Clearances and temperature

[07GTS]

found this video was a good explanation of how main clearances change with temp and why we have to start of with a curtain value, this is also why big hp builds usually have more clearance and interestingly why i think F1 engines have to be pre heated before they can even be started as they are so tight in clearances

 

[hjtrbo]

I did see this. Good video. Makes understanding the importance of oil pump pressure vs flow relevant.

 

[Immortality]

Isn't it amazing how much alloy grows with heat.

I saw that last week but forgot to post it. Steve is a very clever man.

 

[07GTS]

yea Steve does some good stuff and explains alot in an understandable way in his videos, like most shops he dosnt give away all secrets but he goes much further then alot do and does some crazy builds

 

[Deuce]

I also so last week.
I realise alloy expands more than cast iron or steel when heated the same, but how much less do our blocks expand? And how much do our cranks grow?

 

[Immortality]

I'm subbed to his channel "everything is better with boost"...

I also so last week.
I realise alloy expands more than cast iron or steel when heated the same, but how much less do our blocks expand? And how much do our cranks grow?

Got a 304 crank and heat gun?

I believe alloy grows substantially more than cast iron.

 

[07GTS]

as i shifted to a iron block i have to set my lifter preload to suit iron with alloy heads, can go slightly less preload as it expands less overall, so crank is iron of sorts so it will expand but at a slower rate to the alloy block so my iron block now i went slightly more mains clearance and it also stays a closer expansion to the block, thats where the fun begins in building engines as u have to think what heat (power) is it going to be used at, then u have to build in clearances for that temperature/loads and keep in mind the colder temps also for when it cools down

got to wonder then if u build and engine in stone cold 0c winter or a 45c day summer ur going to get some different clearance checks, prob best to do in a temp regulated room for the high end stuff, then u have the thoughts when u go a stronger crank that will flex less u can also run tighter clearances if temps allow for it

 

[Immortality]

Definitely. Temps when machining are critical.

I know at work when our knife sharpeners were lazy because the knives would come back bowed and it was because instead of taking a few small cuts to clean up the blade they would just wind the cutter down hard and take a massive cut and putting a lot of heat into the steel.

A few years ago there was a great video on Youtube from Guy Martin where he's working on a Spitfire rebuild project, on one particular episode they were machining the pins that hold the wing spars on the plane body, they machine (surface grind) the pin to final size, he then holds the pin in his hand as they explain about the fine tolerances required, then they go to fit the pin but find it is now oversize and won't fit because of the heat from having it in his hands for a period of time.

edit: here we go (time stamped at the right bit).

Absolute bloody legend is our Guy Martin.

 

[hjtrbo]

David Vizard on youtube is putting out some good content also.

https://www.youtube.com/@DavidVizard

Also, this fella here just gets into it. No bullshit, just back to back dyno tests.

https://www.youtube.com/@Garage4age

 

[Deuce]

Got a 304 crank and heat gun?

I believe alloy grows substantially more than cast iron.

Sold my old crank to a mate who needed it so cannot experiment sorry.

Yeah agreed, but would like to put an actual tangible number on 'substantially'