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Applied Pressure


Before you can truly begin any serious tuning, you have to be sure that the engine you are going to spend hours working on is in good sound condition. It makes no difference whether the engine you have is a week old or if it has 30,000 km on the clock. There is only one way to accomplish this tune up correctly and that’s with a leak down test process. Compression tests might suffice for a ‘run about’ sedan, but remember, we’re talking about an outright street race, hi-performance engine.  The main theme behind a “leaking down test” is to pump a given amount of air into a cylinder and then measure how much escapes via the piston rings and valves.  You might be surprised when you hear the excessive compressed air blowing by a worn and leaking exhaust valve or perhaps an equally worn out intake valve. (Exhaust valves wear faster than intake valves).

Similarly, air can blow by the piston and it’s rings and enters into the sump.  While performing the test, keep in mind that a good healthy engine can leak less than 5%, while a chronic leaker can exhibit numbers nearer the 50% mark.  Some of the best-sealed engines in the drag racing circles are found under the bonnets of NHRA stock racing cars.  Take the ‘leak down’ numbers into account and what should they be?   Less than 3% on some of the better engines.  Use your own judgment when it comes to a leak down test, the figures should be well noted from cylinder to cylinder. Be advised that an engine that leaks over 10% is asking to be stripped apart, closely examined and accurately measured up to see where it can be improved upon.  Compression testers are available from a number of sources (single-gauge models).  Aircraft supply shops are also a good source if you can’t easily locate a leak down tester at your corner speed shop. Whatever you do, make sure the one you purchase or use is of a good quality.


Compression tests are routine tune-up steps, but on a high-performance application, they should not take the place of a leak down test.  Essentially, the idea of a compression test is to obtain a reading that is close to that specified in a factory service manual.  Now, if you have bumped up the static compression ratio (high compression pistons), changed the camshaft profile i.e. (changed the lift and duration figures from the standard factory figures), then the compression test numbers you get will be totally meaningless to anyone and that leaves you with an educated guess.

There are two areas however where a compression test can be of some assistance.  Low readings usually indicate that the rings or valves require maintenance. This can be checked by squirting some lightweight oil into each spark plug hole. Crank the engine over with your bump switch for a few seconds to allow the oil to get in under the rings and into the places that will help seal off the rings as best as possible and then repeat the compression test.

If the compression readings are significantly higher, then you have a problem with the rings, piston or cylinder bore.  If no changes are evident, then the problem lies with the intake or exhaust valve or both.

A drastic drop in pressure in one (or more) cylinders can mean numerous things. The worst could be a cracked piston or broken rings and a broken ring land combination.  The most common problem is a blown cylinder head gasket.  If a pair of side-by-side cylinders show approximately the same compression readings (while other cylinders are good), this is a good sign that the head gasket is blown between the cylinders. This is by far the most common problem, especially if the engine has been bored out to the max, bringing the cylinder bores closer together, thus narrowing the deck surface between the two cylinders.

Many engine builders opt for the largest oversize slugs available and most often end up fitting foreign pistons to the build and end up machining off the top of the piston, pockets or dome – a common practice amongst engine builders in time, somewhere along the line.

But if you can afford the right equipment then you will find the correct hardware at your local speed shop.

Valve Head Gear


One area of the power search that most of the enthusiasts tend to forget about are the rocker arms and their geometry. These are probably the best lessons anyone can learn. In most cases you simply purchase a new set of rocker arms and bolt them onto your cylinder heads. Unfortunately, the trouble with that plan and particularly with small and Big Chevrolet, FoMoCo (Ford), Windsor, Cleveland and 385 Mopars and a few others is that the factory rocker arms can often be way out in the ratio department. Using a small block Chevy engine as an example, the OEM or (original equipment manufacturer), specs call for a rocker ratio of 1.5:1. This in simple terms means that the rocker arms will multiply the camshaft lobe lift by 1.5 times. If the lobe lift on a small block camshaft is .400 of an inch on both the intake and exhaust lobes, you can multiply it by the rocker ratio of 1.5 and the gross valve lift should be .600 of an inch.

Unfortunately, a stamped steel rocker ratio might only check out at 1.43:1 or even less. As a result, the gross valve lift works out to .572 inch. The valve train effectively has lost about 5% of the total lift. This only gets worse as the lobe lift numbers increase (the camshaft becomes more radical).

What’s the answer to the problem at hand? There are several solutions, but if you can’t afford a trick set of aftermarket roller rockers, the answers start hiding themselves from you-rapidly. The most inexpensive option is to check a box full of rockers until you find all 16 of them that have the highest effective rocker ratio and are that close to one another. In order to accomplish this, you will have to get into action and install a solid lifter on one rocker arm to zero lash. Next is to install your dial indicator to read off the valve stem side of the rocker arm. Turn the engine through one complete revolution with a power bar fitted with an extension and socket.

Compare this gross (zero lash) to your camshaft specs. You might be surprised to see that the numbers do not correspond. To verify the figures, either verify the number with your camshaft specifications car or check the lift at the lifter and multiply the number by your rocker ratio. This number is the theoretical gross valve lift. In many situations, a factory rocker arm will have a ratio that is significantly less than you would of imagined.

As mentioned previously, most small block rockers ‘check’ at between 1.4:1 and 1.47:1, very few attain the advertised number of 1.5:1 in the ratio department. To correct the problem you can either rummage through boxes of new rockers until a ‘perfect’ set is found, or install a set of aftermarket rockers. If you install aftermarket rockers, be absolutely sure to verify the ratio. Performance aftermarket parts aren’t perfect either.


Is there a difference in lash procedure between an engine equipped with stock rockers and one equipped with roller rockers? There’s none in terms of lash numbers, but there is one thing you have to remember. When lashing valves with OEM rockers, you can sometimes slide the feeler guage in at a at bit of an angle. This isn’t possible with a roller tip rocker. If your engine is equipped with roller rockers, be certain that you slide the feeler guage in a straight line between the rocker tip and the top of the valve.

In any case, the idea is to use a ‘go-no-go’ system, keeping it as smooth as possible. In other words, if the cam company calls for .024 inch lash, then a .024 inch feeler guage will fit, but a .025 won’t. After some practice with your particular combination you’ll get a real feel for the correct lash. Some guys like a ‘tight’ pull on the feeler guage, others don’t it’s just a matter of a personal likes or dislikes of styles.


When working with aluminium cylinder heads and/or aluminium cylinder blocks, cold lash numbers can vary greatly from the hot figures. So why does this happen? Simply because aluminium moves by expanding and contracting a great deal more than cast iron when heated up. Because of this you can understand why and how valve lash figures become decidedly different with ally combinations. Although it’s difficult to provide the hard and solid numbers for all camshaft and engine combo’s, Chevy offered this advice as a rule of thumb: ’Cold-lash all ally engines .010 inch tighter than the Hot-lash specs’.

Generally, you can use this as a good starting point and go on from there. Some ally head to iron block combinations are very close to an all iron engine in terms of cold lash. Others might be and well be anywhere from .005 inch to .010 inch tighter. Your best chance is to contact your guy who grinds camshafts for you and ask him for a specific cold-lash number for the particular combination you may have.


Eyeing the timing marks is always going to hinder any mechanic in a dark engine compartment and is never easy and to make matters worse, the timing marks become harder to read when unnatural or partial light is directed into the engine compartment. Even the addition of a degreed balancer or a timing tape can still make for some partial visual impairments. Most of the time the problem isn’t always the degreed markings on the balancer. Instead it’s the timing mark pointer that’s not accurately lining up and showing you the exact marking that can be exactly pin pointed. Trimming your standard pointer to a ‘V’ shape at the zero marking. The pointer is easier to read and eliminates confusion over the timing marks location.

In addition to this, aftermarket companies have designed bolt-on timing pointers with an adjustable pointer that can be easily set up to read ‘on-zero’ or from four degrees retard to 16 degrees advance. From this simple little addition of the adjustment, the pointer makes any timing checks easy and simple and also solves the timing-out, pointer problems that can sometimes plague engines and engine builders. Occasionally, the TDC mark on a factory harmonic balancer will be slightly out and so can the timing pointer. This is unacceptable to any standards and all adds up to an extremely inaccurate ignition timing numbers as well as valve lash figures that can be out.


A valve springs life is always critical to any performance street rod engine.  How can the valve’s spring life be considerably improved?  The first step is to pre-stress new valve springs prior to their installation. In other words, the springs are squeezed to the limit by a soft-jaw vise and compressed several times before installing the valve spring to its place. The idea isn’t to damage the spring in the vise but instead, the spring should be compressed just nicely, without pushing the spring into a coil-bind, but just enough to push it to the limit a few times but not over.  (Watch the spring carefully as you compress it together). Install the spring on the cylinder head and check the seat pressure. If the spring fails miserably, “tag” it or return to the selling dealer and install a new one. If you don’t have access to a soft-jawed vise something soft should be attached to either side of your vise jaws.  The cushion you have now added saves the valve springs from being scarred by the course steel lining jaws of the vice.

Here’s another method you can try for improving the life of the spring:

Inspect the inner spring and dampener carefully. You might find that some valve springs have added “flashing” on the spring ends.  (This is common on some types of dampers.)  If that’s the case with your set of springs, use a small die grinder and very carefully smooth over the odd burrs and high spots that are present. Similarly, some dampers have very sharp edges on the “flats.”  The life of the damper can be improved by gently de-burring and chamfering them, and it can be done in five minutes flat - if you have the right tools laid out and at your disposal.
It should be pointed out that damper failure is more common than we’d like to think (especially on high lift, radical profiled cams).

Occasionally, a damper will physically “unwind itself” and the lower portion of the assembly will work its way between two lower coils of the outer spring. Naturally, this stacks the spring into a coil bind. When this happens, all kinds of carnage can occur if you don’t nip the problem before this can happen. In most cases, selecting the correct length of damper will suffice, but if the problem hampers your application, you can solve it by shortening the damper a few mills. You might try this old racer trick (its been around for about 30 years or more).  Sand blast the damper after it has been de burred and the edges chamfered.


When the time comes to installing the valve springs on the cylinder heads, have a close look at the relationship between the inner spring and the damper to both the cylinder head seat and the valve spring retainer. Because of the many different types of designs manufactured in springs, valve retainers and spring seats, there might be some coil-bind at these locations, but no coil-bind on the outer spring. Have a close look as the engine is turned through a cycle (manually), don’t use the starter to spin the engine over, it will be too fast and your eye wont be able to follow the springs exact motion, not to mention what can be damaged along the way.

In the case of a poorly selected spring (or spring retainer), don’t be surprised if you see coil bind on the inner spring(s). If that’s the case, you will have to pull everything to pieces and install an inner valve spring that suits both the application and the spring retainer. This exercise must be executed clinically or you will end up with catastrophic complications that will set you back thousands of rands and sleepless nights.

While you’re at it, regularly check the springs with a seat pressure tester (inexpensive models such as this Moroso unit are readily available). These testers simply slip over the rocker arm.  Add a bit of muscle power and pull down on the tester. The number that appears on the beam scale (its like a beam torque wrench) will give you the spring seat pressure reading. If the seat pressure is down from the manufacturers specifications, you can bet your bottom dollar that the valve springs are tired and need to be replaced with new ones. Make it a practice to check the spring seat pressure every time the valves are lashed. The checking process adds about 15 minutes to the routine maintenance schedule and is always very rewarding once the above process is completed with dedicated accuracy.


Setting the valve lash on any solid lifter engine can get old in a hurry. Especially if you have to climb inside the car, tap the ignition switch and run around to the engine and check the balancer-timing tab location. Temporary remote starter leads are one answer, but who wants to burn their hands every time you hook it up?  The solution is a permanent bump starter switch.   Moroso and other companies offer state of the art waterproof switches that can be mounted somewhere in a convenient location.

Wiring the bump starter switch is simple. Wire one lead to the battery cable lead on the starter while the other lead is routed to the switched “Starter” or “S” terminal on the starter. When in operation, the ignition switch remains untouched. Simply press the bump starter and allow electrons to spin the engine over to the appropriate balancer location. When a “bump” starter switch is installed, it takes away most of the aggravation usually experienced, the down side is that you’ll still have to use a large half-inch drive bar to rotate the engine to the exact pointer location. In most cases, you can ‘bump’ the engine to a point, which is close enough to your mark, and then use the power bar to move the balancer and timing marks up to the exact position.  This procedure eliminates the brute force required to turn over the engine. The final grunt work can place the timing marks in the ideal position. Fitting a ‘bump’ switch will relieve you from some tedious pressure when getting down to the basics and for the effort of fitting one you will never look back.

Engine Tuning Tips

Here’s A Box Of Tricks
To Make Your Passes Quicker!

Hi Performance Street Rod skills aren’t hard to learn and in many situations they’re almost simple. Unfortunately, its tough to tune a car with a set of braced up Weber carbs if you don’t know how to set up a single carb. By the same token, it’s impossible to cool down a high compression, radical big block engine if you’re having trouble cooling down your mom’s old Malibu.

In sports they call it ‘basic skills’, if you don’t have the basics down pat, you cant run the quick E.T’s. To make it worse still, there aren’t any many weekend workshops or places you can go to learn the basic skills of ‘engine tweaking’ and modifying your muscle car to cut down those tenths. No, there’s no university to teach you the skills of engine building, engine tuning and hot rodding, but there is a substitute for the ‘school of hard knocks’.  Check out the following how-to guide, there’s a boxful of tips below to get you there quicker.


Power Steering

Brakes and their relative components are always a plenty at scrapyards and well priced. Steering racks, pumps and steering boxes are usually the steering parts that get the most money for any scrapyard dealer, so expect to pay a little more for good steering parts and components

Don’t touch a steering rack if it has been involved in a front-end crash or collided with a pavement. You can’t be mistaken if you are viewing the vehicle at the scrap yard, the wheels will tell you a story by the way they are facing. If possible check if the steering wheel turns the front wheels ok.

If one comes off the shelf make sure the tie rod ends are not bent and the housing is not damaged. The steering shafts that travel up and down inside the steering rack housing are prone to leak very easily if anything is even slightly distorted. This is like measuring a piston with a mic, you can’t always see the fault with the naked eye.

If you do purchase a second hand steering rack and pinion have it checked by a professional brake and steering shop. They have specialise and have the right equipment to detect the slightest leak that will only become apparent once the steering rack is fitted, you will more than likely be buying into troubled waters, not to mention that you would be putting peoples lives at risk. A steering rack ior steering box is not an easy item to remove and refit although it may look easy, its not.

Steering racks, steering boxes and the pumps are a specialist field and best left to the guys that do this finiky job every day. I have tried reconditioning steering racks in my day with very little success. It’s pretty much like stripping 100 different gearboxes; it’s a whole new learning curve. My advice to anyone reading this, contact the experts that have been in the business half their lives like the pros at Brake and Steering, they will give you good sound advice and point you in the right direction. They also collect and deliver and are a nationwide setup.

Overheating & Cooling

Cylinder Heads and Pistons

For many years cylinder heads were made from cast iron and still is used for most diesel engines. However, in the 60’s aluminium took over, initially for it’s superior heat conductive properties, but these days also to reduce engine mass.

When you are looking to buy a cylinder head there are also important criteria to consider. Firstly you have the option of buying a cylinder head on an exchange basis with a guarantee. There are many exchange shops around that offer cylinder heads on an exchange basis. The cylinder head is a part on a motor vehicle that is vulnerable to drastic heat exchanges within an engine.

Cylinder heads are the first components that will let you down if you abuse them and this I mean they don’t like drastic changes in temperature all round. An engine is designed to run at between 80-89 degrees C and any more for a long period usually results in a blown cylinder head gasket if you are lucky and only get away with the head being skimmed and refitted with a new cylinder head gasket.

The not so lucky will endure the pains of replacing the cracked head with another one. Extreme overheating can also cause the block to crack or a combination of the two. Head and block sealer is an additive that can be used to temporarily seal a fine crack and maybe get you home. I have driven with head and block sealer from Harrismith to JHB without loosing too much water and only just made it home. Read the instructions carefully. The contents of the tin must be administered in a certain way for best results.

For the not so fortunate a cracked head is the result once it is determined by a compulsory pressure test. To have a pressure test the cylinder head must be removed from the sub assembly. I have witnessed desperate clients pleading to have the head stitch welded and machined. These guys usually take drastic measures only to sell the vehicle to some poor individual that buys it thinking he got a good deal on the car or bakkie, only to walk in weeks later with the same piece of junk and place it on the counter. When you see this go down you can only pitty the man and advise him accordingly.


Most modern day cylinder heads are all made from alluminium alloys, although most diesel engines still come with cast iron castings for the cylinder heads. Heads don’t like the heat to soar over the desired operating temp limit when driving so make sure your thermostat is replaced at regular intervals. Years ago I discovered and pointed out a faulty batch of thermostats supplied by Landrover.

We fitted one to a 4 cylinder turbo diesel that we had remanufactured the (head, block and sump), for a Landrover dealership. The vehicle overheated and had to be towed back from Central Africa somewhere. I couldn’t believe that a new engine we had remanufactured could overheat and seize. My gut feeling told me to remove the thermostat on inspection. If you place a cold thermostat in a kettle you will see it start opening before the kettle reaches boiling point, this one remained closed. The result was, we were off the hook and Landrover SA discontinued the batch of thermostats.

When overheating an engine not only do the cylinder heads become stressed, but the pistons also made from aluminium alloy collapse, distort and shrink slightly. The change cannot be detected with the naked eye but when measured with a micrometer these changes are magnified. An example would be a new piston measuring 91.88mm to fit a std bore of 92mm should not collapse more than anything under 3 hundredths of a millimeter. With a standard piston to bore clearance of 2 hundredths of a millimeter this would mean the piston to bore clearance is now borderline at 5 hundredths of a millimeter, providing the bore is still standard and ‘on size’, (give or take another 100 th of a millimeter for bore wear), and its over the top.

This is the limit and experience has show that any more than this, results in an engine that uses oil and will show signs of loss in power. In most cases severe overheating will cause the rings to glaze the bore and collapse, thus loosing power due to the tension loss in the spring qualities left in the piston rings. Rings also tend to seize within their ring grooves of the piston due to the lack of spring tension forcing themselves outwards against the bore of the sleeve and sometimes break the ring land. You will immediately notice a nice constant stream of smoke emitting from your exhaust as you drive and guess what, your sub assembly will now have to be removed to replace the pistons, which ultimately means it’s time for an engine change or complete engine overhaul.

My advise is not only replace your thermostat on a regular interval but change all your hoses when they have reached the 100,000 km mark and always fill the radiator with at least 50%, good anti freeze-anti boil additive.

Viscous Fan Coupling

Another cooling component that is most often overlooked is the viscous fan coupling or clutch fan coupling. It is important to understand how it works. This component is probably responsible for more engine failures than any other cooling part on a vehicle simply because it’s failure is so gradual and unnoticeable. I have seen guys build up a new engine and not bother to replace the viscous coupling. Manufacturers fit them to most model cars and trucks as they are fuel savers and they allow the engine to produce more power. A fixed fan will also drain horse power from an engine powerplant.

The viscous fan is free to turn on it’s axis as the motor revs. In other words the engine RPM and the viscous RPM differ in their speed of rotation. It is designed to start locking-up at round about the time the engine reaches it’s desired temperature range which is controlled by the thermostat. The thermostat actually controls the viscous fan in principal because it regulates the engines expected temperature range. As the radiator cools the hot water from the engine, the thermostat allows only enough water in at a time, keeping the water at a constant temp within the head and block. The viscous coupling will then only engage again once the temperature rises again.

The problem arises however when the viscous comes to the end of it’s life span which is difficult for most people to understand because it always appears to be spinning in time with the engine revolutions. There is only one way to check it and that is when it is cold, on start up in the morning. You will hear the distinct rush of air as you rev up the engine. This noise will then fade away and quieten down completely after a 30 seconds or so. Watch the temperature climb on the temp guage, listening all the time. Once the temp reaches the half way mark after a few more minutes, the viscous fan coupling will reengage itself and you will again hear the wooosh of air being propelled through the fan blades as you rev the motor.

This indicates that the viscous coupling is working. If the temp guage reaches the half way mark and I mean, not a hair over the half way mark and the guage keeps climbing over the half way mark then you know it’s time to replace the coupling. They don’t come cheap so what a lot of guys do is remove them and fit solid fans adaptors. The problem with these are that when the vehicle attains a speed of lets say 110 km/h the fan reaches a static condition whereby the fan actually slows down the air flow through the radiator. Fixed fans are fine for round town vehicles that don’t exceed this kind speed. They are however very reliable in that they never give up sucking air and are great for traffic congested driving as they are constantly working whereas a viscous coupling only starts to really work when it gets to the desired operating temperature.


The Idiot Light

I have seen many a motorist drive his or her vehicle regardless of any warning signals. Even when the red light on the dashboard comes on they still keep on driving as if the light were a disco light. This light is often referred to as an ‘idiot light’, the red one with the outline of an oil can on it, it’s unmistakable, you can’t miss it, it’s bright red and red means stop. You should pull over and immediately switch off the car. Get a tow truck, no matter where you are; the costs incurred will leave you flat broke and carless for weeks unless you have a Motorite Insurance policy.

Oil pressure failure is usually attributed to a faulty oil pressure switch, a loose or severed wire and ultimately oil pump failure or a lack of oil channeled through to a particular part of an engine. Sometimes one of the oil channels gets a particle usually like a dislodged piece of matter large enough to partially block the oil channel causing the flow of oil to drastically slow down to a particular area of the engine. This may stop oil flow to a single crankshaft journal for instance and cause the crank bearing to seize thus damaging a big end or main bearing journal on the crankshaft.

Why a piece of debris can become lodged or dislodged is besides all logic if the engine was assembled by the original manufacturing engine builder at the assembly plant, but these things can happen, no one is perfect. Usually one would expect the oil filter to filter everything that passes through it. Change your oil and oil filter every 10,000 km’s without fail. Oil is the life of an engine so use good multi-grade engine oil. Filters can be purchased at your local motor spares shop. Here you can purchase excellent quality filters and engine oils.

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