A Damaged Piston.... but why?? **with pics**

[jacko-sti]

Hi everyone,

Ever since i bought my car, i've had this annoying ticking noise, so i've decided to give it a go and investigate/fix it.

i got the engine out the other day, and today managed to borrow the tool from my local Subaru dealership to get the the pins out to free the piston, and this is what i found:





ive been trying to work out what could possibly cause this and i think i've narrowed it down to a possible 3 things.

1. Det/Pinking (with it been a jap import i was getting extreme amount of det/pinking before it was mapped by Dynamix)
2. A bent rod.
3. A last owner has run it with little/no oil.

i've also noticed that the top piston ring isn't moving as it should, its kind of stuck in place where the score marks are. i'm guessing that if its been running like this for a while, and that side of the ring has been knip'd in, then the piston would be traveling off centre..... therefore catching the chamber wall. but what could cause this tho??


any ideas anyone??

many thanks

Jacko

[Ian200sx]

how did the block look? looks like its been dragging. could be from a heat problem. Is it round? could be lack of oil at some point or just a number of worn parts.

[jacko-sti]

how did the block look? looks like its been dragging. could be from a heat problem. Is it round? could be lack of oil at some point or just a number of worn parts.

well the inside of the chamber is abit scored but not too badly.

i cant see it been worn parts, as its only done 50k miles, but then again, i have no idea what sort of life its had before i got hold of it.

one thing i did notice the other week is that when i put really thin oil in it, to try flush it out, the ticking noise did get quieter, but then after a fresh oil change, it was back to normal again.

i've also fitted a new oil pump on as i didn't have the best oil pressure. but still the same ticking noise.

i wonder if i have a problem with the oil feed to it................ :? :?

[P20SPD]

I suspect that that piston/bore was running a tad lean, and given that some of the engines of your cars age, were built with such wide tolerances that meant that some were almost interference fit, you have the problem you have.

[Nige]

can you take a closer pic of the `black mark / indentation` around the top edge of the piston in the first pic ?

Looks very similar to det damage I suffered, the bits of piston then wedged down the side of the piston / bore and caused similar damage in my engine.

some pics of my engine damage. Much more serious than yours appears to be.... Caused by a failure in the mechanical injection system causing very lean running at high revs.

CLICK PHOTOS FOR HIGH RESOLUTION VERSION



removed pistons from the Bores. All big-end bearings are spot on, the tiniest of wear, very happy with them.

The bores all appear to have been unmarked, apart from No4 which has a small vertical line near the inlet side of the engine, I`m guessing a piece of Piston was dragged down the side. It is not feelable by finger nail and just by finger tip.


CLICK PHOTOS FOR HIGH RESOLUTION VERSION
No 1 Piston


No 2 Piston


No 3 Piston




No 4 Piston









No 4 Bore




The `line` has been highlighed by a torch from underneath, it was the only way I could get it to show up on the camera.

[Ian200sx]

the piston has dragged, it could be tolerance issue's but i thought that was a 96-99 problem (piston slap)? i thought det wrecked the top of the piston, rings etc not the whole top and skirt? If you've had oil presure issues then i'd go with blocked oil way or pump. take it to a good engine builder and they'll tell you.

[Mad Monk]

In the photos 3 and 4 look like they have melted, have they?

[Nige]

I`m not trying to confuse the issue and take this off topic. Sorry about that.

My pistons were damaged by running at high revs, for sustained a period (ie morning at donington on a trackday) with the AFR at between 16 & 17 on WOT.

I NOW know that was the AFR, at the time I had no idea. I have since fitted a wideband AFR meter which was used to diagnose the problem when I changed the engine and also to keep an eye on it in future.

I posted the pics so jacko could see what det damage looks like and compare to the top edge of his piston that all...

[jacko-sti]

cheers for all the replys guys, i think i found the problem anyhow, it looks like i had a blocked oilway, siting one of the bottom end bearings was a small bit of metal blocking flow of oil through the crank, therefore not supplying the bores with any oil, the damages piston was the last in the line, to get a supply of oil up the bore.

heres the weird bit of metal blocking the oil.


ive started the rebuild with all the new bits... it was like christmas opening all these



then i cracked on with the rebuild.

ACL big end bearings fitted and crack fully assembled



ACL bottom end bearings instaled, read for crank.


crank lined up.


other half of the block bolted on.



just missing the pistons now:(


ive got to wait untill i get the right piston rings as they sent me 92.5mm rings... not the 92mm i needed
:evil:

[RX7]

How much do the parts for a Suburu rebuild cost mate ?