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Piston ring problem

 
Old Apr 17, 2019, 07:46 PM
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Piston ring problem

Dear all,

I am Vincent, a new member, want to ask about piston ring problem.

I just rebuilded my EVo 6, 4G63 engine with new Wiseco WSC-K596M86 pistons.

Crankshaft is Manley GSC-1002 and ACL race bearing (both new).

Engine was running about 600 KM with normal driving (no engine stress or revving).

3 days ago, we were tuning engine/ECU, boost target 1.5 bar, 7500 RPM max.

After just 2 driving/pull (less than 7K RPM), engine sounded strange.

We dismantled engine and found 3 out of 4 pistons have problem.

Piston rings are jammed.

What can be wrong that causes piston rings jammed?

I enclose pictures for reference.

FYI, I drive this EVO for years without problem before rebuilding.


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Old Apr 17, 2019, 07:58 PM
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Hi Vincent. Welcome aboard @vincent.semesta

Hey, sorry to see the rebuild fail like that. Im not the best engine guy but wonder if the PTW clearance was too tight? (piston to wall). Possible piston ring gap issue? (too tight?)

Im sure the guys will chime in & give some insightful comment

Joe
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Old Apr 17, 2019, 08:32 PM
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Joe I think you nailed this one. Looks like too little piston to wall clearance to me. Especially if that's what it looks like after such a short time. Forged pistons grow more than cast too. Clearances are a very important thing!
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Old Apr 17, 2019, 08:49 PM
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Thanks MinusPrevious and LumpySticks.

My mechanic said the same, may be wall clearance.

We brought engine block to machine shop where it was bored.

They measured engine bores piston by piston, everything is according to Wiseco manual.

This machine shop is quite familiar with EVO block.

Is there something wrong with con rods? They are used not new.

All bearings are in good shape.
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Old Apr 17, 2019, 08:53 PM
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"Possible piston ring gap issue? (too tight?)"

We did not touch anything with ring gap.

I sent email to Wiseco but have not received response from them.
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Old Apr 17, 2019, 09:10 PM
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The rings are file fit, so they would need the gap adjusted. But that 100% looks like insufficient piston to wall clearance
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Old Apr 17, 2019, 09:46 PM
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"But that 100% looks like insufficient piston to wall clearance"

Wall clearance is 0.101 mm based on machine shop.

Is this too tight?

What wall clearance should be for 1.5 bar boost (GT3076 trubo)?

I never drive car daily time, always night time.

Temperature here around 23 - 26 deg C at night with high humidity.

Sorry for all different measurement unit.

I have no idea in mile, inch, Fahrenheit.
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Old Apr 18, 2019, 12:17 AM
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1 inch = 25.4mm
F = C 9/5 + 32
1 mile = 5,280 feet
1 foot = 12 inches

0.101mm is about 0.004-inch
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Old Apr 18, 2019, 01:50 AM
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Originally Posted by vincent.semesta View Post
"Possible piston ring gap issue? (too tight?)"

We did not touch anything with ring gap.

I sent email to Wiseco but have not received response from them.
0.1 mm is ok for wiseco pistons provided it is the real and correctly measured PTW
Rings that come with wiseco, as has been posted above, are filt to fit rings.. i.e. you need to measure the ring gap and file the ring to get the propper ring gaps...
You can take those rings out and measure the gaps.. ring gap instructions are included with the pistons/rings when you buy them but off the top of my head, they should be .45 for top, .55 for second ring.... as defined by wiseco..
Take a picture of the ring ends I bet they are polished..

Looking at the pic of the pistons the PTW looks too small.. so I kind of doubt that it is .1 mm.. (where did they measure the piston dimension????)
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Old Apr 18, 2019, 02:35 AM
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Piston ring problem









Thanks 2006EvoIXer.

"you need to measure the ring gap and file the ring to get the propper ring gaps"

We didnt do this thing, big mistake.

I thought pistons were new and just installed them.

Mechanic also did not mention to measure ring gap.

We both made very big mistake.

"where did they measure the piston dimension"

Mechanic suspects problem is caused by wall clearance.

Then we brought engine block and pistons to machine shop.
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Old Apr 18, 2019, 02:43 AM
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"they should be .45 for top, .55 for second ring"

Are they in mm or inch?

It is more than 0.45 mm and 0.55 mm when I bought them.

It is too big if it is in inch (0.45 x 25.4 = 11.43 mm).
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Old Apr 18, 2019, 02:57 AM
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Piston ring problem

I dont have filler gap to measure.

Gap is around 1 mm for top ring.



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Old Apr 18, 2019, 07:40 AM
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Is it .1mm now that you wore .08mm off the pistons?

You may not have finished gapping the rings, but wiseco's rings only usually about .08-.1mm removed, so they would still run fine until you really turned it up.

So, again, those pistons look like insufficient PTW, or it could be detonation. But I'm still leaning towards PTW.
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Old Apr 18, 2019, 08:10 AM
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Piston ring problem

"Is it .1mm now that you wore .08mm off the pistons?"

From picture, caliper showing 1.00 mm.

Based on caliper, top ring gap is around 1.00 mm.

"it could be detonation"

There was no sign of detonation.

I drove the car that night while tuner sit next to me.

We just started tuning ECU, then stop after 2 pull.

FYI, there is dyno machine in my town nor tuner.

People here call tuners from Jakarta, Malaysia, Singapore.

All tuning must be done on public street/road.

Luckily there is no road speed limit.

We can drive as crazy as we want as long as nobody complains (usually noisy sound).




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Old Apr 18, 2019, 08:15 AM
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I'm not talking about the ring gap, I'm talking about the piston to wall.

You came here with a blown up engine and the correct theory of PTW issue is something you are denying even though it's very clear that's what it is. Either clearance was overall too tight, or the bores were out of round or not straight and ate itself up.

You cannot measure ring gap with a caliper. the difference between .015" and .020" is not discernible by the naked eye. You have to use feeler gauges.
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