Just to add to the list - have had no3 big end failure on 93` wrx - 53,000 miles - initially thought noise was piston slap but seemed to get more noisy when engine warmed up. have stripped engine down no`3 big end was worn through down to the copper - other big ends and mains were also worn heavily at only 53,000 miles i am very disapointed - especially as i have been told countless times that these engines are bullet proof!!!.

 

Any more info on the incident:
Did the car recently have an oil change? What oil did you use? Was the oil filter first primed with oil and the car turned over without firing? Did you have a high speed run prior to the failure? Did you maybe take the car up to the limiter?
Also what fuel are you running on? A standard WRX needs to run at least 98 Octane else weird **** can happen.

[Edited by b5m - 21/11/2001 06:25:43]

 

Isn't booting it from cold one of the prime culprits? (***** the rest of the motor, too.)

Richard.

 

How many miles had it when you first bought it, Dose it have full history[

[Edited by dfullerton - 11/21/2001 8:48:44 PM]

 

the oil was changed roughly 2000 miles ago - used castrol formula RS 10-60 fully-synthetic. Pre-filled filter with oil prior to fitting. no high speed runs prior to failure rather than failing suddenly the knocking slowly got progressively worse over a couple of weeks.
Have never `booted it` from cold until its up to temp., owned it since 45,000 miles with no prior history - looking at its bearings richard burns possible owned it befour doing all this years rally events with it!!!!!!!!.

 

Silly question, but what fuel do you use???

Tony

 

Do you have a seperate oil temperature gauge? I wouldn't assume that just because you have water temp at normal level means that the oil is up to operating temperature... although the oil warmer donut may help in this respect. My M3 gets full water temperature well before the oil temp hits 50deg c, let alone the 80+ deg c operating temps... good job BMW fitted an oil temp gauge... otherwise much wear could ensue as owners boot it before safe operating temps are achieved. The M3 manual supplement states that light throttle and 4000rpm should not be exceeded before the oil reaches at least 50deg c.

 

less than 55k miles on an regularly serviced, pretty standard engine? Jesus, these scooby engines are shockingly poor. Some std ones seem to last a fair time tho.

Agree fully about the oil temp gauge, i bought one for same reason.

steve

 

Steve, it takes around 4-5 miles in any car for the oil to warm up to its optimum temp, thus the reason i try to keep under 2500rpm til it is, also most scoob engines will last 200k, but if run on the incorrect fuel type ie, 95 ron in a jap import it wont last anything like that
What this does sound like is it wasnt slap, it was det but as we dont know what fuel the car was run on we dont know

Tony

 

possibly due to fuel - though dought it - did run it on 95 ron when i first bought it but changed to super and then to optimax after around 1000 mls. - looking at plug no`3 there looks to be significant burn out of the electrode - poss due to early combustion - then putting massive load throught the big end? - what is stange is that all the big ends are worn pritty heavily including the main crankshaft ones - possibly due to loss of oil pressure caused by no`3 failing.

this is a standard out the box 93 import no mods at all.

anyone else have similar failure if so how many miles.

 

possibly due to fuel - though dought it - did run it on 95 ron when i first bought it but changed to super and then to optimax after around 1000 mls. - looking at plug no`3 there looks to be significant burn out of the electrode - poss due to early combustion - then putting massive load throught the big end? - what is stange is that all the big ends are worn pritty heavily including the main crankshaft ones - possibly due to loss of oil pressure caused by no`3 failing.

this is a standard out the box 93 import no mods at all.

anyone else have similar failure if so how many miles.

 

dont have a separate oil temp gauge - but even when warm i dont drive the car hard only up to 6000 rpm.
55,000 miles driven hard shouldnt even be a problem though!

 

What would have happened is that No 3 failed but not so suddenly so you didn't recognise the noise, due to the low oil pressure, and continued running, all the other bearings have now worn badly and progressively.

Think back to when you really thought that you could hear something, then consider the sort of driving/drives that had occured in the run up to that point, it may well be that your problem does follow the pattern that has emerged but that the incident was largly not recognised as it was not a catastrophic failure at the time.

The Castrol is considered to be one of the "better" oils and certainly is used by some of the "heavy hitters" on this board. Although the oil filter was filled as part of the service was the engine cranked until the oil pressure light went out before it was started ? This can be achieved by unplugging the crank position sensor and the the engine will crank without firing. I would suggest that is an essential part of the "manual for minimisation of the risk of big end failure"

 

edited cos the phantom poster struck at me as well

what is going on ? I didn't even know that either of the posts had actually been made, the m/c just sat there and then timed out.

[Edited by Bob Rawle - 11/22/2001 11:03:04 PM]

 

Bob,

Interestingly, the subject about cranking the engine without firing
came up in recent conversation. I would agree that in certain circumstances this is required, but I can't see how it would make any differance after an oil change.

My reasoning is this, what would be the differance between starting the car after an oil change, and starting the car every morning, after the oil has drained into the sump overnight. This assumes that the oil change has been done correctly, with the filter being pre filled.

Having had the oppertunity to look more closely at the various internal parts of our engines, the one part that really worries me, is the oil PRV.

IMO, it's a very poor design, and more than likely to fail at some point in time, even if only for a very short period of time (fractions of a second) before it starts working again. Over a period of time, this would certainly cause premature baring failure.

Mark.

 

Hi Mark long time no hear, when you change the oil you remove the filter and release oil from places where it would normally stay if just stood over night, i think you would agree that all precautions are sensible when it comes to this sort of thing. The PRV is one of the things that is easily modified though (reminds me to ring J about those shims. If the PRV sticks open though, it would, of course, possibly explain some of the cases where big ends have gone after a fast drive and following a slowing down, stuck PRV = low oil pressure at lower revs but it should still be holding tick over pressure as a minumum even so. If it fails stuck closed then high oil pressure and possible blown seals would be the result so only loss of oil would cause bearing failure then.

BTW for the un-initiated PRV equals Pressure Relief Valve and its basically a hardened steel punger backed by a coil spring that is designed to be pushed open and off of a valve seat to limit the oil pressure. There are some sharp edges on the plunger which could dig into its guide causing it to stay stuck in one place. The simple solution is to remove the plunger and polish the sharp edges off then replace it with an extra shim fitted to increase the spring pressure thus increasing the oil pressure, about an extra 0.5/1.0mm will increase pressure to 7 bar from 6 bar although, depending on tolerances, some cars run this high anyway, mine runs at 6.5 bar for instance.

I spend many boring drives watching the oil pressure guage and over 2500 rpm it never moves from 6.5 bar, below those revs its proportional to the actual revs thus indicating that the PRV is fully closed but that the oil pump is not spinning fast enough to make the pressure to crack the PRV.

[Edited by Bob Rawle - 11/23/2001 5:42:54 PM]

 

Bob

Surely the PRV must be capable of flowing a large amount of oil so as not to exceed the maximum pressure (ie if it has reached max pressure by 2500 rpm, then at 7500 rpm the oil pump is presumably flowing 3 times the oil volume, but 2/3rds of it is being bled straight back to the sump. Therefore if the PRV stuck open at 7500rpm, then there would be almost nil oil pressure when the engine returned to idle.

IIRC the original thread on this said that there had been no cases of No. 3 bigend failure on an engine that had been rebuilt - would the sharp edges on the PRV plunger usually be removed as part of a rebuild, and hence the PRV would not stick again??

Presume that No. 3 bigend is the farthest bearing from a direct oil feed and hence this is always/usually the part that fails.

Seems to me that there is a lot of logic to this explanation. I suspect that by the time an engine had been removed and stripped, the PRV would likely have unstuck itself, hence no evidence of why the engine blew.

Bob - just how easy is it to get to the PRV and sort this?

Dave

 

interesting point about the PRV - I will strip it out and look for scores in its bore - andf sharp edges - will keep you posted.

- incidently when main dealers service these cars do they pre-fill the oil filter and crank the engine untill pressure is there befour firing ?.

 

The PRV only has to "crack" to control pressure, it does not need to flow a large amount of oil, given that the idle pressure and flow should not be overly influenced by the valve being opened.

The pump will flow 4.2 litres/min into 1 bar of pressure at 700 rpm, at 5000rpm it will flow 42 litres/min into 3 bar of pressure. The relief valve has a pre-load of 7.86kg assembled, if someone with an engine in bits (Mark or Pat ?) can measure the seat diameter then its possible to calculate the deflection and flow thro' the valve at 6 bar pressure. The relief valve will open enough to bleed excess flow back depending on the "resistance" to flow of the bearing system in the engine.

No 3 big end is no further from the pump than any, in fact it is equi-distant with No 2. there is no evidence to suggest that no 3 suffers any more than any other from what I have seen and been advised of. No 4 actually seems to fail more than no 3.

Interestingly the oil filter itself (official Subaru ones that is) has a bypass valve built in which operates and opens at 1.6 bar.

The oil pressure warning light is only good at telling you the ignition is on and the engine is stopped as it is set at 0.15 bar.

Its relatively easy to get at the PRV, remove the timing belt covers and its accessable behind the centre one lower right of the toothed crank pulley.

 

still have the engine stripped to bits so will strip the complete oil pump - cheers....

 

Hmmm

Had an interesting conversation with 2 Scooby owners last night in Brum... One had not heard of Scoobynet the other had, but had never accessed it..

One commented on the No 3 Big end failures... He had seen quite a few, after modifying a few Scoobies... Was a bit upset when he saw my engine bay.. that I did'nt have an oil cooler!

He said they had sorted out the number 3 problem... it was due to oil pressure problems and oil temparature. The problem had been minimised by putting an oil cooler on....

 

So how do they fix the oil pressue problem? Is it possible to replace the standard unit with one with a higher pressure threshold? Take the lowest the pressue should be and get a sender just below that? If your pressue drops at high revs(normally 6bar?) would this be too late?

An oil cooler should only come in when you really give it some stick. So if you have an oil temperature gauge and it never ever goes above 110C then you should be ok? If I remember correctly most oil coolers only operate due to the thermostat at about 100C? Most oils work correctly between 80C and 100C.

[Edited by b5m - 11/27/2001 7:55:02 AM]

 

Even my MY86 EA82T engine has got an oil cooler, so I'm a bit surprised that some EJ20Ts do not. In every turbo charged engine, the oil will heat up fairly quick, and will continue to do so even during 'normal' use, hence the need of a cooler. Thicker, more heat resistant, oil will also help to cure the problem.

Problems with 3rd cylinder seem to be temperature related, as I have also seen them on NA EJ20s, especially when they run on LPG. The comment about the burnt electrode also hints at this.

Marnix

 

The engines do have an oil cooler, its installed directly over the oil filter and is an oil/water type. it also acts as an "oil warmer" as the engine warms up.

Oil pressure can still be over 2 bar even with a big end gone, normal pressure is 6 bar plus. (oil pressure warning switch is set at 0.15 bar)

 

just to update you all - have stripped the pressure relief valve its bore is unmarked and piston moves freely in it -

interesting comments about oil temperature related.

 

Has anyone modified the fuel line to a parrallel set up instead of series feeding the injectors? I saw a thread which detailed this as a possible safety measure to aid fueling to the problem cylinder.

F

 

Which cylinder do you think is a problem ? Its not no 3 (clue) least not on pre MY99 cars. Actually the leanest cylinder pre-MY99 is actually no 2, this is due to the inlet manifold design. Post that they run pretty much the same. (observations having looked at lots of spark plugs). Parallel rails controled by a single regulator are ok, separate regulators need to be perfectly matched otherwise different fuel pressures occur in each rail.

 

Bl**dy marvelous...
Without any warnings my STi 5 cut out & it seems I am another person that has had the big end failure. No one can look at it until the new year. Was wondering who else has had this happen to them & the likely costs involved in repairing the problem.

Not sure what number has gone until it is stripped down.
Can anyone recommend adding any other parts to try & stop this happening again (ie oil cooler etc).

I only had the car 8 days from the dealer & am expecting them to sort out the problem. Was driven as my STi 4 had been. Always waited for temp to be okay & also 4-5 miles to be driven before opening up the revs.

Im totally gutted.
Andy.