Richard Hammond's Engineering Connections

[Crucial_Xtreme]

He covers engines but has a decent amount of time on aerodynamics. Good interesting video.

[youtube]http://www.youtube.com/watch?v=7YQ0_CG9kp0[/youtube]

[Tommy Cookers]

I watched this when broadcast, and have just looked at the thread from about 2 years ago

I still have a question ....... PISTONS ?

This programme (or another similar one by RH) seemed to clearly say that the piston had to be a push fit (tight) at room temperature, and the engine (Renault) would not run unless pre-heated to something like normal running temperature.

What piston (and/or liner) material would have needed this fit ? (presumably not now permitted with engine freeze rules ?)

[Crucial_Xtreme]

I watched this when broadcast, and have just looked at the thread from about 2 years ago

I still have a question ....... PISTONS ?

This programme (or another similar one by RH) seemed to clearly say that the piston had to be a push fit (tight) at room temperature, and the engine (Renault) would not run unless pre-heated to something like normal running temperature.

What piston (and/or liner) material would have needed this fit ? (presumably not now permitted with engine freeze rules ?)

Not sure Tommy. Here's what I found here in the forums though.

Renault recently reveals some F1 engine particularity on a public web note (maybe it was only in french?). They said that F1 engine cannot do cold start physically. Piston is slightly oval while cylinder is round and so the piston is stucked in the cylinder. When heated up & due to thermal dilatation, piston & cylinder get their "working" shapes and engine can be started. If I remember well, minimum temperature was 50°C.

A shame the website I saw it do not keep a lot of archives, I cannot retrieve it

Link

F1 engines, as most high level race engines, are preheated before fireing up.

This means, there is a external heater and pump connected to them and hot water/antifreeze is circulated through the system.

After this procedure (which takes ~20 min for a DTM engine) the water and oil is close(r) to operation temperature, and the parts in the engine are warmed up, and are closer to there designed tolerances.

Chances are, that due to the very tight tolerances in a F1/race engine, you would not be able to turn a engine over at 20°C, or if, wear and friction would be extremly high.

I will try to find a photo later.

Link

[Tommy Cookers]

Thanks for that !

Now I remember that at the time I was squinting at the TV looking for pistons thinking they might be ringless (they weren't).
About 30 years ago Honda's last attempt at a motorcycle GP 4 stroke (running around 20000 rpm and having very unusually shaped pistons) was said to have (tried ?) ringless pistons.
The ring acceleration in a 19500 rpm F1 engine (as was) would be unprecedentedly high, I'm guessing that the rings (& pistons) are a bit unusual in some respects ?

I think I looked at the older engine rules and decided that it couldn't be (around the time of the programme) some fancy piston material like MMC or ceramic (having a very different expansion chcracteristics, needing a tight fit when cold ?).
Today's guess is that the pistons are so squat (stroke is only 39 mm or so) that the clearances have to be very small to avoid rocking/slap related problems, also this is bound up with this anti-friction oil (and petrol !) that we hear about ?
A bit different to the days when a loose fit was the thing for racing !