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Subaru Main Bearing Clearances after Line Hone

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I understand why main clearance is critical in EJ engines. My clearances were about 4-5 thousandths so my machine shop sent it out somewhere to get line honed.

I don't think they did a great job. The bores are out of round but my machine shop said if the bearing clearances measure okay it should be fine, even for track use. My measurements:






The #5 seems to be too big and I'm worried most of the oil will flow there and I'll lose pressure. Should I run it as is?

I'm kinda confused with what you're saying there? My 5c worth, because I've been bit, myself.

Line boring doesn't, of itself, have any real affect on main clearances, provided they're within spec's - they're down to the bearing ID and journal diameters, and would normally be corrected by maching the journals undersize and using the correct, undersize, bearing shells.

If you were fitting ARP studs, that can cause some distortion of the bearing bores, line boring would usually be avoided unless the bores are oversize and lack the desired crush, are not round, and/or are out of line.

I have some concern that your "machine shop" is specialising in BS, rather than actual mechanical knowledge - the bores SHOULD NOT be out of round ( I assume you fitted and torqued all the fasteners before checking), that's 100% down to incompetence by the supposed line borer, probably either using incorrect torque, or not using all the studs, when tightening the halve together prior to the boring. That they are out of round means the shells will be out of round when installed, and that is going to play havoc with the clearances around the journal - that the "machine shop" says it's fine is BS. try a dummy build and there is a good chance it'll even clamp the crank in place and make it difficult, even impossible, to turn by hand.

If you're sure of your measurements, you could check with your BBB, or Citizens Advice (not sure what you have there), to see if you can make a claim against them - this may be along the lines of getting their cock-up remedied and making a claim for that but, again, you need advice.

There are some very competent machine shops that specialise in Subaru engines, and some decidedly 'cowboy' places* that specialise in ripping of clients with shoddy work - before going any further, I'd suggest sending your block to one of them - after checking out what sort of reputation they have, some big names will only take the required care for big clients - and have them check the work and, if required, have it redone with the studs and torques you will be using for the actual build. Some companies will offer oversized OD main bearing specially for that engine which will avoid further machining of the case halves.

Oh, it would be a good idea to send the crank and bearing shells, as well, to make sure that is machined correctly and the clearances are actually where they should be.

*I've had some quite expensive, and hard to replace, parts ruined by supposedly competent "machine shops" - my advice is to look around and find a place that will do the work properly, and stick to it! It can be more expensive and a hassle but, as the saying goes, "pay once, cry once" - saving a hundred bucks by cheaping out can cost thousands when it takes out everything else because that 'cheap' move didn't work out.

Thank you for your advice Gord.

I do have ARP head studs on my build but not the ARP case bolts. I figured they would do the line honing with a torque plate on, but my local machine shop said they didn't need the studs to do the work. (Although the bores are out of whack regardless if I tighten the studs or not).

The bores are definitely out of round and some of them have a bit of taper. I torqued the whole block together, heads and all, and took some measurements. They are all out of round by 4-5 thousandths. This is way over the limit correct?

Since you said this, I have gotten the information of where my block was sent out and I will personally go to them with the block and see what they can say about it. I have a feeling I will only get consistent results if they do a line bore instead of hone.

You could try and get your money back from the idiots who were supposed to do the work, but in your position I'd be looking for an actual, reputable, machinist to check the block over and see if it can be salvaged. There should be numerous Subaru forums over there, and I'd suggest checking them out and seeing which are recommended, and which are less so...

Unfortunately, you may be in the same place I was a time or three, with butchered parts that would cost more to remedy than starting afresh.

There aren't a lot of things that REALLY grind my gears, but paying good money to "specialists" to do work and having them demonstrate only incompetence - or worse, having often expensive or hard to find parts rendered useless - is one of them!

Forgot, if it turns out the actual specialists tell you the block is f***ed, pay them the money for their time checking it, some won't charge but that's their labour time and that costs $$$.

Hopefully, there will be a Subaru nut, or two, who can better help you, maybe even your part of the North American continent. Try a forum search for "Subaru","STI", etc.

Unfortunately there are no Subaru shops anywhere near me that do engine building. My only option would be to drive to the US.

I took the block to this other shop that did the line hone and talked to them about it. They seem to really know what they're talking about. They showed me their notes they took when they honed it and everything seems like it was round. Somehow when the cases were split and put back together, everything shifted on one side, causing the out of roundness. I checked the dowels and they look fine.

They told me to put the crankshaft in the block and see if it spins nicely. They said the crank might help align the case halves better. So I gave that a shot and the crank does not spin easily at all. Eventually I put a wrench on it and was able to spin it but it did not feel good. Pulled the case halves apart and all the bearings are scored.

Have you ever seen this happen?

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I haven't had it happen, personally, but as soon as you mehntioned the out of round it's what I expected to happen. The scoring may be down to the finish of the journal oil-way hole - if the crank is too tight to turn by hand, please don't force it in the future. As it is, some of those bearing shells may be toast now.

Hmmm, "everything shifted to one side" - to me that screams that they failed to do the job correctly, removing a very small amount off each half, but possibly only on one side. It's impossible to say from here. That they also said "the crank might help align the case halves better" is also a concern - the crank-case halves are aligned by dowels, and they are 100% responsible for the case alignment - hmmm, i wonder if they even had them installed while doing their "machining" in the first place - the crankshaft cannot, and must not, be considered, in any way, to be an alignment tool.

I really wish one of the SUBARU chaps would add a commentary here.

You don't need to drive to the 'States, to have your cases checked, you can have them freighted instead. When you have the actual SUBARU specialist(s) narrowed down, ask them the best way to send the cases, and anything else they require - and/or contact the freight company/ies you're considering and ask if they have a crating service.

I think Gord has offered great advice. It seems you've found the work isn't acceptable.

I don't know a machine shop in Canada that I could suggest. I'm not saying there aren't any, I've just not had experience that leads me to be able to suggest any...yet.

If you don't have a local place to do a great job, I agree I'd ship it somewhere competent.

Specialists in the platform will generally want to build the whole engine with new parts for you so they can deliver a known good complete product back to you. That will narrow your options significantly.

In terms of a place I know line bores all their Subarus and MIGHT be open to this, you could ask AR Fabrication.

So I took the block back and spoke to the machine shop about my concerns. He said the measurements of the bores line up in a way where it seems the two case halves are not aligned properly. You get wildly different results measuring at each side of the parting line - 4-5 thousandths difference. However the honing marks show that the honing stones touched every surface.

It seems that it's either the dowel pins that align the cases do indeed have too much play, or the cases are distorted in a weird way. Machine shop said the only real way out of this is to get a new block. Just to entertain this idea (and rule out a bent crankshaft), I went to my original machine shop where they unfortunately only had ej25 cases. They gave me one to take home and test - bolted it together and the crankshaft spins nice and freely! (but still a clearance issue of 3-4 thousandths).

If I have to get new cases, this puts me in a position where I am either converting 2.0L to 2.5L, or having to shell out quite a bit of money for new 2.0L case halves.

Do you know if there's anywhere that would machine and upsize the dowel holes? Maybe there's somewhere that will dowel all the mains?


I'm happy to help try to deliver what you're after, but I also feel compelled to say this sounds like an awful lot of work to put into a used set of EJ20 case halves, and new case halves make more sense to me.

You are likely already having to be overbored, the cases have been line bored and need undersized bearings, they need dowel work, bores may be weakened and more prone to cracking. Basically you're talking about investing almost new case half money to end up with something that likely won't be as good as new, and perhaps won't give you the option to rebuild again because it's already been machined. Especially when it comes to decking, even a small amount really screws up mechanical timing on these engines.

I'd go new EJ257 halves, but that's just me. If you want to continue working on your existing case halves, you could ask AR Fab about machining for RCM dowels as well.

Thank you for your response Mike.

I do understand what you are saying about doing a lot of work on used halves. The only reason I really wanted to keep these was because they didn't need to be overbored and they have been honed to match my pistons. The deck had also been surfaced.

If I do go with new case halves, I either have to match the machine shop's spare 2.5L block to my 2.0L heads and do some hybrid build, or buy a new 2.0L block (which ranges $1500+).

I can't seem to find anywhere around Ontario that will sell me a 2.0L block for a reasonable amount. Do I get another used one? Or just shell out the money?

I'm worried about the hybrid build as I've heard they can be a tuning nightmare (in addition to the $1000 pistons that would be required).


Wow that's almost double what I'm used to 2.5L case halves costing. I haven't bought 2 liter halves in probably 15+ years so I guess things have changed. It's too bad, we scrapped tons of 2 liters nobody wanted. It sounds like you might as well see how much more it would cost to do the upgraded dowels etc. on your case halves before deciding which path to take, as long as your heads have barely had any material removed from the decks.

The hybrid build requires proper chamber work to be great, though some bandaid it with hybrid pistons and super conservative tuning.

A small positive point, that I don't think I mentioned earlier, is that some companies, such as KING Bearings, have a lines of special main bearing shells specifically for the Subaru engines - they have a slightly larger outside diameter, which means no more material needs to be removed from the mating faces when line boring.

Oh, if there is any chance of upgrading to ARP case fasteners, go for them now, because if you go for them later the additional clamping force means you'll need to line bore/hone again because the cases distort slightly under the higher forces.

It's a LOT of messing around, that really shouldn't have been needed, but if the engines are that sensitive to tolerances (as I said, not that familiar with them), might pay to have them properly checked to make sure there aren't other issues that will bite you later.

They are that sensitive to tolerances.

I don't know how much power this engine is being built to make, but a lot of what's mentioned is massive overkill for most builds. What are the torque, RPM goals for this, fuel being used, use case i.e. road course or otherwise?

I will check with all the machine shops in my area if they can do mains dowelling. I've heard of two types of mains dowels for subarus: one type goes around the bolts (a hollow dowel), just like the dowels on the deck surface that go around the head studs. The other type are separate solid dowels that get put beside the bolts. I've attached two images of what I'm talking about. Either of these should be sufficient for simply aligning the case halves, correct?

The hybrid build might be more work than its worth. I haven't heard of a lot of them being reliable. Especially since I'd have to find a shop willing to match the combustion chambers.

The goals for my build: 400WHP, 8k rev limit, 94 pump gas, Garrett G25-660, for use on circuit track/road coarse. Going into my Factory Five 818 kit car (I made a post before). Pulling a lot of g's and spending its whole life at high RPM. Wanted to keep the torque low so I don't blow up my 5-speed. I understand some of this might be overkill, but I know Subarus blow up all the time due to the fragility of their casings, as well as bad tunes.

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Yes lots of Subaru builds aren't reliable, but that's most often from negligence. My 2013 season championship and 3 overall track records was on a stock EJ257 shortblock I went on to run the first 9 second stock shortblock pass on, then swapped the engine into my winter beater. Cheap engine, expensive oil supply solution, because that's the real weak point on a 4xx HP track Subaru.

One of the biggest reasons people have issues is they spend money on stuff they don't need, and don't spend on things they do need. I'm suggesting considering not spending money on pinned mains, ARP case bolts which I wouldn't even use at 700 HP let alone 400 HP you're hoping for, and I wouldn't risk running old case halves that have been sitting. I'd get a stock shortblock that's more than up to the task, know I'll have oil pressure unless the engine is starved, and spend the money on oil supply parts instead of upgraded internals. Oil starve the engine stock or built, and it's done along with your pricey turbo, so I'd really focus there to protect your investment.

One of my Subarus has a one off billet pan, pickup, baffle a friend and I designed, and my time attack Subaru has a dry sump system. If you're quick enough, you'll run into issues requiring a serious solution, but hopefully you'll just need a good off the shelf upgraded pan, pickup, baffle plate. This can be figured out driving on a cheap stock engine rather than spending months building something custom fancy which can get hurt in an instant if you oil starve it.

A possible solution to the engine parts, especially the cases, may be to keep a look out for a rusted out car, with a compatable engine block, for sale in your area - remove the engine and other parts you may wish to keep as spares/cores and part out the rest, or send it straight to a wrecker/recycler.

Another way to think of it is if you put a cheap stock engine in, sort the car out, then want more power than a stock engine can handle later, you can probably re-sell the stock engine for a little less than you bought it for used. But if you put the cheap engine in, oil starve it and kill it, at least you didn't kill a costly (time and money) custom engine build. Again just my 2 cents, and we are happy to help whichever path you choose to go down.

Have a great day folks!

Thank you for your responses.

I seriously considered just getting a stock, used longblock and running with that until it blows up. The main reason I was sticking with the built motor is because I have the parts already - forged pistons and rods, bearings, studs, springs, cams..etc. I was under the impression that a lot of Subaru builds fail in the ringlands with high heat (which could be helped with forged pistons). I was also recommended to run forged rods above 400 crank hp. The lighter parts I also hoped would help me rev.

I will consider more oiling mods. Currently have 2 baffles, sti pan, killerB pickup and an external oil cooler. I attached a picture of my baffle. Would I need to upgrade to a race oil pan?

In the meantime I went to another machine shop. They said they have experience and equipment to do line boring - this would oversize the hole and would require king oversized bearings (MB5740xpg). I was thinking of going this route especially considering I measured the main bores again (after splitting the cases many times) and the measurements did not change. Sounds to me like the dowels are not an actual issue and the machine shop that did the hone was trying to cover up for their bad job.

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Good work double checking the mains. Yea line boring, honing, running bearings made for that sounds a good move. If you don't need case bolts or dowel work, that makes working with what you have more reasonable financially so that's great news.

I expect your vehicle/engine platform to generate enough lateral load (over 1.0-1.2 G) that you will likely experience oil starvation with what you have, and I'd look at the RCM pan/pickup/baffle kit as an affordable option. If the car comes out so well and you're driving it so well that kit isn't enough to avoid starvation, then it gets more costly, but hopefully that will be enough.

Mike, as part of the problem seems to be oil building up in the outer head as it's unable to drain against the "G" loading, has anyone in the Subaru fraternity experimented with electric scavenge pumps fitted to pump the oil from the heads back to the sump? Perhaps switched to just turn on when the "G" load at the head may require assistance - a couple of simple relays and mercury switches would do the job if the ECU and/or PDM didn't support it.


As you said, oil staying in the head is part of the problem. I thought about exactly what you're describing back in the mid 2000s and decided against it due to location and packaging. In another vehicle platform without the exhaust manifold right there, I'd be more open to trying it.

Part of the issue is you have to modify the valve covers for ports near their bottom if you're going to suck oil out with electric scavenge pumps, and that's right on top of the exhaust manifolds, which is also right up against the frame rail, with little room for heat escape. It's a challenge to make any hose let alone a pump live near there. Then it would be a mess to get all the hoses in and out of that area. Once you grab the oil you have to get it to the pan which is surrounded by the exhaust manifold for in front, and right up against the crossmember on the back side so you'd be running hoses practically touching the exhaust manifold. It seems it would be one big fire hazard, and I don't know that it would solve the issues to be honest. I think you'd still need the better pan, pickup, baffle or it wouldn't really help, and then still might not make a big difference, or might aerate the oil enough that it wouldn't be a solution. By the time you buy all that, 2 scavenge pumps, modify valve covers, etc. it felt like it would be a rather expensive, sketchy because of packaging, would crowd the engine bay even more, and maybe not even help in the end, so I never actually did it.

Improving the pickup, pan, baffle, reducing crankcase pressure is as far as I go before dry sump.

The in between I've seen some people take is running a mechanical multistage scavenge pump in a semi dry sump configuration, but then you have that pump, the tank, all the plumbing, plus the stock oil pump, without the benefit of a real dry sump system, and most of the cost and complexity, so it hasn't made sense to me.

Thank you for your responses. I do have an update on the situation.

First of all, you are correct. These cars can generate lateral loads in excess of 1.5Gs with aero. I decided to bite the bullet and upgrade. I went with the RCM baffle and the IAG competition oil pan. These all have viton/nitrile flaps that are mounted horizontally and vertically.

In your experience Mike, do these flaps go bad and need replacing with time? Luckily the IAG pan uses an o-ring to make removal easy.

Also if the issue is truly the oil pooling in the heads, the 818 is a great platform to experiment with scavenge pumps pulling from the valve covers. There is plenty of room all around the engine as there is no frame member in the way & you can access all around the oil pan, in addition to plenty of space for hoses & pump mounting. Maybe I can give that a shot if I do start to starve.

As for my engine, I was able to take it to the diesel shop that said they can line bore. They mentioned that they have never done a Subaru before, but have experience with Porsche/VW. Regardless, I got the engine back and they did a great job - all the bores are perfectly identical and round within a tenth of a thousandth. I put the King oversized bearings in and my bearing clearances all land within 0.0010 - 0.0018, which I am fine with. I was also able to put the crankshaft in and it spins freely. Finally!!

It seems line honing a Subaru properly is not possible. They must be bored.

One last question I have is how can I check thrust clearance? Previously I just used a feeler gauge between the crank and the bearing, but I've heard that is not the way to go.

Personally, for the thrust I just use a DTI* (Dial Travel Indicator)in line with the crank and zero it when GENTLY pushed back with a screwdriver or other lever, and then measure it with the crank pushed forwards. Work it a few times, back and forward, to check everything's seated, and you should be right.

Honing is fine, IF it's done correctly, which was the root of your problems.

Anyway, good to read you've got that sorted.

Ah, thank you for the feedback, Mike, I can't recall the last time I even looked at a Sub' engine, let alone exactly how it's installed in the vehicle. From what you say, there isn't even room for pipes to be fixed to, then run along, the heads to the front, or back, where hoses could be hooked up to pumps.

Pity, thought I might have had something useful there - but such is life :-(

Sounds good Neeraj!

The flaps harden up some over time so I have a hunch they may become a little less effective in sealing at that point, but I've not seen them degrade to a point of failure, or to a point where oil pressure behavior significantly changed, so it's an observed change, but hasn't yet become an issue in my experience.

As long as you can keep what's in the pan at the start of a G load from escaping, and access most of it with the pickup, you'll have a window of opportunity regardless of what may stay in the head. How long oil supply lasts will vary with G load, how much was in the pan to start with, and a huge factor is engine speed. I know you want to rev high. Just remember that means high oil pump speed and output, quicker evacuation of the oil in the pan. Shifting up an extra gear to get revs down for sweepers helps significantly.

Thank you for the information.

The idea of high-revs was to allow me to hold a gear a bit longer on some courses and auto-x (which I will be starting off with). I will have to keep an eye on my logs to see if there is a pressure drop.

In other news, I got my crankshaft polished as the shop I took it to said it looked like a mess (even though I had it polished twice before). I got it back and it looks so much better - it clearly needed to be done, but it increased my rod clearance just slightly. I now have 2.5-2.6 thousandths on the rods, whereas previously I had 2.4.

Is this too much rod clearance? I've heard the ideal is around 2.2.

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