Fixing DS bonnet
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  1. #1
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    Default Fixing DS bonnet

    I have discovered a small crack, about 8mm long on the down-turned lip of the bonnet just forward of the hinge attachment area. Has anyone tried welding this sort of thing up or is the aluminum too thin? Any other recommended repair techniques? I had wondered about epoxy and an aluminum backing plate but it is the sort of area which will be subject to flexing when the bonnet is raised.

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    Default need help too

    I'm hoping you get a reply to the "cracked aluminium" question as an ID bonnet I have, has a 20mm split in the centre right up front at the nose. I also wonder how to repair this aluminium. Michael

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    The bonnet on my 2nd front car ( FrankenD) had been riveted with a stiffening plate either side of the base and filled with epoxy to repair a split, by a previous owner. This did not work.

    It now has a TIG weld repair for the split, the stiffening plate removed and rivet holes welded.
    Job done. No filler.

    A competent welder fabricator will make this type of repair for probably $100 or so, depending on the age and length of the split as the aluminium oxidises and must be perfectly clean prior to the repair.
    Hope this helps.

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    TIG welding is the best option now. There would be mobile welding professionals who could come to you I'm sure. Gas welding is possible, but requires a great deal of skill to get it right.

    The hinges tend to become stiff over time and the bonnet will then flex a fair bit just ahead of the hinge. So a bit of hinge lubrication would go a long way to preventing this.

  5. #5
    Real cars have hydraulics DoubleChevron's Avatar
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    I was thinking, slotting the crack out then sticking a brace behind the area stuck in with maleable urethane adhesive would be the best repair. By making the area rigid with welding/re-enforcing.... it will crack again... must crack again But if you make the area slightly flexible with a panel adhesive you may fix the problem?

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    Quote Originally Posted by cresco750 View Post
    I have discovered a small crack, about 8mm long on the down-turned lip of the bonnet just forward of the hinge attachment area. Has anyone tried welding this sort of thing up or is the aluminum too thin? Any other recommended repair techniques? I had wondered about epoxy and an aluminum backing plate but it is the sort of area which will be subject to flexing when the bonnet is raised.

    Thanks.
    I've successfully repaired a similar crack in a DS19 aluminium bootlid by forming a generously sized piece of 1.5mm thick aluminium to fit inside the cracked area and epoxy glued it into place. Cheap, it works, no distortion from welding, no heat affected zones and the load is spread over a large area. I've also used this technique to rescue a badly rotted aluminium Dee roof. The repair piece has to be closely formed to the parent shape and the glued surfaces have to be very clean. I use the long cure Araldite, not the 5 minute merde.
    roger
    Attached Thumbnails Attached Thumbnails Fixing DS bonnet-ds19bootrepair.jpg  

  7. #7
    Fellow Frogger! Bruce Llewellyn's Avatar
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    Default Crack repairs

    Quote Originally Posted by DoubleChevron View Post
    I was thinking, slotting the crack out then sticking a brace behind the area stuck in with maleable urethane adhesive would be the best repair. By making the area rigid with welding/re-enforcing.... it will crack again... must crack again But if you make the area slightly flexible with a panel adhesive you may fix the problem?

    seeya,
    Shane L.
    Hi everyone,

    What will happen with the maleable adhesive is that the crack will continue to grow from the bottom of the slot. Paint won't sustain the movement.

    There are a number of standard repair techniques for aluminium airframes in AC 43 which use flush rivets. AC 43 is available from the US Federal Aviation Administration or from the pilot supplies shops on major airports.

    I have used the insert patch technique on a cracked D bonnet where the bonnet was both cracked and stretched. This came about from the bonnet hinges getting sloppy and hooking into themselves. Any time you see a D with a sneer, this is probably what happened.

    Because the D bonnet is softer than SAE 2024 alloys it is necessary to use either soft rivets or solution treated rivets which are soft as treated but harden over time. AD rivets (as stocked by aircraft maintenance orgs) are too hard in their normal state.

    Self setting (blind or "Pop" rivets) can also be used, however solid rivets can be double countersunk so as to come up flush on both sides.

    The bonnet can be shrunk back into shape using panel beating techniques subject to the following;

    1) Use an aluminium hammer. These are not available, one has to get a lump of aluminium (SAE6061 T4 extrusion is good) and make a hammer. Draw file the faces, polish with wet & dry sandpaper up to 1200 grit and finish with tripoli soap or brasso. Lock the hammer up so people don't mistake it for a soft face hammer and ruin it.

    2) Backing (dollying) should be done with a hardwood dolly or a linen or leather bag of oiled steel shot blasting shot. About 1.5 th 2 kg for the bag. If using hardwood take the time to shape it properly to a curve that matches the shape you require.

    3) The area to be worked must be annealed before starting and usually during work. This can be done with a suitable heat gun or a propane torch. The technique is to strip all paint, glue etc from inside and out and rub ordinary sunight soap on one surface of the metal. Fill a bucket with cold water and have it ready. For small areas a cotton cloth (not synthetic, which can melt) should be soaked in the bucket.

    Warm the non soaped side until the soap turns brown, then quench with water. This softens the metal so it can be hammered.

    Wash off the singed soap...

    4) The same sort of technique can be used as for hot shrinking steel panels, hammering up a local high spot, annealing it, upseting it to shrink etc.

    Do not try to "pick up" aluminium panels with a pick type hammer. Only use flat faced hammers with a good to mirror finish.

    Remember that every time you hit it it is getting harder, so plan every hit.

    Now, I have not done this myself but I am told;

    Welding can be done by TIG or MIG using a steel block to back the joint. It will be necessary to anneal and planish the weld to remove the shrinkage. this is done by annealing then thinning the bead of weld metal by hammer and dolly. For this a steel hammer and dolly can be used, polished to mirror finish and oiled using engine oil.

    Don't grind the weld untll the panel shape is fair or you will have no metal available to upset to correct the shrinkage.

    Good luck...

    Bruce.
    Last edited by Bruce Llewellyn; 17th January 2012 at 02:31 PM. Reason: Typos

  8. #8
    Fellow Frogger! Bruce Llewellyn's Avatar
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    Default Split lip

    Quote Originally Posted by IDear View Post
    I'm hoping you get a reply to the "cracked aluminium" question as an ID bonnet I have, has a 20mm split in the centre right up front at the nose. I also wonder how to repair this aluminium. Michael
    The primary cause for this is buckling of the reinforcing strip inside the bonnet. If this is not fixed (usually by making a new one) the bonnet skin will split, as the center of the bonet will be flexing up and down under air loads and every time the car hits a decent bump. The reinforcing strip is probably cracked all the way through if the skin has grown a 20mm crack.

    Simple repair is to stop drill the crack, drill out the existing rivets and make a new reinforcing section (3 mm 6061 T3 or T4). This requires a bandsaw or jigsaw and the ability to turn a partial edge on the replacement section.

    Unfortunatly Citroen used old style large size aircraft rivets on this area. I have used MS 20470-8 s here but these are expensive, not easy to get (aircraft spruce and specialty) and had to be annealed before being driven. It is possible to use small countersunk bolts here (with plain washers top and nyloc nuts) instead. Paint both the reinforcement and the mating part of the bonnet with etch primer or it will give trouble. Apply lanolin grease or vaseline to the bolts before assembly.

    Once the new strip is in place it is possible to glue a strip of thin aluminium to the back of the crack, file out and fill the crack with a good quality body filler (about the size of a pea...) and touch up the paint.

    Stop drilling is the technique of drilling a small hole (3/32") at the end of the crack. This provides a radius instead of the tip of the crack which is infinatly sharp (or zero radius)

    Once again, good luck.

    Bruce.
    Last edited by Bruce Llewellyn; 17th January 2012 at 02:47 PM. Reason: Bolt details

  9. #9
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    Quote Originally Posted by Bruce Llewellyn View Post
    Hi everyone,

    What will happen with the maleable adhesive is that the crack will continue to grow from the bottom of the slot. Paint won't sustain the movement.

    There are a number of standard repair techniques for aluminium airframes in AC 43 which use flush rivets. AC 43 is available from the US Federal Aviation Administration or from the pilot supplies shops on major airports.

    I have used the insert patch technique on a cracked D bonnet where the bonnet was both cracked and stretched. This came about from the bonnet hinges getting sloppy and hooking into themselves. Any time you see a D with a sneer, this is probably what happened.

    Because the D bonnet is softer than SAE 2024 alloys it is necessary to use either soft rivets or solution treated rivets which are soft as treated but harden over time. AD rivets (as stocked by aircraft maintenance orgs) are too hard in their normal state.

    Self setting (blind or "Pop" rivets) can also be used, however solid rivets can be double countersunk so as to come up flush on both sides.

    The bonnet can be shrunk back into shape using panel beating techniques subject to the following;

    1) Use an aluminium hammer. These are not available, one has to get a lump of aluminium (SAE6061 T4 extrusion is good) and make a hammer. Draw file the faces, polish with wet & dry sandpaper up to 1200 grit and finish with tripoli soap or brasso. Lock the hammer up so people don't mistake it for a soft face hammer and ruin it.

    2) Backing (dollying) should be done with a hardwood dolly or a linen or leather bag of oiled steel shot blasting shot. About 1.5 th 2 kg for the bag. If using hardwood take the time to shape it properly to a curve that matches the shape you require.

    3) The area to be worked must be annealed before starting and usually during work. This can be done with a suitable heat gun or a propane torch. The technique is to strip all paint, glue etc from inside and out and rub ordinary sunight soap on one surface of the metal. Fill a bucket with cold water and have it ready. For small areas a cotton cloth (not synthetic, which can melt) should be soaked in the bucket.

    Warm the non soaped side until the soap turns brown, then quench with water. This softens the metal so it can be hammered.

    Wash off the singed soap...

    4) The same sort of technique can be used as for hot shrinking steel panels, hammering up a local high spot, annealing it, upseting it to shrink etc.

    Do not try to "pick up" aluminium panels with a pick type hammer. Only use flat faced hammers with a good to mirror finish.

    Remember that every time you hit it it is getting harder, so plan every hit.

    Now, I have not done this myself but I am told;

    Welding can be done by TIG or MIG using a steel block to back the joint. It will be necessary to anneal and planish the weld to remove the shrinkage. this is done by annealing then thinning the bead of weld metal by hammer and dolly. For this a steel hammer and dolly can be used, polished to mirror finish and oiled using engine oil.

    Don't grind the weld untll the panel shape is fair or you will have no metal available to upset to correct the shrinkage.

    Good luck...

    Bruce.
    Wow! I must recall all this when I repair my Space Shuttle.
    Cm'on were talking cars here not solution treated rivets.
    roger

  10. #10
    BVH Roger Wilkinson's Avatar
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    Go easy, roger. Bruce's info is sensationally detailed, even if most of us may not use it.

    Roger

  11. #11
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    Thanks everyone for the advice and suggestions. Based on the small size of the crack I think I will try the TIG welding option and hopefully that will be the end of the issue.

  12. #12
    Fellow Frogger! Bruce Llewellyn's Avatar
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    Default Rodgers' space shuttle repairs.

    Wow! I must recall all this when I repair my Space Shuttle.
    Cm'on were talking cars here not solution treated rivets.
    roger
    Hi Rodger,

    The space shuttle airframe is 2024 T3* basically the same as an airliner, so one would not need to use solution treated rivets, ADs will do.

    The problem is that AD rivets are readilly available (soft ones are not) but ADs are too hard for the aluminium used for D bonnets and land rovers, so the panel metal squeezes out rather than the rivet setting properly.

    If you find a source of soft contersunk 1/4 aluminium rivets, please post the info as these are used to hold the steel bonnet frame onto the skin. I have a nasty suspicion that Citroen used aircraft rivets simply because they are available courtesy of France being part of NATO. That is why western european aircraft (Aerospatiale, Fokker, Dornier, MBB etc) are full of imperial size fasteners.

    The SAAB 99 I have has AN-5 bolts holding the front calipers on- about $50 each from Hawker Pacific if one needs to replace one. These are the equivalent of SAE grade 12 which just shows the aircraft industry really does try too hard sometimes!

    The Mirage III operated by the RAAF aparently use a DS 7 cylinder hydralic pump as the emergency hydralic system pump. CX wiper arms are available new (at hienous price) because the Eurocopter Squirrel uses one. Being a 24v aircraft, the wiper motor is different...

    So the space shuttle repair isn't that far from the truth, and Citroens really are getting close to rocket science.


    * except for the inner cabin structure (pressure hull) which is welded 6061 supposedly so it doesn't leak...

    Bruce.

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