Why are F1 engine clearances so small?

[PlatinumZealot]

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!

[spacer]

Because of the unequal thermal expansion coefficients between materials used in the engine (i.e. pistons vs engine block).

Or uneven geometric thermal expansion inside components (i.e. pistons being oval when cold, but round when hot).

All of this to achieve "optimum" clearance in running conditions.

[Tommy Cookers]

Because of the unequal thermal expansion coefficients between materials used in the engine (i.e. pistons vs engine block).

Or uneven geometric thermal expansion inside components (i.e. pistons being oval when cold, but round when hot).

All of this to achieve "optimum" clearance in running conditions.

needing the piston tight when cold implies that the block expands more than the piston when hot
this would not happen even with a Magnesium block (not allowed for years), because the piston is always hotter

IIRC the second is the reason
the bore:stroke ratio of current F1 is unprecedentedly huge, around 2.6:1 (eg 98 bore 39 stroke)
the pistons have very squat flanks but a relatively huge crown and pin region
with exhaust flow on one side and inlet flow on the other, the crown shape changes as it heats unevenly with running
so it's made out-of-round when cold to become round with running (so needs the engine heated to become free)

[PlatinumZealot]

Let me throw a cruve ball....

In the video where they were preparing the Leighton house car for start up, the narrator said that when cold, the engine is so tight it cannot be turned by hand tools. How true is this?

Imagine the engine builder has just assembled an engine and it won't turn! wouldn't that be just wrong?

[Jersey Tom]

Let me throw a cruve ball....

In the video where they were preparing the Leighton house car for start up, the narrator said that when cold, the engine is so tight it cannot be turned by hand tools. How true is this?

Imagine the engine builder has just assembled an engine and it won't turn! wouldn't that be just wrong?

Could certainly conceivably be true. If the clearances are what they should be when the engine is hot and running, who cares what they are at ambient? (A temperature at which the engine will never be operating).

[Tommy Cookers]

In the video where they were preparing the Leighton house car for start up, the narrator said that when cold, the engine is so tight it cannot be turned by hand tools. How true is this?

the same was said of the Renault on a lightweight BBC programme with Richard Hammond (someone tell him that the 60s Mustang was not a muscle car !), which caught my attention
IIRC the answer in my post was sourced directly or otherwise from a old thread

[strad]

It does seem odd when you consider they have to carry extra oil in a separate tank because it goes thru so much.

[Cuky]

it is done like that to get more efficient performance from such small engines. Here you have a documentary from BBC that talks about that.
[youtube]http://www.youtube.com/watch?v=7YQ0_CG9kp0[/youtube]

[flynfrog]

I think this is the case with most race engines. Bearings will be tight when cold. Pistons will be out of round ect. Even in entry level 2 stroke motocross engines you have to take it easy when cold give the iron liner time to expand so the the aluminum pistons that warms up quicker wont push the oil film to far and cold stick the piston.

[flynfrog]

It does seem odd when you consider they have to carry extra oil in a separate tank because it goes thru so much.

I wasn't aware that they carried oil in any other place other than the tank on the front of the engine> Where else are they carrying?

[riff_raff]

.....In the video where they were preparing the Leighton house car for start up, the narrator said that when cold, the engine is so tight it cannot be turned by hand tools. How true is this? .....

This is nonsense. Since most of the materials in the engine, where there are sliding/rotating interfaces, have a similar CTE rate, there would be little change in clearance with temperature. The clearance between a steel or Ti conrod bearing bore and a steel crank pin would not change appreciably from RT to operating temperature. Nor would the clearance between an aluminum piston skirt and an aluminum cylinder bore change significantly from RT to operating temp.

In reality, very tight running clearances don't make a huge difference in power for most components. The only fits that really matter in this regard are valve seat contacts and compression ring conformability. It's not small clearances that matter, it's the precise control of operating clearances that matter.

[amouzouris]

I am under the impression that F1 engines are put together while hot..in their operating temperature... so that's the reason that when they cool down it is almost impossible to turn them by hand.. in addition..clearances do make a lot of difference in power..as a very simple experiment in the video posted above from 'richard hammond's engineering connections' illustrates..they make a cannon that uses pistons instead of cannon balls...a very small clearance difference doubles the distance the piston is projected!

[strad]

It's not small clearances that matter, it's the precise control of operating clearances that matter.

True,,that's what blueprinting is all about.
They carry extra oil in a second tank and can pump from the secondary to the primary tank when they get low. You have never heard them mention this during the race? They do.

[autogyro]

Richard Hammond did not show the affect piston rings would have had on the cannon's effectiveness.
A loose piston with good ring sealing would have gone much further.
The force he applied to the piston was parallel to the bore with no side contact issues as there are in a reciprocating engine.
The experiment was a poor attempt to explain the issue.

Reduced clearances allow for far better control over lubricating oil giving far more reliable contact prevention.
This is crucial for piston to cylinder wall and crankshaft journal clearances.
The piston design simply could not work with larger clearances and high RPM and the forces onto the crankshaft would soon break the oil film of a large clearance journal.
The tight engine at RT is a by product of this caused by different material expansion rates.

[Tommy Cookers]

the old thread ..... 'F1 pistons and their makers' ....... is a great read and might lead to enlightenment
regarding piston shape changes
also try threads listed in the above thread as related
it's all in there somewhere !