Why are F1 engine clearances so small?

[PlatinumZealot]

We know f1 cars use narrow face width gears on the front of the engine to drive the camshafts unlike road cars that use high inertia belts and chains. Since valve opening needs to be even more accurate at high rpms in these engines How is backlash controlled with These gears?

[autogyro]

Why does 'backlash' need to be controlled?
Belts and chains use 'tensioners' to maintain timing under load.
There is no need to do this with gear sets as the timing will only change under load due to tooth wear.
In some non F1 engines a dual floating idler gear is used to reduce 'backlash'.
I do not know what current F1 engines use.
In a well designed gear driven cam engine, the camshaft will not be allowed to overrun the crankshaft to over advance the cam timing.

[Brian.G]

We know f1 cars use narrow face width gears on the front of the engine to drive the camshafts unlike road cars that use high inertia belts and chains. Since valve opening needs to be even more accurate at high rpms in these engines How is backlash controlled with These gears?

A scissor gear perhaps? Or perhaps nothing,

[PlatinumZealot]

Why does 'backlash' need to be controlled?
Belts and chains use 'tensioners' to maintain timing under load.
There is no need to do this with gear sets as the timing will only change under load due to tooth wear.
In some non F1 engines a dual floating idler gear is used to reduce 'backlash'.
I do not know what current F1 engines use.
In a well designed gear driven cam engine, the camshaft will not be allowed to overrun the crankshaft to over advance the cam timing.

Toyota uses a scissor gear in the front of some camshafts.... The Toyota Starlet GT. I have pulled down that engine.
Gyro Back lash should be a big deal at such transient rev changes as seen in F1!

But I will take your lat sentence.

[autogyro]

'Gyro' (hmm) backlash does occur at very low rpm, i.e tick over on some gear drive output designs.
It is why Ken Wallis always uses a direct drive prop on the Wallis autogyro designs. (no problem with electric drive of course)
A high reving engine that needs a reduction gearbox to slow the prop always gives excess wear due to backlash vibration, it can be very bad and even lead to breakage.
Weslake designed a one off prototype engine for Ken that suffered from this problem as did the Norton Wankel prototype they gave him but to a lesser extent. The engine designed and built for Ken by Hewland was not as bad and had a damper fitted.
On light aircraft it is useful to use 'boxer' and long stroke engines to keep rpm to 4000 or lower with a direct drive.
It may be why there have been almost no real development in light aviation engines since the 1930s.
There are modern high reving engines in drones where the regulations dont seem to matter, no idea how reliable they are.
Cosworth do one as do Ilian.

This same problem can occur at very low rpm in gear driven cam engines including F1.
However, F1 engines dont usualy run at very low rpm.
It might also be a reason for 'blipping' the throttle at idle to keep the revs up and the gears driving.

[Raptor22]

Ok, we all know why F1 tolerances have to be tight.

BUT

Why are the clearances between moving parts so tiny?
Even as close as requiring the engine fluids to be warmed up before the engine can be started!

These are custom built engines, blue printed is another word for them. Its achievable therefore the engine builders opt for small clearances to ensure good fit between parts. There is less movement of the components relative to each other and this reduces wear.
Yes the oil has to be warmed to lower the viscosity to enable it to reach between the bearings surfaces but this is small price to pay for superior sealing, and bearing running

[Raptor22]

We know f1 cars use narrow face width gears on the front of the engine to drive the camshafts unlike road cars that use high inertia belts and chains. Since valve opening needs to be even more accurate at high rpms in these engines How is backlash controlled with These gears?

Through very accurate gear tooth hobbing

[langwadt]

'Gyro' (hmm) backlash does occur at very low rpm, i.e tick over on some gear drive output designs.
It is why Ken Wallis always uses a direct drive prop on the Wallis autogyro designs. (no problem with electric drive of course)
A high reving engine that needs a reduction gearbox to slow the prop always gives excess wear due to backlash vibration, it can be very bad and even lead to breakage.
Weslake designed a one off prototype engine for Ken that suffered from this problem as did the Norton Wankel prototype they gave him but to a lesser extent. The engine designed and built for Ken by Hewland was not as bad and had a damper fitted.
On light aircraft it is useful to use 'boxer' and long stroke engines to keep rpm to 4000 or lower with a direct drive.
It may be why there have been almost no real development in light aviation engines since the 1930s.
There are modern high reving engines in drones where the regulations dont seem to matter, no idea how reliable they are.
Cosworth do one as do Ilian.

This same problem can occur at very low rpm in gear driven cam engines including F1.
However, F1 engines dont usualy run at very low rpm.
It might also be a reason for 'blipping' the throttle at idle to keep the revs up and the gears driving.

would there really be any backlash to speak of in the valve train drive? assuming the crank has higher inertia that
the cams the drive would the drive always be one-way?

I can see why it might be problem for an engine driving a propeller where the propeller might have bigger inertia
than the engine itself

[autogyro]

If you turn over a camshaft which is not connected to the crank, you will find that the valve springing will jerk the cam forwards as each lobe goes over center.
At low rpm with a loose gear drive this will set up an oscillation that if allowed to continue will break something.
In an aero engine application the airscrew makes the problem worse although the reduction gears at low rpm is where the effect occurs.

[Tommy Cookers]

'Gyro' (hmm) backlash does occur .......
It is why Ken Wallis always uses a direct drive prop on the Wallis autogyro designs. (no problem with electric drive of course)
A high reving engine that needs a reduction gearbox to slow the prop always gives excess wear due to backlash vibration, it can be very bad and even lead to breakage.
Weslake designed a one off prototype engine for Ken that suffered from this problem as did the Norton Wankel prototype they gave him but to a lesser extent. The engine designed and built for Ken by Hewland was not as bad and had a damper fitted.
On light aircraft it is useful to use 'boxer' and long stroke engines to keep rpm to 4000 or lower with a direct drive.
It may be why there have been almost no real development in light aviation engines since the 1930s.
However, F1 engines dont usualy run at very low rpm.
It might also be a reason for 'blipping' the throttle at idle to keep the revs up and the gears driving.

I can see why it might be problem for an engine driving a propeller where the propeller might have bigger inertia
than the engine itself

backlash is often seen as the cause of the problem when it is just the symptom (removing backlash doesn't cure inadequate design)
eg propellor inertia depresses the natural frequencies of the whole system
major and ill-defined torque vibration (aerodynamic ripple and plane of rotation blade flexing) is always a design problem

BTW the 'real developments' in light aviation engines have been numerous and have all failed to be good enough
(Detroit V8s from Buick/Rover to bigblock, Renault, Porsche, Honda etc and diesels)
part of the long life (2800 hr TBO) of the 'old-fashioned' engines is due to their pushrod seperate-cylinder air-cooled design
(only one ever cylinder fails a compression check and is easily sorted in situ and without dismantling the whole engine)

reduction gearing is both pointless and worse than useless below 300 hp
(variable propellor pitch though is usual above 120 hp, and is very compact, very light and very reliable)

real diesels are always found in big ships and have never had reduction gears (that's a big selling point)
they are the most efficient piston engines (cruise BTE 50-55%)

don't many aircraft and F1 engines have resonance rpm (to be avoided) below their normal running rpm ?
eg Peugeot F1 engines had ring flutter resonance around 11000 rpm and blew up after a few seconds at that (ask Mr Brundle !)
isn't that type of thing part of the throttle blipping culture ?

[autogyro]

reduction gearing is both pointless and worse than useless below 300 hp
(variable propellor pitch though is usual above 120 hp, and is very compact, very light and very reliable)

Airscrew reduction gearing is a result of using over square high reving engines.
4000 rpm is about the maximum before reduction gearing is essential.
Variable airscrew pitch is indeed compact but we try to keep things as simple as possible.
The electric drive we are looking into will have variable pitch however. (sweet spot balance)

The main problem (from experience with at least twenty different engines) is the lack of decently designed airscrews for light aircraft.
Wooden airscrews are still the best and that needs a skilled craftsman.
Ken Wallis still carves his own and builds his own steel/wood composite rotor blades.
They both have an unlimited fatigue life and far superior performance to other types.
Metal blades dont work nearly as well.

The best engine IMO for light aircraft is the Subaru four (without reduction gearing).
Wallis has one on test in a W116 and the low weight is a great benefit, as is the water cooling which allows a heater.
I tried to get Prodrive to build a modified group N rally engine some years back for turbocharged altitude record use.
They were interested but Subaru put a stop to it.
Usual atitude to aviation development by the manufacturers.

I agree that gear train backlash should not be a problem in a well designed powertrain.
However at the limit of top performance there usualy has to be a compromise.
In this case backlash might occur and it is then essential to run the system in such a way so as to discourage the problem.
Pre heating water and oil systems and blipping the throttle to keep the rpm changing are two ways to help keep a high performance system in one piece.

[Tommy Cookers]

there is inherent contradiction in improving light aviation by designing and developing reduction gearing (IMO your posts show that)

modern (hopefully inexpensive) car or motorcycle engines have power and transmission integrated as a 'power pack'
this architecture should be considered for its scope in cheap light aviation
the existing 'gearbox' structure should surely be retained for use as a prop reduction drive
so that any engine eg 4 cyl inline is useable

motorcycle engines (having a central takeoff via reducing 'primary drive') are perfect (ready made) for this
(also twin cylinder mc engines have useable reduction)

the flat 4 aircraft engine was introduced as a the cheapest possible engine in the 30s depression
cheap because it was a sidevalve/flathead, allowing the whole engine to be one iron casting (with seperate alloy heads)
before this all small (aircraft) engines were inline (even in the USA)

back on thread, anyone ?

[autogyro]

Sorry yes back on track F1 engine clearances.
There should be a great deal more to debate on this.

I must answer one point though.
Motorcycle engines with gearboxes look ideal at first glance for light aviation use and they have a place in certain applications.
However one problem is nearly always overlooked.
The thrust on the airscrew drive shaft.
This can easily damage a light and fairly weak gear casing and usualy needs major expensive modification to become reliable.
Thrust bearings and new housings have to be made.
On a pusher design the thrust is reversed of course.
It is far easier and more reliable to choose a low reving engine to match a direct drive airscrew.
The extra thrust bearing can easily be fitted on the engine block.

[Edis]

The clearances between the bore and the piston is actually larger when the engine is cold. This is because the operating temperature of the piston is higher than the aluminum block or liner. The piston itself is conical and oval. The reason for the conical shape is the higher operating temperature near the piston crown, while the oval shape is due to compensate for the change in shape caused by the cylinder pressure when the engine is operating.

The clearances between the crankshaft and crankcase, and camshaft and cylinder head is smaller when the engine is cold. This is because the steel crankshaft or camshaft will expand less than the aluminum crankcase or head by the heat. This issue is generally smaller with iron block engines, and many aluminum blocks use cast in iron inserts for this reason.

Another reason for small clearances is the use of low viscosity oils. To reduce the frictional losses in the bearings a thinner motor oil (typically similar to 0W-20) is used in combination with a higher surface finish. Unless the bearing clearances are reduced the resulting oil flow through the engine would be very high, which is undesirable.

[autogyro]

Thanks for that Edis, great explanation.
So it is the crank and cam journal clearances that make it essential to heat up the oil and water to running temperature.
I presume the pistons would therefore still be below their working temperature and with to wide a bore clearance at start up?

Motor cycle powertrains used for light aviation would need expensive modification to include an airscrew thrust bearing.
In most cases this would start with a complete casing redesign. I think this is relevant to the thread as follows.

I would be interested in learning what fore and aft thrust bearings are used in current F1 engines and the bearing materials used throughout the engines.
There must be problems maintaining both dimensions and location on the shaft bearings.