Buying a Six-Cylinder Bristol

We are often asked for advice on buying classic Bristols. We hope that the following general guidelines will answer the most commonly asked questions. Please contact us if you have any further queries — your questions may well find their way into future versions of this document. Note that we are unable to give opinions regarding specific cars, nor to recommend any Bristol specialist over another.

Why Bother?

There are probably as many answers to this question as there are owners, but most would put the driving experience very high on the list. They are responsive, modern-feeling cars with high-revving engines (especially by 1950s standards), slick gearchanges (even by today's standards) and light, accurate steering. They are comfortable and refined and capable of covering hundreds of miles in a day in comfort. The more powerful models in particular are perfectly capable of keeping up in modern traffic. They are well-made and, if properly maintained, very reliable. Our annual high-mileage award in 2003 went to the owner of a 406 which had covered over 14,000 miles in the previous year.

If your six-cylinder Bristol is running correctly, your passengers are liable say things like, “I can hardly believe how sophisticated it is. It's fifty years old, for goodness' sake!”

What is it?

As described in the history section of this website, the Bristol Aeroplane Company made its first car in 1946. It was based on pre-existing BMW technology, rescued from Eisenach at the end of World War II. The Bristol 400 essentially combined the best features of the pre-war BMW models, coupling the chassis of the 326 with the race-bred engine of the 328.

The Bristol engine

For many enthusiasts, the Bristol engine alone is worth the price of admission. Like many of the best “classic” designs, it now seems very old-fashioned in some respects, but appears hardly to have aged at all in others. On the old-fashioned side, it is a long-stroke, physically tall engine with what L.J.K Setright described as “a forest of pushrods” operating the valve gear. Conversely, it has very modern-looking hemispherical combustion chambers with short and straight inlet and exhaust ports, benefits of which include high specific output, commendable fuel economy and a zestful and free-revving nature.

The Bristol engine is based on a pre-war BMW design which, according to Jeff Daniels's Driving Force, can trace its origins back even further to the Austin Seven, which was built under licence by Dixi in Germany. When BMW acquired Dixi at the end of the 1920s, it embarked on a series of engine developments. With increases in bore and stroke, an increase in distance between the bore centres, two more cylinders and two additional main bearings – by which time it bore very little resemblance indeed to the original Austin Seven unit – the 747cc four had become a 1,971cc six by 1935.

The final development was an all-new aluminium alloy “hemi” cylinder head for the BMW 328 sports car. The advantages of hemi heads were well understood by this time, and they were used on virtually all of the leading contemporary racing cars, such as the Mercedes and Auto Union “Silver Arrows”. However, there was a practical difficulty in operating the valves with a single camshaft, since the inlet and exhaust valves were necessarily on opposite sides of the engine. BMW's solution was to keep the existing camshaft but add a curious “double-pushrod” arrangement to operate the exhaust valves, with additional short pushrods going across the top of the cylinder head. The result was a six-cylinder engine with a total of eighteen pushrods. However, as Jeff Daniels adds, “this odd adaptation not only worked, it worked extremely well, raising the power output from 50 to 80bhp and helping to make the 328 into a classic.”

When Bristol “liberated” the remains of BMW at the end of World War II, they put the 328 engine back into production with only minor changes. The threads were changed from metric to Whitworth, higher grade materials were used (for example, the cylinder liners were made of Brivadium, an extremely hard alloy used in Bristol's aircraft engines) and, according to L.J.K. Setright, the engine was built to a generally higher standard. The Bristol 400 used either a Type 85 engine, with one Solex carburettor and 75bhp or, more commonly, a Type 85A with three SUs and 80bhp.

Bristol developed the engine extensively over the following years. The original output was eventually more than doubled, with 170bhp at 7,000rpm available in the Bristol 450s that raced at Le Mans. This remains a respectable figure for a 2-litre engine today and was a considerable achievement in the 1950s.

Although the factory never released official figures, we estimate that approximately 2,600 Bristol engines of all types were produced from 1946 to 1961. Not all of them were destined for Bristol cars – at least 400 were installed in AC Aces, Acecas and Greyhounds. The bad news is that it will cost several thousand pounds to have a tired engine rebuilt by a good specialist. The good news is that it is a well-engineered and durable unit, and will normally cover over 100,000 miles without difficulty provided that it is maintained properly and provided that it is not driven hard before the oil has warmed up.

All six-cylinder Bristols were based on the same BMW-derived combination of chassis and engine, with relatively minor changes until the last Bristol 406 was built in 1961. The What to look for section is therefore identical for all models, at least in the mechanical department.

The mechanical components of the 400 are described in considerable detail in this article from Automobile Engineer, February 1950. The following changes were made for subsequent models:

401 (introduced 1948, discontinued 1953)

A memorable and aerodynamically efficient body, with push buttons for door handles and a drag factor (0.354 according to one source) that still compares well today. A larger car than the 400, and a full five-seater. Mechanically exactly as the 400, except that the three SU carburettors of the 400 engine (designated the 85A engine) were replaced with three Solex units for the 401 engine (designated 85C), raising the power output from 80 to 85bhp. Additionally, the chassis was extended backwards to support the new bodywork.

402 (introduced 1948, discontinued 1950)

A rare (approximately 20 examples) convertible version of the 401.

403 (introduced 1953, discontinued 1955)

An upgraded version of the 401, described by former club president Godfrey Oxley-Sidey as “a 401with the bugs taken out”. The main mechanical changes on the 403 are:

  • 100A engine with 100bhp replaced the 85C. The main differences between the two engine series are described below. The 403 was a much livelier car than the 401, with 0-60 available in 13.4 seconds rather than 16.4
  • Front anti-roll bar fitted
  • “Alfin” drum brakes fitted, initially on all four wheels but later only on the fronts (the rears were declared to be over-braked). More leverage on the pedal unit to reduce pedal pressures.
  • Heating and ventilation significantly improved, with an air recirculation facility.

Several owners have upgraded 401s to 403 specification and beyond.

404 and 405 (introduced 1953 and 1954, discontinued 1956 and 1958)

A new body style, with a grille apparently modelled on an aero engine nacelle rather than following the BMW “double-kidney” design. The 404 was a “2+2”, with a shortened wheelbase (8' rather than the 9'6" common to all other 2-litre Bristols). The 405 was Bristol's only four-door car. Mechanical changes from the 403 were:

  • 100B (404) or 100B2 (405) engine with 105bhp. These engines are identical to the 100A except that the compression ratio is raised from 7.5:1 to 8.5:1. 100B has a single six-way exhaust manifold, 100B2 has two three-way manifolds. The 404 was optionally available with a 125bhp 100C engine, which had more advanced valve timing.
  • The same gearbox was used, but it was fitted with a neat remote-control selector with a short gear lever, rather than the previous gear lever, which disappeared into the floor close to the driver's feet. This gear lever somehow seemed to improve further an already excellent gearchange, and several of them have been retrofitted to older cars. The last few 403s had both the 100B2 engine and this gear lever fitted as standard.
  • Overdrive was fitted to the 405. Several earlier cars of all types have had overdrive retro-fitted.
  • Disc front brakes were optionally available on the 405.

Approximately 40 405 Dropheads were produced, with coachwork by Abbotts of Farnham. These have the 100B engine and nearly all of them have disc front brakes.

406 (introduced 1958, discontinued 1961)

The 406 was a larger car than its predecessors, and more of a luxury car than a sports saloon. Future Bristols up to the 411 would retain the same basic bodyshell design.

Mechanical changes relative to the 405 were:

  • Type 110 engine enlarged to 2.2 litres by extending both the bore and the stroke. Power output still 105bhp, but produced at 4,700rpm instead of 5,000 and with better torque characteristics. Various other detail refinements – for example, this is the only Bristol engine with a timing chain tensioner.
  • Servo-assisted disc brakes all round.
  • Rear axle located by a Watt linkage, rather than the A-frame which had been used since the 400.

The 406 was the last six-cylinder Bristol. Cars generally had become very much faster through the 1950s; what had been a very rapid car by the standards of 1946 was now beginning to look expensive relative to the performance offered (somebody had commented that you could buy seven Jaguar litres for the price of two Bristol litres). From now on, all Bristols would have Chrysler V8 engines and automatic transmission. They were much, much quicker, but somehow they weren't quite the same...

Upgraded cars

Since the 400-406 are all based on essentially the same chassis, it will come as no surprise to learn that component interchangeability is close to 100%. It is not unusual to find early cars with later engines, overdrives and/or disc brakes. The more powerful engines in particular are highly prized and find their way into all kinds of unlikely places (we are aware of at least one pre-war BMW 327 with a Type 110 Bristol engine).

Overdrive is a most worthwhile addition - it transforms the cruising ability of the car. Contemporary road tests spoke of standard 401s being able to “cruise effortlessly at 80mph,” but “effortless” was measured by different standards fifty years ago! Overdrive was fitted as standard to 405s and 406s. There is a hard way and an easy way to fit overdrive to the remainder. The hard way is to use a Type A overdrive, which was the type fitted by Bristol. Unfortunately, this is a complicated installation, involving modification of the chassis to prevent the overdrive unit from fouling a cross-member. The easy way is to use a smaller Type J overdrive, not available in the 1950s, with an adapter kit that is available through specialists. From the driver's seat, there is no noticeable difference between the two installations.

Engine variants

In theory, any of the Bristol six-cylinder engines could be installed in any of the cars. In practice, it is not too uncommon to find 400s, 401s and 402s fitted with later engines. The opposite situation is rarer but not unknown.

There are three main series of Bristol engine, with a number of variations existing within each series:

85 series engines

The original Type 85 engine was essentially the pre-war BMW 328 unit, built of higher-grade materials and with Whitworth rather than metric threads. Bore and stroke 66 x 96mm, giving capacity of 1,971cc. 85 series engines were fitted as standard to 400s, 401s and 402s.

100 series engines

Compared to the 85 series engines, these have larger valves, greater valve overlap, larger main bearings (2.125" diameter instead of 2") and a Hobourn-Eaton oil pump rather than a gear-type pump. Valve gear is lightened to improve refinement at high rpm. 100 series engines were fitted to 403s, 404s and 405s. The higher-performance variants, specifically the 125bhp 100D2, were also fitted to AC Aces.

110 series engines

Introduced in 1958 for the Bristol 406. An increase in both bore and stroke (to 68.69 x 99.64mm) brought the capacity up to 2,216cc. Various detail engine changes included re-shaped pistons and the addition of a timing chain tensioner. No more powerful than the 100B2 that it replaced (105bhp), but a lower power peak (4,700rpm) and a flatter spread of torque.

Two sports series of engines were built in smaller volumes:

FNS series engines

Supplied to Frazer Nash for their limited-production post-war sports cars. Increased valve overlap and larger inlet tracts compared to the 85-series engines on which they are based.

BS series engines

These are the “Bristol Sports” engines. Fitted to Arnolt-Bristols, Coopers, ERAs, Lotuses, Listers, Tojeiros and a number of “one-offs”. The few Bristol saloons fitted with BS-series engines are deceptive and thrilling cars. There are several variations, including magneto or coil ignition and chain or gear drive for the camshaft. Unlike the FNS engines, the BS models are based on the 100-series block with its larger main bearings. (Members may refer to Godfrey Oxley-Sidey's Bulletin article for further information about the BS series.)

The characteristics of the various engine types can be summarised thus:

EngineCar typesBHPat RPM CompressionCarburettors
85 400 75 4200 7.5 1 x twin-choke Solex
85A 400 80 4200 7.5 3 x SU
85B 400 (option) 90 4500 7.5
85C 401 85 4500 7.5 3 x Solex
100A 403 100 5000 7.5
100B 404 105 5000 8.5
100B2 405 105 5000 8.5
100C 404 (option) 125 5500 8.5
100D/D2 AC Ace 128 5750 9.0
110 406 105 4700 8.5
110S 406Z
AC Greyhound
130 5750 9.0
FNS 1 Frazer-Nash 126 5500 8.5
BS1 Mk 2 Arnolt 130 5500 9.0
BS1 Mk 3 142 5750 9.0
BS1a Mk 3 148 5750 10.0
BS4 Mk 1 & 2   142 5750 9.0
BS4a Mk 1 & 2 155 6000 11.0

What to look for

General

The first problem with test-driving an unfamiliar make of car is precisely that: its unfamiliarity. When we talk of a “responsive, modern-feeling car” — responsive compared to what? We would always suggest driving a “known good” example right at the start of your project in order to get a feel for what the cars should be like. The few dealers that specialise in Bristols will generally have cars in stock that range from fairly good to exceptional. There is also much to be said for joining the owners' club, attending events and talking to current owners.

A note on originality

With some makes of car, originality carries a high price premium, even down to matching engine numbers. It is certainly an attractive bonus if a car still has the engine with which it left the factory, but this does not seem to make any appreciable difference to Bristol values. Several of the earlier cars have been fitted with later engines and brakes and with overdrives; far from reducing the car's value, this generally enhances it. Radial-ply tyres were not available when the early cars were new, but they behave well with them. Flashing indicators were not fitted until the introduction of the 405; several owners have fitted them and disconnected the semaphore indicators in the interests of safety. Generally, enhancements which improve the car's usability are regarded as desirable provided that they have been competently fitted.

The following sections presuppose some familiarity with assessing cars in general, and are intended only to point out specific features of the Bristol. These sections are organised against the same headings as the Bristol 400-403 workshop manual, which is available in facsimile form from the club.

Engine

The engine is well-made and should be very durable if used sympathetically and serviced regularly. It should be possible to achieve 100,000 miles between rebuilds. However, it could cost up to £10,000-£12,000 to rebuild a worn out engine, so it pays to make sure you get a good one.

According to the 401 handbook, the correct oil pressure at 3,000rpm with an oil temperature of 70°C is 60psi. It will normally take several miles' driving to get the oil up to working temperature. The general rule is to take it easy until the oil temperature gauge lifts off its (30°C) stop, and (again according to the handbook) not use full performance until the oil temperature has reached 40°C. So be wary if the owner thrashes the car from cold...

A Vokes-type paper element oil filter was fitted originally; almost all engines by now will have had an adapter fitted so that a normal disposable screw-on oil filter can be used. In many cases, an oil cooler will have been fitted too, although Bristol Cars and other experts insist that this is not necessary except in the most extreme conditions.

It is worth checking to see that the starting handle is present (in the boot on the 400, clipped to the right hand side of the engine bay on other models) since it is useful for setting valve clearances and for fitting fan belts as well as starting the engine.

The engine uses small 10mm spark plugs; the original plugs are no longer available. Fortunately, motorcycle plugs fit and work at least as well as the originals.

Cooling System

There are two coolant drain taps, one at the bottom right of the radiator and the other at the left rear of the engine block. Ideally both should turn freely and release coolant. In practice, the block drain in particular is very frequently silted up. It is rather difficult to judge whether the block is silted up to any significant extent, but it is possible to check whether the radiator is working at full efficiency by placing ones hand on it (being careful of scalding, of course) in various places when the engine is warm. The radiator core should be warm right across its surface, although it will be cooler at the bottom than at the top. Cold spots are a bad sign.

Despite the advice in the handbook that pure water should be used in the summer, we suggest using a modern antifreeze solution all year round in order to minimise corrosion.

Fuel System

401-403s have aluminium fuel tanks, which are held in place by steel straps. If moisture has been allowed to penetrate between the tank and the straps, corrosion will follow. Removing and repairing the tank is a time-consuming process.

On all models except the 400, which has no fuel reserve, the fuel feed unit consists of two copper pipes of different lengths (for main and reserve feed) descending into the tank from above. Occasionally these pipes crack, resulting in a car which seems to run out of fuel even though the tank is still half full.

Clutch

As with most cars with floorboards and separate chassis, the clutch and gearbox are relatively easy to get at. The clutch is the same one as is used in the MGA.

Gearbox

Durable and well-engineered, and with a light, slick change that adds greatly to the pleasure of driving the car. Bristol saloons have a freewheel on first, which occasionally fails under “traffic lights grand prix” conditions. The handbooks of the later cars warn, “The freewheel will carry all normal loads but it is possible, particularly with the higher power of the latest engines, to impose very severe stresses which can result in gear fracture.” Some freewheels have been replaced with fixed first gears. Arnolt Bristols and ACs have fixed first gears, presumably because these were more likely to be entered for the “traffic lights grand prix”.

All gearboxes have synchomesh on second, third and top gears. On all 400s and early 401s, Bristol's own synchromesh mechanism is used. On later 401s (from chassis 1006 onwards) and all later cars, a Borg-Warner synchromesh is used. Although the short remote-control gear lever can be fitted to any gearbox, a service bulletin advises against fitting this to a gearbox equipped with the Bristol synchromesh.

Rear suspension

A well-located live axle, with long longitudinal torsion bars (ending roughly parallel with the fronts of the front seats) and a double articulation connecting each of these to the axle. Additional location provided by an A-frame above the differential (400-405) or a Watt linkage (406). Early 400s have lever-type shock absorbers connected directly to the torsion bars; later 400s and all other models keep the housings (without internals) but use proprietary telescopic shock absorbers instead. Telescopic shock absorbers were originally made by Newton & Bennett; modern Koni or Spax will fit with minor modifications.

Front suspension

This is a double wishbone design with a single transverse leaf spring forming both the lower wishbones. The exposed ends of the leaf spring should be covered with leather gaiters, intended to keep grit and dirt away from the leaves. The gaiters deteriorate with age and it is not unusual to find that they have been removed. New gaiters are available.

Early cars have Bristol's own lever arm shock absorbers, later examples (from chassis 1006) have telescopic dampers. As with the rear suspension, modern dampers can be made to fit.

There is a one-shot lubrication system which supplies oil to the king pins and steering rack. This is a reliable system, but it does appreciate being used regularly. It often gets disconnected and replaced with grease nipples, necessitating a lot of work to put the one-shot back into operation.

Brakes

Steering

Wheels, brake drums, hubs and tyres

Although all cars were originally fitted with cross-ply tyres, radials have been found to work well; they are however not recommended for the Type 400 wheel, which requires cross-plies. Michelin X have been available since the cars were nearly new and give good performance, but are expensive (about £200 each). Some owners have found that Vredestein tyres give comparable performance at much lower cost. Taxi tyres will fit, although opinions differ on their performance: they are not rated at the maximum speed achievable by the Type 401.

Chassis

This is a large (6½ inches deep) and almost indestructible box-section frame. The 404 has a shortened chassis with a wheelbase of 8'; all other Bristols up to and including the current Blenheim 3 (but not the Fighter) have a 9'6" wheelbase. It is possible that you will find corrosion in the main chassis (in the 400, there is a water trap where the body meets the chassis). It is more likely that you will find corrosion in the extension legs behind the rear wheels that are connected to the telescopic dampers. This is time-consuming and expensive to fix, and is an MoT failure point.

One-shot lubrication system

One-shot lubrication systems were fairly common on upmarket cars in the 1950s. If used regularly, they can give excellent service. When a pedal in the passenger compartment is pressed, a measured "shot" of oil is sent to each king pin, to the steering rack and to the steering pinion. The pedal should be pressed every 70 miles (according to the 401 handbook) or 100 miles (406 handbook) in normal conditions, more frequently in very wet or muddy conditions. The oil reservoir should be filled with either engine oil (401 handbook) or heavy gear oil (406 handbook).

If the one-shot system is working properly, it is usual to see oil dripping down the insides of the front tyres when the car is parked. If you see a stream of oil on one side but not the other, it is possible that the system might be blocked on that side. It is also possible for the non-return valve to stick open, so that oil seeps out regardless of whether the pedal is pressed.

Electrical system

Many owners fit flashing indicators (semaphores were standard on 400-404) and higher-intensity tail and brake lights. Alternators are often fitted in place of original dynamos. It should be noted that there are only two fuses on the entire car, that many circuits are unfused and that rubber-insulated wiring is likely to have deteriorated considerably after fifty years. Re-wiring is a substantial project but a worthwhile one.

Body

The 400 has a steel body on an ash frame. 401-403 and 406 have an aluminium body built up on a framework of steel tubes – the Touring Superleggera construction. 404 and 405 revert to an aluminium body on an ash upper frame. The combination of steel chassis, aluminium and timber on the 404 and 405 is particularly vulnerable and care should be taken to ensure that the structure is sound.

On the aluminium-bodied cars, corrosion will appear where steel meets aluminium, particularly where insulation between the two metals breaks down. On the 401-403, this tends to be on the sills and immediately above the front bumper. Although seldom terminal, this can be unsightly and is expensive to repair. All body panels for these cars have to be made from scratch.

The interior is trimmed in high-quality leather; it is extremely difficult nowadays to obtain leather of the same thickness. A car should ideally have a high-quality retrim or an attractively patinated original interior. A vinyl or cloth interior, or an original leather one that is tatty to the point of falling apart, would typically cost over £6,000 to replace.

How to buy a six-cylinder Bristol

These cars were expensive to build when they were new; it is therefore unsurprising that they are expensive to rebuild now that they are decades old. Most of the classic car magazines publish price guides updated (allegedly) on a monthly basis and, rather than publishing a table of figures here, we would refer you to these.

There are always personal reasons for wanting to restore a car: perhaps it has been in your family for generations, or perhaps you enjoy carrying out the work yourself. Unfortunately, it is highly unlikely that you will find valid financial reasons for restoring a Bristol since, for most models, the cost of restoration will far exceed the return. One specialist indicated that a full rebuild of a 401/403 could cost £80,000-£100,000 (Classic Cars, January 2004). At the time of writing, an excellent 400, 401, 403, 405 or 406 can be bought for the cost of an engine rebuild plus an interior retrim, with the rest of the car effectively for free.

Cars for sale can be found in the club newsletter, in the classic car magazines, at a small number of specialist dealers, at classic car auctions and occasionally on eBay. The rarest models, such as 402s, 405 Dropheads and the few cars with bodies by coachbuilders such at Farina and Zagato almost always seem to change hands through the club — so, especially if you want one of these, we urge you to join!

The painless way to Bristol ownership is to buy a car in excellent condition, and which requires no major work. One specialist suggests the following:

  1. Do your homework (this article should have given you a head start on this).
  2. Buy a car on which any major work has been carried out by previous owners.
  3. Buy a car with recent history. A service history that finished ten or twelve years ago is meaningless. If the car has not moved for several years, it may have deteriorated significantly, even if it looks wonderful.
  4. Get it inspected by a Bristol specialist. Most specialists are happy to undertake assessments for their normal labour rates plus reimbursement of their travel costs.
  5. Buy the best that you can afford.