F1technical.net

Hey guys i was just curious if a 81.5mm piston can fit on a 81mm bore because in the past f1 cars this type of method (well not exactly) and makes alot of power because the gas is very compressed and tightly squeeze inside the engine and i know it is preheated before starting engine to expand the metal to let loose the piston, because of this it can create alot of power naturally aspirated like the mclaren mp4/4, if this is possible it can be used in drag racing and road racing.

Only possible if the bore is round and the peg - sorry piston - is square.

Leominster12 wrote: ↑

25 Mar 2019, 20:00

..... in the past f1 cars this type of method (well not exactly) ....

afaik
the pistons would distort at high power due to asymmetry of temperature distribution and load distribution
this was compensated by making them more than usually out-of-round when cold
generating interference in a cold bore

re the actual question ...
a friend had persistent trouble with cylinder liner splitting in his Renault R8
the cause was finally found - pistons 10 thou 0.25mm oversize but only 3 liners correspondingly (rebored presumably) oversize
the other liner was standard size and was (at first) replaced with an identical liner

Well now i know you can’t start the engine when the temp is cold
Thanks for the answer and opinion.

No. Just no.

Ouch.

gruntguru wrote: ↑

26 Mar 2019, 05:51

Only possible if the bore is round and the peg - sorry piston - is square.

Sorry

My post on grades of fit has been pulled down, sad, there was a lesson in this story.

A small 81.5 mm piston could certainly fit in a large 81 mm bore.

Not every person who enters this forum is working on a thesis, early high school kids post here too, give them an educative experience and not rip shreds of them and ridicule them.

3jawchuck wrote: ↑

26 Nov 2019, 17:44

A small 81.5 mm piston could certainly fit in a large 81 mm bore.

Depending on tolerances, sure. I dont think many engines have +/- .020" on internal features parts though.

F1 engines might have, what, 0.1mm interference on the pistons when cold?

Very small clearance, but no interference.

Bear in mind the crank must be turned during engine assembly, timing etc.

0.1 piston interference wouldn't allow you to spin the engine cold without doing serious damage. No amount of interference would, really. I actually doubt you could install the pistons with that much interference without scuffing the bores or damaging the skirts.

Same with the bearing clearances, very tight when cold (which is why they run hot water through the engine before fire up) but there's no interference.

Agree. I never heared of any or incountered any interference-fits when it comes to rotating or sliding parts.

So what would the origin of the whole engine cant turn over when cold myth be? Just to protect the bearing coatings on everything? Obviously a .1mm interference is a sweat fit, and a tight one at that.

Maritimer wrote: ↑

21 Dec 2019, 19:07

So what would the origin of the whole engine cant turn over when cold myth be? Just to protect the bearing coatings on everything? Obviously a .1mm interference is a sweat fit, and a tight one at that.

The orgine of the whole engine can't turn over when cold means clearances between moving (rotating and sliding parts) are very small indeed. but still there are clearances betwen parts. without those clearances however small they might be, the engine will not turn even when hot. 0.1mm clearance means 0.004". one can find normal road going car engines with piston to bore cl;earance (build) of 0.025mm clearance meaning 0.001".