A little perspective here guys... the coefficient of thermal expansion for 6061 aluminum has the units of 13 x 10^-6 inch per inch per degree... So for a thermal change of let’s say 600 degrees F change there would be a dimensional change of ten thousandth of an inch per inch of length, diameter, whatever... That is the way it works. So across 60 degrees change one thousandth of an inch is expected but the difference in growth between steel and a 6k series aluminum is at most 10% so were talking about fractions of an RCH that ends out just adding to the residual stresses in the material that are inherent in any design/applicaiton/reality.

As far as gear engagement... a properly designed gear set is never in full contact on both the leading and trailing edge of a tooth unless they are simply said... poorly designed. Check out something called involute gear design.


You can have some slack in between the gears and still have full 100% engagement as long as the direction of rotation isn't changing so that allows for lots and lots of allowable growth.

Trust me... you not crossing any new ground here... It's all been thought about, figured out and solved if not used to their advantage b4.

impatientinventor - 25 November 2009 02:38 AM

A little perspective here guys... the coefficient of thermal expansion for 6061 aluminum has the units of 13 x 10^-6 inch per inch per degree... So for a thermal change of let’s say 600 degrees F change there would be a dimensional change of ten thousandth of an inch per inch of length, diameter, whatever... That is the way it works. So across 60 degrees change one thousandth of an inch is expected but the difference in growth between steel and a 6k series aluminum is at most 10% so were talking about fractions of an RCH that ends out just adding to the residual stresses in the material that are inherent in any design/applicaiton/reality.

You are correct about the thermal expansion coefficient of aluminum. Most aluminum alloys are between 12.9 x 10^ -6 and 13.2 x 10^ -6 inch/inch - deg. F. However, with a range of 6.4 to 6.8 x 10^ -6 inch/inch - deg. F for most steel alloys, steel has only HALF the rate of thermal expansion compared to aluminum. A 1-inch diameter aluminum piston in a well cooled engine operating at 180 deg. F will lose less than a thousands of an inch in clearance, but a 3-inch diameter piston operating at 350 deg. F in an air cooled engine will lose over 5 thousands of an inch in clearance. And that does not account for the possibility that the piston is operating hotter than the cylinder.

An aircraft engine with 5 inch pistons has a real problem in this area. That is why they are built very loose and burn a lot of oil. The following chart is from a technical article about cylinder barrel temperatures.

http://www.sacskyranch.com/cylinder_temperature.htm






Another poster made a comment about metals expanding in all directions. That is true, but one must be careful in understand that the expansion is from the physical center outward, and that is why an inside radius grows outward, not inward.

wilmywood8455 - 24 November 2009 11:10 PM

Audiophile426 - 24 November 2009 08:40 PM

I think that the areas where clearances tighten are where two materials with different coefficients of thermal expansion are involved or where parts warm up at different rates. So, do F1 engines use ceramic bearings? i know a lot of hi performance engines do but i almost remember hearing that they were banned in F1. I would imagine that there is a big difference in the thermal coefficients between ceramics and metals like steel and aluminum.

ALL clearances tighten with heat, some more than others. Materials expand in all directions. Th single clearance that tightens the most, I think, is piston to wall, assuming aluminum alloy pistons and some sort of ferrous cylinder wall (or sleeve). The piston crown, combustion chamber, upper end of the cylinder and the exhaust valve and port see more heat than any other areas.

First I must correct this statement:

"ALL clearances tighten with heat, some more than others. Materials expand in all directions."

Yes, materials expand in all directions from the center outward, and that is why a hole or any inside radius will expand OUTWARD!

Now for the ceramics. I found some data:

http://matse1.mse.uiuc.edu/ceramics/prin.html

Table 2 is about a quarter way down the page. It is in a dimensionless length per length format so you can use any units for dimension and growth (e.g., inch) so long as they are the same. However, it is in deg. C so you will have to divide by 1.8 to convert to deg. F.

Table 2: Comparison of thermal properties of different ceramic materials.
Coefficient of Linear Expansion 1/ ° Cx10-6

Aluminum metal -- 23.6
Copper metal -- 16.5
Alumina -- 8.8
Fused silica -- 0.5
Soda-lime glass -- 9.0
Polyethylene -- 60-220
Polystyrene -- 50-85


That is enough for now -- it is time to socialize and eat turkey. Enjoy.

ok... what are we trying to get at here again? What ae we debating or are we all just spouting off truths and misintrepreting others...

Yes things grow or shrink relative to eachother as temperatures change but it is taken into account because the engines and transmissions don't blow up that often and it is almost never because of a bad design... it is most often because some part of the design failed to work the way it was designed to... not because the design was wrong.

Now I'm doing it... What are we debating again?

In 2009 we had fewer in race engine failures than at any time in the history of F1.

Design, materials and lubrication all working together!

mmi16 - 29 November 2009 03:40 PM

Design, materials and lubrication all working together!

I don't know about that. Freezing development, and limiting RPM/HP goes a long way in making what were once marginal parts into reliable parts.

When you have RPM/HP caps in place reliability increases like a snowball. Less stress on reciprocating components mean lighter components, which in turn means less stress etc.

I miss the occasional "kablammo".

these blocks were origonally designed for 24k rpm but then the FIA went and got a bundle of sticks and shoved them in a dark place... and along came 19k rpm limit. Then because the longevity of the V-10 reduced to 19k rpm was so huge they decided to go even further with an 18k limit... I so miss the 20+k rpm engine sounds. We will likely never hear that again... ever.

Compared to the last days of the V-10 F1 now sounds like IRL.