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Old 01-14-2014, 10:34 PM   #1
BeastianSTI
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Default Rebuilding 05 STi

Hey guys,

So my 2005 STi block blew a ringland @ 145,000 miles. Instead of trading the car off, I want to build it with forged internals. I've pulled WRX engines a couple of times, so I don't think this will be any different. Also stripped it down to the shortblock, but didn't do any part installation after that, aside from torqueing heads to block.

I'm kind of mapping and planning it all out, but will need some help here and there from you guys haha. I have been very interested in doing this myself for a while now, so this is finally my chance.

I'd like to have this guide for semi-technical people that need to rebuild they own block. Nothing too crazy.

What i'm thinking the order of things will be:

1. Remove engine and strip apart everything; labeling all bolts using cardboard / perm. marker. Painters tape for hoses / wires just in case.

2. Send to machine shop to determine what size i'll need to bore to since the cylinder wall may be scored. Shop will be using ej257 torque plate. Having the machine shop deck short block and heads, bore to 99.75mm ( 20 over ), redo valve stem seals and pressure test heads to make sure its all good.

3. Have heads and block hot tanked.

4. Order full gasket set. Will need 99.75mm head gasket or 100mm depending. I'm not sure how thick the gasket needs to be though, to maintain compression. Kind of confused about that.

5. Order ACL race rod / main bearings based on what I find on the block and after inspection of crank surface that mates with the rod bearings.

6. Order CP Pistons for matching 99.75mm pistons or whichever bore.

7. Spray block down with brake parts cleaner, especially in oil galleys for any excess metal from machining.

8. - TBC ... let me get this far.






Is my EJ257 #3 or #5 thrust for mainbearings ? Whats the easiest way to tell?



How will I know what thickness of headgasket to get to maintain safe compression?



When pistons say they're 99.75 bore, does that mean that they fit perfectly for a 99.75 block bore? How do you know what size to bore the block to?



Some people say not to use plasti-gauge in the measurement process whatsoever, which I completely understand and agree that it could be better. I think for the rods you measure the internal diameter of the rod, and then use a micrometer to measure the crank. Do you just subtract those two numbers to determine what size bearing you need, less some clearance constant? How would you measure the diameter of the main bearing areas ( not the bearings )?

Thanks guys!
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Old 01-15-2014, 11:01 AM   #2
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Bump - too many questions?
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Old 01-15-2014, 12:10 PM   #3
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The thickness of the head gasket will depend on how much needs to be taken off. The machinist should be capable of telling you what size you need when he is done. Many people don't suggest boring out our engines depending on the power level they run. If you plan on doing any internal work now wouldbe the time to do it. If youdo decide to bore out 25 over I have a brand new set of cp pistons for sale. I decided to go the route of buying a block assembled from element tuning so I won't need them m
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Old 01-15-2014, 12:23 PM   #4
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Your car is most likely a #5 thrust bearing. Number 3 bearings are located pretty much in the middle of the crank. The number 5's will be where the fly wheel attaches to. if i'm right, mostly all ej25 motors after 01? were number 5.
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Old 01-15-2014, 12:43 PM   #5
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Thanks for the response guys--

I'm shooting for 1.5 DOM level power. Nothing too far over 430WHP. I'm planning on keeping the STI rods, since they should hold fine for this application. So do most people rely on the machine shop to tell them what size piston / rings / head gasket?

What is a safe compression ratio to go with, with pump gas?
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Old 01-15-2014, 01:54 PM   #6
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Also, do I need to have the crank / mains remeasured, even if there wasn't any crank related issues?
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Old 01-15-2014, 02:03 PM   #7
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Also, do I need to have the crank / mains remeasured, even if there wasn't any crank related issues?
Always. Ive torn apart several blocks that have been OOR (out of round) pretty bad and some even had completely misaligned bores. Heck ive pulled a few "newer" (less than 20k miles) cases that were off by as much as .004

Having an improperly shaped or sized journal or bore can cause oiling issues and spun bearings. I have seen misaligned crank bores even snap a crank.

As for relying on the machine shop to tell you what size pistons pistons you need, I would definitely follow their advice. You have no idea if the block is scored or how much wear has actually taken place unless you measure for yourself with a Dial bore gauge (not a cheapo one either). Judging by your questions im assuming you dont have mics or bore gauges so yes I would not divert from what you builder says. However, Rings should come with the piston set, and unless you are going over a 100 mm bore stock gasket will do unless you need a specific thickness due to machining the deck of the block or heads or both

As for CR I would stay 8.2 for safety. At 8.9 you raise the risk of knock on pump due to more heat generated from compression, and pump fuels inconsistencies. If you were running E or meth or Racegas then you can get away with the higher compression as the higher octane will help combat knock, due to their higher resistance to detonation

Last edited by 2Fast4U1DAY; 01-15-2014 at 02:25 PM.
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Old 01-15-2014, 10:48 PM   #8
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Always. Ive torn apart several blocks that have been OOR (out of round) pretty bad and some even had completely misaligned bores. Heck ive pulled a few "newer" (less than 20k miles) cases that were off by as much as .004 Having an improperly shaped or sized journal or bore can cause oiling issues and spun bearings. I have seen misaligned crank bores even snap a crank. As for relying on the machine shop to tell you what size pistons pistons you need, I would definitely follow their advice. You have no idea if the block is scored or how much wear has actually taken place unless you measure for yourself with a Dial bore gauge (not a cheapo one either). Judging by your questions im assuming you dont have mics or bore gauges so yes I would not divert from what you builder says. However, Rings should come with the piston set, and unless you are going over a 100 mm bore stock gasket will do unless you need a specific thickness due to machining the deck of the block or heads or both As for CR I would stay 8.2 for safety. At 8.9 you raise the risk of knock on pump due to more heat generated from compression, and pump fuels inconsistencies. If you were running E or meth or Racegas then you can get away with the higher compression as the higher octane will help combat knock, due to their higher resistance to detonation
So whAt exactly is that procedure called ? Boring the main journal ? And how much does that normally cost to have done ?
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Old 01-16-2014, 09:18 AM   #9
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So whAt exactly is that procedure called ? Boring the main journal ? And how much does that normally cost to have done ?
It is called align (or line) boring/honing. Ive never had one align honed to have a price point but Ive heard as much as 300-600. Just depends on the shop.
I just got a new case and crank when I did my build because I had partially spun a main bearing (oil pickup failure) and I knew it would be worse than just the 134k normal wear on the engine plus I was in sort of a hurry to get my car back on the road.
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Old 01-16-2014, 09:25 AM   #10
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To have a shop do all that, it may be cheaper to just pick up a new heat treated crank off ebay thats already to spec and balanced. Theres a seller on there that sells OEM Subaru cranks for 325 shipped. Do that, new bearings and pistons and call it a day. I went with King Bearings for my build. ACL had mixed reviews on them. If your bearings in there now aren't scored or scuffed even, I would say you're probably fine. You may as well upgrade as much as you can.
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Old 01-16-2014, 09:37 AM   #11
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The block should also be stamped some where on there AB AB or sometimes AA AA or even BB BB. This is your piston size. A is slightly smaller? than B. You would have to double check that. Manley sells drop in pistons that are sized by A and B. I think A, the specs are 3.170-3.174 and B is 3.175 to 3.179.

As long as the cylinders measure out to with in these, they should be able to do a finish hone on it so your rings will set. Double check thoses numbers though. I have them on my phone some where but I can't look at this time.
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Old 01-16-2014, 10:28 AM   #12
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I too have read ACL bearings have been questionable lately. Perhaps their RACE bearings are what ppl r using currently. King might b another to look at.

I say, keep compression low. Raising compression is more of a naturally aspirated thing. You have a turbo so no need to risk det. By bumping up compression.
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Old 01-16-2014, 11:46 AM   #13
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Hmm... Yeah, i'll take a look into other bearing options for sure.
Keeping compression @ 8.2:1.

Wow, that's really steep to have that done. I'll have em measure out the crank, and if it's wacky, then buy a new one I suppose. Engine has a cracked ringland right now, so it's prolly going to need a rebore for sure.
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Old 01-16-2014, 11:47 AM   #14
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The block should also be stamped some where on there AB AB or sometimes AA AA or even BB BB. This is your piston size. A is slightly smaller? than B. You would have to double check that. Manley sells drop in pistons that are sized by A and B. I think A, the specs are 3.170-3.174 and B is 3.175 to 3.179.

As long as the cylinders measure out to with in these, they should be able to do a finish hone on it so your rings will set. Double check thoses numbers though. I have them on my phone some where but I can't look at this time.
While this may be true the op needs to find out what his bores sit at currently and their condition. Without this buying pistons is pissing in the wind
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Old 01-16-2014, 11:50 AM   #15
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Hmm... Yeah, i'll take a look into other bearing options for sure.
Keeping compression @ 8.2:1.

Wow, that's really steep to have that done. I'll have em measure out the crank, and if it's wacky, then buy a new one I suppose. Engine has a cracked ringland right now, so it's prolly going to need a rebore for sure.
No drop ins for you :-/. See if you can get away with 99.75 by having your machine shop inspect the case... if not I would try to get another case as to preserve as much cylinder wall thickness as possible
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Old 01-16-2014, 01:07 PM   #16
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I figured I wouldn't be able to drop one in. I want a build that will last for a while. I suppose I wont need to buy the electronic bore gauge / micrometers, and can instead trust the machine shop for measurements?
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Old 01-16-2014, 01:30 PM   #17
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Ideally you could go with 99.75mm, but 100mm is a also a pretty common size, I know it takes away cylinder wall thickness, but at 400whp I think you'd be ok. Just bring the pistons in with the block for the bore/hone and they'll match each piston to each cylinder bore. You should get the pistons back numbered so you know which one goes where.
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Old 01-17-2014, 02:16 PM   #18
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Ok - so is it the crankshaft itself that gets out of spec, or the journals in the block that the main bearings set into?
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Old 01-17-2014, 02:26 PM   #19
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Ok - so is it the crankshaft itself that gets out of spec, or the journals in the block that the main bearings set into?
The mainline will grow in diameter and/or get out of alignment on a block that's had lots of boost or big horsepower in general. I know one shop that charges $400 to line bore.
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Old 01-17-2014, 02:37 PM   #20
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aka half the price of a whole new case, huh? For the amount of machining that is going to need to be done to clean the block, deck it, re-bore and check the mainline, I could get a whole new case and put stock bore forged pistons in, it sound like.
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Old 01-17-2014, 05:28 PM   #21
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aka half the price of a whole new case, huh? For the amount of machining that is going to need to be done to clean the block, deck it, re-bore and check the mainline, I could get a whole new case and put stock bore forged pistons in, it sound like.
This is what most do. Granted a brand new case is over a grand last I checked so you could save a little money, its just not as significant as on other platforms
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Old 01-22-2014, 12:08 AM   #22
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So... I only measured compression on 3 cylinders,... 150... 140....80! Looks like I'm gonna need to rebuild it for sure.
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Old 01-22-2014, 03:08 AM   #23
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So... I only measured compression on 3 cylinders,... 150... 140....80! Looks like I'm gonna need to rebuild it for sure.
Yup shes toast.
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Old 01-28-2014, 11:00 PM   #24
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Hey guys,

Do I need new head bolts if I pull the block apart, or can I keep the ones that are in there ( stock @ 100k)?
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Old 01-29-2014, 10:37 AM   #25
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Bumpppp. Anyone ?
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