EJ25D heads with EJ251 Block swap? Questions!

[mattpowers]

Hi guys,
I have done a fair bit of research, but wanted to make sure I'm not overlooking anything before I move forward with my plan. I have a 1998 Outback (EJ25D) with an Auto transmission which has some severe rod knocking. I also have a donor vehicle (2001 Outback), with a good motor. I was going to keep the EJ25D head and pull the EJ251 block into my car. This is all just for a daily driver / road-trips.

It looked like I could swap the block into my vehicle with no issues. Here are my questions:

1. What headgasket should I use? I had read conflicting posts, but it sounded like the EJ25D HG was the safest bet.

2. Do I need to swap the crank sprocket from the EJ25D onto the EJ251? Someone mentioned that the crankshaft position sensor may be an issue?

3. Is there ANYTHING else that needs to be addressed to do this swap?

I couldn't find any guides on how to do this particular swap, but from what I read, it seems straightforward.
Thanks!

[86bratman]

Use 04-07 Sti headgaskets for this build, it is the most durable option for this build. Compare the crank gears, if they are the same use whichever you like. But if they're different use the 25d one. You'll also want to use the metal coolant pipe that runs from the water pump to the heater core hoses from the 25d. I have been a part of a few of these hybrid builds in the past. Don't over think it, it really is that simple.

[mattpowers]

Use 04-07 Sti headgaskets for this build, it is the most durable option for this build. Compare the crank gears, if they are the same use whichever you like. But if they're different use the 25d one. You'll also want to use the metal coolant pipe that runs from the water pump to the heater core hoses from the 25d. I have been a part of a few of these hybrid builds in the past. Don't over think it, it really is that simple.

Awesome. That's what I was looking for. One other thing I read, in the Haynes manual it says you have to remove the camshafts to get the heads off on the EJ25D. Is that true? Was hoping it might be more plug-and-play.

[86bratman]

That is true, the head bolts are directly behind them, but not a big deal in all reality. Just be sure to keep the lifter buckets in order if you take them out. Proper placement of them is critical to valve clearance and can cause issues if they are mixed up.

[meepers]

Yeah. Definately do NOT flip the head over with the buckets in to check the heads after you pull them. I can tell you it majorly sucks having to go through each shim individually to find what you need.

01 outback is phase 2. You will definately need to swap crank gears. Slides right off. Oem subie gaskets are the best. Ej25d gaskets are a bit thicker then the sti gaskets. There is a compression ratio matrix around here somewhere. Just double check it with your block/heads/gasket to get the rc you want. Also replace at the very least all your timing belt idler gears. A waterpump kit would be best tho.

Everything else is a direct bolt up affair.

[meepers]

http://www.b4et.com/docs/cr_matrix.pdf

Definately would consider the ej25d Mls gaskets for c/r

[86bratman]

Not all phase 2 engines use the 32 tooth crank gear, that is why I said compare them. As a matter of fact, of the 5 ej251s I've personally pulled apart not a single one of them has had the 32 tooth crank gear, all have been 7 tooth exactly like phase 1.

Using the 1.3mm phase 1 gasket will put the quench height very far outside the optimal range, reducing power and economy. While the STi spec gasket may increase compression to 10.3:1, it also maintains proper quench. the combination of these factors will increase power and also net better fuel economy. My friend runs this combo in his 99 gt and has been averaging 30+ mpg for almost a year since I built it for his car.

Another thing you'll want to consider, which gasket in question is known to blow consistently and for no good reason.

Also if you'll do the numbers yourself on the compression matrix listed above you'll find many things to be inaccurate, making it basically useless.

[meepers]

Right on Bratman. I haven't dealt with any phase 2 sohc motors, and was just going off the research I found when seeing if there was any possible way to run a phase 2 wrx ecu with my phase1 dohc cams. That's why I love sli sooo much more then nas. So much actual hands on knowledge here.

[mattpowers]

Not all phase 2 engines use the 32 tooth crank gear, that is why I said compare them. As a matter of fact, of the 5 ej251s I've personally pulled apart not a single one of them has had the 32 tooth crank gear, all have been 7 tooth exactly like phase 1.

Using the 1.3mm phase 1 gasket will put the quench height very far outside the optimal range, reducing power and economy. While the STi spec gasket may increase compression to 10.3:1, it also maintains proper quench. the combination of these factors will increase power and also net better fuel economy. My friend runs this combo in his 99 gt and has been averaging 30+ mpg for almost a year since I built it for his car.

Ok awesome. I'm getting more confident in this by the minute. One thing I wasn't sure on regarding the actual procedure was if it's necessary to find TDC on Cylinder 1, using a compression tester, etc? In the manual it points that direction. I would assume I need to do that, instead of just lining up all the marks, so that the cams, etc, arn't actually in TDC for cylinder 2? I feel like I've seen people just go with the crank & cam marks and never do compression to see what cylinder is lined up, but maybe I'm missing something.

Thanks for all the excellent information! This will be a big endeavor for me, and I should be pulling the 2001 motor on Saturday. Hoping to do the whole thing next week.

Since my car has 215k on it, I'm going to go with the bare minimum in $$. Sounds like valve cover gaskets are a must, as well as a new manifold gasket. Was going to reuse head bolts, and inspect the T-belt when I'm in there. I think it was done like a year or two before it was wrecked (on the donor motor). May replace it just on good principle.

[86bratman]

Do not under any circumstances time a Subaru at top dead center. You will bend valves that way, they are meant to be timed with all pistons halfway through their stroke. Just use the alignment marks and go with that. Remember, use the dashes, never the arrows/triangle marks when timing a Subaru. The arrows are for valve clearance checking.

[mattpowers]

Yeah that was what I thought initially, but my trusty Haynes manual confused the issue a bit. Was definitely aware that the arrows were not for setting the timing. Thanks for all the advice! With a little luck, I should be digging into it this coming week. Will let you guys know how it goes.

[86bratman]

I have the Haynes, as well as the factory service manual in pdf form that can be downloaded from this site. Haynes does leave some to be desired, but it's a decent reference. Anything critical I'll always verify with the fsm before taking action.

[mattpowers]

Well, things are well under way. I've got the heads mounted on the new engine, new STi head gasket, and lots of fixes here and there. I'm currently waiting on valve lifter shims to finish putting the cams back in and assembling. I also managed to push the rear main too far in, and had to rip it out and start again. I did manage to fix a bunch of vacuum and coolant hoses that were weathered and cracking, as well as replaced belts that were worn. Pulling the motor is definitely a good way to give your whole car a check-up. I've cleaned a ton of things and am replacing a bunch of gaskets as well as the oil separator, main seal, plugs, oil filter, etc.

I did have to swap crankshaft sprockets. The 2001 motor had a lot of teeth on the back side, and the 1998 one only had 6. I also had to swap the water pipe (as mentioned) that bolts to the top of the block. The 2001 water pipe only had room for one of the coolant temp sensors. Also, maybe everyone else knows this, but I had to reuse the DOHC head bolts, as the SOHC ones are longer.

One thing I am hoping is not an issue is the valve clearances. I am fixing the 7 worst ones, but leaving the ones that were close to spec. The worst valves were the four intake valves on the passenger side. They all were tighter than .006 (smallest feeler I have), so I am reducing all of those shims, in hopes of getting them back into spec. I also had two exhaust valves that were rather loose in measurement, so I will be fixing their shims as well. I guess my only concern was that with the STi headgasket, I may be cutting the clearances pretty close. Should have the motor back together this weekend, and will be able to do a hand-test tomorrow or saturday.

[cj91legss]

So How'd it go? What's the drivability like?

[mattpowers]

Sorry for the long delay, but the car runs great! Big thanks to Bratman for all the help. The Sti gasket works great. I have put about 3000 miles on the car since doing the work. Shimming the valves was easy, and helped quiet the motor. The only issue I had was when I swapped heads I didn't replace the camshaft oil seals, I reused them. Don't do that. I had a pretty nasty oil leak and had to pull the timing belt and cam sprockets to fix it. The only little tip I could give on busting the sprockets loose is using a crappy timing belt and two vice grips to hold those gears in place. Just wrap it fully around the sprocket, clamp it down on itself, then wrap the crank sprocket and clamp it on itself. Zip ties work reasonably well too. Thanks again to everyone! Hopefully someone else finds this stuff useful as well!

[cj91legss]

House the power?

[mattpowers]

It's certainly not a racecar, but it is running stronger than when I bought it 45,000 miles ago. Getting about 25mpg. I think cleaning the heads, cylinders, and adjusting the valves went a long way to helping it run well.

[cj91legss]

Good deal. I was curious because of the difference is gasket thickness and quench.

[86bratman]

The reason you can run the thinner gasket with this build is because you're using the phase 2 block and pistons. The pistons in these sit below the deck by 0.4mm as opposed to the phase 1 that protrude in most cases 0.3mm. Using the 0.5mm gasket puts the quench height right in the "perfect" range for a street car. I've done a few of these now and they are a nice upgrade to a standard 25d. And as long as you do the proper prep work you don't have to worry about when you'll blow your next head gasket.

[shoguy]

I missed seeing this before when you had it apart. Certain 99 outbacks in late production had a 251 block, crank, and rods with 25d pistons and heads, labeled as EJ25D series. I am currently rebuilding one right now. To turn yours into one of those all you would have had to have done is throw your 25d pistons in and use 25d head gaskets. You might be running slightly (very slightly) lower compression right now. But as long as it's happy, that's good!