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Piston crown damage

jtornatore00

Probationary Member
8
1
Sep 17, 2021
Coalport, Pennsylvania
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

DSM Wiseman
7,016
2,006
Nov 19, 2011
oklahoma city, Oklahoma
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

Probationary Member
8
1
Sep 17, 2021
Coalport, Pennsylvania
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
 

jtornatore00

Probationary Member
8
1
Sep 17, 2021
Coalport, Pennsylvania
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
 

DSMPT

DSM Wiseman
1,529
1,072
Jun 12, 2014
Japan / Mexico, Arizona
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.
 

1990TSIAWDTALON

Moderator
8,323
4,201
Nov 14, 2013
Independence, Kansas
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.
 

1999RSfwd

Proven Member
136
68
Nov 24, 2016
Dresden, Tennessee
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.
 
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