Main studs & align hone.

[stealthfti]

I have every block I build checked and measured for main bore alignment. About half of them are within specs. But, depending on the purpose of the build, I may have even a within-specs block align honed. Why?

I have my blocks align-honed, or align-bored, for two main reasons [no pun intended]:

...to establish the true center of the universe that the crankshaft centerline is, for all other machining and surfacing work;

...and to allow my machinist the leeway he needs to get the correct bearing crush for my main bearings. When I tell him I want one and a half thou clearances on my mains, that is what I get. The align honing lets him do what he needs to do to get the mains to within a tenth of a thou.

I do not doubt that things move around under high load and high RPMs. I also do not doubt that there is likely little HP output difference after such a procedure. But, I don't do it for more horsepower. I do it for longevity and reliability. I have never considered the procedure to be a waste of money or effort.

To me, it is where things start.

TF

[Ol' CW]

Originally Posted by Packard V8

What keeps the Pratt & Whitneys, Continentals and Lycomings from falling out of the air?

For one thing, they hold a lot more oil than a SBC, around 12 or 14 quarts. They also have about a 8:1 CR and make around 1HP for every 2 cubic inches. They usually cruise at 2300 RPM or less with a big fan and a cooling shroud around them on 100 octane gas with lead in it to lubricate the valves. Plus everything is aluminum except the cylinder barrels, crank and rods

Yes, oil is a major coolant in the engine, but the bearings are still going to get hot in a high output engine. Tight fit and good interface between the brg and the web can and does transfer heat away from the bearings.

Originally Posted by stealthfti

...to establish the true center of the universe that the crankshaft centerline is, for all other machining and surfacing work;

...and to allow my machinist the leeway he needs to get the correct bearing crush for my main bearings. When I tell him I want one and a half thou clearances on my mains, that is what I get. The align honing lets him do what he needs to do to get the mains to within a tenth of a thou.

I do not doubt that things move around under high load and high RPMs. I also do not doubt that there is likely little HP output difference after such a procedure. But, I don't do it for more horsepower. I do it for longevity and reliability. I have never considered the procedure to be a waste of money or effort.

There is what I was trying to say, well put Stealth

[thadeausmaximus]

Porsches and all of the air cooled aircraft engines I've seen have aluminum cylinders. On Porsches they have a silica/aluminum coating on the cylinder bore to prevent wear. We run about 12 qts of oil and it is mostly oil cooling that keeps the engines together. Normal head temps are above 380F (Thats where the head temp sensor maxes out after a couple of minutes running). ~320 RWHp out of a 3.8L 12:1 CR Air cooled flat six. There is more to be had and we are working on finding it.

Thanks for this forum so I can learn to find ways to go faster.
Thad