Cosworth 2.5 engine problem
 

Hi guys,

Had a bit of a disaster at the end of November.

I think I’ve done a big end bearing, and I wonder if anyone can come up with any ideas as to why. Here’s the car spec –

’04 STi JDM model, a year ago I had the engine converted to a 2.5, using the crate Cosworth short engine, with STi crank. It has the usual goodies; Simtek ECU (which incorporates a knock sensor), FMIC, K&N filter, cold air inlet pipe, etc.
It has the standard VF37 turbo, running about 1.7 bar boost, and around 390 ish bhp.


I carefully ran it in on good mineral oil for 1500 miles, no more than 0.5 bar boost, no more than 3500 rpm, no more than 75 mph.
I then changed to Shell helix semi synthetic, and had the thing mapped by Bob Rawle. He set the rev limit to 7000 rpm (until I’d done 4000 – 5000 miles).
I still didn’t give it any major beans until I’d done 3000 miles, then changed oil to Silkolene 10w 50 full synthetic.
I never did get Bob to increase the rev limit, as it had so much torque that I never felt the need to scream the nuts off it (even though the factory motor was set at 8250 rpm).
I have never let it get low on oil, and I always get the oil temp up to around 70 deg. before I drive it hard.
I have done only one track day, but never did more than 5 or 6 hot laps at a time, cooled down for 20 mins or so, before the next few laps.

At the end of November, when the first snow came, I took the car out to run an errand, and the knock sensor kept flickering. I turned off the stereo, and noticed a little of that ‘London cab’ noise when pressing the throttle. I gently nursed it the 2 miles back home, and it has stayed in the garage since.

The car had done 7000 miles (including the 3000 running-in miles) before the trouble began.

Anyone else had problems with the Cosworth engine?
Any clues as to what may have caused this (if, indeed it IS a big end bearing issue – could it be something else, such as a snapped rod bolt?)

Any input would be welcome, as I’m bloody pi**ed of that I’ve spent so much time and cash trying to make it as bullet-proof and reliable as I could, and something which should have been one of the toughest components of the engine seems to have failed.

without stripping it down to find out you won;t know, any guessing is pure speculation.

who built it?

Cosworth.

o off the shelf engine, i get ya.

Oil surge from track use, cracked oil pick-up pipe, faulty oil pump..... the list could be endless?!

As said... it needs to be stripped or at least taken to a specialist to diagnose.

So you track'd it on a running-in map ?

If it was a snapped rod bolt, I would suggest you would not have much of a crank case left! :D

Thanks for the comments, guys.

Yes, of course I will be getting it to a specialist to strip it and diagnose the exact problem, I was just putting a few feelers out to see if anyone else had experienced similar problems, and more specifically, with the crate Cossie lump.

Dunx - no, it was properly mapped, but Bob put the rev limit at 7000 rpm as a safety margin from the 3000 mile point until I'd done 5000 miles, but as I said, I never felt the need to have the full 8250 rpm limit reinstated after I'd done the 5000 miles.

For information I spanked the backside off my 2.5ltr Cossie lump in my previous Spec C, running more power (ranging anywhere from 460bhp to 600bhp) for both public track, competition track and road use for over 3yrs. It still lives on today with the new owner (it will have run for 4yrs in April 2011).

Never "rumbled" a bottom end in that timeframe, but I suspect anyone of several things could of caused your accelerated wear on the big ends, if that is what the actual issue is.

Hope you getting it sorted out. :)

As said she needs a proper teardown. Your running in procedure was far too light IMO not that it would affect your bigends, but deffo affect your oil consumption.

What a nightmare dude. Where about are you from.

I presume its knocking? I dont recall you saying it was, apart from the knock sensor flashing away which could mean a bad batch of fuel.

The Cosworth engine should be bullet proof if tuned safely for this power level, as Shaun mentions, they will happily run 600+bhp.

Best get a second opinion on the noise.

Andy

would that be the case 2ltre heads on 2.5 short engine?
Trev

2.0 JDM heads/cams are ideal on a 2.5. That's what I've been running on my spec C for around 3 yrs now at circa 500/500. Trackdays, scoobysprint (winner) 11.0 1/4 mile times and around 10,000 miles per year on the road.

Andy

AVCS ones?

Andy, when using this combination, do the heads need to be machined to match the bores and does the squish area of the heads need any modification?

What turbo are you running on your Spec-C these days or is it still on the 321T?

Cheers
Richard

Ideally JDM AVCS for a wider powerband than non AVCS. Yes the combustion chambers should be modified but I wouldn't modify the squish area.
Still on the 321T with additional porting work and 15% meth.

cheers

Andy

As said I would get a second opinion on the noise. It doesnt sound like you are describing big end failure. You know that noise and it is sickening and brings you out in a cold sweat.

If the noise you are hearing is detonation then there could be some kind of issue with the fuel system, but needs investigating urgently. Does the noise go away when not on boost?

Ain't that the truth!

You get panic attacks, short sharp breathing and a sick feeling (a bit like how I'm feeling at the prospect of going back to work tomorrow :()

£,£££ signs flash before your eyes too. :(

Hiya,

Unfortunately it is the big end bearing (no. 4) that's shagged. The crank is buggered too, so will need a new one, as I've been told not to bother with a re-grind.
Does anyone know if the Sti (non-billet) crank used in the Cosworth engine is nitrided?
Anyone have a good deal on a new crank and ACL race bearings?
Any ideas how to stop this problem happening again? Been told it was probably oil surge that caused it, but shouldn't the Sti baffled sump prevent that?

Dejectedly yours,

Andy :(

Find cause of the failre. Its highly likely to be a build problem or tolerance issue.

I'm guessing air in the oil supply. As Shaun mentioned that could be anything from oil surge to a pump seals, or issues with the pick-up pipe.

I've damaged an engine (I caught it before it started knocking) due to a faulty oil pickup gasket...it was sucking in air and draining down overnight. Every cold start after standing, the oil pump had to re-prime - that 5-7 seconds of faint clatter on every single cold start was the giveaway clue that something wasn't quite right.