99 2.5 DOHC build (w/phase ll block)

[rallyak]

As some of you know I own many subaru's, one with 800k on it and still running. The other day I pick up a engine to rebuild in my spare time. When looking at it it looks like a normal DOHC 2.5 but after inspecting it closer I realized is was most definitely different than the other 2.5 I've worked on.

First, I noticed six bolt holes in the rear of the block for mounting the transmission, I shrugged my shoulders and didn't think anything about it. After I had it torn down,I was measuring crank and realized this engine was different. After some research I found that in 99 they made basically 2.5 hybrid with 10:1 CR that you can run on cheap gas with all factory parts with no custom or special head gaskets. This is exactly what I was trying to achieve with custom heads.

I found an service manual that gave some info for 99 engines but of course I can't find it so I will update that info here when I find it again.

Here's some pics of what I found:

[86BRATMAN]

That particular 25d still runs the same pistons as the 97/98 models, along with the same 610 head gasket. It's compression ratio is actually still the same as the earlier variants as well.

You can swap ej251 pistons, run an 04-07 sti head gasket and 25d heads to up the cr to 10.4ish and not have to worry about the typical 25d blown head gasket issue.

Most of what you've said is common knowledge in the second gen legacy circles. It is indeed a phase 2 bottom end with 52mm rod journals and #5 thrust location. It has the 136.1mm 251 rods, just with old 25d pistons and 1.3mm head gaskets.

[rallyak]

Yes, your 100% correct I just measured the pistons and the dish and it for sure the same piston with newer block and rotating assembly.

[rallyak]

You can swap ej251 pistons, run an 04-07 sti head gasket and 25d heads to up the cr to 10.4ish and not have to about the typical 25d blown head gaskets.

You happen to have the thickness of the STI gaskets. I think I found the part # 11044AA642 or 11044AA770, I believe it's the first one.

[86BRATMAN]

That's the one you need. The other is 08+ if memory serves, the coolant passages were changed in those for quicker warmup time for emissions. I've not actually measured them but everything I've read says they're 0.5mm compressed.

[mike-tracy]

How do you tell externally which ones have the higher compression pistons? I've seen one that came from my old 99 SUS that had different piston tops compared to the countless other ej25d's I've seen, and the 8-bolt case of course.

[rallyak]

Thanks for the reply on the gaskets. This build is for my moms car and it getting stock oversized pistons, but for mine I will go the other route for more fun factor.

[86BRATMAN]

If the motor is stock 99 25d it should have the same square dish as 97 and 98s, the only 25d that got different ones was the 96 with its almost flat top pistons.

It's possible you got ahold of one that someone had already been into at some point and had the shortblock swapped.

[rallyak]

If the motor is stock 99 25d it should have the same square dish as 97 and 98s, the only 25d that got different ones was the 96 with its almost flat top pistons.

It's possible you got ahold of one that someone had already been into at some point and had the shortblock swapped.

Yes it has the square dish pistons.

[rallyak]

I was able to play and measure the block and crank the other day. I used to work at a machine shop when I graduated high school and have access to some equipment. First this engine had less than 100k on it and wasn't taken care of. The crank was on the loose side, most of the journals were greater than .002 clearance which I've run motors with extra clearance before with no problems but it a good idea to run HV pump. After I measured the journals I checked for straightness, Chocked it up in the lathe and gave it a spin. What I found was the crank was bent .003 and the allowable limit is less than .001. At this point I have three options,
1) cut this one to .010/.010 and get new bearings.
2) Buy one that's been cut and most likely welded .010/.010 or
3) get a new one from Subaru.
Option one is my personal choice if I'm the one running the lathe and can set my own clearances, but I went with three and bought new from Subaru.

Now for the block, the bores looked great and the cross hatch hone look real good still. No major piston scuffing (light in two holes). They measured great with minimal low spots. But then I bolted the toque plate on and every thing changed. The bores were distorted about .0003 in places and when I heated the block in the oven to 200 degrees it to .0005. I know some of you a thinking so, when the piston to wall clearance is around .0015 that get real tight when the bore gets distorted .0005. Most Subaru have way too much clearance piston to wall clearance anyway, real common piston slap.

So the block is getting bored with the toque plates, I believe if it not done with the plates your wasting your money in my opinion. It gives the rings a better surface to seal against.

[rallyak]

I've been real busy lately but I received goodies so I can assemble the short block.

The machine work looks great and clean and everything measures perfect and tight. Here's some pics of some of the balance work.


The shop said it wasn't necessary but I'm buliding this for longevity, and if every thing is balanced there is less wear on bearing and runs smoother. You can see the shiny spots on the rods and on the piston there a dip on one side.

Rods installed and ready for a little goop to seal it and other half installed. I was so involved I forgot to take pics of installing pistons and pins, which one of the new piston pins was .015 too long and needed to trim it down on the lathe. With the pin too long the snap ring wouldn't fit correctly and that could of been very bad.

Short block done, waiting for another day I can work on it. Also sourced a cast impeller water pump to keep every thing cool. Subaru claims 20-30% better flow with the cast iron design.

[Legacy777]

Nice pics

Yeah, I would definitely recommend and go out of my way to use the cast impeller design over the stamped design.

[rallyak]

Did the finishing touches on the engine before installing in the car.

Also installed the "filter mag" and a magnetic oil plug from Subaru.

The engine all built and ready to install.

I installed it on 2-4-15 and I will tell you, this is the quietest and smoothest DOHC 2.5 I have ever seen. Also very smooth excelleration and at an idle you can barely feel it. I'm sure this engine should last 500,000 to 700,000 miles as long as the rubber band and water pump gets changed every 100,000 miles.

[Legacy777]

Engine looks good!


So Subaru makes a magnetic oil pan plug???

[rallyak]

Yes they do, I have one on each of my cars and the filter mag. Keep any flake of metal out of the bearings.

[Legacy777]

Wow, that's good to know.

[86BRATMAN]

What pistons did you end up using in this one?

[rallyak]

I used the phase I .10 over Top Line for this one. Mine is getting the phase II pistons for the higher compression.