The AUSubaru.com.au Forums

hey can anyone shed some light on this, the boss has an ej25 engine in a 2001 impreza wrx sti thats reasonably modified by mrt, the engine has a bearing knock in it... pretty sure its a ej25 anyway, i haven't sighted the numbers on it.

now mrt and or other people have been telling him all kinds of wonderful information concerning rebuilding the engine, apparently a race engine is completely different to a normal engine to rebuild... apparently the car has acl race bearings in it, but another bloke said that it has stock bearings in it. i've heard that it has forged pistons in it, and other people have said standard pistons.... you get the picture anyway.

now mrt think that if i've never built a race engine before i shouldn't be rebuilding this engine... i have rebuilt engines before, i have not done a subaru engine yet, although tomorrow i'm pulling a forester engine apart in search of a big end knock, so i'm about to commence my first subaru engine.

now, correct me if i'm wrong, but an engine is an engine... i can't see that bearing specifications are different on a race engine to a standard engine?? i like genuine bearings more so than aftermarkets because i think you can achieve more accurate tolerances. are forged pistons any different in terms of rebuilding the engine than standard pistons? i am guessing for a race engine you need to check all measurements/tolerances etc and be more fussy than a normal engine? everything would need to be done up with a torque wrench but i'm like that anyway. what is going to be different??

i can't see myself having dramas with this, is there anything i should be looking out for? i have access to all subaru workshop manuals, and if i get stuck i have access to subaru technical help, as i work for the subaru dealer.

robert.

you should kick it in....you answered your own questons...just be more anal when checking stuff but its all the same just stronger with forgys and acl gear...a race motor is just a motor thats been taken a bit more to its limits thats all

thats what i thought. i'm happy to rebuild the engine for him, and i can't see it being a problem. i have to say taking the engine out of the forester today was the easiest engine removal i've done in my life!!! the sti will be a smidge more fiddly with the plumbing and front mount intercooler and so on, but if its been mantled, it can be dis mantled and then re mantled. i'm a mechanic, its what i do!!

thanks for the second opinion anyway.

robert.

thats ok....it sounds like she is in good hands..

i think a true race engine would be running tighter tolerances than standard and forged pistons usually run different tolerances to allow for different thermal expansion. But where exactly the line between a standard engine and a street engine is im not sure.

Bearing wise .. i dont think there is a huge difference in aftermarket - oem bearings .. neither of them like detonation much.

MRT suck and they are liars, go to Rexnet, OZLiberty, RSLC etc and search for yourself.
Theres not that much difference between the re-building of the Forester to the STi, same lay-out etc etc.

How many km's on it?
Why did it get re-built before if someone says its got ACL stuff in it already?

Its also a 2.0l, not 2.5, and have fun with the piston clips....

Just incase you need them, i have a set of EJ257 (2.5L Sti) pistons, never been used. Removed from a short motor i bought and built up with forged bits.

Let me know if you need them they will go pretty cheap.

I say go for it! The performance company's sound like they're spinning crap to get more business - and charge a truck load for it...

Have fun with it!

Bennie

Just watch bagging companies here - a forum I am in over here is in the death throes due to bad mouthing a business online - costing the owner of the site thousands(although a fair comment)

Race motors are built to run a finite life...they are "race" motors and a built as such to run as hard as they can for a limited time. A street motor is coming to a balance with race and standard without chewing the engine to bits. For the streeter/daily driver with longer trips, IMPO, dont waste your cash on a "full" race motor - will be a dog to drive and will have a very, very short life as it is built to race, not daily drive.

Race bearings are in their nature softer to absorb the crud that is pumped around a race motor(minis use the same methodolody due to having the gearbox in the sump using the same oil as the motor!!:shock:)so some of the minute bits are embedded in the bearing surface material and held there vice pumping around the engine. Now in saying this it wont like bits of main/rod caps being bounced around...

Mini race motors are stripped every 5 meets(pretty much a season...) and the bearings are pretty much cactus however the cranks(the achilles heel of a mini and only 3 main caps too) are usually spared a regrind to the next oversize - at least for another season but they are all crack tested prior to another use. NEVER!!!! get a crank hardened - they will break in half(especially when iron cranks in EN16T type steel is being used...they shatter!!).

Subaru motors would be better for more work due to the properties of the alloys at use in them - they are more stable and are easier to work with.

To me tuftriding/nitriding/twin double overhead chroming/"balancing" a motor is thousands that could be put towards functional mods in breathing and other areas. Just doing a mini engine this week-end after the crank broke(and I mean broke into 3 pieces!!) so will think that the next O/S may not save it.... These are just my views and mostly based on 50 year old technology - but there are some businesses out there that will try and pull the wool over your eyes...be careful:)

Hooroo

I have never rebuilt a suby motor either but have played with bikes and other motors for a while and have found that running forged pistons that they tend to make a bit more noise when cold as the pistons need to warm up a bit to expand to the right size. Thats why most companys use hypertuenic/cast pistons dont seem to expand as much.

Race motors etc should be warmed up at idle speeds etc no high revs etc because of excessive clearance of piston to bore clearance rings could be broken etc.

As a motor that is used every day i would be using a good set of hypertunic pistons. Less expantion of piston

Good tuners etc can get good power using these still.
Main problems are when motor is not propperly balanced and detonation problems will cause piston /conrod problems etc.

I would be spending money on getting it balanced etc vibrations cost power and reliabilty in any thing that spins

I should fix up balancing and say blueprinting. I think this is the biggest furfy a motor rebuilder can spin you as a consumer. My father was a mech engineer and made all of his engine components for both cars and trucks(cummins/DD and the likes - enitire crankshafts from a six foot long, 600kg lump of cylinder steel) and the "blueprinting" of a motor is a complete waste of time as it has already been done. Unless you are totally making a different motor out of the bits you have, dont let the so called speed shops bullshit you and charge you thousands to "blueprint" your motor.

Balancing is another issue - I wedge cranks and weigh piston/rod assemblies to within grams of each other but have never spent thousands on a blueprint...I laugh every time I see some sucker here in Canberra get ripped by the really unscrupulous dealers in this place. Relieving stress points on components like using an oil stone on sharp edges, champhering the bore edges, main and rod caps, arp hex bolts, attention to detail and a clean assembly area. The machining is best left to a pro and make sure they itemise it BEFORE you commit otherwise they will take you for a ride. I did it and was pissed when the bill was double what I had budgeted for.

Running in a motor too is another bone of contention. I use the procedure found here:

http://www.mototuneusa.com/break_in_secrets.htm

and have never had an issue with premature wear or poor performance. Build your motor carefully and run it in like you stole it. Run it in softly and it will be a soft motor forever and a good chance it will be using oil from the first turn of the key. I am a big user of Hypatec pistons - they are aluminium alloy, 210grams(for a mini that is)each and a low reciprocating mass(even on a mini the factory pistons weigh nearly 60 tons when they shoot to the bottom of the bore again on the firing stroke...a great piston and very robust upto 7500rpm(thats a lot for a mini...lol).

Bottom line is do it yourself where you can - there is nothing more satisfying than doing it yourself. I was lucky as I had a father who let me tear things apart for the fun of it and then put them back together again. Part of the fun of growing up I think. Also remember that you have this inate pride you did most of the work yourself. I love the assembly of a motor and a few ales between friends. I have yet to tackle a Subaru motor yet...that will be an adventure!:D

Hooroo

Yep I'm with this fella , gotta get the gas pressure behind the rings to push their running surfaces out against the bores to make them seal .

Blueprinting is a very time consuming business and in a roadie it's not worth the cost and effort . Balance and elimination of stress risers is well worth the effort .

I wouldn't go out of my way to fit forged pistons to a road motor in fact often if you can get them factory pistons are generally quite good .
BMC Mini pistons you probably can't get anymore but the aftermarket has the 'ole A Series pretty well covered .
BTW I never raced my S engine but with a factory 648 cam and BMC 4 ring flat topped pistons at 1293 it went to 8 once - last 500 was pretty rough but being young and silly had to prove it could do 60 mp/h in 2nd ...!
I had the luxury of a std journals size EN40B nitrided crank in an S block .

IMO sube EA81/82 and BMC/BLMC A series share similar design limitations , three main bearing cranks and siamese port heads . Real S and EA82 heads are bad for cracking between the valve seats too .

Memories aside factory std pistons have reliability on their side and are quiet . Forged pistons may be good for being light and having the strength to cope with innertial loads at high revs but roadies don't see constantly high revs normally . A good road engine makes lots of torque in the low to mid range because that's what works with std gearing .

A .

Excellent - another one wiley in the ways of A-series oil leaks and Lucas, Prince of Darkness electricals.

Well there you go - I have learnt my thing for the day in that I didnt know that the EA engines have 3 bearing mains...All good.

Mini motors are a contancerous beast - at least the Subaru motors dont mark their territory wherever they go with oil and the likes!

I reckon, getting back to the subject, get the bits and pieces balanced, weighed and put together. Save the cash for something special like the interior and petrol(seeing as it is costing more and more every day...)

Hooroo