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1G Can i use these pistons?

vetexr

Probationary Member
11
1
Jul 29, 2017
Reykjavik, Europe
I am rebuilding a 1991 4g63t and when i took the head of i saw that the pistons had valve marks and i believe the timing belt snapped when the previous owner had the car which lead to the valves hitting the pistons and cause the marks, is it ok to use these pistons with new piston rings or should i buy new pistons? Check photos,
Thanks in advance.
 

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Mech Addict

Supporting Member
474
173
Jun 9, 2019
Jackson, Wyoming
I can’t imagine anyone can be “100% sure” based on a photo. You’re getting honest advise from members with experience with these cars. Snapped timing belt is a notorious failing of this design, so many have witnessed the consequences. There is some risk with any repair, including that new parts are flawed, too. You might want to remove the pistons and check the wall clearances before you decide. Did you have a recent compression test? Maybe you would need new ones anyway. If they still fit properly, then at least one respectable member thinks it’s fine. Others may think differently. I’ve not dealt with this, but they don’t look too bad for stock re-use.
 

Mello

Proven Member
1,260
412
Jul 4, 2003
Albuquerque, New_Mexico
They will be okay. If you're rebuilding & taking the pistons out, smooth off the high spots and clean up the gouges left from the valve contact.
 
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TK's9d2TSi

Supporting Member
4,640
1,896
Sep 11, 2017
Cincinnati, Ohio
Like @Mech Addict said, they’re just witness marks left from when the belt broke at one point. Measuring the pistons and cylinder bores are more crucial than those marks. My pistons also had marks but not as bad and they worked fine. They won’t touch on a engine that’s timed correctly.

457D94F3-5529-4B36-93DC-73FC189C417F.jpeg
 

RyeDawg

Proven Member
30
6
Nov 19, 2008
edmonton, AB_Canada
This past spring my balance shaft belt snappped and caused the timing belt to jump . All my valves got bent in the process. My pistons looked very similar to yours. I ended up taking a dremel and cleaned up each piston so that when the pistons got hot the thinner metal wouldnt heat up and chunk off. The car runs great!
 

DSMPT

DSM Wiseman
1,285
832
Jun 12, 2014
Japan / Mexico, Arizona
Are you 100% sure? check these photos
In most of case, yes usable unless ring lands are smashed. But those marks would possibly cause some hot spots, so it's better to make the contact marks smoother by removing burr's sharp edge.
If you are worried, replace them. For sure that would be the safest way.
 

1990TSIAWDTALON

Moderator
7,359
3,468
Nov 14, 2013
Independence, Kansas
I was going to mention to check the ring lands to make sure the rings will float. If they are tight then that is where you run into a problem. Most times it is ok.....MOST times. I will be removing mine and checking the lands but my motor is on a stand not still in the car. I expect things to be ok but I will have them out and check that anyway. Thanks Hiroshi!
 

vetexr

Probationary Member
11
1
Jul 29, 2017
Reykjavik, Europe
I was going to mention to check the ring lands to make sure the rings will float. If they are tight then that is where you run into a problem. Most times it is ok.....MOST times. I will be removing mine and checking the lands but my motor is on a stand not still in the car. I expect things to be ok but I will have them out and check that anyway. Thanks Hiroshi!
Alright i will be removing the pistons tomorrow, if they’re okay what piston rings do you recommend?
 

1990TSIAWDTALON

Moderator
7,359
3,468
Nov 14, 2013
Independence, Kansas

Mech Addict

Supporting Member
474
173
Jun 9, 2019
Jackson, Wyoming
I’m wondering the same thing, for whenever I decide my motor needs a rebuild. The factory cast aluminum pistons were made with a steel strut integrated to make them less prone to expansion when operating. This allows for tighter wall clearance, so better ring seal, less slap. Chryslers used these for years also, going back at least into the 60s. I couldn’t find any specifics on whether the NPR have this feature. Perhaps others know. I would imagine that having pistons, pins, and rings all from the same mfr has less chance of improper fit or compatibility.
 

DSMPT

DSM Wiseman
1,285
832
Jun 12, 2014
Japan / Mexico, Arizona
I have seen many misinformations about NPR. Maybe I should correct a little bit here.

NPR "Piston rings" is the one manufactured by Japanese company (NPR = Nippon Piston Ring) and supplied for many name brand aftermarket piston companies and car companies.
NPR "Pistons" is manufactured by NPR America and NOT OEM for Mitsubishi, those are OEM "Style" pistons, but those pistons work great on our 4g63, have been proven by so many DSMers.

"Art-piston" and "Riken piston ring" is the one OEM for Mitsubishi (I am not sure about the latest Mitsubishi cars but at least around the era of DSM 80s 90s)

As for the piston rings, Riken, TPR, NPR and Hastings they all work great. In North America, maybe it's easier to find NPR and Hastings rings than Riken and TPR's.
Riken, TPR and NPR are Japanese and they are the supplier for the most of major car/piston companies.

The factory cast aluminum pistons were made with a steel strut integrated to make them less prone to expansion when operating. This allows for tighter wall clearance, so better ring seal, less slap. Chryslers used these for years also, going back at least into the 60s. I couldn’t find any specifics on whether the NPR have this feature. Perhaps others know.
If you are talking about the metal reinforcing plates that are stuck inside of piston skirt, Yes NPR pistons do have it.
 
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1990TSIAWDTALON

Moderator
7,359
3,468
Nov 14, 2013
Independence, Kansas
I pulled my 16 valve bending machine apart tonight and the ring lands are fine, rings are still floating nicely. Rod bearings looked fantastic too. :thumb:
I DID find a issue, can anyone spot it??? :hmm:
Pops
 

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Mech Addict

Supporting Member
474
173
Jun 9, 2019
Jackson, Wyoming
:aha:I have about zero experience in rebuilding engines, but the wear Pattern on that bearing in your hand seems a little uneven. But maybe that’s normal? You also seem to be focused on one particular rod journal, so while I can’t tell what it’s showing, you’re sort of hinting the issue is there.
 

1990TSIAWDTALON

Moderator
7,359
3,468
Nov 14, 2013
Independence, Kansas
There is only ONE oil squirter left. 3 have their tubes broken off. I have a line on a used set I believe.
Bearings and journals all look fantastic for all the hell I put that motor thru. 44 lbs of boost to 9k and it still looks really good. I was impressed. A few cylinder wall scratches, maybe rings butted but I will hone it and re-ring and bearing it.
 

Mech Addict

Supporting Member
474
173
Jun 9, 2019
Jackson, Wyoming
So what do you suspect caused the squirters to break? Related to the valve collision? Btw, what caused the valves to hit the pistons in the first place; timing belt failure.
 

1990TSIAWDTALON

Moderator
7,359
3,468
Nov 14, 2013
Independence, Kansas
Crank pulley walked off the snout on my way to a car show of all things, 2 years ago, instantly bending all 16, they look horrible but none broke. I am not real sure on the squirters. It was getting late last night so I will have to look it over again today. Nothing in the pan so I am going to look it all over, clean it all up and go back together. I was real happy with the way the insides looked and the fact that the rings floated in the lands. I think I will have to remove one side of the kiggly girdle to get to the squirters.
 

AMSOIL Dlr #352885

Proven Member
42
12
Dec 1, 2020
Grimesland, North_Carolina
Okay, not trying to Hi-Jack VETEXR's thread.
BUT, Guess what?
Bought Rally set up (Lots of good intentions & parts but, very sloppy work) w/ engine where the t-belt idler started falling off (Previous Owner Blunders) while in a rally competition, 4G63T bent all valves & split the guides. This project has stalled due to Piston re-use decision or the Cost of new Pistons.

Hoping to Build Car with my Automotive Class as Project Auto-crosser to give Student's the practice/importance to details for any task taken on.

I normally will re-use piston(s) that have kissed the valve head and created clearance indentions in OE valve pockets, IF no obvious cracking & ring grooves are free w/ proper ring side clearance.

These got beat quite a bit, but it sounds like many DSMers have reused pistons from this issue multiple times with very little poor outcomes.

I believe this engine had an in-frame build at some point, due to condition of rings and rod bearings look very good.
Even the Piston to Cylinder clearance, ring end gaps are well within the Service Specifications or on low side of service limits.

Of course we will inspect pistons closer and clean up burrs, but I believe, all we need will be another set of rings while fully pulled apart & possibly lower bearings.
The Bearings look very good still and still have crush tension, thinking of re-using to show students if parts show proper serviceability qualities, there are alternatives to just throwing new parts in, just for tear down inspections.
 
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