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So I Pulled My 26 Apart Today..

femno

By femno,
in Engines & Forced Induction

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femno Grand Master

femno

Posted
Posted

Hey all,

After having an intermittent oil burning and low comp problem, today i pulled apart my engine.

I found an unacceptable amount of piston slap on all cylinders...

Number 6 top ring came out in about 3 pieces. This would explain my intermittent comp.

Number one ring was split in half.

All of the rings looked like this, the rest intact apart from 1 and 6:

Cross section:

post-17897-1190018986_thumb.jpg

All intake components are spotless, free of dirt etc, cooler was cleaned when engine was built. HKS pods.

When the car was tuned, the tuner advised me that the knock sensors werent working, as they heard knocking during tuning and had to take boost out, it didnt read knocking on the pfc, but the tune was fine.

All ring lands are not broken, acl pistons and acl steel rings.

What causes this to happen to the rings?

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munro'sgts-t Collaborator

munro'sgts-t

Posted
Posted

well mate im no engine builder or tuner but if your knock sensors wernt working how could they tell if its wasnt nocking any more after they turned the boost down just cos u cant hear it dnt mean it aint knocking, and also maby the machine work was not accurate enough maby the piston to bore clearance was to big ect

femno Grand Master

femno

Posted
  • Author
Posted
why did you proceed without working knock sensors dude? thats like guarantee'd rebuild.... :(

I did not proceed with the tune, the tuner did and told me after when i picked it up.

So detonation causes this problem?

Minor detonation over a period of time has pounded the shit out of the rings and worn them out like the pic?

femno Grand Master

femno

Posted
  • Author
Posted
well id say its all a tuning issue. were the pistons at all pitted? with the good pistons/rings.. install them and check the ring gaps. (top and second)

Nar no pitting.

Check the ring gaps of the worn out rings?

STATUS Grand Master

STATUS

Posted
Posted
why did you proceed without working knock sensors dude? thats like guarantee'd rebuild.... :)

Not really, if you have the correct det listening equipment they are not needed.... think Haltech, Microtech etc

It is way to often i see the PFC knock meter used to tune cars, it is an indicator.

all decent tuners will be using something like this http://www.skylinesaustralia.com/forums/in...howtopic=176922 those who arent are winging it.

Risking Grand Master

Risking

Posted
Posted

The guys are right, a tunner who does power FC's and relys on the knock sensors should not be tunning an engine full stop.

Give them a real ecu like a haltech, autronic motec etc and see em freak trying to figure out what real detonation is.

On aside not the cross sectional area of an ACL ring (actualy made by mahle) is that exact shape from new.

If the rings are cleanly broken its more than possible they have been like this since installation and its the builder fault not the tunner. "most" engine issues wont smash rings before they do damage to the lands. You issue sounds very much like an assemble problem.

femno Grand Master

femno

Posted
  • Author
Posted

But if they dont rely on the knock sensors how do they know if there is detonation or not? yes by use of the standalone knock sensor equipment but why mention the knock sensors werent working?

The rings are blue around the inner edge, as if they have gotten freakin hot, and the outer edges are very sharp. I really dont think they are meant to be like that.

Is there any sort of testing of the rings to find out what has caused this?

Could there be anything else that may also have done this to the rings?

Not for anything but this engine has already cost me thousands from the first build, and more thousands are being spent - again. I just cant have this happening again.

Ive spoken to a few people and another possibility was dirt entering the engine, but from where? All manifolds etc are spotless, as is the cooler, the engine has never been run without filters...

Risking Grand Master

Risking

Posted
Posted (edited)

installation errors

Oh and from memory the rings that ACL use with their RB26 pistons are meant to be solid rectangular 1st ring and stepped 2nd ring so its possible you rings were put in arse about as well. (yes it does matter)

Those stepped rings are a very brittle matterial and easy to break when installing too.

Edited by Risking
femno Grand Master

femno

Posted
  • Author
Posted
installation errors

Oh and from memory the rings that ACL use with their RB26 pistons are meant to be solid rectangular 1st ring and stepped 2nd ring so its possible you rings were put in arse about as well. (yes it does matter)

Those stepped rings are a very brittle matterial and easy to break when installing too.

Im 90 percent sure the 2nd rings were stepped as well liek theyre sposed to be, but ill double check tomorrow, havent got the pistons here.

T04GTR Grand Master

T04GTR

Posted
Posted

you still need to get a feeler guage and chech the ring end gap.

as brad said. it aint screwd together right.

and on the tuning thing. torque production is an indication of timing. you increase it till it stops making torque. it wont ping for a a while yet. but thats how timing is usually done, pump in timing till no more torque is produced. theres no point adding timing if it stops producing a posative increase in torque.

femno Grand Master

femno

Posted
  • Author
Posted

But will the reading be valid? Both top and second rings are worn, obviously more so the top rings.

and if the rings have worn on the outside then ill have a wayy bigger end gap.

Ill measure them tomorrow anyway, ill see if i can measure whats left of the top rings in terms of the step in the pic above.

wrxhoon Grand Master

wrxhoon

Posted
Posted
Hey all,

After having an intermittent oil burning and low comp problem, today i pulled apart my engine.

I found an unacceptable amount of piston slap on all cylinders...

Number 6 top ring came out in about 3 pieces, some of the ring was missing too. This would explain my intermittent comp, would have been pieces of ring under my valves...

Number one ring was split in half.

All of the rings looked like this, the rest intact apart from 1 and 6:

Cross section:

post-17897-1190018986_thumb.jpg

All intake components are spotless, free of dirt etc, cooler was cleaned when engine was built. HKS pods.

When the car was tuned, the tuner advised me that the knock sensors werent working, as they heard knocking during tuning and had to take boost out, it didnt read knocking on the pfc, but the tune was fine.

All ring lands are not broken, acl pistons and acl steel rings.

What causes this to happen to the rings?

You say you have unacceptable amount of piston slap , like how nuch clearence? What was the clearence ( piston to bore) when it was built? Was the ring gap meassured in the bore ? if yes what was the gap? Are the bores worn now? Can you still see the crosshatch hone ? How was th engine run in?

My guess is that the piston rings were broken in assebly or maybe you didn't have enough gap and they broke when they got hot and expended. I can't realy say without knowing the answers to the above . Don't forget when using forgies you have to have bigger piston to bore clearence than cast pistons .

Beer Baron Grand Master

Beer Baron

Posted
Posted

like dave said measure the gaps on the ones that AREN'T broken. obviously you can't measure the end gaps on the ones that are failed, but measuring the others should give you an idea as to whether or not it's an assembly problem.

NXTIME Grand Master

NXTIME

Posted
Posted

Since he says that there is piston slap, I would take it that the (forged) piston to bore clearance was taken into account. However, it may not have been down according to the specific piston manufacturer's specs. I had a previous engine have that much piston slap that I could physically move and see the pistons left and right in the bore. Next rebuild was much tighter and engine was perfect.

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