what is it about the crank/bearings design that means they run dry - or drier than a normal "straight 4,6" whatever?

i was laughed at by a local tuner the other day when i asked them to do this - it was dismissed as internet bullsh*t. there 900bhp engine doesn need it, why would mine.

whilst im dont beleive all im spoon fed by some, its hard trying to understand how it actually happens on subaru engines and not others?

 

Jef, yeah the flat-4's cylinders are closer together - more 'bunched up' - as the two opposing pairs of 'boxer' cylinders/pistons phsically allows. This, welcome!, compactness to the resultant engine, and by extention its short crank, means that the bearings are not so wide as most other more conventional in-line engines' ones.

So the lack of width means there's a directly proportional lack of surface area which can be be oiled, too. That, and the fact that all that torque is being put through said depleated area - i.e. if you recall from your physics lessons: Force / Area = Pressure (the greater the force, and/or the lesser the area, equals a larger pressure). So this inceased pressure on the area-challanged bearings obviously isn't going to help matters when anything dodgy might be happening to the bottom end...

 

thanks for that, surley thst would mean most of these engines would be susceptiable to this failure? due to smaller bearing sizes.

when in fact its probably nearer to less than 0.1%

im not discounting what you say mate but to me it sounds more like an oil drainage issue, from crank/big end bearings, ie too effeceint at draining - altho then it would be like that on every start up

lol think im going to give up - its getting a bit confusing for me haha

 

Even though they are narrower, etc, I don't think there's necessarily any evidence of failures that can be directly attributed to the bearings' design.

But, logically, it follows that should anything awry happen to the bottom end, then their design surely cannot help matters(?) i.e. a greater loading on a lesser volume of oil film.

 

very true mate

cant think about it anymore - im struggling to get my head round it lol

cheers

altho it is a practice i will definatley follow, for the sake of time taken it would be daft not too imo.

 

Did they actually do it?

Is this the same chap who reckons these stories don't actually exist? The prevalence of them on this forum alone suggests that he is wrong, and in this context his flat out refusal to acknowledge it seems a little odd.

Their car is a Mitsubishi isn't it?

Without wanting to state the blindingly f'ing obvious (and I'm not ticked off with you here, I'm just accenting the point), Subaru engines are different to every other manufacturer's engines. Indeed one type of Subaru engine is different to others made by the same company.

To re-use the analogy, why do you think one manufacturer's cars have accelerator pedals that stick to the floor, and not others (unless of course they are Aygo clones)?

If it's a potential cause of failure, it's a potential cause on all EJ series engines, correct, although Subaru have modified the crank lubrication, among other things, over the years so you would think newer cars should be less susceptible.

However, you're asking questions here that can only be accurately answered via thousands of pounds worth of detailed research into the engine's oil system performance. We are all, to a significant degree, guessing and surmising. Although your chap with the 900bhp car is guessing too.

Stop and think for a second what changes between a "normal" startup and an oil change then. "Draining" is probably a factor but not in the way you're surmising there.

Give this a try. It's educated guesswork and may or may not be correct but it makes its own internal sense, and I don't yet recall anyone popping up giving a reason why they think it's wrong.

Incidentally, the thread I wrote that post in concerns just the sort of post-oil change bearing failure that your 900bhp man reckons don't exist. Maybe you should pay him a little less attention?

 

well said splitpin

 

I'm abit unsure on this subject

i think when you do a fresh engine build you have plugs out and crank sensor disconnected and fill oil filter and oil pump before then crank till you get oil pressure

but for engines that have done a few miles just fill oil filter and start as normal because there would be oil coating bearings from old oil and there would also be oil in the oil pump Chambers which when you turn over engine will supply the bearings

i also think that just disconnecting the crank sensor is not good enough if people say this must be done as you will still get compression in the cylinders which will put the stress on bearings so to me the plugs would have to be removed

 

Cat, when you do an oil change and refill you now have air above the level of oil in the pick-up pipe. It's this air that needs to be purged through the pump at as low pressure as possible. Otherwise, if the engine's firing, then the huge combustion forces could just drive air out between the bearings/big ends and possibly lead to bearing-journal contact.

It's sufficient, so the theory goes, to just take the combustion forces out of the equation, as the pressure difference between the engine firing, and not, is significant i.e. due to the motor turning at c.1500rpm vs c.200rpm or so, respectively. It can only help by removing the plugs, but, by comparison, the 'extra' reduced compression it affords, percentage-wise, is minimal. But it's well worth practicing, obviously, if doing the oil/filter/plugs service.

That's the theory, anyway.

 

No. On a fresh build, pre-filling the filter is often an outright bad thing. If the oil pump isn't well primed already (or filled with assembly lube) the oil in the filter will trap air beneath it and often prevent the system priming. You'd be better off fitting a dry filter and then cranking, or using a large syringe to force-prime the system through the oil pressure sender fitting while slowly turning the crank backwards.

This is a fundamental error. It simply isn't sufficient to have "a coating" of oil in bearings that are trying to withstand significant combustion forces. All that will happen under those circumstances are that the bearing surfaces will be forced together, literally pushing the oil molecules out of the way. You need consistent oil pressure to maintain the integrity of the bearing.

You will still get compression in the cylinders, but the force generated by this is a tiny fraction of that exerted by combustion. As you say removing the plugs is the best case scenario but this doesn't appear to be a pivotal issue.

 

i see what you mean but this could still happen with the crank sensor disconnected as it would still pump the air into bearings and have pressure if the plugs are not removed

so plugs really need to be removed along with crank sensor or it can still do the same damage as just starting it as normal

so just disconnecting the crank sensor in my opinion is not good enough

 

i see what you mean and think it's best to have plugs and crank sensor removed for the right way

and not like some say just disconnecting the crank sensor

 

The air will still need to be pumped through, yes. However, when it is done slowly on the starter at a couple of hundred rpm, the potential for damage is a minute fraction of what you'd get when you've got burning mixture forcing the pistons back down, and the engine turning over at well over 1000rpm.

Everything is a compromise, and one of the problems with removing the plugs, aside from the ballache involved in doing so, is the risk of drawing muck from the plug wells into the cylinders.

I'm as cautious as anyone but I don't pull the plugs unless I was going to do so anyway. If you wanna do it, go for it by all means, but IMO the single most important aspect of this thing is the crank sensor disconnect. If I could only do one thing or the other, I'd do that in preference to pre-filling the filter.

 

splitpin, thanks for some more detailed info -

you have to know tho, how easy it is for internet myths to start - i was just asking for a little undeerstanding as to why people suspect this problem to arise

and you rightly said- without very expensive analysis it cant really be proven, either way

subarus by nature are driven hard, can be had for not a lot of many, and as such often owned by irresponsible people, who thrash fck out them. they then end up in some geniune owners hands, and the engine dies - a lot of the time people jump on the "oilchange" band wagon.


like i said origionally its a protocol that i persoanlly follow - just trying to understand it a bit more

lol yeah and you right , was a mitsubishi owner who said that.

also to me sounds like it could be oil pump issues if air is being forced into bearings until oil pressure is up - again why is it not happeing with other engines?

 

It does! But real or imagined, the Subaru engines seem more susceptable to this than some others?
Many cars have the oil filter mounted upright (as opposed to hanging down, like the Subaru fitment) and despite there being a rubber valve in the filter to stop drainback of the oil contained in the filter, oil still drains back overnight. On servicing a number of engines with this arrangement I've packed rag around the filter base to catch oil as the filter is unscrewed only to find there was little or no oil remaining in the filter! In these cases, every cold (and not so cold) starts would mean the filter has to re-fill and a slug of air is pushed through to the bearings before actual oil pressure is established. My daughters old MR2 (120k) and a work collegue's BMW 3 series (94k) were typical examples of this.
OK so this is not as bad as complete drain-down as in an oil change but it's half-way there! Lets be thankful that the Scoob filter does not drain back!!!

JohnD

 

Oh, of course. You only have to look at some of the stuff that circulates round here to see that!

Leaving aside the technical differences between engine designs for a second, how do you know it isn't?

It may well be that this can and occasionally does lead to damage, if not outright failure, on other types of engine, but it may also be that those cars are in a segment of the market or are simply too boring for the owner base to coagulate in the style of sites like this place or Nasioc.

For all we know, and picking a random example, the Daewoo Nexia has a huge problem with oil starvation, but because they're sh*tty old clinkers, and because the people who buy cars like that tend not to be enthusiasts, any owner whose engine gives up out of warranty won't be jumping onto their favourite petrolhead website asking how it happened, they'll just scrap the thing and buy a Fiesta or Corolla next time.

There is no such thing as Snet for Nexia owners, because nobody who owns one wants to admit it, let alone talk to other like minded people on the interweb. Where owner sites do exist, without someone from here keeping a close eye over there, we don't know exactly what is going on (although someone like Internet Brands could probably unearth some interesting statistics from a bit of data mining).

That isn't a technical issue, it's a social one - although it's directly connected to the fact that the Impreza is, as you say, a cheap, very high performance car, which both attracts a certain type of owner, and tends to be driven in a way that most Nexias would never experience.

The issue of air being pumped through the oil system will happen to other engines. By definition it has to after an oil change, and as John says, probably at other times too.

If you're asking why it seems to be more of a problem on Subarus, then the technical aspect to the answer is because while all four stroke internal combustion engines are relatively narrow variants of the same concept, the details are considerably different.

The oil pump on the EJ engine has a certain size and flow rate. The oilways have specific diameters and overall capacity. The bearings are a certain size. The physical layout of the engine, and the way the oil system fits into it, will have a material effect on the way the system functions. Even the quality of the internal finish on oil passages will have a small effect on the way fluid passes through them.

The other aspect is simply one of timing. How long the ECU waits for the engine to turn on the starter before initiating fuel and spark will have a significant effect on how well established the oil circulation is at the moment combustion begins.

It's clearly, at most, a marginal issue, and it may well be that we'd never be here talking about this if Subaru had programmed the OE ECUs to wait another couple of revolutions before firing the engine.

 

it all just seems a bit too unlikley imho

ive worked in the trade for 10 odd years, mostly doing services and mots, both in indepandant and dealer garages

tbh very rarley did i come across bottom end failures in that time, and my bosses would take on anything for money.

but i have to just base my opinion on my experience - i take in information fromt the like of you and other knowlegable people, but it still doesnt convince me enough to eliminate a touch of bandwagon jumping when bottom ends let go.

i just think its far more likley a case of abuse and lack of maintenance along with the fact its a cheap, turbocharged engined vehicle

im more than happy to be proved wrong mate, im not one that cant admit when they are wrong but there needs to be definitive proof - of which it seems its impossible to get

i appreciate your input into the thread

 

It would be interesting to know how many re-built engines with race quality bearings (ACL, Cosworth etc) have suffered bearing failure.
Maybe the words said to me in conversation with a well respected Ford tuning Guru some years ago that unlike the Sierra Cosworth lump which was developed originally with 400bhp but diluted down to 205 bhp for the production version, whilst the Subaru unit was basically a shopping trolley pumped up to 205 bhp! Maybe a bit of a sweeping statement at the time, but could you dispute it?

JohnD

 

I've thought that! There's no reason why that could not be programmed into the ECU, at least for cold starts! Obviously, the ign. and fuel are switched on as soon as the crank sensor detects movement.

JohnD

 

Indeed not. It's completely arbitrary and the behaviour at startup can be altered on most cars.

No, it's not immediate. The exact determining factor varies with the different ECU types but all of them operate a deliberate delay to allow the engine to stabilise on the starter before allowing it to fire. On the programmable ones it's easy to alter the ROM data to make it turn a bit longer if you're of a mind to.

Whether Ecutek and the open sauce people have worked out how to do it, I have no idea.

 

lol this thread i getting confusing, all i need to know is during oil change, i should pre fill the oil filter before fitting the new one and then disconnect the crank sensor so the car doesnt fire up and keep doing it till the dash light goes off. correct?

 

Yes.
Yes.
Yes. Oil light normally goes out within 20secs. If it doesn't, then continue cranking - in no more that 10-20 second bursts - until it does go out...

 

cheers

with regards to cranking it, i take it because it wont start, u'll be turning it on the starter motor for 10secs then letting go and doing it again till the light goes out?

 

Yes. I think it would be okay to do it for 20 secs, but not sure. The pinion or motor may overheat??? 10secs burst will be fine though (feels a long time though, and makes you grimace lol). Let it recover for 10s or so between... cranks

 

What i was trying to say is that disconnecting my crank sensor is hard as mine has no plug on the end like described, it goes off into a wire and connects under the engine somewhere. Im not sure if this is common with classics as I have a 93 wrx import and its my first scoob.

I do know that the the second green fuse in the engine bay is the fuel pump / ecu fuse (bf2 from memory) so if i pull that would that achieve the same effect?

 

anyone no what oil and filters people have been using when they get these problems after the oil change.
adam

 

ariser, read here :-

https://www.scoobynet.com/general-te...r-removal.html

 

Mesmerised by Joz 8968 avatar...
It fair hypnotised me that did...
Bigunns them!
Sorry it's off topic

 

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<<< 'Tis a noodle baker, that's for sure!

 

pleased to hear it.

As for recalls. I can't see any manufacturer recalling/admitting issues with an engine after an oil change and certainly not publicly, if there were known problems maybe the dealers will be informed.


As for internet bullsh*t, iVe spoken to many customers who have some weird and wonderful tales that came from the internet.

Not that i'm knocking internet forums as you have probably have noticed i'm a member of one. I think they are a great source of information generally