M20 Dreaming

Hi Guys, I have been working away this week on the Tub and have progressed quite well. Started by getting the 1.6mm and 1.2mm sheets from local supplier, then marked and cut the floor plan in 3 parts, (centre, 2 side pods) then mad the sides of the cockpit and front bulk head. This is all 1.6mm sheet. The only steel in the tub is the rear bulkhead and the uprights that anchor the front of the rear suspension trailing arms and the engine front mounting plate will also be mounted to these. The side pod bulkheads were then folded up from 1.2mm sheet these are then glued together back to back for added stength an also this gives a much better flange to clue and rivet to the floor, sides and top panels. I have attached some pics so please feel free to comment. This will be it for this time home as I'm off to work again on Tuesday.
Cheers Leonmac
 

Attachments

Last edited:
Hi Terry, I have "Sikaflex 221", but have not done any gluing at this point. This was recommended buy the alloy supplier, it is used for contruction, Truck bodies,and alloy semi trailers, Bonds well to steel and is none corrosive and can painted. I will be using 3/16" alloy rivets at 1" spacing through out the tub.
Cheers Leonmac.
 

Terry Oxandale

Skinny Man
Sounds like it's made by Sikens, so I'll run over to the body shop supply house and see if it's available. Great job and keep the photos coming.
 
Hi, managed a bit more work before the week finished, I did some more with the suspension trailing arms and bottom links the stubs are only pressed in at this point but they look to be the right length so will silver braze them in once they are all fitted up to make sure its right. I also started the top suspension bracket which bolts to the lugs on top of the Diff housing and the bottom links to lugs cast into the housing bellow the side plate's. The trailing arms and links are 1.25" tube with 1/2" rod ends. I hope to have the whole rear end finished next trip home.
Hope you like what you see and feel free to make sugestions.
Cheers Leonmac
 

Attachments

Terry Oxandale

Skinny Man
Really nice work Leon. Really looking forward to your build-up.

I Googled Sikaflex 221 to read about it (the "...flex" caught my eye), and it begs me to ask a question that perhaps I should already know, but here goes.

When I bond the panels to my frame, will I want an elastic adhesive, or should I go for something more rigid? I've been under a long impression (perhaps from some aviation related pieces in my youth) that this type of bonding should be rigid. With a thin enough layer, just about anything could be in essence "rigid", but when I read the spec sheet for this product, I began questioning if it would be right for me, and provide the support for the riviting I want.

Any advice or wisdom on this concern?
 

Terry Oxandale

Skinny Man
Thanks Jack. As usual, you're on top of it. The fast work times of this stuff is going to be a challenge...but then what would be the fun of all this.

I'LL pm you the rest.
 
Terry,
you may slow it down a little by putting the components in the refrigerator for about 10 minutes before mixing. Will allow a couple minutes addition to the cure without changing any tensile properties. Don't leave it in there too long though!

You may also call Plexus directly. They may advise about a slower cure product. Just tell them what you are using it for. They have a helpful technical department.
 
Terry/Molleur, I have had the same thoughts about totally ridgid glue or something with a little give in it. As you said Terry, if you put it in thinly and the rivets in tight then it will be pretty darn ridgid. The 2 trains of thought have their merits, My concern with "flex" is the obvious flogging of the rivets but!!! if there is no flex then there is "Fatigue cracking". Now the thing is that I have had a lot to do with truck bodies and the thing is these have to do Hundreds of thousands of miles, and here in NZ we don't have nice smooth concrete roads and I've seen boddies that are 20 years old and done Millions of miles and they have no or very little sign of rivet movement. The other thing with the likes of "Plexus" is the time factor, its fine if your doing small jobs, but trying to do the size parts that I'm doing would be a nightmare.
It is one of the great things with this forum is the ideas and info that you all have and it gives us all great insight into so many products. The other thing is Terry is nailing to a tube chassis and I'm doing a complete Mono so there may be some difference in stresses, I guess somome has to be the lab rat, we will see how it goes???
Cheers Leonmac
 
Leon,
Comments appreciated. I have rebuilt/panneled a Lotus 7 and used Sikaflex along the chassis tubes, more as a sealant than adhesive. Worked wonderfully for that. Re-riveted the entire car. The remnants of the drilled out rivets were bound in epoxy
by drilling small holes in the chassis tubes and pouring it in, tilting/shaking the chassis to get them in position. Worked a treat! No rattles either. Welded up the holes when done.
 

Terry Oxandale

Skinny Man
I finished a short conversation with the tech at Plexus, and he said the MA832 would provide the longest work time. As Jack suggested, cooling the adhesive will increase work time even more. I expect I'll spend 15 to 20 minutes per panel to set, clamp, and begin riveting the panels in place. The tech said the viscosity of the product was a little thicker than mayonaise. I was concerned that the adhesive would not squeeze out into a fine film under the panel as I clamped and rivieted everything in place, but the tech said it will flow out under compression very well. The shear strength they list is for a .012 thickness bond. I told him my application will be more like 3 to 4 mils, and he confirmed this would increase shear strength slightly, and it will present a more rigid bond.
 
Last edited:
in the discussion of flexible vs rigid adhesives, I have a couple thoughts, which may be wrong, but here they go, regardless -

1) I'd think in a bonded and riveted chassis with thin panels, the bonds are carrying far more of the structural load. Paneling a Caterham is different, unless those panels are true shear panels.

2) given that the bonds are likely carrying the loads, you'd want rigid bonds or else the bond may allow loads to concentrate on a particular area, which is generally not what tubs/monocoques are good for, unless they have inserts designed for a point load.

3) maybe flexible glues would maybe be appropriate for bonding dissimilar materials, with different temperature expansion rates.
 

Terry Oxandale

Skinny Man
My head is hurting now. Leon brings good points as well as "spud" (a potato? :)

My understanding of the bond is its job is to relieve the rivets of the forces the sheeting assumes. My assumption (I hate using that word, but its applicable here) is that the bond is or should be stronger than the sum of the rivet strengths. A flexible bond (and in practicality, the very thin bond I'm writting about is essentialy rigid) on a riveted panel is much like having the motor mounts of a solid variety, but the transaxle mounts being made of rubber. The solid mounts will fatique or crack in time. My guess is that the inflexible nature of an elastice 3 or 4 mil bond will stay within a safe window of rivet hole/rivet size toleraces as applied to my car, but its not a mono design.
 
Boy this has got us all thinking now, I have not used the Sikaflex as yet and reading the post here they all have valid points, I don't surpose there are any Ex Mclaren or for that matter any ex Can-Am guys that could tell us exactly what was used in the day when these cars were new. I don't surpose any of the Kiwi contingent would Have a contact for Duncan Fox as he has done the restoration on the M8A for the Mclaren trust and I'm sure he would know what is required, not that he would likely tell you if you asked. I have a friend who was an Air Frame Technician with the RNZAF and is a Pilot for Air NewZealand for the last 20 odd yrs I will have a word with him. It makes for interesting reading thats for sure. Cheers Leonmac.
 

Terry Oxandale

Skinny Man
Some other recommendations that have been given to me from folks that have done this kind of work is:

Scotch-Weld 2216, and Norton 04674SpeedGrip. Interestingly enough, they appear to have comprarable Shore ratings as what you're using, so it all seems a wash. The only significant difference is the considerably extended work time (90-120 minutes), which is really good for my needs.

Other questions that have come to mind are; 1) does any aluminum oxide (for aged panels) inhibit a good bond? And 2) will the rivets dimple the panel due to the un-cured nature of the adhesive squeezing out in the immediate area of the rivet head (in other words, will the adhesive be thicker between the rivets versus under them, causing the panels to distort as they are riveted in place), or should one bond the panel and only rivet it after the adhesive has cured? I ask this because it appears to be a common requirement that the adhesive be of minimum thickness to attain the maximum bond. Thus, I wonder if the riveting process would reduce this thickness (and reduce the bonds effectivenes) if the adhesive was still soft during the riveting process.

Should I talk to an A&P mechanic?
 
Last edited:
Top