Lotus Elan

lattice strengthening within Sprint cill

PostPost by: stuartgb100 » Sat Sep 10, 2005 7:45 pm

The outer n/s cill on my 71 Sprint has a 4 inch split. There is a full length
hairline split on the underside of the n/s cill. The o/s cill underside is beginning to show a similar hairline split.

I'm told that there is a top and bottom steel channel within the cill (approx 4 inches apart) which is interlaced with a zig-zag of reinforcing rod. At each end of the bottom channel it then extends to run over the front and rear wheels to fix to the chassis.

The purpose is to provide front to rear rigidity. However, it is also the means of providing seat belt anchor points!!

I have the feeling that this is not to be an easy job.

Has anybody experience of this repair, please?

Regards.
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PostPost by: nebogipfel » Sat Sep 10, 2005 9:56 pm

You can see the steel within the sills to assess the condition by removing your seats and then the inner sill carpeted panels. If the reinforcing rods in the sills of your car are not rusted then the repair is simple, requiring conventional glassfibre repairs.

It would be wise to add more thickness/strength at the same time because cracking in this area is not unusual.

If the reinforcing rods are rusted new sections can be welded in to restore the structural strength but clearly the glass of the sill would have to be cut away to facilitate welding and to avoid fire!.

If you need to do extensive repairs to the sills then make sure the shell is well supported to avoid sagging or twisting particularly if your car is a drophead, and especially if you remove the shell from the chassis.
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PostPost by: bill308 » Sun Sep 11, 2005 2:55 am

Hi,

The most likely cause of this problem is rust. As the rust progresses it expands and bursts the encapsulating fiberglass.

I had a severe case of this problem on my S2 Elan. The car was being stored outside and got caught in a flood that was deep enough to enter the interior. Water managed to find its way into the lower rod cavity, which is not perfectly sealed where the truss emerges from the fiberglass. Also, polyester resin is not a perfect barrier to moisture and having been partially submerged for several days the resin will retain some moisture.

In my case, the lower rod was trashed from about 6-inches high in the forward foot well to about 6-inches high at the rear bulkhead. A good part of the interconnecting latticework was also damaged.

A second area of concern is the rod embedded in the glass running over the rear wheels. On my car these rods were destroyed because a long tenax fastener pierced the under fender fiberglass cover and water, most likely thrown up by the rear tire, found its way into the loose cover.

I did manage to replace the damage but is was a miserable time consuming job. Here's saga of what I did:

1. I supported the frame on 2-jack stands at the corners of the front frame and the rear center on stacked concrete blocks. I used wood cushions at the 3-points of contact. The sills are not under any real load when supported in this manor, so I found they do not need additional support.

2. Door, seats, interior trim, and carpets in the area were removed.

3. The encapsulating glass was cut completely through on each side of the rod, along its entire length, until undamaged rod was exposed for an additional 3-inches or so. I used a combination of an air panel cutter (high speed with an abrasive wheel with about a 3-inch diameter and about 1/16 in thick and a hack saw blade wrapped in tape to cut on the pull stroke. Remnants of the glass matrix were stripped from the rod so the rods condition could be evaluated.

4. The damaged portion of the rods were severed and removed and about 1/2 the length of each of the remaining cross braces were removed, including the seat belt anchor boss.

5. Remaining areas of the rod were cleaned and prepared for welding. The cross brace stubs were cleaned over their remaining lengths as the plan was to coat them with a high quality epoxy and joint them to their new mates using a steel sleeve. I had used this technique about 10-years earlier and the resulting limited repair proved quite durable.

6. The remaining local fiberglass floor was chamfered to accept multiple overlapping layers of fiberglass matt and polyester resin sufficient to restore the original strength and contours. This chamfering was accomplished with a die grinder and various disk and drum sanders as necessary. This is a very messy operation, done on your back, looking up. Take precautions from the fiberglass dust. Wear eye protection and a good dust mask.

6. The removed/damaged rod was laid on a flat surface and a new mild steed rod, I believe 3/8-inch diameter, was bent to conform to the damaged piece. A series of 1/8-inch mild steel rod/wire pieces were bent into the shape of V's. These would replace the damaged portions of the lower cross braces. 1/8-inch mild steel rod/wire pieces were bent to an appropriate shape to provide support for the seat belt anchor nut. These wire pieces and the seat belt anchor nut, were welded to the lower rod in the required position.

7. The newly bent, lower replacement rod assembly, with the seat belt anchor nut, was offered up to the remaining good portion of the rod in the body and butt welded in place. Ensure you have sufficient clearance from the adjacent fiberglass, as fire is a concern. Have on had water, wet rags, and a fire extinguisher. My brother (Elan +2 owner) was kind enough to do the honors and used a MIG welder to perform the mating. My brother is not a professional welder, but he had the equipment and did a good job. Still, had I to do it again, I think a professional would be best, as one wants to perform the weld with as little heat as necessary and as quickly as possible. One who does this sort of thing every day will likely do a cleaner and safer job. As I recall, we only lit up the fiberglass once and it was extinguished with in a couple of seconds, so no real damage was sustained. The repair was cooled with a wet rag and water when necessary. It?s difficult and nearly impossible to complete the weld in one shot without having to cool the local area and come back to it. We also had to fiddle with the TIG adjustments to ensure good penetration and a good weld. In the end, the welds weren't real pretty, but they were solid and would be hidden from view. Stick welding is also an option. We used what we had. This concluded the welding.

8. Next, the wire V-pieces needed to be attached to the new lower rod. First, clean the affected area to remove oil and contaminants. I used acetone. Again, in the past, I had good luck with limited repairs of this nature by wrapping the apex of the V-pieces with stainless or monel (safety wire) wire to the lower rod. I used about 10-12 wraps with a twist finish. When the connection to the upper stubs is made, this wire wrapping would be saturated with epoxy. Previous repairs made in this manor were still solid 10-years later. The advantage here is that there is no resulting distortion and there are no latent residual stresses introduced by welding. I also find this method easy and forgiving. Still, welding the apex of the V's to the lower rod is a viable option.

9. Cut the length of the V-leg to nearly butt the stubs emanating from the upper rod.

10. With the V's in place, trimmed to length, and clean, I liberally coated the V-legs and the insides of the tubes with a high strength epoxy. I slid as long a steel sleeve/tube as possible over the lower V, aligned the lower V and sleeve with the upper sleeve and slid the sleeve up to join the lower to its upper sister together. The sleeve position was adjusted so that it was half way on both the upper and lower wire stubs. Additional epoxy was allowed to seep into the sleeved join to ensure good coverage. This lapping joint is very strong. I then saturated the V-wire wrapping and repeated this process for the remaining joints and allowed the epoxy to cure.

11. After the epoxy cures, the truss is quit rigid, as it should be. The thing about trusses is that all members are in almost pure tension or compression. This results in a very rigid structure with minimal material (weight).

12. I coated/painted the truss at this point with an epoxy resin coating. The purpose was to protect the steel from future exposure to moisture. Polyester resin is not a good barrier to moisture but epoxy is.

12. With the truss now complete, I turned my attention to closing up the fiberglass wounds, and they were significant. The first step was to lay wax paper on a board, the length of the floor, so that fiberglass could be saturated with polyester resin and offered up from below and wedged into place against the bottom surface of the floor. This method ensures that the bottom surface will be solid and straight, minimizing post cure grinding and shaping. Cut fiberglass matt to length and width. I think I used about 4-layers, the upper most layer thinner in width than the lower strip to match the chamfer previously ground in the bottom of the floor glass. Coat the underside of the previously prepared and chamfered lower surface of the floor with resin. Layup and saturate the matt strips on the wax paper/board with resin and offer up the patch with backing to the lower surface of the floor and wedge tightly into place. Allow everything to cure. Properly done, resin will ooze out leaving a desirable high glass content patch over the length of the scare. The glass fibers are where the strength is, the resin merely ties it all together. After removal of the supporting board and wax paper, trim the bottom surface and edges to shape. The challenge in this process is to coat and saturate all mating surfaces and lift the patch into place before the resin begins to harden. This is important, so make sure you know what needs to be done and do it quickly. To speed the saturation of the strips of matt on the board, pour the resin onto the board mounted matt, as it should be on a horizontal board. Lay on the next layer, pour on the resin, patting it in with a big enough disposable brush, next layer, next layer. Make sure you mix enough resin to complete the job and add an appropriate amount of catalyst for the temperature conditions. Polyester resin cures faster in large quantities so it may make sense to mix a large batch, but separate it into several smaller containers. Figure on a 5-10 minute pot life. It?s a good idea to mix a waste batch so you can test the available work time. This is wasteful but operationally conservative. If you don't use enough catalyst, the application of heat with a heat lamp may save you, but be careful with the heat. Wear gloves. I like latex surgical gloves and may layer 2-3 gloves so as things get messy, I can peel off the outer glove. I had help from a friend (S3 Elan owner) for this process and needed him.

13. With the underside closed up, attack the upper surface. This is a little easier but the length of the scare still requires the closing to be performed quickly. One can opt to do this in overlapping stages though. When done, the V-joint wrappings to the lower rod will be embedded in the polyester/glass top layer and hidden from view.
14. Close the front firewall scar and the rear bulkhead scar. If you?ve been successful to this point, the remaining scars will be easy.

15. Go down to the local pub or bar and drink heavily; you deserve it if you followed through on this.

Did I mention this was a miserable time consuming job?

Variations on this procedure should be considered or you could contract with a pro.

Good luck.
Bill
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PostPost by: stuartgb100 » Sun Sep 11, 2005 5:32 am

Bill,

Many thanks for the blow-by-blow details.

Can this be done without "disturbing" the outer cill section, or am I into more repairs and a paint job too?

As I understand it, there will be several layers of mat dressed around the top and bottom channels that will have to be cut away?

BTW I'm just across the border in Suffolk.

Regards and thanks,

Stuart.
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PostPost by: nebogipfel » Sun Sep 11, 2005 10:40 am

Stuart, Bill has given you a very comprehensive answer to your question :)

The only thing I would add is that although his frame had rusted and as he says the pressure was probably causing the splits this may or may not be the problem on your car.

My own car was badly split along the bottoms of the sills but the metal frame within was not rusted.

Unfortunately the Elan shell is not particularly strong. Beautiful - Yes. Light and functional - Yes. But not strong!

You need to strip the interior out and have a look, it may not be as bad as you think.

It is unlikely that you can make repairs properly without affecting the paintwork to some extent - certainly difficult if you need to replace some of the steel frame.
John

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PostPost by: stuartgb100 » Sun Sep 11, 2005 11:09 am

Many thanks for all the help.
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PostPost by: bill308 » Sun Sep 11, 2005 4:27 pm

Stuart,

John is correct. In your case, sill damage may not have been caused by rust expansion. Many people jack or support their cars on at least the back end of the under sill, box section. I can see where this can cause a crack to begin and expand over time. However a crack begins, this crack can become a conduit for water entry and should be repaired as soon as possible. I think if your problem is not too bad, you could try a neat, under car, fiberglass patch. If the patch fractures over time, you likely have something going on inside and would have to address a more extensive repair at that time. This is what I did originally and it lasted some years, before comming back. Once rust begins, it just won't stop on its own. If there is some minor apparent rust on the rail, you might want to treat it with a little rust converter, before reglassing and sealing it up.

As far disturbing the exterior paint, the extensive repair I performed in general was hidden from view. Repairs extened up into the front and rear wheel well areas which could be convered with undercoating. The outside bottom edge, of the under sill box section, showed trimmed fiberglass because of the way the patch was offered up and squeezed. Also the front and rear ends of this box section might be visible, but just barely. Initially, my car had this box section painted black, which I thought improved the sill contour of the car, which was painted Lotus yellow. So I guess what I'm saying is that one can do extensive repairs to this area and as long as you are somewhat careful, all the scars can be hidden and the exterior paint need not and should not be disturbed.

With the car supported in the manner I described, both lower truss rails were removed and I found no tendency for the floor or sills to distort significantly, even with some weight (leaning onto the members) loading. I think is because, even after making a front to back cut through the box section, eough of it remains to provide some support. Also, the floor is not perfectly flat but has molded in contours to help provide strength. However, at no time was the floor or sill tested with full body weight and the interior was generally kept empty until the new rails were welded in and and the exterior box section was reglassed to restore most of the original strength.

Bill
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PostPost by: stuartgb100 » Sun Sep 11, 2005 6:23 pm

Many thanks to you both.

I will first investigate, and then if need be follow the detailed advice very carefully.

Regards.
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PostPost by: worzel » Tue Sep 13, 2005 7:26 am

Hi All

Had the same problem on one side only some years ago.

I used a different method- but the purists won't like it!

Basically I cut out the rusted sections and then between the bottom and top halves of the sill I bonded in one inch thick fibreglass posts about every five inches. This restores the strength and if you insist on jacking the car under the forward corner of the rear arch (as I do) the strut inside the sill merely transfers the loads thru a vertical plane (I take the precaution of spreading the load via a wooden block).

During the 10 years since effecting the "repair" I've never had any problems.

If you think about it the connecting "wires" on the original are quite thin anyway and I don't think they would take too kindly to being stressed.

John
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PostPost by: lotus026 » Tue Sep 13, 2005 3:39 pm

I also had a split sill on my '65 Elan - and wasn't caused by rust in the lattice; seemed to be more because of poor assembly at the factory! Mine was split about 1 1/2 feet long right at the bottom of the sill, where there was an obvious join to the floor panel - and the original join had basically fallen apart, so the passenger side floor was bouncing up and down (well, mostly down!) since it was right by the seat. I ended up grinding it all out and laying up fresh fiberglass into the joint mostly from the top; wasn't that hard - especially compared to having to deal with lattice replacement or repair!
Hope that you are so lucky with what the problem is.....:)
Dave
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