Benoit Grinter

The medial collateral ligament (MCL), also called the superficial medial collateral ligament (sMCL) or tibial collateral ligament (TCL), is one of the major ligaments of the knee. It is on the medial (inner) side of the knee joint and occurs in humans and other primates. Its primary function is to resist valgus (inward bending) forces on the knee.

It is a broad, flat, membranous band, situated slightly posterior on the medial side of the knee joint. It is attached proximally to the medial epicondyle of the femur immediately below the adductor tubercle; below to the medial condyle of the tibia and medial surface of its body.

It resists forces that would push the knee medially, which would otherwise produce valgus deformity. It provides up to 78% of the restraining force that resists valgus (inward pressing) loads on the knee.

The fibers of the posterior part of the ligament are short and incline backward as they descend; they are inserted into the tibia above the groove for the semimembranosus muscle.

The anterior part of the ligament is a flattened band, about 10 centimeters long, which inclines forward as it descends.

It is inserted into the medial surface of the body of the tibia about 2.5 centimeters below the level of the condyle.

Crossing on top of the lower part of the MCL is the pes anserinus, the joined tendons of the sartorius, gracilis, and semitendinosus muscles; a bursa is interposed between the two.

The MCL's deep surface covers the inferior medial genicular vessels and nerve and the anterior portion of the tendon of the semimembranosus muscle, with which it is connected by a few fibers; it is intimately adherent to the medial meniscus.

Embryologically and phylogenically, the ligament represents the distal portion of the tendon of adductor magnus muscle. In lower animals, adductor magnus inserts into the tibia. Because of this, the ligament occasionally contains muscle fibres. This is an atavistic variation.

An MCL injury can be very painful and is caused by a valgus stress to a slightly bent knee, often when landing, bending or on high impact. It may be difficult to apply pressure on the injured leg for at least a few days. It can be caused by a direct blow to lateral side of knee. The most common knee structure damaged in skiing is the medial collateral ligament, although the carve turn has diminished the incidence somewhat. MCL strains and tears are also fairly common in American football. The center and the guards are the most common victims of this type of injury due to the grip trend on their cleats, although sometimes it can be caused by a helmet striking the knee. The number of football players who get this injury has increased in recent years. Companies are currently trying to develop better cleats that will prevent the injury. MCL is also crucially affected in breaststroke and many professional swimmers suffer from chronic MCL pains.

There are three distinct levels in a MCL injury. Grade 1 is a minor sprain, grade 2 in a major sprain or a minor tear, and grade 3 is a major tear. Based on the grade of the injury treatment options will vary.

Depending on the grade of the injury, the lowest grade (grade 1) can take between 2 and 10 weeks for the injury to fully heal. Recovery times for grades 2 and 3 can take several weeks to several months.

Treatment of a partial tear or stretch injury is usually conservative. Most injuries that are partial and isolated can be treated without surgery. This includes measures to control inflammation as well as bracing. Kannus has shown good clinical results with conservative care of grade II sprains, but poor results in grade III sprains. As a result, more severe grade III and IV injuries to the MCL that lead to ongoing instability may require arthroscopic surgery. However, the medical literature considers surgery for most MCL injuries to be controversial. Isolated MCL sprains are common.

Credit Cards

Body mass index (BMI) is a value derived from the mass (weight) and height of a person. The BMI is defined as the body mass divided by the square of the body height, and is expressed in units of kg/m2, resulting from mass in kilograms and height in metres.

The BMI may be determined using a table[a] or chart which displays BMI as a function of mass and height using contour lines or colours for different BMI categories, and which may use other units of measurement (converted to metric units for the calculation).[b]

The BMI is a convenient rule of thumb used to broadly categorize a person as underweight, normal weight, overweight, or obese based on tissue mass (muscle, fat, and bone) and height. Major adult BMI classifications are underweight (under 18.5 kg/m2), normal weight (18.5 to 24.9), overweight (25 to 29.9), and obese (30 or more).[1] When used to predict an individual's health, rather than as a statistical measurement for groups, the BMI has limitations that can make it less useful than some of the alternatives, especially when applied to individuals with abdominal obesity, short stature, or unusually high muscle mass.

BMIs under 20 and over 25 have been associated with higher all-cause mortality, with the risk increasing with distance from the 20–25 range.[2]

Adolphe Quetelet, a Belgian astronomer, mathematician, statistician, and sociologist, devised the basis of the BMI between 1830 and 1850 as he developed what he called "social physics".[3] Quetelet himself never intended for the index, then called the Quetelet Index, to be used as a means of medical assessment. Instead, it was a component of his study of l'homme moyen, or the average man. Quetelet thought of the average man as a social ideal, and developed the body mass index as a means of discovering the socially ideal human person.[4] According to Lars Grue and Arvid Heiberg in the Scandinavian Journal of Disability Research, Quetelet's idealization of the average man would be elaborated upon by Francis Galton a decade later in the development of Eugenics.[5]

The modern term "body mass index" (BMI) for the ratio of human body weight to squared height was coined in a paper published in the July 1972 edition of the Journal of Chronic Diseases by Ancel Keys and others. In this paper, Keys argued that what he termed the BMI was "if not fully satisfactory, at least as good as any other relative weight index as an indicator of relative obesity".[6][7][8]

The interest in an index that measures body fat came with observed increasing obesity in prosperous Western societies. Keys explicitly judged BMI as appropriate for population studies and inappropriate for individual evaluation. Nevertheless, due to its simplicity, it has come to be widely used for preliminary diagnoses.[9] Additional metrics, such as waist circumference, can be more useful.[10]

The BMI is expressed in kg/m2, resulting from mass in kilograms and height in metres. If pounds and inches are used, a conversion factor of 703 (kg/m2)/(lb/in2) is applied. When the term BMI is used informally, the units are usually omitted.

BMI provides a simple numeric measure of a person's thickness or thinness, allowing health professionals to discuss weight problems more objectively with their patients. BMI was designed to be used as a simple means of classifying average sedentary (physically inactive) populations, with an average body composition.[11] For such individuals, the BMI value recommendations as of 2014[update] are as follows: 18.5 to 24.9 kg/m2 may indicate optimal weight, lower than 18.5 may indicate underweight, 25 to 29.9 may indicate overweight, and 30 or more may indicate obese.[9][10] Lean male athletes often have a high muscle-to-fat ratio and therefore a BMI that is misleadingly high relative to their body-fat percentage.[10]

A common use of the BMI is to assess how far an individual's body weight departs from what is normal for a person's height. The weight excess or deficiency may, in part, be accounted for by body fat (adipose tissue) although other factors such as muscularity also affect BMI significantly (see discussion below and overweight).[12]

The WHO regards an adult BMI of less than 18.5 as underweight and possibly indicative of malnutrition, an eating disorder, or other health problems, while a BMI of 25 or more is considered overweight and 30 or more is considered obese.[1] In addition to the principle, international WHO BMI cut-off points (16, 17, 18.5, 25, 30, 35 and 40), four additional cut-off points for at-risk Asians were identified (23, 27.5, 32.5 and 37.5).[13] These ranges of BMI values are valid only as statistical categories.

BMI is used differently for people aged 2 to 20. It is calculated in the same way as for adults but then compared to typical values for other children or youth of the same age. Instead of comparison against fixed thresholds for underweight and overweight, the BMI is compared against the percentiles for children of the same sex and age.[14]

A BMI that is less than the 5th percentile is considered underweight and above the 95th percentile is considered obese. Children with a BMI between the 85th and 95th percentile are considered to be overweight.[15]

Studies in Britain from 2013 have indicated that females between the ages 12 and 16 had a higher BMI than males of the same age by 1.0 kg/m2 on average.[16]

These recommended distinctions along the linear scale may vary from time to time and country to country, making global, longitudinal surveys problematic. People from different populations and descent have different associations between BMI, percentage of body fat, and health risks, with a higher risk of type 2 diabetes mellitus and atherosclerotic cardiovascular disease at BMIs lower than the WHO cut-off point for overweight, 25 kg/m2, although the cut-off for observed risk varies among different populations. The cut-off for observed risk varies based on populations and subpopulations in Europe, Asia and Africa.[17][18]

The Hospital Authority of Hong Kong recommends the use of the following BMI ranges:[19]

A 2000 study from the Japan Society for the Study of Obesity (JASSO) presents the following table of BMI categories:[20][21][22]

In Singapore, the BMI cut-off figures were revised in 2005 by the Health Promotion Board (HPB), motivated by studies showing that many Asian populations, including Singaporeans, have a higher proportion of body fat and increased risk for cardiovascular diseases and diabetes mellitus, compared with general BMI recommendations in other countries. The BMI cut-offs are presented with an emphasis on health risk rather than weight.[23]

In the UK, NICE guidance recommends prevention of type 2 diabetes should start at a BMI of 30 in White and 27.5 in Black African, African-Caribbean, South Asian, and Chinese populations.[24]

New research based on a large sample of almost 1.5 million people in England found that some ethnic groups would benefit from prevention at or above a BMI of (rounded):[25][26]

In 1998, the U.S. National Institutes of Health brought U.S. definitions in line with World Health Organization guidelines, lowering the normal/overweight cut-off from a BMI of 27.8 (men) and 27.3 (women) to a BMI of 25. This had the effect of redefining approximately 25 million Americans, previously healthy, to overweight.[27][28]

This can partially explain the increase in the overweight diagnosis in the past 20 years[when?], and the increase in sales of weight loss products during the same time. WHO also recommends lowering the normal/overweight threshold for southeast Asian body types to around BMI 23, and expects further revisions to emerge from clinical studies of different body types.[29]

A survey in 2007 showed 63% of Americans were then overweight or obese, with 26% in the obese category (a BMI of 30 or more). By 2014, 37.7% of adults in the United States were obese, 35.0% of men and 40.4% of women; class 3 obesity (BMI over 40) values were 7.7% for men and 9.9% for women.[30] The U.S. National Health and Nutrition Examination Survey of 2015-2016 showed that 71.6% of American men and women had BMIs over 25.[31] Obesity—a BMI of 30 or more—was found in 39.8% of the US adults.

The BMI ranges are based on the relationship between body weight and disease and death.[11] Overweight and obese individuals are at an increased risk for the following diseases:[33]

Among people who have never smoked, overweight/obesity is associated with 51% increase in mortality compared with people who have always been a normal weight.[36]

The BMI is generally used as a means of correlation between groups related by general mass and can serve as a vague means of estimating adiposity. The duality of the BMI is that, while it is easy to use as a general calculation, it is limited as to how accurate and pertinent the data obtained from it can be. Generally, the index is suitable for recognizing trends within sedentary or overweight individuals because there is a smaller margin of error.[37] The BMI has been used by the WHO as the standard for recording obesity statistics since the early 1980s.

This general correlation is particularly useful for consensus data regarding obesity or various other conditions because it can be used to build a semi-accurate representation from which a solution can be stipulated, or the RDA for a group can be calculated. Similarly, this is becoming more and more pertinent to the growth of children, since the majority of children are sedentary.[38] Cross-sectional studies indicated that sedentary people can decrease BMI by becoming more physically active. Smaller effects are seen in prospective cohort studies which lend to support active mobility as a means to prevent a further increase in BMI.[39]

In France, Italy, and Spain, legislation has been introduced banning the usage of fashion show models having a BMI below 18.[40] In Israel, a BMI below 18.5 is banned.[41] This is done to fight anorexia among models and people interested in fashion.

A study published by Journal of the American Medical Association (JAMA) in 2005 showed that overweight people had a death rate similar to normal weight people as defined by BMI, while underweight and obese people had a higher death rate.[42]

A study published by The Lancet in 2009 involving 900,000 adults showed that overweight and underweight people both had a mortality rate higher than normal weight people as defined by BMI. The optimal BMI was found to be in the range of 22.5–25.[43] The average BMI of athletes is 22.4 for women and 23.6 for men.[44]

High BMI is associated with type 2 diabetes only in people with high serum gamma-glutamyl transpeptidase.[45]

In an analysis of 40 studies involving 250,000 people, patients with coronary artery disease with normal BMIs were at higher risk of death from cardiovascular disease than people whose BMIs put them in the overweight range (BMI 25–29.9).[46]

One study found that BMI had a good general correlation with body fat percentage, and noted that obesity has overtaken smoking as the world's number one cause of death. But it also notes that in the study 50% of men and 62% of women were obese according to body fat defined obesity, while only 21% of men and 31% of women were obese according to BMI, meaning that BMI was found to underestimate the number of obese subjects.[47]

A 2010 study that followed 11,000 subjects for up to eight years concluded that BMI is not a good measure for the risk of heart attack, stroke or death. A better measure was found to be the waist-to-height ratio.[48] A 2011 study that followed 60,000 participants for up to 13 years found that waist–hip ratio was a better predictor of ischaemic heart disease mortality.[49]

The medical establishment[50] and statistical community[51] have both highlighted the limitations of BMI. Part of the statistical limitations of the BMI scale is the result of Quetelet's original sampling methods.[52] As noted in his original work, A Treatise on Man and the Development of His Faculties, the data from which Quetelet derived his formula was taken mostly from Scottish Highland soldiers and French Gendarmerie.[4] The BMI was always designed as a metric for European men. For women, and people of non-European origin, the scale is often biased. As noted by Sabrina Strings in her book Fearing the Black Body: The Racial Origins of Fat Phobia, the BMI is largely inaccurate for black people especially, disproportionately labelling them as overweight even for healthy individuals.[52]

The exponent in the denominator of the formula for BMI is arbitrary. The BMI depends upon weight and the square of height. Since mass increases to the third power of linear dimensions, taller individuals with exactly the same body shape and relative composition have a larger BMI.[53] BMI is proportional to the mass and inversely proportional to the square of the height. So, if all body dimensions double, and mass scales naturally with the cube of the height, then BMI doubles instead of remaining the same. This results in taller people having a reported BMI that is uncharacteristically high, compared to their actual body fat levels. In comparison, the Ponderal index is based on the natural scaling of mass with the third power of the height.[54]

However, many taller people are not just "scaled up" short people but tend to have narrower frames in proportion to their height.[55] Carl Lavie has written that "The B.M.I. tables are excellent for identifying obesity and body fat in large populations, but they are far less reliable for determining fatness in individuals."[56]

For US adults, exponent estimates range from 1.92 to 1.96 for males and from 1.45 to 1.95 for females.[57][58]

The BMI overestimates roughly 10% for a large (or tall) frame and underestimates roughly 10% for a smaller frame (short stature). In other words, people with small frames would be carrying more fat than optimal, but their BMI indicates that they are normal. Conversely, large framed (or tall) individuals may be quite healthy, with a fairly low body fat percentage, but be classified as overweight by BMI.[59]

For example, a height/weight chart may say the ideal weight (BMI 21.5) for a 1.78-metre-tall (5 ft 10 in) man is 68 kilograms (150 lb). But if that man has a slender build (small frame), he may be overweight at 68 kg or 150 lb and should reduce by 10% to roughly 61 kg or 135 lb (BMI 19.4). In the reverse, the man with a larger frame and more solid build should increase by 10%, to roughly 75 kg or 165 lb (BMI 23.7). If one teeters on the edge of small/medium or medium/large, common sense should be used in calculating one's ideal weight. However, falling into one's ideal weight range for height and build is still not as accurate in determining health risk factors as waist-to-height ratio and actual body fat percentage.[60]

Accurate frame size calculators use several measurements (wrist circumference, elbow width, neck circumference, and others) to determine what category an individual falls into for a given height.[61] The BMI also fails to take into account loss of height through ageing. In this situation, BMI will increase without any corresponding increase in weight.

Assumptions about the distribution between muscle mass and fat mass are inexact. BMI generally overestimates adiposity on those with leaner body mass (e.g., athletes) and underestimates excess adiposity on those with fattier body mass.

A study in June 2008 by Romero-Corral et al. examined 13,601 subjects from the United States' third National Health and Nutrition Examination Survey (NHANES III) and found that BMI-defined obesity (BMI ≥ 30) was present in 21% of men and 31% of women. Body fat-defined obesity was found in 50% of men and 62% of women. While BMI-defined obesity showed high specificity (95% for men and 99% for women), BMI showed poor sensitivity (36% for men and 49% for women). In other words, the BMI will be mostly correct when determining a person to be obese, but can err quite frequently when determining a person not to be. Despite this undercounting of obesity by BMI, BMI values in the intermediate BMI range of 20–30 were found to be associated with a wide range of body fat percentages. For men with a BMI of 25, about 20% have a body fat percentage below 20% and about 10% have body fat percentage above 30%.[47]

Body composition for athletes is often better calculated using measures of body fat, as determined by such techniques as skinfold measurements or underwater weighing and the limitations of manual measurement have also led to new, alternative methods to measure obesity, such as the body volume indicator.[citation needed]

It is not clear where on the BMI scale the threshold for overweight and obese should be set. Because of this, the standards have varied over the past few decades. Between 1980 and 2000 the U.S. Dietary Guidelines have defined overweight at a variety of levels ranging from a BMI of 24.9 to 27.1. In 1985 the National Institutes of Health (NIH) consensus conference recommended that overweight BMI be set at a BMI of 27.8 for men and 27.3 for women.

In 1998, an NIH report concluded that a BMI over 25 is overweight and a BMI over 30 is obese.[27] In the 1990s the World Health Organization (WHO) decided that a BMI of 25 to 30 should be considered overweight and a BMI over 30 is obese, the standards the NIH set. This became the definitive guide for determining if someone is overweight.

The current WHO and NIH ranges of normal weights are proved to be associated with decreased risks of some diseases such as diabetes type II; however using the same range of BMI for men and women is considered arbitrary and makes the definition of underweight quite unsuitable for men.[62]

One study found that the vast majority of people labelled 'overweight' and 'obese' according to current definitions do not in fact face any meaningful increased risk for early death. In a quantitative analysis of several studies, involving more than 600,000 men and women, the lowest mortality rates were found for people with BMIs between 23 and 29; most of the 25–30 range considered 'overweight' was not associated with higher risk.[63]

The corpulence index uses an exponent of 3 rather than 2. The corpulence index yields valid results even for very short and very tall people,[64] which is a problem with BMI. For example, a 152.4 cm (5 ft 0 in) tall person at an ideal body weight of 48 kg (106 lb) gives a normal BMI of 20.74 and CI of 13.6, while a 200 cm (6 ft 7 in) tall person with a weight of 100 kg (220 lb) gives a BMI of 24.84, very close to an overweight BMI of 25, and a CI of 12.4, very close to a normal CI of 12.[65]

The exponent of 5/2 was proposed by Quetelet himself in the 19th century:[4]

However, it was not used much later, until the following formula for computing Body Mass Index that accounts for the distortions of the traditional BMI formula for shorter and taller individuals has been proposed by Nick Trefethen, Professor of numerical analysis at the University of Oxford:[66]

The scaling factor of 1.3 was determined to make the proposed new BMI formula align with the traditional BMI formula for adults of average height, while the exponent of 2.5 is a compromise between the exponent of 2 in the traditional formula for BMI and the exponent of 3 that would be expected for the scaling of weight (which at constant density would theoretically scale with volume, i.e., as the cube of the height) with height; however, in Trefethen's analysis, an exponent of 2.5 was found to fit empirical data more closely with less distortion than either an exponent of 2 or 3.

BMI Prime, a modification of the BMI system, is the ratio of actual BMI to upper limit optimal BMI (currently defined at 25 kg/m2), i.e., the actual BMI expressed as a proportion of upper limit optimal. BMI Prime is a dimensionless number independent of units. Individuals with BMI Prime less than 0.74 are underweight; those with between 0.74 and 1.00 have optimal weight; and those at 1.00 or greater are overweight. BMI Prime is useful clinically because it shows by what ratio (e.g. 1.36) or percentage (e.g. 136%, or 36% above) a person deviates from the maximum optimal BMI.

For instance, a person with BMI 34 kg/m2 has a BMI Prime of 34/25 = 1.36, and is 36% over their upper mass limit. In South East Asian and South Chinese populations (see § international variations), BMI Prime should be calculated using an upper limit BMI of 23 in the denominator instead of 25. BMI Prime allows easy comparison between populations whose upper-limit optimal BMI values differ.[67]

Waist circumference is a good indicator of visceral fat, which poses more health risks than fat elsewhere. According to the U.S. National Institutes of Health (NIH), waist circumference in excess of 1,020 mm (40 in) for men and 880 mm (35 in) for (non-pregnant) women is considered to imply a high risk for type 2 diabetes, dyslipidemia, hypertension, and CVD. Waist circumference can be a better indicator of obesity-related disease risk than BMI. For example, this is the case in populations of Asian descent and older people.[68] 940 mm (37 in) for men and 800 mm (31 in) for women has been stated to pose "higher risk", with the NIH figures "even higher".[69]

Waist-to-hip circumference ratio has also been used, but has been found to be no better than waist circumference alone, and more complicated to measure.[70]

A related indicator is waist circumference divided by height. The values indicating increased risk are: greater than 0.5 for people under 40 years of age, 0.5 to 0.6 for people aged 40–50, and greater than 0.6 for people over 50 years of age.[71][better source needed]

The Surface-based Body Shape Index (SBSI) is far more rigorous and is based upon four key measurements: the body surface area (BSA), vertical trunk circumference (VTC), waist circumference (WC) and height (H). Data on 11,808 subjects from the National Health and Human Nutrition Examination Surveys (NHANES) 1999–2004, showed that SBSI outperformed BMI, waist circumference, and A Body Shape Index (ABSI), an alternative to BMI.[72][73]

A simplified, dimensionless form of SBSI, known as SBSI*, has also been developed.[73]

Within some medical contexts, such as familial amyloid polyneuropathy, serum albumin is factored in to produce a modified body mass index (mBMI). The mBMI can be obtained by multiplying the BMI by serum albumin, in grams per litre.[74]

The Montrose Basin Heritage Society was formed in 1999 to bring together information about the basin, including its history and archaeology The Montrose Basin was hit by a tsunami in 6100 BC , generated by the massive underwater Storegga Slide, in Norway

In addition to referring to the creme-de-la-creme of Disney attractions and park rides in general, an E - Ticket can also used to describe

Removing the cylinder head is straightforward on pushrod engines, but more complicated on overhead-camshaft ones because you have to disconnect the timing belt or chain.

Methods vary from one engine to another, so if possible consult a handbook for your make of car to verify all the details.

Buy a new head gasket and a new rocker-cover gasket. Make a sketch of all the connections to the head so that you can refit them correctly.

Disconnect the battery earth terminal and cylinder-head connections. Drain the coolant.

Leave the manifolds and carburettor attached if possible. If you do remove them, fit new gaskets (See Exhaust manifold gasket replacement).

Undo the nuts or screws holding the rocker cover to the top of the head. Carefully lift off the cover.

If it sticks, tap the side gently with a soft-faced hammer. Set the cover upside-down on clean newspaper to catch oil drips.

You may need to loosen the rocker-shaft support pedestal nuts or bolts gradually in sequence, then remove them. Lift off the rocker shaft and put it on clean newspaper.

On engines with separately mounted rocker arms, take off the nuts holding the arms and the pivot balls, then remove the arms and set them all in a row on a piece of paper numbered with their correct order, so you can refit them in the same places.

Lift out the pushrods and stick them through numbered holes in a piece of cardboard or plastic foam; they too must go back in the same places. Keep them in a clean place.

Use a socket and bar to loosen the nuts or bolts securing the head in the reverse of the tightening sequence for the engine (see car handbook). Some engines need a special adaptor tool to fit the bolts.

Carefully lift off the head, complete with manifolds if possible. You may need a helper to lift the head. If it sticks, tap the side gently with a soft-faced hammer.

Set the head right way up on wood blocks to protect its machined undersurface. Remove and discard the head gasket, after checking that the replacement one is the same in every detail.

Take care not to let any dirt or carbon particles fall into the engine while you are working on it.

If the engine has a timing belt, remove the screws or bolts holding the belt cover to the front of the engine and pull the cover clear. Take care not to get oil on the belt.

Slacken the locking device of the belt tensioner (See Adjusting a camshaft timing belt).

Push the tensioner wheel out until you can free the belt. Take the belt off the camshaft sprocket, taking care not to rotate either the camshaft or crankshaft.

Undo the nuts or screws holding the camshaft cover to the head. Carefully lift off the cover: if it sticks, tap gently on each side with a soft-faced hammer. Set it upside-down on clean newspaper to catch oil drips. Remove and discard the gasket.

If the engine has a timing chain, after removing the camshaft cover, remove the nut from the camshaft sprocket. Pull off the sprocket and support the chain. Be careful not to drop any part into the chain case.

To remove the cylinder head, use a socket and bar to loosen securing nuts or bolts in the reverse order of the special tightening sequence for the engine. Some engines need a special tool to fit the bolts.

Carefully lift off the head - you may need a helper. If it sticks, tap the side gently with a soft-faced hammer. Set the head right way up on wood blocks to protect its machined undersurface. Remove and discard the head gasket, taking care not to let any dirt or carbon fall into the engine.

Refitting is mainly a reversal of the removal procedure, but there are certain extra steps for both pushrod and overhead-cam engines (see below).

Check that the head and block faces are absolutely flat, using a steel rule (See ). See, too, that they are clean. Lay the new gasket on the block, right way round: the upper side is marked 'top', 'haut' or 'oben'.

Lower the head into place, taking care not to displace the gasket. Refit the head nuts or bolts and tighten in the correct sequence to the required torque setting.

Refit all other parts, except for the rocker or camshaft cover and the air cleaner, in the reverse order of dismantling.

Check the valve clearances at the 'cold' setting (See Checking and adjusting valves). Refit the rocker or cam cover, using a new gasket.

Refill the cooling system and start the engine. Check for coolant leaks (See Checking and topping up car antifreeze coolant).

When the engine is at its normal working temperature, switch it off and check the valve clearances at their 'hot' setting if specified (see the car handbook).

After tightening the head bolts, refit the pushrods in their original places, followed by the rocker shaft or separate rockers.

In either type, be sure that the upper end of each pushrod is engaged with its rocker and that the lower end is seated in the tappet before tightening the nuts or bolts.

Tighten rocker-shaft nuts or bolts in the recommended sequence and to the recommended torque - consult the car service manual or a dealer.

Before installing the cylinder head, turn the crankshaft with a spanner on the pulley nut until No. 1 piston is at its top-dead-centre (TDC) position of its compression stroke.

Verify this from the TDC mark on the crankshaft pulley. Turn the camshaft until the mark on its sprocket is in the correct position for No. 1 cylinder firing. Now refit the head and tighten its bolts.

Check that the crankshaft and camshaft are still at their marks, then refit the drive belt or chain.

Slowly turn the crankshaft two full turns in the normal direction of engine rotation.

Make sure the timing marks are again in alignment then, for a belt-driven camshaft only, adjust the tensioner (See Adjusting a camshaft timing belt).

If the marks do not line up, reposition the crankshaft first, then the camshaft.

1 BATTLESHIP ROCK TRAIL IN NATURAL BRIDGE STATE RESORT PARK · 2 DOUBLE ARCH TRAIL IN DANIEL BOONE NATIONAL FOREST · 3 RAVEN RUN NATURE SANCTUARY TRAIL · 4