US1 Fountain

iTrader: (1)

Why aren't the blocks and internals heated to operating temp to simulate true running condition when doing the machine work? It seems, to me, that by checking it while cool will make for a perfect motor before it is started, then moves away from that perfect motor as it heats up.
Thanks

wjb21ndtown

Engineers build and tolerace components to measure properly in a controlled environment (generally room temperature, with a controlled humidity level). I use to have to keep logs of the temperature and humidity levels in my office (where I did plate measurements) and in the CMM room at ACR - an aerospace company. They do this on purpose. It creates a lab setting with a "control" atmosphere. It's the only way to get true #'s. You can't really measure something accurately at 200-300 degrees. Everything is toleranced to "nominal" and engineers account for heat expansion with controlled #'s added later.

Your motor is actually designed to run with X bearing clearances and you achieve those clearances by machining them to the tolerances recommended, and then heating up your motor. That's why you're supposed to warm your motors up before you beat the snot out of them...

Also, different metals react differently. Some metals expand I.D. bores when heated, and some actually shrink lightly. It depends on the grain of the metal and the type of alloy... It's a science and they've researched it for hundreds of years, and dedicated college degrees to understanding it. I'd except it as the best way. There's no sense in trying to re-invent the wheel on something that they've virtually perfected.

4mulafastech

Interesting thread. I too wonder what effect the change in temperature has on bore distortion. Seems to me you want the bore round at running temperature as long as the pistons/rings are round too. Aren't pistons somewhat oval at room temperature so they are round at running temperature? I believe the effect thermal expansion has on cylinder roundness has a lot to do with the uniformity of cylinder wall thickness and design, as well as material grade. The attached link shows equipment used to hone blocks at running temperature. According to the graph the cylindricity (roundness) of a cast iron SB-2 block changes .001 from room temp to 220F. An aluminum Brodix changes .003.

btw, I have no idea if this equipment works well or the validity of their claims, I just came across it...

http://www.c-ktechnologies.com/images/hothone.pdf

JeremyAnderson

Oh the Hone Hone........ There has been great debate on hot honing. Some say its nessesary some say its a waste of time.
Many times we do things because we can, not because we need to. The bottom line on clearances in an engine comes down to trial and error. The actual piston to wall at temperature is near 0, but cold it may be .010 depending on the application. The Idea is an aluminum piston grows at a greater rate than the cylinder bore. At operating temperature the piston will grow enough to take up most of the claerance, but not seize.
I don't set my bearing clearance to what a book says, instead I set it according to how the last set of bearings looked upon tear down.
I think I just confused myself.......

wjb21ndtown

"Build it tight, and everyone will know. Build it loose and no one will know but you..."

We had nitrous motors that we built at 0.010 piston to wall clearance, and only ran one ring. The motors were so lose that they would have a slight knock at idle, but they would sound great at 2500 rpm staged up and run like a raped ape...

I would never recommend that for anyone running a motor on the street, or in a marine app, but the point is that build clearances vary from application to application.

GPM

Got to wonder what's happening inside the blower motor when the water temp is less than 100 and the Egts are 1400

JeremyAnderson

I have always loved that saying! It is very true!

BillK

I am certain that finishing the block at operating temperature is absolutely the best way to achieve the best cylinder sealing and enable you to run the tightest running clearances. But .... the guys that do this, mainly the Nascar teams, also have elaborate rigs to heat the engines to operating temperature before they are started on race day. If they did not heat the engines prior to starting them, there is a good chance that damage would occur.

In the real world, you have to compromise. You have to build an engine knowing that the owner might decide to go for a ride on 40 deg day and not warm it up Manufacturers design pistons, bearings and other parts with this in mind.

JeremyAnderson

not all the NASCAR guys hot hone

SkiDoc

iTrader: (4)

Great thread, these are all questions I have had before. There is good reason to not reinvent with the wheel with every build. Thanks.