Two urban legends about the F7P / F7R engine: bearings without a locating tab and hydraulic lifters

Since 2007, Mespiecesauto re-manufactures automotive parts for classic and sports engines. And if there is one world that has always surprised us with certain persistent mechanical beliefs,
it is that of the Clio 16S and of the Clio Williams.

Two urban legends regularly come up around the engines F7P and F7R :

conrod bearings without a tab that would risk spinning?
the hydraulic lifters that supposedly must be filled with oil before reassembly.

In this article, we will revisit these two myths, explain why they took hold, and above all demonstrate what really happens from a mechanical point of view.

1. Conrod bearings without a locating tab: a very widespread fear

The first legend generally appears in two situations: during a major engine failure, or when reassembling an engine.

In the event of a failure, one sometimes finds conrod bearings that have spun in their housing. The conclusion is then often quick:

“The bearing spun because it had no locating tab.”

This idea has spread widely in the Clio 16S and the Clio Williams.
Result: when an owner restores their engine, they obviously do not want to go through the same mishap.

Before ordering their bearings from Mespiecesauto, the question therefore comes up regularly:

“Your bearings do they indeed have a tab?”

The answer may be surprising, but it is essential:

The tab does not hold the bearing in place.

The bearing's actual retention is not provided by the locating tab, but by the clamping of the conrod cap onto the conrod. More precisely, it is the slight protrusion of the bearing in its housing, generally called crush, that keeps it in place once the assembly is torqued.

How does the bearing actually stay in place?

A conrod bearing is not simply laid in its housing.

When correctly fitted, it protrudes very slightly from the conrod and the cap. We are talking here about a few hundredths of a millimetre, depending on the design and the manufacturer.

At the moment of tightening, the cap compresses the bearing into its housing. This compression creates a radial force and prevents the bearing from moving.

It is this mechanical clamping, and not the locating tab, that ensures the bearing stays in place.

The locating tab, for its part, mainly serves to position the bearing correctly during assembly. It prevents an assembly error, but it is not designed to hold a bearing against rotation if it starts to seize on the crankshaft.

Simple demonstration

You just need to do a very simple test to understand.

Take a bearing with a tab and place it only in the conrod cap, without refitting the cap on the conrod.
You will find that it is very easy to push it out of its housing, in either direction.
Now, correctly fit the two half-bearings in the conrod and in the cap. Then tighten the bolts to the prescribed torque.

At that point, try to push the bearings out of their housing.

It is impossible.

Why?
Because the bearing is now held by the clamping force between the conrod and its cap.

It is this demonstration that lets you understand something important:

If a bearing spins in a conrod, it is not because it has no tab.
It is because another mechanical problem caused it to lose its retention or to seize.

What can really make a bearing spin

The real causes are generally to be found elsewhere:

lack of lubrication ;
oil pressure too low ;
incorrect oil clearance ;
crankshaft marked or out of spec?
ovalised conrod big end?
poorly matched conrod cap;
fatigued or poorly tightened bolts;
dirty assembly ;
greasy or contaminated bearing back;
abnormal overheating?
engine speed or load too high in poor conditions.

In other words, the presence of a locating tab will never save a bearing that starts to seize on the crankshaft crank pin.

The force involved is far too great. The tab can be marked, crushed or torn off, but it cannot prevent a bearing from rotating in a failure situation.

The real question is therefore not:

“Does the bearing have a tab?”

But rather:

“Are the conrod, the crankshaft, the oil clearance, the bolts and the assembly compliant?

2. Hydraulic lifters: do they really need to be filled

The second legend concerns the hydraulic lifters. It comes up especially during the reassembly or overhaul of a Clio 16S or of Clio Williams.

On forums, Facebook groups or in some workshop discussions, one regularly reads:

“They must be soaked in oil.”

“They must be primed before fitting.”

“They must be filled with oil.”

Here again, the idea seems logical at first sight. A hydraulic lifter works with oil, so one might think it should be filled before reassembly. Yet this reasoning can lead to a mechanical problem.

What is a hydraulic lifter for?

To understand the problem, we first need to go back to the role of the hydraulic lifter.

Before this type of system, many engines used mechanical tappets, adjustment shims or rocker systems with adjusting screws. In that case, the valve clearance had to be set manually.

On a rocker system, for example, you act on an adjusting screw to obtain the correct clearance between the valve actuator and the valve itself. The problem with these systems is that they can change with wear, expansion, mileage and mechanical stresses.

Incorrect clearance can lead to:

greater mechanical noise;
a drop in performance?
poor opening or closing of the valves?
premature wear of certain valve train parts;
in some cases, more serious mechanical degradation.

The hydraulic lifter was therefore designed to manage this clearance automatically. Its role is to compensate for variations in clearance between the cam and the valve, without periodic manual adjustment.

The operating principle

A hydraulic lifter is mainly composed of a body, an internal piston, an oil chamber, a check valve and a spring.

Its operation is relatively simple:

When the cam does not press on the lifter, the internal spring pushes the lifter piston slightly. Engine oil then enters through a small orifice and fills the internal chamber. The lifter naturally takes the right height to eliminate the clearance between the cam and the valve.

As soon as the cam begins to press, the pressure increases in the lifter. The check valve closes and the oil remains trapped in the internal chamber. As oil is almost incompressible, the lifter becomes almost rigid and transmits the cam's force to the valve.

When the cam releases its force, the pressure decreases. The lifter can then rebalance itself in order to compensate for wear, thermal expansion and small variations in clearance.

A hydraulic lifter is therefore not a simple bucket filled with oil.
It is a small system for automatic compensation of valve clearance.

What happens when you fill a lifter in an oil bath?

When you take a hydraulic lifter and operate it in an oil bath before fitting, you are not only lubricating it.

By pumping the internal piston in the oil, you gradually fill the internal chamber of the lifter and expel the air inside it.

At first, the internal piston moves down and up fairly easily. Oil enters through the orifice, the check valve lets the oil through and the air bubbles escape. After a few movements, the internal chamber fills completely.

From that moment on, the behaviour of the lifter changes:

the lifter becomes hard.

Why? Because oil is almost incompressible. Once trapped behind the check valve, it prevents the internal piston from retracting freely. The lifter then finds itself in a “pumped up” position,
close to its maximum height.

To return to our rocker example, it is like screwing the adjusting screw all the way in before starting the engine.

The problem at reassembly

The problem is that a fully filled lifter can become temporarily too long at the time of reassembly.

In this situation, it can press on the valve stem even when the cam is supposed to be on its base circle. In other words, the valve may not return perfectly to its seat.

The possible consequences are as follows:

the valve does not close completely?
compression drops on the cylinder concerned;
the engine may start badly or not start;
the engine may run unevenly on the first start;
in some unfavourable cases, the piston / valve clearance can be reduced
a piston-to-valve contact can even occur

By pumping a hydraulic lifter in oil before assembly, you do not only prime it: you can temporarily turn it into an incompressible part.

The internal travel of the lifter on the Clio 16S / Williams

On the Clio 16S and Clio Williams hydraulic lifters, the internal piston travel is about 2.1 mm. There is a height variation of approximately between 16.15 mm and 18.20 mm.

This travel is precisely what allows the lifter to work within a compensation range. At the factory, at Renault, assembly was carried out under controlled conditions:
new parts, calibrated cylinder head, valves, seats, camshafts and lifters to specification. The lifter could then naturally end up in a working position close to mid-travel.

But during an engine rebuild, the conditions are not always those of a new assembly. The cylinder head may have been resurfaced, the seats may have been recut, the valves replaced, the camshafts changed, or some components may have different tolerances.

In this context, fitting a lifter that is already filled with oil and locked in the high position is not ideal.

The right method: lubricate, but do not pump up

The goal is obviously not to reassemble the lifters dry. The parts must be clean and correctly lubricated at assembly.

However, it is preferable that the lifter is not fully filled. Ideally it should be fitted emptied of its internal oil, or at least able to compress.

For this, it is possible to empty the lifter:

either by removing the internal piston when the design allows it;
either by gently pushing back the piston with a small vice in order to expel the oil from the chamber;
either by simply checking that the lifter remains compressible before fitting.

When emptied, the lifter ends up in a lower position. You then obtain the maximum clearance available at reassembly.
Once the engine is started, the oil pressure will naturally do its work: it will progressively fill the lifter and it will position itself correctly within its operating range.

The right logic is therefore not to fill the lifter before fitting, but to fit it clean, lubricated, free, and able to compress.
The oil pressure will then do the rest.

This distinction is important: lubricate a hydraulic lifter is necessary. The pump up fully before reassembly can, on the contrary, create a problem
on the first start.

Article written by Benjamin
Engineer and founder of Mespiecesauto
Specialist in reverse engineering, developer of parts for Clio 16s & Williams since 2007.

Clio 16v & Williams engine: 2 mechanical urban legends