The Ford SOHC Pinto & Sierra Cosworth DOHC Engines high-peformance manual: For Road & Track

Chapter 1

Problem areas

STANDARD CONNECTING RODS

Forged connecting rods

In all Pinto engines the standard forged connecting rods are reliable to about 6700rpm with the standard weight pistons and piston pins fitted but are prone to breakage if the engine is subjected to sustained or continuous revs over 6700rpm. The point of breakage is almost always about 25mm/1in below the piston pin (gudgeon pin) boss.

Early forged standard connecting rod.

The connecting rod is basically well-designed in most areas. The big end is well-proportioned with 9mm diameter bolts. The small end (little end) of the connecting rod is quite large and, if anything, over-built but the all important I-beam of the connecting rod is marginal, considering the weight of the piston and piston pin. To be fair, this is a road-going production engine and not a racing engine. For all normal use these connecting rods are more than adequate, and connecting rod failure has never been a problem on standard engines used normally.

From a high-performance point of view, the standard forged connecting rods don’t ‘look right’ and, once these engines are tuned to produce more power and run to higher revs, the connecting rods break regularly. True, the connecting rods will turn high rpm (8000rpm and more) for a very short length of time, but this is hardly the reliability needed for high performance applications. Constantly changing connecting rods to preclude failure - and even then not really knowing whether or not the rods are going to break - is not normal race engine practice.

The reliability of this connecting rod is improved by approximately 300 rpm (maximum rpm 7000) if the small end boss is lightened and a lightweight forged piston and piston pin used. The forging flash on the I-beams is not removed or touched in any way so that the maximum amount of material is kept. Although polishing the sides of the I-beam would be desirable, there’s just not the material available to remove anything without detriment to the strength of the rod (the lesser evil).

Forged standard connecting rod with lightened small end.

Later, cast connecting rods

The later ‘wide’ cast connecting rod, as found in all 2000IS engines and all 1988 on Sierra and Transit engines with a large ‘205’ cast in the block, is a definite improvement over the original rod, but it, too, has a strength limitation in the I-beam. If the early forged connecting rod was of the same proportions as the cast version there would be few breakage problems.

Regard the standard cast connecting rods as useable for applications where up to 6900rpm is required on a more or less continuous basis with standard pistons and piston pins, and 7200rpm when lightweight forged pistons and piston pins are fitted. Anything above these engine speeds has an element of risk attached and standard connecting rods subjected to higher rpm, such as 7500rpm, must be changed frequently to prevent breakage. Consider a normal season’s racing (800 kilometres/500 miles) as the life of one set of these standard connecting rods.

The later cast connecting rod should be used just as it is (no polishing). Ideally, you should use brand new connecting rods which have been straightness tested and crack tested. Do not use any standard-type connecting rods that have previously been used in a competition engine. Next to new rods, used rods out of passenger car engines that have never been stressed by high rpm usage (5000rpm and above) are best.

Later cast steel standard connecting rod is capable of 7500rpm with a lightweight piston and piston pin and 7200rpm with the standard piston and piston pin.

Cosworth rods

The Sierra Cosworth connecting rod is very strong (as in being bullet proof to 9000rpm) and is a standard Ford part which is a near ‘drop in’ fit for Pinto engines and it does solve the problem of Pinto connecting rod failure, but these rods are a comparatively recent arrival. Note that using the Sierra Cosworth connecting rod in conjunction with a standard type Pinto piston will require the use of an alternative piston pin retention method (such as Teflon buttons) because the small end is of the floating type on the Sierra Cosworth and not a press fit like the Pinto’s.

Caution! - The Sierra Cosworth connecting rod is 1.5mm/0.060in longer than the Pinto rod and this means that, depending on the piston used, it may be necessary to machine the top of the piston to compensate (Cosworth pistons have a lower piston pin to crown height). Holbay Engineering can supply custom machined forged pistons for this combination which will see the top of the piston flush with the top of the block at top dead centre (TDC).

Standard connecting rods - summary

The standard early forged connecting rod with a standard piston and piston pin fitted has a continuous rpm rating of 6700rpm. These rods (with standard pistons and piston pins fitted) will break above 6700rpm after some use. The reliability of the connecting rod is improved if the small end of the connecting rod is lightened to the extent that the wall thickness of the small end is reduced to 3.5mm-4.0mm/0.138in-0.157in and further improved if lightweight pistons and piston pins are fitted.

The standard piston, piston pin and rings together weigh 767gm/27.05oz. The weight reduction brought about by changing to lightweight pistons, piston pin and rings that together weigh about 515gm/18.16oz, plus the reduction of about 65 grams created by removing material from the small end of the connecting rod, reduces the overall weight acting on the I-beam of the connecting rod by around 580gm/20.45oz and lifts the maximum rpm rating to about 7000rpm.

The later cast connecting rods are slightly stronger, but not much. Changing the piston, piston pin and piston ring assembly to one that weighs 515gm/18.16oz instead of the usual 765gm/26.98oz improves the reliability of the connecting rod to an absolute maximum of 7500rpm but not for applications where these revs are used on a continuous basis.

If the standard connecting rods are going to be retained, the fitting of the lightest possible piston, piston pin and ring combination is recommended. The cast standard connecting rod weighs 680 grams, while the forged standard connecting rod weighs 700 grams (or 635 grams lightened as suggested).

Nothing can alter the fact that the two standard type connecting rods are not suitable for all-out competition use and, as a consequence, alternative connecting rods have to be used. With the lightest forged pistons fitted to either of the standard connecting rods, the maximum revs possible are 7300-7500rpm with limited reliability. The connecting rods will only take this sort of treatment for a limited period of time and it only takes one connecting rod to break and the engine will be totally wrecked ...

With either type of standard connecting rod fitted, maximum engine rpm must be limited to avoid connecting rod failure. Use a governor-type distributor rotor (readily available for the standard Bosch distributor used on many of these engines). Governor rotor cut-out speeds start at 6200rpm and the cut-out rpm is cast on the rotor. Alternatively, an electronic rpm limiting device can be fitted into the ignition system. The use of both methods will give peace of mind.

Standard distributor rotor on the left and governor rotor on right.

CAMSHAFT LOBES AND ROCKERS

Many standard Pinto engines have had camshaft failures of one sort or another. The oil spray bar is usually blamed (it can be a source of problems if an oil hole becomes blocked) but, in reality, there is so much oil from all the rockers flying around that this idea can usually be discounted. The real problem on standard engines was one of rocker hardness and camshaft lobe hardness.

The original rocker geometry of the standard engine was always correct, but it certainly wasn’t after a replacement camshaft with a different base circle diameter (any significant amount - 1.0mm/0.040in, plus) was fitted. On high-performance engines this is where the real problems started because this was a new factor unrelated to the original rocker/cam lobe surface hardness problem.

Early standard engines often had the problem of one or two rockers (or more) and, perhaps, the cam lobes wearing away rapidly. On checking surface hardness of the worn rockers it was common to find the hardness value slightly down on that of the surviving rockers, even if the surviving rockers looked to be on the point of failing themselves but were actually still giving good service. The tops of the camshaft lobes would also show around 0.75mm/0.030in wear even though the engine would still be running well, if noisily.

There are now plenty of camshaft manufacturers (including Ford) making complete kits for these engines. Because of the known problems, replacement camshafts and rockers are all checked for sufficient hardness. Outright failures are few and far between, although the overall wear characteristics remain unchanged.

CAMSHAFT PILLARS

The front pillar is extremely strong and never causes any problem. The centre and rear pillars are extremely weak and do not represent good design. These two items must always be handled with extreme care to avoid damage (breaking them off). Ford never saw fit to improve the strength of the pillars during the life of the Pinto engine.

The material thickness of these pillars is marginal at best and, further to this, the factory drills an oil feed hole for the spray bar in the middle of the centre pillar - at the thinnest point on one side!

The two weak camshaft pillars.

The centre and rear pillar can be strengthened to a satisfactory level, but this involves detailed engineering work and the brazing of mild steel straps over them. These modified pillars will not break even in the most rigorous of service. A close fitting steel mandrel (0.0005inch/0.013mm) has to be made that fits into the centre and rear pillars tunnels (bearings out) and then the pillars have the straps braized on. The mandrel prevents distortion occurring during braizing. As a further alteration the oil feed to the rockers is not taken off the centre pillar but rather off the front and rear pillars only. This means making up a new spray bar and drilling into the pillars (involves some re-work). What this does is allow the oil fed to the highly stressed bearing in the centre pillar to oil the bearing only and not be drained off to feed the rockers as well. If the valve spring pressure and the lift are kept within reasonable limits and the geometry is correct the standard pillars do not normally break in a high-performance application.

CAMSHAFT BEARINGS

The early centre and rear camshaft bearings (white metal type) would also wear out prematurely on standard engines. On early engines fitted with white metal camshaft bearings, the centre bearing would invariably be well worn after even a moderate (50,000km/30,000 mile) usage. Later standard engines feature hard wearing bronze bearings and, while the underlying problem is not actually resolved by this modification, the symptoms are reduced to an acceptable level.

The centre bearing takes the maximum flex from the camshaft (caused by the valve spring and camshaft action) and this is why it suffers first from wear problems. Centre bearing wear is increased when strong valve springs and a high lift camshaft are installed.

Just to exacerbate the problems caused by a worn centre bearing, the oil spray bar is fed from this bearing.

PISTON TO VALVE CONTACT

2000cc engines have deeper combustion chambers and so, when fitted with a standard camshaft, do not suffer piston to valve contact even when a cam drivebelt breaks. On the 1600cc and 1800cc engines (with standard camshaft) if the drivebelt breaks valves will be bent.

Any Pinto engine can have inlet and exhaust valve reliefs professionally machined into the tops of the pistons to prevent piston to valve contact - this is particularly important for road cars where reliability is essential. If the cylinder head is planed a lot, and the camshaft has more lift than standard, machining deep enough valve reliefs becomes difficult (regard 3mm as a safe maximum) but whatever valve relief depth can be safely obtained should be obtained. Reliability is the most important attribute of any high-performance engine.

Auxiliary shaft and the gear which can wear.

AUXILIARY SHAFT GEAR WEAR

When assembling the short block the first to be checked is the mesh of the distributor drive gear with the auxiliary shaft gear. If an auxiliary shaft is found to have its gear teeth worn to a knife-edge, the reason for this is poor gear mesh. This is not a common problem, but it does crop up occasionally and will cause grossly fluctuating ignition timing.

The procedure for correction (using good used parts or brand new parts) is to install the auxiliary shaft and location plate, then rotate the shaft by hand to check for freedom of rotation and also check the endfloat (lash). Endfloat should be kept to 0.125mm/0.OO5in.

The next step is to fit the distributor you are going to use, oil drive shaft and oil pump. Once they are all bolted in, rotate the auxiliary shaft clockwise and then anti-clockwise, note if there is any difference in the effort required to turn the shaft in different directions or whether rotating one way feels a bit ‘gritty’- this ‘grittiness’ is easily felt when turning the auxiliary shaft by hand via the belt drive cog. Correctly matched gears have very low drag in both directions. If you feel that all is not well, remove the location plate and make up a packing piece 0.5mm/0.020in thick and place this behind the location plate. This packing will shift the auxiliary shaft forward, and there should be a resultant reduction in drag as mesh is improved. It’s possible that more than 0.5mm/0.020in will be necessary (up to 0.75mm/0.030in). The repositioned auxiliary shaft will not normally suffer gear wear again.

LOOSE SPROCKETS

Check the fit of the drivebelt sprockets on the crankshaft, auxiliary shaft and camshaft. If the fit of any sprocket is loose (as opposed to a tap on fit) it will eventually become very loose and will rattle when the engine is running. If a securing bolt for any one of these three sprockets is left loose, or works loose, the engine will usually emit a knocking noise. If left too long in this loose condition the parts concerned will be seriously damaged and require replacement.

VALVE GUIDES

The standard valve guides are integral cast iron ones and they do wear. The best method of restoring standard worn valve guide bores to better than original is to have K-Line inserts fitted to them. Many engine machine shops/engine reconditioners have this equipment.

Chapter 2

Short block components

PISTONS AND CONNECTING RODS

The choice of parts depends on the application. The majority of modified engines (1600, 1800 and 2000) are built using standard parts such as oversized standard cast pistons and connecting rods in freshly rebored cylinders. There is little point in using a block which has more than 0.05mm/0.002in bore wear: in fact, there’s very little point in modifying an engine that has any bore wear at all. There is no substitute for a perfectly parallel cylinder bore. AE cast aluminium over size pistons are available for all Pinto engines in plus 0.020inch/0.5mm, 0.030inch/0.75mm, 0.040inch/1.0mm and 0.060inch/1.5mm over sizes.

The standard cast aluminium pistons for all Pinto engines are rated as being suitable for use up to about 7000rpm; which means that the standard pistons are slightly stronger (in rpm terms) than the standard connecting rods. An engine used on the race track equipped with standard type cast pistons and standard connecting rods and being revved consistently to 7000rpm will most likely end up having a connecting rod failure rather than a piston failure.

In most instances it is the 2000cc version of the Pinto engine that gets modified because it is the largest capacity engine. Most of the alternative equipment is made to suit these engines so the following information refers mainly to them.

Standard 2000cc Pinto piston and pin.

A standard type cast piston is available from AE in plus 0.090inch/2.25mm for 2000cc engines which takes the capacity out to 2.1 litres. There is no weight difference over the standard piston. These pistons are ‘drop in fit’ items once the block has been bored out, and are compatible with the standard type connecting rods.

Note that engines (with components based on standard units) that survive occasional high rpm use (7000rpm plus) do so because the components are not continuously subjected to this sort of treatment. Occasional short duration revving to 7500rpm is not the same, in component stress terms, as revving to 7500rpm at each and every gear change.

Lightweight forged pistons are available from specialist piston manufacturers such as Omega, Accralite, Mahle and Holbay and will withstand 9000rpm plus. These pistons all have 24mm diameter piston pins and round wire circlips. When using standard type Pinto connecting rods in conjunction with these forged pistons (not to 9000rpm), such pistons will allow the standard method of piston pin retention (interference fit) in the connecting rod to be used or, alternatively, honing out the rod’s piston pin tunnel to give a 0.010mm/0.0004in clearance and a fully floating piston pin.

To reduce ‘ring drag’ these lightweight forged pistons have rings of narrow section - top 1.0mm/0.040in; second 1.5mm/0.060in; oil control 3.0mm/0.118in.

Caution! - never re-use round wire circlips.

New standard connecting rods are going to last longer than used standard connecting rods (all things being equal) but continually fitting new sets of standard connecting rods is false economy unless competition class rules require original equipment parts to be used. Buying non-standard heavy duty ‘bullet proof’ connecting rods in the first place is the most cost effective method for engines that will be regularly required to rev at over 7000rpm.

Buying expensive non-standard heavy duty ‘bullet proof’ connecting rods as made by Holbay, Arrow or Farndon, for example, in the very first instance is cost effective in the long run as the connecting rod failure problem essentially ceases to exist. Farndon, for example, make three lengths of connecting rod for Burton Power. These connecting rods’ centre to centre lengths are standard at 5.000inch/127.0mm, 5.060inch/128.5mm (which is the Sierra Cosworth centre to centre distance) and 5.150inch/130.8mm.

The 5.150inch/130.8mm centre to centre distance connecting rods are designed to fit into engines with specially machined Accralite 91mm, 92mm and 93mm forged pistons which have gudgeon pin holes placed higher in the piston than standard. Accralite, as a consequence, make two very similar pistons of the same diameter sizes but they do NOT interchange. This piston and connecting rod combination is designed to reduce the connecting rod angulation to the minimum possible within the confines of the engine design. Holbay do the same basic combination (long connecting rod, short piston height) to order. This is the ideal setup for these engines even though it is expensive.

An alternative is to fit connecting rods out of a 1600cc Fiesta diesel engine. These connecting rods are available at a very reasonable price new, and even cheaper second-hand from a scrapped engine. The other advantages of using the Fiesta diesel engine connecting rods is that they are very strong and will withstand 8000rpm on a continuous basis when the small end is lightened; their longer centre to centre dimension (0.125in/3.2mm) also reduces the connecting rod angulation.

There is, however, some complication with using Fiesta rods as they are not a ‘drop in’ fit. The small ends of the 1600cc diesel connecting rod are of the floating type and so Teflon buttons will have to be used to locate the piston pin in a Pinto application as the standard type press fit piston is going to be used (that’s genuine Ford V6 pistons, AE replacement Ford V6 pistons or Kolbenshmidt V6 replacement pistons). The problem with these connecting rods is that the big end bearing tunnel diameter is much smaller than