Technical Information (MGB 10)
MGB Engine Rebuild Info
MGB Engine Rebuild Info
WE REGRET TO INFORM YOU THAT BRITISH AUTOMOTIVE NO LONGER REBUILDS
MGB OR MGA ENGINES. HOWEVER, THE FOLLOWING INFORMATION IS RETAINED AND
RE-EDITED FOR YOUR REFERENCE.
Engine rebuilds are usually rebuilt in the following sizes: .020",
.040" and .060", OEM pistons. Also available are engine rebuild sizes
83mm (3.268" - 1924cc) and 83.5mm (3.288" - 1948cc). JE custom
forged pistons. However, .010" .020" .030" .040" & .060" may
in the same manner. This may be beneficial to prospective MGB engine
rebuilders who require precise CR control.
NOTE: Even larger capacity engines of 2000cc are being built by companies
here and in the UK. This requires offset boring techniques which, we prefer
to stay away from.
Normally, we supply JE pistons in a flat top configuration with a piston
height of 1.700". This additional height over the OEM 1.660" allows
additional material removal where necessary. Incorporated in the piston design
is an unsually thick piston crown, this allows us to machine the appropriate
cc dish without piston crown breakthrough.
However, if you have calculated the exact piston cc dish you require
this can be done during the piston manufacturing process. This also applies
to the piston pin height.
For further information see MGB11 "MGB PISTON CHOICE"
OEM PISTON CHOICE
We seldom see the use of +010" oversize pistons so we shall
concentrate on the following oversizes:
Oversize Bore Size Capacity
020" 3.180" 1822cc
030" 3.190" 1834cc
040" 3.200" 1846cc
060" 3.220" 1868cc
8.7:1 compression ratio (CR) pistons 1963-71 were designed with a
piston dish cc (cubic centimeters) capacity of approximately 6cc,
and were designed to be used with cyl/heads having a combustion
chamber volume of 42.5cc-43.5cc. These cyl/heads are identified as
Part # Engine # Casting # Year
48G318 18G/GA/GB 12H906 1963-67
48G538 18GF/GH/GK 12H2389 1968-71
8:1 CR pistons (18V 1972->) on were designed with a piston dish
capacity of approximately 16cc and were designed to be used with cyl/heads
having a combustion chamber volume of 39cc. These cyl/heads are
identified as follows:
Part# Engine # Casting # Year
48G644 18V584/5 672/3 12H2923 1972-74 1/2
BHM1062 18V797/8 801/2 CAM1106 1975 on
NOTE: The above is applicable to the USA market. UK and over markets
have similar cylinder heads with different indentification markings.
The use of 8.7:1 CR pistons, with cyl/heads designed for use with
8:1 CR pistons, will result in abnormally HIGH CR's unsuitable for
street usage with today's low octane fuel unless octane boost is
added; otherwise, detonation and engine damage will occur.
Conversely, the use 8:1 CR pistons with cyl/heads designed for use
with 8.7:1 CR pistons, will result in abnormally LOW CR's. Although
you will not suffer from detonation problems, the vehicle will
certainly lack performance quality.
Information on CR's can also be found within the website.
As outlined above, British Automotive no longer has as an engine rebuild
program. However, the following information outlines exactly what went
into our rebuilding program.
The following information shows exactly what goes into the engine
rebuilding process and, as you will see, it is very extensive; far
beyond what may be carried out by other engine rebuilders who
advertise rebuilt engines in the $1200-$1500 price range. After
final assembly, the engine is test run, and adjustments made to the
ignition timing and carburetor emission levels. This assures you
that there are no unpleasant surprises when you start your vehicle.
On customer installed engines, it is very important that the
following items be given priority:
1. Oil cooler & oil cooler hoses must be thoroughly cleaned & flushed
out. The oil cooler, in particular, is notorious for harboring
micro particles of engine debris. We highly recommend replacement
of the OEM oil cooler hoses with the stainless steel braided type.
2. Radiator should be boiled out and flow tested, if there are any
doubts replace it.
3. Replace the heater control valve, unless recently replaced.
4. Reverse flush your heater core, this can be done very easily with
a regular garden hose.
5. Add 50/50 coolant.
6. Install coolant recovery system. New engines run considerably hotter
than older ones. British Automotive's expansion tank is ideal if a
problem is encountered with coolant loss via the radiator overflow hose.
MACHINE WORK - CYLINDER BLOCK
Chemically dip cyl/block and paint.
Re-deck cyl/block if necessary.
Flycut exhaust valve notches in cyl/block.
Rebore & hone cylinders (sleeve installation additional $).
Regrind, heat treat and nitride camshaft.
Install new camshaft bearings.
Machine pistons to 9:1 GCR or your GCR choice (applies to JE custom
forged pistons only). See further information within website.
Magnaflux and recondition conrods (new bolts/nuts).
Magnaflux and regrind crankshaft (journal welding additional $).
Line bore or hone main bearing caps.
Balance crankshaft, pulley, piston/rods, flywheel & clutch cover
All engine plates, OEM ex/manifolds, brackets & covers etc.
chemically dipped to remove rust/corrosion etc. and painted.
MACHINE WORK - CYLINDER BLOCK. REQUESTED WORK AT ADDITIONAL $.
Cross drill crankshaft and nitride (high RPM applications only).
MACHINE WORK - CYLINDER HEAD
Clean and magnaflux cyl/head.
Install silicon exhaust/intake bronze guides.
Install hardened exhaust/intake valve seats.
Carry out valve job (cyl/head crack repair additional $).
Rebush and reprofile rockers.
MACHINE WORK - FLYWHEEL
Lighten and resurface flywheel.
Install flywheel ring gear if necessary.
MACHINE WORK - EXHAUST MANIFOLD
Resurface exhaust/intake manifold if necessary (1975 on
Remove and install new exhaust manifold studs.
All engines run, tested for oil leaks, retorqued and valves
adjusted. Ignition timing adjusted to OEM specs. Carbs synchronized
and exhaust emissions adjusted (carb overhaul additional $). The
following applies to British Automotive's engine installation only:
Radiator boil out (recored or new radiator additional $).
Flush and clean out oil cooler and oil cooler hoses (replacement
steel hoses highly recommended).
12000 MILES or 12 MONTHS warranty, whichever occurs first.
ENGINE COMPONENTS INSTALLED - CYLINDER BLOCK
New piston assemblies.
New camshaft bearings.
New oil pump (modified as necessary).
New lifters (modified).
New crankshaft/flywheel bushing.
New king bearings (Vandervell production).
New timing chain.
New timing chain tensioner.
New connecting rod nuts/bolts/bushes.
New water pump.
New 3-piece clutch assembly.
All new oil seals, gaskets, locktabs, freeze plugs, oil gallery
plugs, hardware, etc.
COMPONENTS THAT MAY BE REQUIRED AT ADDITIONAL $
Flywheel ring gear (worn teeth).
Crankshaft/camshaft gears (worn).
Connecting rods (unreconditionable).
Crankshaft (cracked or otherwise non-regrindable.
Distributor and oil pump drive gears.
ENGINE COMPONENTS INSTALLED - CYLINDER HEAD
New silicon intake guides.
New cast iron exhaust guides. *
New exhaust valves.
New intake valves.
New valve springs.
New rocker shaft (nitrided).
New hardened exhaust/intake valve seats.
New rocker arm bushes.
* NOTE: Due to the excessive expansion characteristics we prefer
to install cast iron guides only, along with "O" ring type
valve stem seals.
ENGINE COMPONENTS INSTALLED - GENERAL
New temp/gauge transmitter (1968 on).
New engine mounts, coolant, vacuum, fuel & emission hoses, belts.
All new filters, gaskets, grommets, hardware, etc.
SPECIALIZED COMPONENTS AVAILABLE AT ADDITIONAL $
Roller rockers (1.5:1, 1.55:1, 1.6:1)
Rimflow exhaust/intake valves.
British Automotive's 1-piece side plate cover (highly recommended).
Obviously, engine rebuild prices can vary with the choice of
different components, but the following should be a guideline:
020", 030", 040", 060" (OEM pistons) Approx. $3500
All custom forged piston sizes (as above)
including 83mm and 83.5mm Approx. $4000
Removal & installation Approx. $ 500
We acknowledge that our engine rebuild prices are higher than our
competitors, we sincerely hope that the literature you have just
read will help to convince you of the professionalism involved in
the engine rebuilding process. With approximately $2400-2900 in
machine work and parts, it is hard for us to work out what you are
getting for your $ in a cheaper alternate engine rebuild.
All engines are assembled with a geometric compression ratio (GCR)
where possible, unless the customer specifies otherwise. Rebuilding
an engine with less than 9:1 GCR means you are not taking full
advantage of the engine's potential to develop worthwhile BHP/TORQUE
figures. While GCR's in excess of this figure will result in higher
BHP/TORQUE numbers, there is a possibility of inducing detonation
with pre-ignition and run-on (diesel) conditions, both of which
could cause engine damage. However, we would like to point out that
the fuel octane rating, ignition timing, lean mixture condition, and
high engine temperatures, all play a part in controlling these
Let's take a look at the specified fuel octane rating required as
per the factory "Driver's Handbook": 1963-71 with 8.7:1 CR engines
require 98 leaded octane fuel; 1972-75 (Fed) require 93 leaded
octane fuel; 1975 (Cal) onwards and 1976 (Fed) onwards require 93
unleaded octane fuel. Today's unleaded fuel octane rating is 92/93
depending upon the area of the country where it is sold. We have had
good success rebuilding engines with 9:1 GCR and using 92 octane
unleaded gasoline. The only area where a problem may arise is
"run-on" conditions. Starting in 1973, all MGB's were fitted with an
anti "run-on" solenoid circuit, so this problem should only be
applicable to 1963-72 vehicles.
We also recommend that you change your oil and oil filter at 500
miles after the initial engine rebuild using 20W/50 (10 deg.F -100
deg.F or over), or 10W/40 (10 deg.F or lower) and at intervals of
3000 miles thereafter. We highly recommend a product called "Tufoil"
which should be added (8oz) at 500 miles as outlined above, and a
4oz treatment every 3000 miles thereafter.
It is your investment and a considerable amount of money is tied up
in your engine rebuild, therefore, always keep your engine in tune
and remember lean fuel mixtures (air leaks etc.) and rich fuel
mixtures (sticking automatic choke etc.) will damage your engine.
CAUTION: If you have decided to proceed and fit OEM pistons, be
advised that it may be difficult to arrive at the desired 9:1 GCR
and in all probability will exceed this figure. See additional
information within the website.
While indicated GCR's are calculated by measurements, the effective
compression ration (ECR) is determined by checking the actual
closing of the intake valve. See MGB11 "MGB PISTON CHOICE"