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Engine Tech Talk

General Advice
Engine Preparation
Engine Rebuild

Whether you drive a modern or older car, it is possible to improve engine power efficiency by fitting selected performance products which simply bolt on to the engine externals. High flow air filters allow the engine to breathe better which, coupled with adjustments to the carburation or injection, will provide an improvement in power and response. Most factory fitted ignition leads are carbon cored and these will deteriorate with age. Fitting a high specification lead set will restore engine performance (especially under heavy engine load conditions), and will improve cold start operation. While on the subject of ignition, if your car is an older model, fitting an electronic ignition kit will ensure peak performance - and there are no points to worry about. Engine driven cooling fans are renown for causing all sorts of problems. In the summer, in traffic, they allow the engine to overheat - in the winter they prevent the engine warming and driving those fan blades around absorbs a lot of useful engine power! The answer, of course, is to fit a thermo-statically controlled electric cooling fan.

The value of any improvement or performance upgrade will be determined by the 'health' or otherwise of the engine in question. The areas of improvement mentioned thus far are fairly modest but to venture much further along the road to high performance will be doomed to failure if your engine is not in a sound condition. Some bolt-on products such as carburettor conversions or engine (chip) upgrades will increase the stress placed on an engine and can exacerbate any existing wear problems, so it is always a good idea to have the engine fully checked over and serviced beforehand. At the very least make sure the engine is treated to an oil and filter change using synthetic or premium quality oil.

Last and probably one of the most popular bolt-on performance enhancing items purchased is the exhaust system. Many original equipment exhausts are restrictive in their design and the full potential of any increase in engine power wilt not be achieved until the exhaust is replaced with a suitable free flow system. A very comprehensive range of manifolds and systems are available for most cars including the increasingly popular stainless steel types.

So let us now move on to the more serious aspect of engine modification. The next logical step is to modify the top end where, in most cases, substantial power gains can be achieved. Choosing the correct stage of cylinder head and matching this with the right camshaft is very important. Most modern engines are overhead cam (OHC) design and removing the head can be carried out with the engine 'in-situ'. For older overhead valve pushrod engines, a cam change will almost certainly require the engine to be removed from the chassis and at least a partial strip down of the bottom end.

Finally any attention or modification to the bottom end will require a complete engine strip down. If the cylinders are to be rebored then an increase in engine capacity is always worth considering. Whilst on this subject, it should be recognised that one of the easiest routes to more power is to fit a larger capacity engine. Many cars have various engine options for any given model so moving up from a 1300cc to a 1600cc engine or a 1600cc to a 2 litre should give a very noticable increase in performance. This type of work should be carried out by professional engine builder but for the competent enthusiasts amongst you here is the following additional advice:

GENERAL ADVICE:

Firstly, what follows is not intended as a complete guide to performance engine preparation. It should be regarded only as a supplement to manufacturers workshop manuals and specialist publications on engine tuning and related subjects.

First decide on your objective - this might sound obvious but many projects are carried out without any real planning. Decisions should be made regarding usage (will it be an everyday road car, occasional use / second road car, or one of the many classes of off road competition cars), cost (unless money is no object you should decide on a realistic budget that you can cover), and what facilities are available to you to carry out the work? This last point is extremely important because, apart from a good selection of tools and equipment to hand, a successful engine rebuild can only be guaranteed if the work is carried out in controlled, dare we say 'clinical' conditions. Taking these points one by one:

• Usage: If the car is to be used on a daily basis then flexibility and smoothness will be as important an issue as extra power. A moderate increase in power over the standard engine can always be gained (albeit at a slight rise in fuel consumption) whilst still retaining the original driveability. However, the products to be used in such conversions should always be carefully selected with careful consideration to other factors such as
• Automatic Transmission: As a general rule be very wary if you are considering any head or cam modifications. Such modifications can drastically alter the operation of an automatic box due to the changes in manifold pressure/vacuum. The ability of many auto boxes to cope with the increased power must also be questioned. 
• Emissions: Current legislation dictates strict controls over exhaust emissions. Over enthusiastic tuning may result in an MOT failure if unsuitable camshafts, carburettors, etc., are fitted. 
• Fuel Injection (MFi): The early mechanical types of fuel injection systems do have a small range of adjustment. Professional recalibration of the injection system will be required for any large increases in performance. 
• CFi/EFi & Engine Management Systems: As used to control all modern car engines. Some early pre' 1992 EFi types (e.g. Mk4 Escort CVH) did have a provision for adjustment of the TPS but adjustment should not be attempted by the inexperienced. For all other types professional 're-mapping' may be required depending on level of tune. 
• Catalytic Exhausts: These are now common place in all modern cars and are very sensitive to changes in exhaust emissions.
  
  
  

For occasional use cars (usually a second vehicle) the above criteria apply but, since power gains are more important than some loss in low speed torque and flexibility, the stage of tune will generally be higher. Off road competition cars allow the most scope for the ultimate stage of tune but will, invariably, have certain restrictions depending on regulations/homologations.

Cost: 'If you can't afford to do the job properly please think again'. The worse thing anyone can do is shop around for the cheapest parts. That is not to say you shouldn't find a cost-effective supplier to deal with. The lesson we are trying to get across here is that not all components on sale are of sufficient quality for use in a standard engine let alone a highly tuned one! Saving a few pounds on a cheaper head gasket will not seem such a good idea when the head has come off again after only a few weeks use. For other performance critical parts the cost of failure can be far greater.

Facilities: you will need a clean, light garage or workshop together with a comprehensive tool kit which will also include the following specialist tools:

• Good quality torque wrench 
• Valve spring compressor 
• Piston ring compressor 
• Feeler gauges 
• A pair of heel bars and / or a puller.
  
  

If you intend to set up cam timing you will also require a DTI gauge and magnetic stand together with a 360° protractor. A good workshop manual should also be to hand.

Engines can be built on a flat bench but the job is far easier when using a proper engine stand. These are relatively cheap to buy (see our tool section) or can be hired. As mentioned previously, cleanliness and degreasing the components is essential, as is a good supply of lint free cleaning cloth. Use compressed air (if available) and/or gallery brushes to clear oil galleries, etc., and assist in the removal of any residual dirt or debris. (Note: always wear goggles and gloves and keep nozzles pointing away from body.

ENGINE PREPARATION

This is a general guide to correct procedures and will apply, wholly or partly to all types of engine rebuild. However, before the engine rebuild can begin the engine needs to be stripped down, cleaned and examined, a procedure which many undertake with undue haste. During the strip down the following should be observed:

• Wait for the engine to cool properly before removing the cylinder head - this applies especially to aluminium types. The consequence of not waiting can result in a warped head.
• Mark the location (and, where applicable, orientation) of all major components especially valves, tappets, camshafts, pistons and rods, shell bearings by placing in clearly marked containers or racks.
• Before removing bearing caps (e.g. camshaft, con rod, main bearing), make sure they are clearly marked for position and orientation N.B. they must go back in the same position or on the same con rod and the right way round.

Once stripped all parts should be thoroughly cleaned and inspected with specific attention to any areas of bad wear or damage e.g.: -

• Blown head gasket / burnt out valves - cylinder heads should always be thoroughly examined for cracks or distortion. Simply fitting a new gasket or valve is not the answer.
• Damaged piston/rings - always check the cylinders for wear and damage. If the pistons need replacing, a rebore is almost certainly needed as well.
• Badly worn crankshaft shell bearings - if the crankshaft is badly scored it must be reground to the next undersize. However, just as important are the con rod and main bearing housings that the shell bearings fit into. These are often overlooked and any wear or distortion in these areas will cause premature engine failure.

Cleaning should include the removal of all oil gallery plugs to enable thorough cleansing with special brushes (see tool section). Many parts can be re-used during the rebuild but the following items should always be replaced:

• All gaskets and seals 
• Shell bearings 
• Timing belts or chains 
• Timing belt / chain tensioners 
• All major fastenings including cylinder head, con rod and flywheel bolts. 
• Piston rings 
• Oil Pump drives

We will now discuss what modifications can be carried out to increase engine performance and some of the pitfalls to watch out for. We shall assume that any remedial work to restore these components to their original specification has been carried out.

Cylinder Heads: Arguably the most complex and important engine component especially when it comes to modification work. If a road stage cam kit is being fitted it will usually involve fitting the heavy duty valve springs. Always refer to the manufacturers fitting guide and check the valve spring fitted length - the valve spring seats in the cylinder head should be machined if there is not enough clearance. New tappets/followers must always be fitted when installing a new camshaft. If you have an older engine which is not suitable for running on unleaded fuel, now is a good time to consider having hardened exhaust valve seats fitted. Any higher stages of tune will usually involve fettling around the ports and chambers to accommodate larger valves and the fitment of specialist high performance parts e.g. 214N valves, bronze valve guides, heavy duty valve springs, etc. This type of work is best left to the experts. Finally, a check on the matching of the inlet and exhaust to the cylinder head ports should be carried out. The exhaust manifold should always be LARGER than the cylinder head ports to prevent the build up of any turbulence or back pressure. The inlet manifold ports should be very slightly smaller than the cylinder head ports or, preferably, matched and dowelled by a specialist. Finally, remember to check that the manifold gaskets do not mask any areas around the cylinder head ports. Large bore gaskets are available for the popular engine types.

Bottom End: The two most important criteria for this area of strength and weight. For the more moderate stages of tune the standard parts can be used.

Cylinder Block: Most standard blocks are strong enough to withstand at least a 50% increase in power or more. Problems usually arise because machining has compromised their structural strength. The two main areas for this are the cylinder bores and the top face. Excessive machining of either of these willresult in piston ring blow-by and/or head sealing problems. As a general rule most cylinder blocks will overbore safely to +lmm (.040") and many to +2mm (.080") - this will give a very useable increase in capacity and power. Exceeding these limits however will greatly increase the risk of cylinder bore distortion and piston ring blow-by. 'Decking' the top face to improve compression ratio and combustion (squish) usually involves machining no more than .5 to 1 mm from the block face and this should have no detrimental effect. However if the block face thickness is reduced to excess this may cause irreversible gasket sealing problems. It should also be noted that excessive machining of the cylinder head and/or block face on OHC type engines might result in inadequate tensioning of the timing belt or chain. For some full race applications the main bearing caps will need replacing for stronger steel items. These cannot be supplied as direct replacement parts and will require in-line boring to the cylinder block.

Crankshaft and Con Rods: These will be ok for most stages of tune provided they are structurally sound. Crack testing is advisable for any serious tuning especially if the components are second-hand and of an unknown source. Apart from conforming to original equipment tolerances they should be free from any marks or blemishes that could cause stress raisers which, in turn could propogate into a crack at some later stage. Pay particular attention to the fillet radii on the crankshaft journals and have these polished and rolled if necessary. Check the outside faces of the con rod beams and polish out any flaws. The con rod cap should also be inspected around the fixing points - these areas should also, be smoothed and radiused. Certain types of crankshafts and rods can have additional heat or surface treatment to enhance their durability. Nitro-carburising of some crankshafts and shot peening con rods can be beneficial if carried outunder strictly controlled conditions. Wherever possible fit heavy duty shell bearings – preferably lead indium or lead copper if available.

Pistons: With the exception of turbo-charged engines most production engines are fitted with cast alloy pistons which are quite adequate for most of the moderate stages of tune. The problem arises when compression ratios are raised to a point where detonation becomes unavoidable and forged pistons must be fitted. Since many other factors are involved, this critical ratio is not the same for every engine. Assuming the fuelling and ignition are set correctly, then 10.5: 1 is generally acknowledged as the very maximum for a good quality cast piston, and even then, you must accept a substantial reduction in its service life. Due to the complex shape of the pistons and their very fine machined tolerances, any additional machining should be carried out by a specialist. Pistons should always be replaced in matched sets but if you are replacing only one or two then do make sure they are match balanced before assembly.

Flywheel: Apart from being a handy place to fit a clutch and starter ring gear, the flywheel's primary function is to smooth out the transmission of. power from the crankshaft and for this you require mass (weight). The problem here is that this weight acts as a resistance to, as well as a store for, the energy produced by the engine. Lightening the flywheel will improve the engine's throttle openings but not the actual power output. Unless the flywheel is abnormally heavy we do not recommend flywheel lightening for road stages of tune. The slight loss of low speed torque and flexibility resulting from the tuning modifications can be greatly exacerbated by a lightweight flywheel. However, for all serious tuning a lightweight flywheel is essential. Standard cast iron flywheels can be lightened but there is always a risk of them exploding if too much material is removed from critical areas. The rule here is not to be over-ambitious when removing weight from a standard flywheel - it isn't worth the risk! The safe answer is to buy a steel flywheel which are available for most popular engine / clutch formats.The final point on flywheels is to make sure it is firmly secured to the crankshaft. Always fit new HT bolts and always double check that they have been torqued correctly. If engine speeds in excess of 7500rpm are anticipated then, wherever possible, the flywheel and crankshaft should also be double dowelled for extra security.

Clutch: Original equipment clutches should cope with moderate power increases (15-20%) but if the standard clutch needs replacing then it would make sense to fit an uprated item. For road car conversions it should be noted that clutch pedal pressures will increase when fitting a stronger clutch. For competition applications a wide range of single, twin and triple plate clutches are available together with the special flywheels required to mount them.

Once all these components have been sorted they should be balanced. This will provide for a smoother more reliable engine, especially at high revs, by eliminating any vibration caused by unequal balance.

Lubrication Systems: All production engines employ a wet sump system where the oil lies in a reservoir or sump below the crankshaft This system works fine for most applications but the following points should be observed. High pressure pumps (typically 25-30% higher than standard) will ensure an adequate supply of oil to the engine, especially during heavy load condition. High capacity pumps (which are also high pressure) are designed to cope with the higher flow demands of engines fitted with ancillary equipment such as oil coolers. For mild stages of tune the standard pump is quite adequate providing it is functioning efficiently. One of the most important areas to watch is the condition of the oil pump drive gear or shaft (sometimes referred to as the quill). These components (especially the quills) should always be replaced with an original equipment new part.

ENGINE REBUILD

The following bullet points highlight important procedures during the re-assembly of a modified engine:

• THOROUGHLY clean and check ALL parts - your engines worst enemy is dirt, and even new parts may need cleaning. This includes the head and block and all oil galleries. 
• ALWAYS fit new high quality gaskets and seals and ensure all shafts and mating surfaces are free from burrs and defects. Use correct sealants or lubricants where necessary. 
• LIBERALLY oil all internal parts during assembly. Use the special assembly lube or gear oil on cam lobes and tappet faces. 
• ALWAYS replace cam followers when fitting a new camshaft. 
• ALWAYS replace con rod, flywheel and cylinder head stretch bolts. All other fastenings should be checked for wear or damage and replaced as necessary. For high spec, engines, race quality fastenings are available for most applications. 
• CLEAN all threads and fastenings prior to fitment and use a good quality torque wrench on all critical components. Apply an anti-seize lubricant to all cylinder head fixings. 
• IF you are fitting high lift cams, special pistons, or large valve heads, always carry out a dummy engine build and check valve to piston/block clearances. Machine piston crowns/valve pockets or block face as necessary. 
• INCORRECT cam timing can severely reduce the power output so do not overlook this important area during assembly. Use adjustable cam pulleys or sprockets where available. 
• CHOOSE compatible parts for your specific conversion. A full race spec, head will be next to useless if fitted to a mild road stage engine. Modified camshafts and cylinder heads in particular should be chosen with care. 
• UNLESS you know what you are doing, avoid over-lightening components. Reducing the weight of some parts may also reduce their strength to a critical level. 
• ALWAYS have the engine assembly balanced - it will make a lot of difference to the smoothness and help maintain optimum reliability. 
• DON'T forget the clutch - depending on the power increase, a suitable heavy duty or competition clutch assembly will be required. 
• OIL and FILTER - the importance of using the correct specification of oil cannot be overstated.

Most engine modifications should be followed up with a professional engine tune. Apart from emissions, the correct ignition timing and fuelling is paramount if you want the best return for all the expense and effort you have put in. Get these important settings wrong and you may loose more than just a bit of power. Over-fuelling (rich mixture) can result in excessive piston, ring and bore wear. Under fuelling (weak mixture) or retarded ignition can cause overheating problems. An ignition set with too much advance is likely to induce detonation or 'pinking' which, if left uncorrected, can shatter pistons and place excessive loads on the bottom end. You have been warned! Lastly, please check that your suspension and braking systems are adequate for the power increase you have achieved.

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