the shreksta

iTrader: (20)

before i bought my impreza i was so scared after hearing horror stories of the bottom ends going,what causes it? my car is a 54 plate wrx and at 58k when it was only 5 years old the bottom end went,the car had regular oil changes BUT everytime it did it was given a flush treatment

it was then fitted with a brand new sti bottom end with a cosworth high pressure oil pump and since that has had no flush treatments

im just wondering what causes them to go as its quite common,is it neglect/thrashing from cold/poor oil used/faulty or poor parts used on the engines

ianbott

Combination of many factors really, I'd suspect it's poor maintenance or neglect ie not warming up or cooling down correctly.
However many different cars receive the same neglect and lack of maintenance but don't seem to suffer from the bottom end knock, the flat 4 is a great motor and very compact but in making it small also made the bearings very small too. On a normal 4 pot engine the bearings would be much bigger giving more support to the crank. I'd guess this is a big contributing factor.

By the way this is all just my own opinion I'm sure others will differ.

the shreksta

iTrader: (20)

thats another thing i dont really get,warming an engine??? should it be left on tickover to warm up or driven off boost for a few miles,surely leaving it on tickover is not the way to do it?

blackvenom

My classic engine is now 13 years old, no issues so far

blackvenom

Mine maybe warms up for 1/2 mins while I put the seatbelt on and choose my music. Then I drive it off boost for first mile or till the water and oil are warmed up.

tubbytommy

iTrader: (20)

oil will take far more than a mile to warm up, more like ten to fifteen minutes on my oil temp gauge in the winter

the shreksta

iTrader: (20)

from starting my car @ 4am its literally a few seconds until i drive off,never go over 2500 rpm tho until warm which i will say is about 6 miles of driving buy then im at work so really my car doesnt use boost until the weekend

ianbott

As above really drive it sensibly for a good 10 mins or so then thrash away lol.

stvscooby

you should not use an engine flush in a scoob

Lee225

iTrader: (1)

I was always told to never flush a scoob engine, kills the bearings apparently!

AndyBaker

Same here, start it up get going and then It's about 6 miles to Bingham and then give it the beans . By the way this is my 4th scooby covering a classic, 03 wrx, 55 plate STI and the S202. Never had any slapping or knocking in any of them and they are driven

topshot

iTrader: (4)

as said before, poor maintenance, driven hard when cold, crap fuel.

I idle mine until water is getting up to temp then drive keeping off boost until oil is warm.

Lee225

iTrader: (1)

Would crap fuel cause bottom end failure?

ianbott

Nearly all manufacturers will recommend driving off straight after starting to aid in warm up times, if you leave it idling it will not warm as quick causing more damage.

Can cause knock which will cause bottom end damage.

Lee225

iTrader: (1)

Surely you need to get oil round engine before driving?

ianbott

Oil will be circulated around the engine within seconds of starting.

ianbott

The quicker an engine warms up the better, most engine wear occurs during the warm up process so if left ticking over for too long the oil doesn't protect at it's best.

wms-racing

It's a design problem, the cranks ony have very narrow big end bearings, the bearings are only 16.5mm wide, most inline engines have bearings 20mm+. Although you can help the engines by warming up properly and using good oil etc, its inevitabe that they don't last as long as other engines. Ive just done 2 hatch STI engines, both mint with FSH, one 28K one 34K, both had bearings worn to the copper! Caught them both in time though.

topshot

iTrader: (4)

Depends, would you rather drive a cold engine under load with cold oil or idle for a bit with less load on engine?
I dont wait until oil is at operating temp but i dont drive off straight away either.

ianbott

Yeah I agree to a certain extent. As somebody else a bit further up said, I will start the car clip my seatbelt select the music the drive off, not instantly after starting but I maintain the letting the car idle causes premature wear on components.

Primeiro

The main causes is poor baffeling in the sump.

Oil surge is an issue & recomend to anyone to go for a baffled sump with uprated oil pump, new age pick up pipe. The group n sump works very well and can be done to your excisting sump if funds are tight ( aslong as sump is in good condition).

Subaru's that get thrown around alot eventualy will suffer and the big end bearings take the hammering, poor fuel and mapping doesnt help either.

Look after your engine and thats the best you can do, otherwise uprate and prevent it never happening.

Keith Collings

iTrader: (3)

Timely thread for me. I have a 2003 WRX - never tracked and Oil/filter changes on time with no flushing. Car has just passed 125K and has been problem free since I bought it new.

Just recently on start up, I've heard what I though was big end knock. It does not happen most times on start up and always passes. It was enough to get my attention though

I've assumed that once the big ends go - they go permanently ?. Or is it possible I am hearing the early signs of failure on intermittent occasions ?

Turbotits

iTrader: (2)

Fron your description. This sound more like piston slap. Its unlikley big end noise will go away. Once there gone there noisey. Piston slap is pretty common on cold start and normally disapears quickly after start up. Normally nothing to worry about

scoobypartzuk

going round corners fast is common problem as oil gets chucked to one side best to run dry sump

Keith Collings

iTrader: (3)

Thanks - I was thinking that but it's a fairly strong noise and I thought slap would be a lighter noise. You've confirmed my thoughts on when big ends go - it's permanent.

Every day it starts without odd noises is a good day

the shreksta

iTrader: (20)

will forging the engine reduce this problem or not?

Primeiro

Forging the engine you are using stronger quality components but will not stop the oil surge which is the main factor.

Uprated sump with baffeling & uprated oil pump helps the matter, the ej wet sump engines store oil in the cylinder head when running & with poor sump baffeling this becomes an issue.

Yes dry sump will eliminate this condition but in the real world 99% of everyone will not be buying a dry sump kit. Grp N engines (built them @Prodrive) run a standard sump which is modified for improved baffeling & in rally conditions this does the job.

If you are modding your engine or wish to do a mod to improve then I highley recommend the grp n sump/pick up pipe & uprated oil pump. Uprate your breather system with a return to sump & it will do the job.

Just to add that detonation is a factor aswell/poor mapping/fueling so these areas as I am sure you guys are aware need to be covered.

dj219957

cough cough