of AC's post-war 2 Litre Saloon

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Introduction/Wood Rot


The biggest source of trouble that led to the deterioration of old coach-built cars such as this AC, was the use of animal glue for the wood frame. This glue fails after contact with water, permitting joints to loosen and plywood to de-laminate. The frame becomes more flexible and this leads to cracking of the body panelling. The panels crack because when the car twists, the unglued joints distort and this over-stresses the panels near the corners of the boot-lid (the welds crack). Water gains free entry to the joints and rot can spread fast. This leads to further loss of strength and stiffness in the body frame, particularly when the boot side panels rot where they bolt to the chassis.

Most of the inner panels are of steel, and so these rust away. Once the inner rear wings have rusted through, the wooden wheel-arches become exposed and these rot too. The underframe is very robust, but can still rust away at the rear end. The rear underpan catches dirt and moisture.

The Challenge

Rebuilding wooden frame bodies seems to fill many enthusiasts with fear and foreboding! It is not especially difficult once you know about a few precautions and specialised techniques and tips. Basic woodworking knowledge is essential, but a high level of skill is not required. Patience, however *is* required! A large saloon car, coach-built, is a real challenge in terms of time invested, and will take a number of years if done in your spare time. Forget monetary values. If you like this fine car, then it is worth the trouble. You benefit from learning new skills and gaining satisfaction from a job well done. An added problem with the AC is that the original factory drawings for the wood frame were destroyed in a fire many years ago! My attempts to address this slight snag are covered in the section about the "Webmaster and his car".

Before You Get Started

Both before starting, and during dismantling, it is vital to build up data. This is partly photographic data of every detail so that you will know how to put everything back together again. Also, dimensions (especially the wood frame) need to be recorded. Dimensions of door surround, windows, wheel arches, length of scuttle, etc. etc. Keep in mind that the left and right halves of the body will differ slightly. If the frame is falling apart and distorted, then you will have to measure partly from panels, and try to establish what the remaining dimensions should be. Keep notes on joints, screws, fixings, routing of wires and pipes etc.

No Jigsaw Puzzles Here!

Contrary to popular opinion, a complex car body is not like a jigsaw puzzle. If you dismantle the wooden frame and reassemble it again (with or without repairs), its shape will have altered slightly. Doors won't close easily, while windows and panels might not fit. This is partly due to the amount of movement possible in each joint before gluing. Also, when removing major wooden parts, the remaining frame might sag or twist slightly. This will be worse if the car is slightly twisted to start with. Hand-made wooden parts don't always fit with engineering precision, and everything is finally pulled into shape when the screws are tightened, but springing out of shape when parts are removed.

The solution is to make alignment jigs - just as AC used jigs during manufacture - and also ensure that the frame is not twisted. Some of these jigs will take the basic form of a rectangle made from strips of wood, with a diagonal brace to keep it rigid. These are tailored to fit into the AC's wood frame at various points, transversely and upright, to ensure that the framework is kept in place/shape while work progresses. Other types of jig can be made to align the wood frame on the chassis, so that it goes back in exactly the original position.

Basic Plan

Unfortunately, the AC was not designed with restorers in mind. Like most coach-built bodies, the wood screws are mostly inserted from the outside, and are thus covered by the bodyshell. The bodyshell, needless to say, is not designed to be removed. But for a thorough rebuild, bodyshell removal appears to be the only way, and some of the wood is inaccessible otherwise. The bodyshell is fragile and it is easy to damage while moving it.

If that sounds too daunting, then there is a still a lot of work that can be done with the bodyshell left in place. A lot of the wood is accessible once the interior trim is stripped out, and the wings and inner wings are removed. This approach involves modifying some of the joints and construction, so you have to be sure that the finished structure is strong, but still as flexible as the original.

Some experts recommend removing the wood frame from the chassis to work on. This might be fine for a small car, but for the AC, I prefer to keep it firmly bolted to the chassis until all wood repairs are done, and the whole thing is firmly glued and screwed. With only a single garage to work in, this was the only option for me anyway. It is, however, important that the chassis is kept flat and not twisted at all. If still supported by the wheels, you need to make sure that the springs are settled, (friction in the springs can keep one corner of the car too high) otherwise slight errors can creep in if the rear chassis is slightly twisted.

Wood Rot and Woodworm - the basics

There are three main problems that cause decay of the AC's wood frame, in the UK climate. Namely: Wet rot, dry rot and woodworm (furniture beetle).

Wet rot: This is the main type of decay to be found on the AC. It is an attack by a fungus. As with many things, prevention is easier than cure. The wood needs to be very wet indeed for this type of rot to occur. Wood that has already been rotted may look sound at first until you try pressing a screwdriver against it, and it leaves a depression. Even a sharp wood-chisel should leave no more than a 'scratch' if pressed by hand against sound ash or beech. The softness may be just under the surface, so one has to be thorough in removing all rotted wood (but not before gathering data on dimensions, taking photos, or making templates etc.).

Dry rot: This is much worse than wet rot, but fortunately is also more rare. The fungus has a white fluffy appearance, and the affected wood will have splits across the grain, and will crumble into powder. It is not quite as bad as information on dry rot within the building industry suggests. Old practice was to remove several feet of sound wood from around the rotted area as a precaution! In fact, dry rot, like wet rot, actually needs very moist wood. Keeping it as dry as it should be will prevent the rot from occurring. It is true that dry rot can be very hard to kill off, and it needs to be treated thoroughly and then rotted wood cut out. It is perhaps worse in buildings because it can pass through - and live in - brickwork.

Woodworm: In the UK, the main source of trouble is the furniture beetle, which leave tell-tale tiny holes. Again, some information on this problem can be alarmist, although it may or may not be bad news if you spot these holes. The beetles lay eggs on the wood and then the larvae tunnel through the wood and spend a number of years doing so. However, they are fussy about their diet. They seek wood with high starch content, and the level of starch in timber depends on the time of year the tree was felled. Therefore, they don't touch some components on the AC, and may leave one or two tunnels through other parts as they pass through looking for 'better' food!

There is always the possiblity that a part with numerous holes visible has been badly undermined by a honeycombe of tunnels. The worst parts are likely to be the plywood. It is worse still if the plywood has delaminated. A lot of holes on the surface of the plywood components probably mean it has been destroyed inside and will crumble in your hands.

If you find active woodworm, leaving little piles of dust, then treat the affected wood (and surrounding wood) liberally with something suitable such as Cuprinol woodworm killer. Brush it on and also use their aerosol version and spray it into the holes. Be careful to wear protection including goggles, as the chemical will squirt out of adjacent holes. The wood should then be treated repeatedly every few weeks until you are sure there is no more active drilling going on.

Any wood that is badly affected, will have to be destroyed (after measuring and photographing).

The furniture beetles won't lay their eggs on painted or varnished wood, so prevention is fairly easy. Any holes remaining on the frame will have to be filled up, and I did this by injecting Aerodux adhesive using a gluing syringe. This, combined with painting the wood surfaces, should keep everything protected. I hope!

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Website started 29th December 2006