so its not an old design. I'll trust BMW did the right thing but have often wondered why they departed from the dished pistons with better squish zones in some model engines. The M54 was known to be a great little engine though.


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PostPosted: Sun Jul 31, 2011 8:28 pm 
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Location: Central MA
Have started back to work over the past couple weeks, mainly breaking down the engine, checking tolerances, and getting the engine block cleaned and ready for reassembly. I'll be finishing off the honing this week, and hope to begin the build-up once the bearings arrive. I've run into a slight problem finding piston rings for my build though. Not sure what to do about that yet, but I'll figure it out as it progresses. Here's a pic of the cleaned block and then after painting. Once I get the bottom end assembled, I'll start on the head. Then I can start playing with the mounting and get the chassis back in progress. I've been hesitant to do much without the engine reassembled since I wanted to get the weight and position of the engine nailed down before I started to play with suspension design.


Attachments:
File comment: Painted block - still a little wet.
004-2.jpg
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File comment: Cleaned rods - also in ultrasonic.
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File comment: Piston after ultrasonic bath.
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005-2.jpg [ 23.53 KiB | Viewed 3337 times ]
File comment: Engine after cleaning the block.
002-2.jpg
002-2.jpg [ 104.62 KiB | Viewed 3337 times ]
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PostPosted: Sun Jul 31, 2011 9:31 pm 
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Good stuff! That engine work has me thinking about rebuilding mine, but I've decided to get the engine running (wiring, fuel) then focus on the chassis/suspension first. If you don't mind me asking, how did you clean up the block?

Looking forward to more progress.

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00 Impreza OBS - RIP
81 Rabbit 1.6D
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PostPosted: Sun Jul 31, 2011 9:59 pm 
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Location: Central MA
A combination of bead blasting and pressure washing with detergents. A bit of a messy job, but the results were close to having it hot-tanked. Just hope I was able to wash out all the material inside the water and oil passages.


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