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  #141  
Old 10-03-2018, 07:21 PM
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heinke heinke is offline
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Post Chassis Mods for Transverse Transaxle

In parallel with building the fuel tank, Iíve been modifying the chassis to make room for the transaxle. Before getting into the details, Iíd like to make the point that this chassis was originally designed for a longitudinal mid-engine placement. So these modifications arenít because the was anything wrong with the chassis, they are because Iím using it for a transverse mid-engine placement. When I purchased the chassis, I knew some modification would be required so none of this was a surprise.

As a reminder, the transaxle is a custom build and itís being designed and built by a friend thatís located in a different city than I am. So my friend Pete put together a ďmock-up transaxleĒ so I could try it out in the chassis and provide back to him some measurements/angles needed for positioning the final drive portion. The mock-up unit consists of scrap aluminum, a scrap transmission case and plywood. While quite crude, it does communicate key information that cannot otherwise be described on paper or verbally.

Here is the mock-up transaxle sitting in the chassis after Iíve cut away some interfering metal.



The main interference was located on the chassis driver side between where the A arms attach. For longitudinal mounted drive train, this chassis member is used as a motor/transaxle mount. It feels a bit weird taking a Sawzall to a brand new chassis but it makes quick work for removing the interfering metal.



After a few iterations of test fitting and cutting away more metal, I had the transaxle in a good location. I also had to cut away a section in the back rear corner of cockpit.



I then mocked up in cardboard a replacement for the metal cut away.





You can see thereís not much room for this important chassis member between the lower A arm and the transaxle case. So my plan of attack is to make a connector piece to weld in and a second piece to glue in.



Hereís the glue in piece.



After welding Ö



And grinding the welds off in preparation for gluingÖ



I think this will be plenty strong given that I now have a ĹĒ aluminum member now connecting the frame rails and tying the upper and lower A arm mounts together.
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  #142  
Old 10-09-2018, 01:28 AM
76mx 76mx is offline
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As long as we are sharing information, let me put two cents in here. Years ago, when we were racing nitro burning Briggs and Stratton go-karts, the metal fuel tanks were prone to cracking at the carburetor. Test them with water all week, everything is fine, take it to the racetrack, fill it with fuel, and the header catches it on fire at the leak. I learned that any fuel would go through a crack that water would not, but it never made any sense to me. Look at any fuel molecule (well, look at any diagram of one) and it is as long as your arm. Then look at a water molecule and it is a simple H2O. How does that molecule not fit through a crack and the one as long as your arm will? Only recently I have learned the answer. It is the surface tension, not the molecule size that is the critical factor. Think about a drop of water on a surface and how it makes a dome. Then think about a drop of fuel and how it flows flat. There is much less surface tension to hold it together and it will leak where other fluids will not. On another note, I take it personal what people do with and to my babies, and Joel is doing a fine job with that chassis.
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  #143  
Old 10-09-2018, 12:36 PM
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heinke heinke is offline
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Post Chassis Mods for Transverse Transaxle (part 2)

In this update, Iíll show the last steps in completing the modifications to the rear suspension mounts. These mods were required to provide clearance for the transverse transaxle.

Iím using the same Loctite brand methacrylate based structural adhesive for bonding in this situation as was used on all the original glued joints in the chassis. I submitted a question to Henkel (parent company for Loctite brand) asking if there is a recommended ďgapĒ between the bonded aluminum pieces. The prompt response from the Henkel engineer was, ďno induced gap yields the best results.Ē

So after spreading a thin layer of glue over entire surfaces of both pieces being bonded, I used lots of clamps to try to minimize the gap as much as possible. I had to quickly remove the glue squeezed out after clamping as the 15 minute work time glue sets up fast.



After 24 hours to let the glue achieve full strength, hereís the result.





The last step in the modification was to put the A arm mounts into double shear, i.e. mounted to chassis on both sides of the heim pivot point. While Iím confident they have the needed strength in single shear, putting them in double shear was easy, provides some extra rigidity, and could be done without adding much weight. Al 6061 angle in 2.5 inch by ľ inch stock was used to fabricate the mounts.



These will be bonded to the frame rails using structural adhesive. I purposely made them a bit oversized to give plenty of surface area for the bonding joint.
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  #144  
Old 10-16-2018, 10:23 PM
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Post Fuel tank installation

Now that the fuel tank has passed leak testing, I decided it was time to install it in the chassis. The fuel tank mounts in the chassis backbone and occupies 100% of the space between the front and rear bulkheads. The fuel leak testing had bowed the tank sides a bit and I needed to push them back flat in order to slide the tank up into the chassis. The tank is held up by 3 sheet metal plates that also double as mounts for the coolant and A/C pipes. The ends on each plate are folded down and butted together such that the middle plate can be fastened to each end plate. Each plate end has holes in them to support the aluminum pipes that transfer vital fluids from the car back to front and vice versa.



Each of the plates was raised with a floor jack during fastener preparation to ensure the pipe work would be above the level of the carís floor. I didnít want the pipes to be exposed for possible scraping when the car is driven over speed bumps. Each plate is held in place with four ľ inch screws and I elected to use Riv-nuts to receive the screws.



The in-tank fuel pump top plate and fuel level sending unit (in shaded area further forward) stick up through the top of chassis backbone.



Here is the in-tank fuel pump unit and foam baffling ready to be installed in the tank.



The only remaining fuel tank detail is to fabricate a filler pipe and provision for a gas cap. Iíll leave that for a later date after more of the front body work and supports are figured out.
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  #145  
Old 10-20-2018, 08:24 PM
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Post Radiator Placement

I decided the next project step is to figure out the radiator placement such that supporting chassis structures for the front clip can be fabricated. The radiator recommended by the chassis designer/builder, Charley Strickland is a 2 pass, cross flow with only an air bleed valve and no radiator cap that measures 26Ē wide by 19 ĹĒ tall. Charley normally orients the radiator straight up vertical in the other cars that use this same chassis. For the Miura though, the radiator needs to be angled forward in order to fit under the bodywork. Thatís not too surprising as the original Miuraís also have steeply angled radiators.

I determined the only way to sort out radiator placement and angle is to mock it up. Iím not sure if a full sized spare tire will be used in my Miura but just in case, I needed to include it in the mockup.







I didnít have most of the actual Miura measurements needed so I took them from the 1/18 scale model I have. For example, I needed to know the distance from front wheel center line to front lower body panel and height from ground for this panel. That way I could make sure the radiator could be located high enough such that it wouldnít scrap when entering parking lots. I also needed to know the distance to the forward most point on the front clip and its height from the ground. This would help me loft a line over the radiator top to determine how much it needed to be angled. Measurements from the model likely wonít be dead accurate but should be close enough for this radiator placement exercise.

I used a couple of aluminum rulers clamped together to loft a simulated line at the middle of the front clip. The front of the car, i.e. most forward point on the front clip is only 15 ĺĒ off the ground. Yes, the Miura is a very low slung car. The wooden block with ruler attached is positioned so it simulates the front top of the car body. I determined the radiator will need to be placed at a 40 degree angle to provide clearance to the bodywork. The final test for the mockup was to make sure there was necessary clearance with the radiator for spare tire removal. That passed, so mockup successful.
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  #146  
Old 10-21-2018, 04:47 AM
Gojeep Gojeep is offline
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Glad you are able to fit it all in place. I guess you will have to design exits for the airstream too once it passes through the radiator.
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  #147  
Old 10-21-2018, 08:19 PM
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Quote:
Originally Posted by Gojeep View Post
Glad you are able to fit it all in place. I guess you will have to design exits for the airstream too once it passes through the radiator.
Marcus,
The good news is that Miura has a couple of grills in the middle of the front clip just for the purpose of letting the hot air from radiator out.



The bad news is I need to figure out a way to make the grills such that all the aluminum slats have clean edges that are nice and even. I think I can do this on my Bridgeport vertical mill but the proof is when I actually get it done
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  #148  
Old 10-22-2018, 05:33 AM
Gojeep Gojeep is offline
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Will the spare work out to be behind those vents so the ducting will be easier?
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  #149  
Old 10-22-2018, 11:26 AM
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heinke heinke is offline
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Quote:
Originally Posted by Gojeep View Post
Will the spare work out to be behind those vents so the ducting will be easier?
Here's how the front end on the original Miura was layed out.



The spare tire well on my chassis is further forward than this but given the low hood line the angled radiator is already real close to the vents so not much ducting will be required. In fact, I think the spare tire will act more like a duct forcing the hot air up to vent.
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  #150  
Old 10-22-2018, 01:18 PM
Marc Bourget Marc Bourget is offline
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Keep in mind you can do a much better (more efficient) job of exhausting the air from the radiators with properly designed (and coordinated) shrouds and fans.



It may provide you with some dimensional "lee way"


FWIW
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