Big ends gone, what could be the cause?
 

Drove to work as normal on Monday, started the car to come home and got the engine knocking :cry:. Bearings gone, the thing is I don't thrash the car, I have my two toddlers in the back 99.9% of the time, I change the oil regularly and it never loses any, the dipstick level never changes. The oil warning light has never been on and the temp gauge has never been above normal. A mechanic told me that this is a common problem and it's always on number three, something about being closest to the turbo and can't take the preasure . Is this true?

my big ends went on my last car due to my thermostat packing up

what car year/ model / mods ?

I say the turbo thing is just a bit of a old wives tail IMO. As there are a number of culprits. The common causes are as follows:

I'd say it one of a few things; a faulty/stuck oil pressure relief valve. Which doesn't really cause a problem, but over a prolonged period of years will cause increased engine wear.

Or. The oil pump cover screws have come loose, which causes pump cavitation and a loss in oil pressure and flow. Again over time this will not be immediately apparent, as it causes increased wear.

The other cuase is a fueling issue. Normally air flow sensor, but a failing fuel pump, air leak on the pick up pipe in the fuel tank (uaully happens if the fuel pump has been messed with or swapped), or clogged pick-up filter or clogged fuel filter or faulty injector etc.. All of this can cause lean running scienarios which causes detonation, the shock load on the pistons when this happens puts more strain on the big end bearings and hence they wear out.

Its likely when you strip the engine, the other bearings will be found to be worn past their prime. It just number three went first, but the other bearings will be on their way out too.

Its a 2001 bugeye WRX, Milltek sports cat downpipe to straight through stainless exhaust, K&N panel filter, uprated fuel pump and mapped to 281bhp.
Fuel pump and remap were done about two months ago and seemed fine. I don't want to get it back after the rebuild for it to go again because the cause is still there, could it just be normal wear and tear?

Oil pressure relief valve was changed at 63000 miles , now at 75500, the fuel pump looks the favourite out of these but the mapper changed the fuel pump before doing the remap so he would have heard any det while he was mapping. Is there going to be a definite cause or can they just go, I'm not going to want to drive the thing when I get it back.

you want it to run >30% increase in BHP and wonder why something goes wrong. engines have a finite life span. only so many revolutions, only so many combustions. taking and engine out of spec (albeit safely) will decrease the life of an engine.

On the other hand, sh1t happens. you bite the bullet and put it down to experience. get someone who know what they are doing with a good track record for building engines but even the best sometime don't know why an engine calves itself.

for example, taken from another thread and i know David wont mind me using this.

:o

Couldn't agree more. It is the risk you take when modifying an engine, no matter how well it has been done, it will shorten the engine's lifespan.

Was it faulty then? If it was, then the bearings may have suffered increased wear and tear in the duration before the PRV was replaced, also seeing the PRV is part of the oil pump casting, so if that was not changed (unless the whole pump casing was replaced), was the bore that the PRV runs in checked for wear and smoothness and to ensure the valve moved freely without binding?

Sorry, my mistake, it was the crankcase pressure valve that was replaced as part of the 60k service not the oil pressure relief valve.

Sorry, you made a mistake IJED2, an wrote mechanic instead of bellend in overalls.

Number 3 is near a turbo and can't take the pressure? Utter Sh!te.

Infact, I can bet this is the only reason yer big end shells didnae f@ck up.

is this something that it changed as standard on a 60k?

No.

Tony:)

Thanks for the reply, it was the first time id heard of it needing to be changed as part of a service so wanted to double check :)

Didn't find the cause of the big end failure and it wasn't no.3 that had gone it was no.1 so i'd agree that the 1 closest to the turbo is bs. The bearing failed on startup though and I wonder if 10w40 is too thick for newage?

closest to the turbo on the impreza engine im not 100% sure if anything in that but i can confirm it is the case with the c20let vaux engine so may not be total rubbish

i wouldnt have thought 10w 40 would be too thick isnt that what subaru recommend, i think they even say use semi-synth, what do they know, i always use the best i can get like millers fully synth 10w -50

as for the comments about your engine as been tuned therefore it will break is bollox mate, you were only running 281hp, tuning isnt the cause as long as it is done properly.

there are lots of possible reasons ,ie sticking relief valve seems to be the common one, another one is the in series fuel rail causing det on usually no.3 or 4 piston.tbh whatever it is its a design flaw in someway, i ahve had alot of tuned jap cars and its only subarus that suffer from the big end problems and what makes it worse is they are a b`tard to change compared to a normal engine where you can just drop the sump.

oilman )opie oils recommends 10x40 in many cases for newage, im running 270bhp and he recommended it for me. Im using Fuchs 10w40 esther based oil. seems ok in mine

Two schools of thought with this:

Subaru actually reccomend 5w-30 for a newage WRX. (contrary to what is often said on here - its in the owners manual if you don't believe me). Old shape classic Imprezas say 10w-40 in the manual, so this is where mix up happens.

However, it also says its not advisable to use 5w-30 if the car is used in harsh/adverse conditions (harsh/adverse = ragging it ;) ). Anyway 10w-40 is acceptable, so should not be an issue, and plenty of scoobs use this grade of oil without a problem - mine included, however in my case it was changed every 6 months regardless of mileage.

A better alternative is 5w-40 which has the best properties of both oils (maintians hot viscosity like 10w-40, but also on par with 5w-30 when cold). But this opens up another cans of worms in the oil debate.

Anyhoo, the bottom line is the oil should not cause a problem; so long as its been changed regularly throughout the engine's life (which is why old invoices are like gold to people buying a car second hand, a stamp in a book doesn't mean much IMO).

I've just read a post by oilman were he recomends 5w40 for newage and as mine failed on startup I think thats what I'll go with, thanks the the advice. :)