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Subaru EJ Motors - Preventing spun bearings

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Subaru EJ motors have a common failure - in stock or modified engines, that is a spun bearing, typically it is a rod bearing.

Thinking aloud, the normal cause for a spun bearing is lack of oil. Whether it be from no oil in the sump, pickup being starved or some other reason as to why oil was not circulating through the system.

Debris and lack of oil changes can also cause this I believe, as the contaminated oil circulates wearing out the bearings, causing larger clearance's reducing oil pressure.

Tuning is also another factor, along with poorly built engine clearance's to begin with - but I want to discuss particularly the EJ oiling system in general.

Now - there are lots of reports of people having maintained there oil changes and having had oil in the engine - yet these motors are still spinning a bearing.

Have noticed a thread on nasioc where some people are porting/smoothing out the oil galley's to help prevent this - is there any truth to this?

Do any subaru engine builders port/smooth out any oil passages/galley's?

The two biggest issues with the Subaru engines in my opinion is that even in 100% stock form they use too much timing and are constantly relying on the knock control strategy. This puts unnecessary load on the bearing shells which is made worse by the small size of the bearings in the first place. The other issue that plagues these engines is oil starvation due to high lateral g forces during cornering. It's very common on a race track but can even be an issue on the road with a modified car with good suspension and tyres.

Smoothing the oil galleries is a common modification that can improve oil supply but that on its own is not enough for these engines in my opinion.

Breather system is also mega important in a boxer. The killer b ball valve look interesting.

@Daniel, that is an interesting product idea. I just had to google it. good find! Unfortunately the FA20 we're dealing with these days doesn't use breathers from the rocker covers however I have considered adding them.

I didn't see this thread till now, In my opinion Subaru do rod bearings because of oil temp. A friend had a Subaru rally car a couple of years back and it had the EG33 flat 6 in it which has coolant issues at high rev's in 3 starts he blew 3 motors because oil and coolant temp went off the scale. Every single failure were rod bearings. I posted this on the other thread its the inside of a sump from a NA normally Subaru Daily driver. The exhaust is to close to the sump and it cooked the oil. We are developing a EJ25 NA to run to 10,000 rpm and have set a gaol of oil temp under 85 and coolant under 100 C. A lot of serious race bikes and cars worry if the oil hits 90 C they prefer it to be 80 C. There was a really good R&D project on oil temps and how changing the grade doesn't help as much as you think.


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Hey Anthony, I'd agree that running the oil too hot will be a big factor in bearing problems. If the oil gets too hot it can break down and at minimum you lose some of the protection the oil normally provides. I personally wouldn't want to see the oil as cold as 85 C though. Oil needs to get to a reasonable temp to allow it to get rid of impurities. Generally an oil temp between about 100 and 115 C is considered by most to be a good range to operate in for a competition car. Our FA20 in original N/A form was seeing 135-140 C before we added a cooler, and now with the turbo, cooler and E85 we see about 110 max for comparison. I'd try and target 85-90 C for the coolant high coolant temps can actually make the engine more likely to suffer knock. We see that on the modern crop of performance engines they will often run around 95-100 C which is too hot for my liking for a race engine.

Hi Andre,

I know this might sound like a wanker but I brought the only F1 flat 12 cylinder Subaru race car in the world last year as a result of which I now have some contacts from the old days were they reved the hell out of the engines.

The reason I mention this is the oil temp and coolant is a really important and under rated issue in a race engine so I will send a couple of them emails and see what they say. You could well be right Andre and I have just stuffed it up the wrong way around but we need some info from the guys that were on the edge.

Will let you know what I find out.

@Anthony that's a pretty cool engine to have kicking around! I'm aware of the engine in very broad terms but obviously not a lot of details are known. What are you intending to do with it?

I don't down play the importance of oil temp at all. As you rightly point out, it's very often over looked and running the oil too hot can be detrimental to bearing life. I'll be interested to hear what you get back from your contacts.

Hi Andre,

I was lucky enough to buy the race spares which included a bunch of Subaru flat 12 part sand a couple of engine in bits. Then I purchased the car with a engine but not the exact chassis but in the deal I got a carbon fiber F1 chassis to suit. So the plan is to get one of the engines rebuilt and running at some point using 2 link ECU's. When that is done I will decide if I am going to return the car to the race track or not.

Will come back to you when I find out more on oil temp.

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From a French F1 engine guy, so my guess we want to run a bit lower for safety sake.

For the preheater temperature, the oil temp needs to be at 60° andwater at minimum 70 °. during the run never go higher than 120° oiland 110° water.


I asked my contact at PWR as they would be the best at cooling in the world. The answer shocked me. Also remember were are you getting the oil temp is important

Typically most petrol engines are happy anywhere from 82-90degC for coolant temps and anywhere from 85-110degC for oil.

Hey Anthony, your project gets cooler each time you post! I'm really keen to see where you go with this and how it works out once you have it up and running. The numbers you've got back are pretty much in line with my own targets and also give the usual kind of broad range that I expect when you ask multiple people about these sort of specifics. I think PWR is closest to aligning with my views. The only thing to reiterate is that keeping the oil constantly at 85 C (or below) does allow impurities to build up. Unlike your French F1 guy, I really wouldn't like to let coolant temp get above 100 C and I'd prefer to be in the 80-90 vicinity as per PWR's recommendations.

I am building another EJ25, and it was by chance I checked this thread for new replies!

Hot oil was a similar theory I had....I figured the factory recommended oil weight of 5w-30 was just a bit too thin, and during the service interval the oil will degrade, thinning out. Put all these things together, the heat from the exhaust manifold + service interval + abuse + knock = Bearing.

I would say running a 40 grade oil is a good start to preventing rod issue, but that won't prevent starvation issues from low oil or as Andre mentioned, agressive cornering.

There is an aftermarket pickup that many people use (KillerB), as the original one has been known to fail, assuming this goes back to the aggressive cornering.

Unless you have an oil pressure/temp gauge and monitor it, I think its all just speculation on what causes these motors to spin rod bearings.

Agree oil pick up is a issue as well, the other thing I think is important is use STD bearings never go to the STD X which are designed to give more clearance. I did it once on big end and through a rod. Then later I decided it was okay to use the higher clearance on the mains and ended up with bearing problems again. You would think a guy would learn I asked a guy in Melbourne that builds high HP Subaru motors and he told me after the Big End problem "Use standard bearing on Subaru, do not use over size".

I learn't my lesson the hard way.

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If you were running the extra clearance bearings you would have needed to compensate for the additional clearance, ie bigger oil oump and maybe running thicker oil to get your oil pressure where it needs to be. Having a little extra clearance I don't think is a bad thing on a Subaru.

Especially considering how prone they are to knock, should having the extra oil between the bearing can't be a bad thing right ? Maybe Andre can confirm

those bearings give an extra thou, if not using a brand new crank, it might be too much on a used crank that's a little worn

It's not just a case of adding additional bearing clearance as the important aspect to check is what your existing clearance is. If that's insufficient then sure, go with the additional clearance bearings. If on the other hand you're already where you want to be then leave it alone. A key place people go wrong with Subaru builds is setting the main clearance too loose. Since the block is alloy the clearance tends to grow as the engine comes up to operating temp. If you start out with a traditional clearance of 2 thou or thereabouts, you'll have excessive clearance at operating temp.

As for the additional rod clearance and knock - This isn't a fix or a solution and the correct way of dealing with this is to tune the engine properly and remove the knock. That being said, I will usually run on the loose side of the factory big end bearing tolerance and match that with a slightly heavier oil viscosity. This ensures I still have good oil pressure and can provide a stronger oil film to protect the bearings and crank journal under high load.

Thanks for the reply Andre - I have heard that the EJ block halves expand a bit being all alloy.

Do you still follow the manufactures bearing clearance's for your builds? I just measured out a crank with some stock sized replacement bearing's from king and they are all right on the end of the factory spec 0.01mm - 0.03mm.

#1 - 0.03mm

#2 - 0.04mm

#3 - 0.03mm

#4 - 0.035mm

#5 - 0.035mm

This was measured with 14c ambient temp, Im assuming if it was measured in the Subaru spec of about 25c the clearance's would probably be a little different (assuming tighter as the case would grow while the crank probably wouldn't move too much)

I was just planning on using the crank as is, its going to be a daily driver/street car with stock internals. Plan was to use the next size up oil pump (11mm oil pump) along with a 40 grade oil (5w-40 or similar). Factory spec is 10mm oil pump with 5w-30 oil.

Would this setup still prove good longevity for street/daily use?

Or am I getting my theories wrong?

@Ben, the clearances will actually become a little looser as the engine heats up. I generally aim for the looser side of the factory Subaru tolerance range and I've had great results with doing so. Your 0.04 is getting a little looser than I'd normally run but depending on the application it's probably not going to be a deal breaker.

Assuming the downside of having clearance's out of spec will effect oil pressure?

For a regular daily driver I am assuming it shouldn't make too much of a difference ?

If under heavy load conditions, this is when I assume it will be more important - as things heat up above their "normal" ranges, clearance's will continue to grow and oil pressure will consequently drop?

You should do a EJ Build series Andre :)

@Ben, yes a clearance that's too large can affect oil pressure but to be fair this can be dealt with to some degree by swapping to a heavier viscosity oil. You're not that far out of the ball park so it's probably not a massive concern for a daily driver.

We are doing an FA build which for all intents and purposes will translate pretty well to the EJ series.

On a similar note, at what point should one consider upgrading from a 10mm oil pump to an 11 or 12mm pump? Is there any disadvantage of running a bigger pump if you are within factory clearances?

@Matthew, when it comes to oil flow, more is almost always better. The pump still uses a pressure relief valve so there really isn't a downside.

@Andre - I thought having "too much" oil flow can cause cavitation and start rising oil temps? Maybe this is only an issue on track cars with sustained high rpm's and not so much for spirited driving or lower to moderate track use.

While on topic of building EJ's - I have been told by a few local machinists that its best to go all out - close the deck, line bore. This is for a target power goal of 300-310kw at the wheels. Some of them swear black and blue this is the way to do it - and while I agree, but for a target of 300-310kw at the wheels is all that machine work really necessary for a street driven car?

I was thinking a hone to suit the next oversize pistons would be all the machining that is required...does anybody have any experience with this?

Plan was to get bores honed to next oversize for forged pistons, brand new subaru crank, play around with standard and 0.001" undersize bearings to get the clearance's where I want them, arp head studs + bolt ons, aim to run about 22-24psi.

@Ben you're only going to end up with the required flow to reach the point that the pressure relief valve opens. Any additional flow will be through the pressure relief valve. You can have potential issues with some engines at sustained high rpm if the oil can't flow back from the head(s). This can end up essentially emptying the sump.

I've tuned plenty of EJ series engines making 300 kW atw with just pistons and rods but the reliability of these engines does come down to a big degree to the quality of the tuning. If the engine is tuned well and isn't knocking then you can make it reliable without spending thousands on it. If the budget is there then close decking the block is a great option but I wouldn't say it's essential at your power target. Line honing is going to be essential if you run a set of ARP main case bolts but with the stock fasteners it's usually unnecessary unless the engine has had a previous bearing issue that's affected the tunnel geometry.

Your wealth of knowledge is invaluable Andre - Much appreciated. Was planning on using the standard case bolts.

Can you confirm I would see tunneling issues with checking main bearing clearance's ? (Case done up to torque spec with bearings installed and measured with a dial bore gauge).

What kind of Piston to wall clearance would you run for a street engine looking around the 300-310kw at the wheels mark? Have seen some people run a thou tighter then what the manufacture recommends to reduce noise (piston slap) as well as increase overall longevity of the build.

Though that said, JE have come out with a new skirt coating - http://blog.jepistons.com/-perfectskirt

From looking at other brands they have always had a skirt coating but this one seems to be made of a different compound and is meant to last.

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