Subaruspike

The engine from my 1998 sti type R has just died and after opening it up, it looks like a some bad detonation has been going on. Anyone any ideas what could cause it ? It's always been run on SUL and I always thought it was running pretty rich, but then this happened
Take a look at the pics and if anyone has an idea what might have caused it, please let me know. It's cylinder 2, not 3 as usual ! Any opinions gratefully received, as I don't want the same to happen to my new engine !

Thanks

ustolemyname??stevieturbo

iTrader: (1)

possibly dirty fuel filter causing weak running, inadequate fuel pump?? while you are using SUL, the japs fuel is 100 octane, while ours is only 97. That in itself is certainly enough to cause destruction especially if mods have been done to the car.

dhorwich

The square you can see is the cut out on the top of the pistion mate...

Dan

rjben

Still confused...I obviously don't belong on this forum..I'll stop know.

dhorwich

The piston is round and has a slight square indentation on the top... most pistons have cut outs on the top.... some have 4 valve shape indentations on so if the cam belt snaps the valves dont hit the pistons..... although they still often do....

Dan

dhorwich

The other 2 pics are of the bottom end.... ie the block with pistons in situ..

Dan

gossythevaleter

Unlucky m8
I run a uk 98 only run it on optimax with NF running at least 102 ron

Pete Croney

I'm inclined to agree with Mark.

Although the piston looks burnt, particularly the bit just down from the missing area, I would expect to see piston material welded on the bore where it had gone, if this was the case.

The pictures aren't great, can we have a picture showing the bore along the line of where the material is missing.

It may well be a combination of the two... burnt and debris damage.

Had you used the car at very high rev's/very high speed before it happened?

BugEyed

Ouch! Looks expensive.

Like Mark and Pete I think it looks more like a piston failure than det. Have you got the pistons out of the bores, or are you "just" replacing the engine? If it is the piston that has failed and you are rebuilding the engine, you need to check out why it happened. Some more photos will help with the diagnosis.

Good luck.

Duncan

Subaruspike

Thanks for the feedback guys. I'm replacing the engine, but am still kean to find out what happened in case the offending component is still in there somewhere !!
Just prior to it letting go I had been cruising on a motorway at 60 ish (morning traffic) for 10 mins, then had given it a bit of a boot up a hill to blow out the cobwebs. A loud clattering noise soon followed .
The engine is still at the garage where the new one is being fitted, so I can't get any more pictures or info at the moment, but I should have it back on Saturday so will post more info and pics then. Thanks for the feedback.
Any ideas what might cause the piston to let go though ? Is it purely down to bad fuel ? Your piston blowing diagnoses certainly makes more sense than detonation, as there is no obvious detonation on any of the other pistons. I'll post more info once I get it back, Thanks.

R19KET

Is the car stock, or do you have any other mod's. What plugs are you using. Have you checked no.2 plug, and the oil PRV yet ?

Mark.

Subaruspike

Car is stock except for decat exhaust.
Other questions will need to wait till I get the bits back. From memory the plug was all oiled up, but then that probably happened after the event. I'll check Saturday.

mrkimpreza

Seems like the same as happened to my engine. Check the MAF sensor, injectors (have them checked and cleaned ultrasonic), 02 and check a few times with select monitor / DeltaDash with the new engine before you trash it.

Check the plugs as well for an indication of lean/rich running and have the oil analysed.

(In my case injectors checked out ok, so as the o2 sensor, oil indicated must silicon polution due to open air filter (induction kit) and some fuel (indication of running rich an average).

The engine was rebuild with a new short block and same sensors. During the running in period everything was fine, then we compared the readings of the (old) MAF against the a new ONE and the voltage the old one gave was to low (4,1 vs 4,3). Consequently there was coming more air in then measured and it was running on the lean side. Most probably this failing MAF (due to open air induction kit) was the reason for my engine failure.

Moral: measure it, only then you know. My old and new engines were running perfectly on the old MAF (until my old engine blew offcourse :-(

Mark.

Mark.

rjben

Real dunb question!!

I can see that the top and bottom pics are looking up at the under side of the head, but what the hell are the other two? Looks like 2 square pistions to me? Never seen square pistions before????

Cheers,

Rob

[Edited by rjben - 5/8/2002 9:57:37 PM]

R19KET

It's a little difficult to tell from the pic's (plus my laptop screen is cr*p) but to me, it looks like the piston let go, and what "looks" like det', is actually where the piston debri has been smashing up and down in the cylinder. It's also common to see this type of damage to the squish area, when this happens.

I suspect that the piston has picked up in the bore, in line with where the ring lan is broken, and you can see the ring. If you turn the engine over, until you get BDC on no.2, you should get a better idea.

Edited to say: I'd also check the oil PRV, to see if it jammed, and what colour was the no.2 spark plug ?

Mark.

[Edited by R19KET - 5/8/2002 11:52:39 PM]