Piston size question

[kt239]

Well finally getting to the point where I can order parts for my bottom end build here and ran into a question pertaining to what size piston I should order. A buddy of mine told me to look on the piston to see if there is any imprint indicating if they are bigger than the original ones as I felt the engine has had work on it before judging by what I seen while I disassembled it. I found just that and it seems to read 0.50 so I would like to see what you guys think..

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It seems to me that they are stock pistons but .50 over but id like to know if my assumption is correct. If so would you think that I can get away with just honing out the cylinders or should I just go with the 86mm pistons and get it bored out some more? Here is a picture to aid in your input..

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They all have that score in the same spots so I just wanted some input on what to do with it. Theres no lip at the top of the cylinder at all based on what I can feel with my nail for what its worth. Oh and for your viewing pleasure check this one out!

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[1990AWD]

Get yourself a micrometer and measure them.

 

[TSIfreek]

Im sure thats a stock size piston so a .030 over will be what you need but I would measure the bore to be certain. The crank is junk as there was lack of oil to that rod journal. You should also have the block checked out if it was a crank walk victom. Find a shop that specializes in these engines in your area as he will be the best place to start.

 

[johneclipse]

only way to tell is to mic it...

 

[kt239]

Yeah definitely gonna measure it to be 100% certain on this one. I do plan on a whole rotating assembly being put in so the crank will be put to a scrap pile. If it was an issue of crank walk wouldn't the new bearings take care of the issue?

 

[TSIfreek]

Yeah definitely gonna measure it to be 100% certain on this one. I do plan on a whole rotating assembly being put in so the crank will be put to a scrap pile. If it was an issue of crank walk wouldn't the new bearings take care of the issue?

Yes as long as the crank has not been machined down that your going to use you will be fine. Check the bock surfaces of the thrust bearing area for any kind of damage. You having a pro put the bottom end together? I would recommend it as its just cheap insurance.

 

[94talontd]

Its a .020 over piston (.050 cm). My buddies pistons had the same thing. Measure it to be sure though.

 

[BK85]

Ditto^

Mine had a .050 stamp on them but when I measured they were 20 over.

I thought the .050 had something to do with the weight.

BK85

 

[19Eclipse90]

94talontd is absolutely correct.

0.020 over is in inches and equals out to about 0.50 millimeters. It's Mitsubishi's notation, an additional 0.50mm makes the piston 85.5mm which is about 3.366 inches, twenty over from the original piston at 3.346 inches or 85mm.

The 63DT F1 is found on 2G original/Mitsubishi pistons.

 

[firefighter]

Figure out what you going to do with the engine that will determine how the block is going to be rebuilt.You caanot order the pistons randomly to the block. The pistons should be ordered to the bore sizes. You have to have a set amount of space between the piston skirt and the cylinder wall. To loose and you get piston slap to tight and you have real problems.It also depends on what kind of piston you are using(forged vs. cast even one manufacture to another.) More important than the piston is the rings, put the wrong end gap and you will have ring failure.From the pictures it looks like you should have the block bored out.The rubbing marks you have are from the piston pin area this is caused by the piston changing dirrection(non wear) more then likely the cylinder is egg shaped. The crank can be cut does not look like crank walk.Before you grind the crank make sure you canget the proper bearings No bearing to fit properly the crank is useless.If the bearing was overheated ( It has blue discoloration)you might want to get the block line bored.As always make sure to get the block boiled out to remove any dirt. good luck to you.

 

[kt239]

@ tsifreak
I will check that out for sure and I am being assisted by my uncle who knows what he is doing as far as this goes. I got the basics down but defiantly having help from someone more experienced than I on the rebuild.

@94talontd/bk85/19eclipse90
Thanks for the input on the markings on the piston and the explanation as to what it means it is greatly appreciated. Still want to make sure so im gonna measure it as soon as I get my measuring device in (hopefully tomorrow). Cause no one seems to have a micrometer I can use for a minute or less.

@firefighter
I plan on getting this here stroker/rotating assembly but wasnt sure on what size pistons to get weather it be the 85.5 or the 86.0 shit maybe id need the 86.5 pistons. I thought having that figured out would be enough to get it to the shop to have the cylinder work done cause you are right they are a little oval shaped. A new crank will be included in the assembly so im prob just gonna pitch the old one.

 

[kt239]

Well I finally got my measurements for the official piston size and their all the slightest bit different but the average size is 84.9 mm and the cylinder average is 85.6 mm. So I'm thinking I'll just get the 86mm pistons to play it safe and get the cylinders bored accordingly. Thanks for the help to everyone that pitched in.

 

[o0GuitarKid0o]

Not to bring this back from the dead but I'm assuming that if there are no markings on the pistons than they are standard bore?

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Just measured my crank and went onto my pistons to find no markings (yes there NT pistons ) with over 150,000 on them

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there's some info from the FSM

I get 3.3412" (84.866mm)

Just trying to figure out my bore size roughly.
I need bore gauges still ...

From what I can see I'm still standard bore . Just want some input !
I'm sure I answered my own question
And really don't think we need more threads on this

Will have a build journal soon with all the specs .