McLaren M20#73

[Andy R]

Hi all, I’m looking forward over the next year +, constructing what I hope is something I’ll be proud of and a blast to drive. The garage has been cleaned and the build table has been made, parts have been acquired and a start is underway.
My build plan is a McLaren M20, an Aluminium monoque - solid riveted and bonded, 427 turbo charged LSX and a sequential transaxle. The colour scheme will be the Woods/Hobbs 73 Black car with a few Kiwi touches. I’ll call it a Recreation Mod
I will be using 5052 H34 sheet aluminium as it is medium/high strength and folds nice tight bends without cracking and comes in thicknesses I need 1.2, 1.6, 2, 2.5 & 3mm. Solid Rivets are the hard 2117 3/16”, Sikaflex 552 High Strength Structural adhesive will be used.
The rear bulkhead and front suspension mount points will be constructed with 4130 .100” alloy steel normalised. Front Arms also will be 4130 tubing, Rear links 7075 tube, threaded for rod ends.
The Suspension Uprights, Pin drives, Rims are here, Body should be ready EOM, so it’s time to put it all together.
Looking forward to this.. Andrew.

 

[Joel K]

Looks like a great project, will be following along.

 

[Neil]

Andy;

This sounds like a nice project! My only suggestion would be to use 2024-T3 instead of 7075-T6 tubing for the rear suspension links if you must use aluminum, otherwise I'd use 4130N for the rear as well as the front. Fatigue is always a consideration with aluminum.

 

[Lee Patterson]

Great project. As a novice, are the rivets applied with by hand or some sort of gun? and do you bond pieces before rivets? thanks

 

[Andy R]

Hi Lee, Rivets are inserted with a rivet gun and bucking bar. https://www.aircraftspruce.com/pages/to/rivet_0guns/rivetkiteconomy.php
They take a little practice to get right but not to hard. Theres lots of Youtube clips.

Hello Neil - I'll be using a heavy wall 7075 tube with 5/8" x 1/2" rod ends . If it fails you can say I told you so cheers Andrew

 

[Neil]

 

[Andy R]

Mocking up front suspension. I want the upper shock tower further out than the original so mount points will be different to original.

 

[Andrew Robertson]

Hi Andy, totally awesome! Love the fusion of old and new - will be following with interest. Where are you based, and are you intending to race it?

Cheers, Andrew

 

[Andy R]

Hi Andrew, A fellow Wellingtonian, and do intend to race it..
I've just completed a 4 week motorcycle tour with the wife in Ladakh-Himachal, Northern India which was a real blast, but now spring is here(cough 6DegC today) will be putting some hours in to progress this along.

On a side note: Any one out there know of any Albins ST6-M Sequential boxes for sale. PM me.

 

[Mesa]

Andy,
Cool project.
A few questions - Are you saying the body will be OEM? I'm not familiar with EOM. Is anyone making an M20 body for purchase? Where are you getting the chassis dimensions from? Seems like one would need the OEM body first before laying out the chassis. Thanks!

Interested in how you reconcile different areas of the project.
I'll be subscribing to this thread for sure!

PS I talked to David Hobbs a bit at Laguna a few weeks ago (didn't he drive the #73?) - I relayed a story from when I was a kid and he was driving the "First National City" sponsored Mclaren tuned BMW 320i. I found it amazing he could sleep sitting right next to the car while the mechanics were revving the engine....., right then Bob Varsha pipes up with "He still does that in the TV production meetings" (laughs all around).

 

[Andy R]

Hi Mesa, End of Month... My body's being made right here in little ole NZ. He might be able to get back to his build now.....
I'm also widening the rear tub Cockpit 50mm as I'm not a massive fella but the bum area on the original is quite narrow. I've also beefed up some panels, the side cockpit bearers are 2.5mm not 1.6mm and the cockpit floor is 2mm not 1.6mm. For the extra 2 kgs I feel better.
As long as the wheels are in the right place and it fits under the body shell I can't see a problem.

Yes one area that I'm having a good think about is the rear suspension and how to connect to the transaxle and shock tower mount points etc. Albins have said they can cnc new side plates to include mount points (like the LG500-LG600) if I had an unlimited budget for sure, but thats a tad costly. I have a few ideas but its food for thought.

He was the driver in 1973. If David Hobbs ever comes down here when its complete he can have a drive if he will sign it.

Andrew.

 

[Andy R]

I little more progress, The Side pod bulkheads have been made, bonded and riveted in place. I haven't fixed in permanently the front side pod bulkhead yet as the steel suspension mount points have to be installed first.
Also fashioned a couple of temporary front upright mounts to position them at the correct height while the the A-Arms are constructed.
The 4130 2.5mm steel plate has been guillotined and press brake folded. The front suspension mounts can be now added.
The rear bulkhead sub frame has also been cut and folded. (will be TIGed) I've run out of steel so some more should be arriving in the next few days to complete the pieces needed to construct it.

The rear drive flanges are made from 7075 and have a square spline machined to fit the 4140 rear axles.
You can see the thick and thinner walled 7075 tube and 5/8" x 1/2" alu rod ends that will be employed for the rear links.
Thats about all I've had time for this week, work gets in the way of play.

 

[Andy R]

The rear sub frame/bulkhead is nearly done. Some more drilling, keying up surfaces to be bonded and a paint, then final rivet. Hadn't tig'ed much lately so it was nice to get back in the swing of it.

 

[Andy R]

Finished drilling, deburring, bonding and riveting the subframe and rear sidepod bulkheads. The Side pod template fits the top nicely. Will skin the subframe with 3mm as bit of protection from engine mishap.

 

[Andy R]

Completed the rear subframe fire wall. Ended up skinning it with 2.5mm. The rear seat back rest is nearly complete. A bit more drilling and riveting and that will be done. Been mucking round with the seating position and foot pedals. More stuff arriving . QA1 proma duals coil overs. The holley efi fuel cell pump #12-145 has dual 255 lph pumps that can be sequentially tiggered as the hp increases. They are in cell and I'm planning on baffling the fuel tank with trap doors so i won't need a surge tank. I'll primarily run on the left tank and have a smaller pump in the right tank to transfer fuel when needed.

 

[Randy V]

I’d like to meet the engine that would exhaust a 255 LPH supply of fuel....

 

[Terry Oxandale]

Roughly one of these maybe. What are we talking about, low to mid 300 pounds per hour, so perhaps a 600+ HP motor?

 

[Andy R]

Randy, keep tuning in...

 

[Andy R]

Work has continued on the tub. The seat and spine structure is nearly ready to be riveted in. This has taken a bit longer than anticipated but is getting there. Under seat ribs connect the spine to the floor that should help to stiffen things up. The seat belt mounting brackets also have to be added now. Looking forward to finishing this and get on with the front tub/suspension.

Brake rotors, hats and Calipers have arrived and have been mocked up. The hat offset is about 1/2” to small as the Caliper radial mount isn’t sitting where I want it on the front upright. so new hats or machine up some custom radial mounts. Will have a think on that one....

The Albins ST6M Transaxle and shifter has been ordered and I should have it by end of year. Still waiting for front and rear clip. EOM. I’m hoping this one

 

[Cliff Beer]

Fantastic work there Andy, looking good. Keep the pics coming.