Engine Block #

[carbonBLUE]

Originally Posted by ichitaka05

He said
"Center of engine block below engine throttle."

ok ty

[Calum]

ok, how much variation are we talking about here?

I've machined parts to plus or minus 0.001 inch on a 40 year old lathe using a high speed steel bit I hand ground on a bench grinder. Surely Subaru's engine manufacturing plant can do good enough to keep things well within tolerance so this isn't required.

[Dimman]

Originally Posted by Calum

ok, how much variation are we talking about here?

I've machined parts to plus or minus 0.001 inch on a 40 year old lathe using a high speed steel bit I hand ground on a bench grinder. Surely Subaru's engine manufacturing plant can do good enough to keep things well within tolerance so this isn't required.

So have I.

But I've also honed connecting rods. Tolerance on rods is in tenths. Tightest I worked on is +.0003/-.0002. Some Mitsubishi rods are +/- .0001

[Jeff Lange]

It varies depending on the engine and tolerances, etc. Here's a somewhat typical crankshaft journal marking to diameter reference chart from a Toyota engine:

Mark 0 - 54.999 to 55.000 mm (2.1653 to 2.1654 in.)
Mark 1 - 54.997 to 54.998 mm (2.1652 to 2.1653 in.)
Mark 2 - 54.995 to 54.996 mm (2.1652 to 2.1652 in.)
Mark 3 - 54.993 to 54.994 mm (2.1651 to 2.1651 in.)
Mark 4 - 54.991 to 54.992 mm (2.1650 to 2.1650 in.)
Mark 5 - 54.988 to 54.990 mm (2.1649 to 2.1650 in.)

The important thing to remember is that these are high production engines, not something that is precision made by hand, etc. Bits wear, etc., this allows the engines to be made with a slightly wider tolerance range for machining, but with precise measurement, the oil clearances are always extremely tight and within a much tighter spec. Engines can be made in volume and at high capacity with exacting clearances without the need to check and recheck and replace tooling as frequently.

Also from what I've seen in most production engines on tear down, they're almost always within the middle of the range. Seeing something like a mark 0 or 5 on an engine is usually very unlikely. On some engines (like the 2JZ), they only have 1 piston size, and the block is more precise for machining, while older engines just had larger tolerances, etc.

Jeff

[Subie]

Originally Posted by Jeff Lange

It varies depending on the engine and tolerances, etc. Here's a somewhat typical crankshaft journal marking to diameter reference chart from a Toyota engine:

Mark 0 - 54.999 to 55.000 mm (2.1653 to 2.1654 in.)
Mark 1 - 54.997 to 54.998 mm (2.1652 to 2.1653 in.)
Mark 2 - 54.995 to 54.996 mm (2.1652 to 2.1652 in.)
Mark 3 - 54.993 to 54.994 mm (2.1651 to 2.1651 in.)
Mark 4 - 54.991 to 54.992 mm (2.1650 to 2.1650 in.)
Mark 5 - 54.988 to 54.990 mm (2.1649 to 2.1650 in.)

The important thing to remember is that these are high production engines, not something that is precision made by hand, etc. Bits wear, etc., this allows the engines to be made with a slightly wider tolerance range for machining, but with precise measurement, the oil clearances are always extremely tight and within a much tighter spec. Engines can be made in volume and at high capacity with exacting clearances without the need to check and recheck and replace tooling as frequently.

Also from what I've seen in most production engines on tear down, they're almost always within the middle of the range. Seeing something like a mark 0 or 5 on an engine is usually very unlikely. On some engines (like the 2JZ), they only have 1 piston size, and the block is more precise for machining, while older engines just had larger tolerances, etc.

Jeff

Is this the reason why a lot of modern engines suffer from piston slap?

[Calum]

Originally Posted by Subie

Is this the reason why a lot of modern engines suffer from piston slap?

That has more to do with the length of the piston skirt, the rod/stroke ratio and in some cases the wrist pin offset.

[Calum]

Originally Posted by Jeff Lange

It varies depending on the engine and tolerances, etc. Here's a somewhat typical crankshaft journal marking to diameter reference chart from a Toyota engine:

Mark 0 - 54.999 to 55.000 mm (2.1653 to 2.1654 in.)
Mark 1 - 54.997 to 54.998 mm (2.1652 to 2.1653 in.)
Mark 2 - 54.995 to 54.996 mm (2.1652 to 2.1652 in.)
Mark 3 - 54.993 to 54.994 mm (2.1651 to 2.1651 in.)
Mark 4 - 54.991 to 54.992 mm (2.1650 to 2.1650 in.)
Mark 5 - 54.988 to 54.990 mm (2.1649 to 2.1650 in.)

The important thing to remember is that these are high production engines, not something that is precision made by hand, etc. Bits wear, etc., this allows the engines to be made with a slightly wider tolerance range for machining, but with precise measurement, the oil clearances are always extremely tight and within a much tighter spec. Engines can be made in volume and at high capacity with exacting clearances without the need to check and recheck and replace tooling as frequently.

Also from what I've seen in most production engines on tear down, they're almost always within the middle of the range. Seeing something like a mark 0 or 5 on an engine is usually very unlikely. On some engines (like the 2JZ), they only have 1 piston size, and the block is more precise for machining, while older engines just had larger tolerances, etc.

Jeff

I was having images of huge differences, but 5 thou total range that most likely doesn't get used, but could be compensated for seems very reasonable.

Thanks for the detailed post.

[xwd]

The A and B on the Subaru engines does indeed identify the cylinder bore size and also the stock piston diameter size. Traditionally the B pistons are smaller than the A pistons. In some of the older engines the difference in size is around .007" total where the top .004 are the As and the bottom .003 are the Bs.

The BRZ factory repair manual will have exact specs on what they mean.

[Dimman]

Originally Posted by Calum

I was having images of huge differences, but 5 thou total range that most likely doesn't get used, but could be compensated for seems very reasonable.

Thanks for the detailed post.

That's 5 tenth's btw. Half a thou.

[Calum]

Originally Posted by Dimman

That's 5 tenth's btw. Half a thou.

yeah, Doh.