Hopper

My '04 WRX PPP Impreza has recently suffered such a failure despite having covered only 36,000 miles and with full Subaru service history.

It has been suggested that the recommended oil change procedure performed at services could be to blame.

I have written to Subaru UK and have now received their response in which they state that such failures are not an area of concern and offer no explanation why mine should have gone within 200 miles of it's last service.

I would be interested in hearing from anyone else who has experienced such a failure in similar circumstances, so that I can determine whether mine is an isolated case as Subaru UK claim or if it may be linked to oil change procedures as suggested elsewhere here.

https://www.scoobynet.com/general-te...rious+knocking

JohnD

iTrader: (5)

I'm led to believe that the big ends are the main culprits, the mains suffering less less problems. You state "main bearing failure" Is it in fact the mains, big ends or both?

JohnD

Hopper

John, it is big end failure taking out the crankshaft it seems.

Have a look at the link at the bottom of my message 'Serious knocking noises' for more details.

I am hoping to hear from anyone who has experienced a similar failure so that I can determine how common (or otherwise) it is.

BTW What is the difference between main and big end bearings? Excuse my ignorance.

Splitpin

The main bearings are the ones that support and locate the crankshaft in the block Hopper.

The big end bearings are the ones in the big ends of the connection rods - and so are connecting the crankshaft to the pistons.

If you're looking for further evidence of cars suffering this issue after oil changes it'd be worth clicking search, although I'm not far how back the Snet search engine allows you to go. Otherwise, if your car is at API, it'd be well worth having a word with David about the frequency with which he fixes engines under such circumstances.

Incidentally - Subaru UK may be justified in their characterisation of this as an "isolated case", at least as far as they define the terms. As per prior posts, I fully believe this to be somewhat of a lottery, and, the bottom line as far as International Motors are concerned is that unless the failure involves a warranty claim, in many cases they would not even hear about issues like this - as the garage who fixes the engine will simply take the money and move on, probably without even thinking too much about the "is there something we can do to prevent failures like that?" question (especially when they're taking the money for fixing them).

Without someone doing some pretty advanced and expensive scientific analysis it is impossible for any of us to know for certain what is happening - and how statistically likely (or otherwise) bearing damage resulting from change-related starvation is - at least without going out of the way to prevent it. It may well be that it's a 5000 to 1 chance, or some other equally small probability.

Doesn't make you feel any better when you're the odd one out, but they may, ultimately be right, at least as far as their definitions of acceptability are concerned. This doesn't change the fact that following the "extended" oil change recommendations may significantly reduce the chances of owners sitting there disappointed though.

APIDavid

iTrader: (4)

It ain't isolated cases at all. I probably get at least 3 phone calls a day [ seriously I DO ] about someone wanting a new short motor 'cos the big ends have gone.

All ages, all models. The big ends are a serious cause of problem on any Subaru turbo engine.

David APi

Hopper

Splitpin,

Many thanks for your continued interest. I think the last message from David at API indicates that it is far from an isolated case though.

As you rightly say, if all they have to go on is warranty claims it may be that they are being misled as to the numbers affected.

For that reason, my next letter to them will ask the question of how many short blocks and crankshafts they supply to all sources.

Presumably they will have records relating to that and it may give a better idea.

I just feel that if a simple change to the recommended oil and filter change procedure helps to prevent other owners suffering the same fate as me, my efforts will be justified.

Thanks for clarifying the difference between main and big end bearings by the way.

I have learned a lot since posting on this site. It is a darned good forum.

Regards

New_scooby_04

iTrader: (4)

David,

Out of curiosity: why, in your opinion, do these seem such an issue on Subaru turbo engines? Is it inherent in the design of the engine; cost cutting on parts; not a problem with the design/materials as much as vulnerability inappropriate servicing or abuse? Or all of the above!

FB Tuning

iTrader: (30)

The width of the shell is a major issue - The Subaru bigend shell is narrower than those found on a lot of Sports motorcycles

A little bit of oil cavitation/starvation or a bit of detonation, and it's bye bye shell + crank

Splitpin

See my theory in Hopper's other thread for part of the story. As per Rich's comment, the horizontally opposed design allows the cylinders to be staggered, which makes for a very compact engine along its "long" axis.

However, the downside is that it greatly limits the amount of space available for the bearings, when compared with an inline four cylinder engine of similar capacity and potential power output. The narrower the bearings, the greater the load per square centimetre - and so the easier it is for any interruption in oil pressure, or abnormal/shock load, to result in damage.

JohnD

iTrader: (5)

The first time I saw a Subaru crank on the bench, I thought "my God, why are the journals so narrow" Does the engine need to be that short? An extra 5-6mm on the bearing width would result in the engine being only marginally longer? It's not as if 2 con-rods share the same crankpin eg. V8
I wonder if ever Subaru produced a brand new flat4, there would be a noticable increase in bearing area?
How does the journal diameter compare to other 2-2.5 litre engines?

JohnD

APIDavid

iTrader: (4)

All, It is a combination of many things that cause crank failure in a flat four Subaru engine.

In no particular order;

Age/mileage. UK cars with high mileage usually fail for knocked out big ends -
eventually.

Lack of maintenance, generally Japanese engines don't like being treated like Vectra or
Mondeos, that will go forever; missing oil changes and being abused. The working
tolerances in any Japanese engine are much better than European cars and don't
like being mistreated.

Det: particularly JDM versions where the map is set for Japanese ambients and humidity.
The top mount doesn't help in this department. There are many long threads
running about TMIC against FMIC. Don't let's start a new one here.

Fuel issues: They run better on V Power or Tesco than anything else and do more miles
to the gallon. Despite the handbook saying 97 is ok, technically it is true. BUT
Super prolongs engine life, creates more power and does more miles to the gallon.
Running the tank low doesn't help the fuel issues. I bet that of all the cars in here
with busted engines, very few of them have much fuel in them. Some are even on
the red light. At which point the system picks up air rather than pure fuel and det
starts.

Oil pumps: Contrary to popular opinion, The oil pumps don't fail as such. Mostly the
problem can be attributed to the keeper plate on the back of the pump coming
loose and weakening the oil pressure as the engine ages. The bolts are rarely
loose at the first cam belt service, but usually are on the 2nd. It afflicts earlier
cars much worse than New age cars. Then there is the amazing oil pressure
relief valve, that can function perfectly until you do an oil change, at which
point it decides to stick. Bringing bearing failure soon after an oil change.

There are more obviously but that'll do for here.

David APi

New_scooby_04

iTrader: (4)

Very educational; thanks mate

David - Yep, I figured those factors might be instrumental, but nice to have it confirmed by someone who sees more broken flat fours than most!

I had someone approach me at a petrol station the other day (whilst I was checking my oil level) as it happens. He was really nice about the car, but said:

"I'd have one, but I know a few mates who have em and have blown engines"

My response, well this one is running about 340-50bhp, similar torque on std internals and has never missed a beat in 5 years. He asked me what my secret was. My reply included the following

- It's not on mega miles
- It's serviced regularly by people who know Subarus with the best quality consumables
- It's been modified properly
- I don't drive like a dick i.e. thrashing it from cold
- I use the best petrol
- I don't run the petrol right down to the bottom of the dial.

Some do break without any abuse/mistreatment, no doubt, but I've been to enough meets to be of the opinion that the driver is a big factor in a good percentage of Subaru failures