2G Piston crown damage

[jtornatore00]

I recently just bought a 97 Eclipse GST with the 4g63t in it. The previous owner said it bent a valve and it would need a new head. I pop the head off and it turns out a valve head broke completely off into cylinder 2, doing some damage. I'm trying to get a second opinion on what I should do about this piston. The walls do not look scored.

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[pauleyman]

No way I would run that. Who knows what damage lurks underneath the crown. New piston time.

 

[jtornatore00]

No way I would run that. Who knows what damage lurks underneath the crown. New piston time.

Is it alright to replace a single piston and not the others? How hard of a job is this?

 

[pauleyman]

yes you can replace a single piston. How hard is relative to your skill level. What is your skill level. Obviously you are doing a cylinder head job.

 

[jtornatore00]

yes you can replace a single piston. How hard is relative to your skill level. What is your skill level. Obviously you are doing a cylinder head job.

This is my first time going into the block, my second time doing a head. I just wasn't sure if it was as simple as pulling the oil pan, unbolting the rod from the crank, and pulling it out

 

[pauleyman]

That is how you remove it but generally you don't just slap it back in. The walls have to be honed, new rings etc.

 

[BLACK'98DSM]

Do you know how to set ring gaps? Do you know how to use a piston ring compressor? Do you know how to hone the cylinder? Do you own a torque wrench and know how to use it? If you answer no to all of these it's not the job for you.

 

[jtornatore00]

Do you know how to set ring gaps? Do you know how to use a piston ring compressor? Do you know how to hone the cylinder? Do you own a torque wrench and know how to use it? If you answer no to all of these it's not the job for you.

Out of all these the only thing I haven't done is honing. And I'd have to find a ring compressor

Also, are there any recommendations on what piston I should get? If everything is stock - isn't it 8.1 compression ratio 85mm bore?

 

[DSMPT]

If you are planning to replace only the damaged piston then what you would need is a stock 2G turbo piston and a new ring set.
If you see any damage on rod journal/bearing when you remove the rod and the piston, should do a full overhaul. If you just want to replace the piston, maybe replace all pistons and hone all cylinders would be a good idea, too. In that case I would go with a NPR piston kit w/ rings. Probably the cost wouldn't be very different from replacing just one piston and a ring set if you don't have a spare in your garage.

 

[jtornatore00]

What do you guys recommend for rings gaps for the new piston? This current setup makes around 20 lbs

 

[1990TSIAWDTALON]

Top - .018
2nd - .020
These are MY numbers that I use. It compensates for future turbo upgrades and thermal expansion on a modest build. For a higher HP build, those #'s would be a bit larger.
If you are replacing just one piston, you need to make sure it is a match to the others as far as compression ratio (and physical looks) so that the motor stays as balanced as possible.
You can rent ring compressors and 3 bar hones to help out in your job.
I use THIS hone for 4g motors (and Saturn)
A ring compressor is pretty cheap, like THIS one, but you can rent them.
Here is a clip from a thread where @dsm-pwr gives the stock gaps, so credit goes to him.

From the Mitsu Service Guide
Install the piston ring into the cylinder bore. Force it down
with a piston, its crown being in contact with the ring, to
correctly position it at right angles to the cylinder wall.
Then, measure the end gap with a feeler gauge.
If the ring gap is excessive, replace the piston ring.

Standard value:

No. 1 0.25-0.40 mm (.0098-.0157 in.)
No.2 0.20-0.35 mm (.0079-.0138 in.)
Oil 0.20-0.70 mm (.0079-.0276 in.)

Limit:
No. 1, No.2 0.8 mm (.031 in.)
Oil 1.0 mm (.039 in.)

HERE is the whole thread and it is a good read. Dale is the machinist that gives out some good info in it. I recommend glancing over it.

 

[TerminalTalon]

What do the cylinder walls look like?

 

[jtornatore00]

What do the cylinder walls look like?

I can't get pictures right now but we couldn't find any marks on them. Plan to thoroughly clean them and oil them before moving anything.

 

[TerminalTalon]

In the end, the right thing to do is a full rebuild. The thought of anyone doing a single piston and doing all of that work to have low compression or failure from something else is a choice I wouldn’t make.

 

[1999RSfwd]

You should really measure the cylinder bore diameters, to see what size they are and if they are still in spec and or out of round. I would hate to see you buy some pistons, just for the cylinder bore to be out of spec. Most people think you can just install a new piston of the "correct" size and you're good to go. This is not always the case, as the cylinders are bored to match the piston, not the other way around. Just something to think about.

 

[TerminalTalon]

A lot of measuring that needs to be very precise. Not for the lightly skilled.

 

[steve]

Besides eating a valve in Cyl 2 is that detonation damage in the other cylinder?

 

[Mech Addict]

I'll be the "other" voice here saying that rather isolated repairs don't always have to turn into big restoration projects. As others have pointed out, the procedure to replace a piston is not that bad, and tools can be rented/borrowed. I would think the key is to clean everything really well after the single cylinder honing. Pulling the motor and doing a full overhaul is the most thorough and reliable way to ensure everything is right, but as the owner, you get to decide if that is worth the risk vs. expense. Since you have the head off, next remove the pan and check that one rod. If that looks suspect, check a few other rods, and perhaps main bearings. Let that inform your decision. If the bottom end is not in good shape, then perhaps fixing the piston is merely a temporary measure at best.

 

[Tyeler18]

2013 Me would tell you to pull the engine for a total rebuild and go. 2013 me still has his 1g in the corner of the garage with no drivetrain in it. 2022 me says slap a stock piston back in it without doing anything other than ring gap and go race it. 2022 me also just slapped a $20 ebay headgasket with reused gaskets, timing belt, tensioner etc, everywhere else in a buddies 260k 2g and road raced it all last weekend between 3 of us with no regrets and no issues. I've found out I've spent too much time "doing it right" and not enough time racing. Shit breaks regardless of how well you put things together.

 

[Mech Addict]

So at least there is consensus on not using that beat up piston any more…
That was actually the question.

 

[waltah]

In the early 1970's I admired and finally bought for $75 and reassembled a '49 Cadillac with about 100k miles out of junk parts, all this in the junkyard -- took me a week to do it. '48 was Cadillac's first year of 'slippered' pistons (trimed skirts on the sides to fit between crankshaft counterweights) and they got it wrong -- all the 48s and 49's developed cracks at the corners of those cutouts. The pistons were strengthened and redesigned to a larger radius on the cutout for 1950 but the engine -- 331 cu. in., V8, 7.5:1 compression ratio -- stayed same. Two barrel WCD Carter carburetor, 4 speed Hydramatic.

Took about a week to discover I had 8 cracked pistons -- once you've heard that clear bell-like sound you never forget it. (Wow ... so that's why they junked such a good car!) I remembered that the next car in line in the junkyard was a '50; I drove back down there, pulled the pistons from the 50, cleaned 'em up, flipped the rings upside down (they were symmetrical but wear to a taper), I put the set in my '49 car. I believe I did ream the slight ridge but don't remember honing the cylinders -- probably I broke the glaze with a sheet of WetOrDry. I drove it over 100k more miles, finally selling it to another enthusiast for $500. It didn't smoke enough to be noticed, used a little oil -- nothing excessive for a car of that mileage/vintage.

I wouldn't try that with any of our cars: I would at least measure everything, replace the rings, and hone the cylinders. Absolutely I would replace the whole set of pistons because they're all supposed to be the same weight and that used to be done by matching at the factory: (I don't know how it's done now -- modern manufacturing may be so much better that any OE piston of the same size will be close enough.) A mismatch will add to engine vibration. But -- the view that any imperfection calls for a rebuild -- no. Only if I expected to push the car would I start by rebuilding it.