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Discussion Starter #1
Just received a set of pistons for my Chevy 396 build..obviously they have been sitting on a shelf for 25 years.
Box says 86 but who knows...anyway looks like a rough casting,not polished like the pics you usually see.
I need to finish the pistons somehow?
Also 3 pistons seem to have a loose fit of the piston pins,as i can push them through the piston with finger pressure.
.990 is the correct pin size...the loose pins measure .989...1/1000 gonna make that much of a difference?
I called Rock auto for 3 new piston pins. ::)
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it should be fine. the pin clean and oiled should slide through with little effort. are you running a cast or forged piston? i use 220 grit to smooth all edges and the dome,the shirt edges. leave nothing sharp anywhere in the combustion area. anything sharp will get hot when running and cause detonation ,dont sand the sides of the piston
 

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Discussion Starter #3
I'm running forged TRW L2242 pistons.
I imagine after sitting a long time,there could be some corrosion.
I imagine cleaning and oiling the pin should help.
I was hoping to hang the rods myself,although I'll need to find a press to push the pin out.
Any other ideas?
Thanks.
 

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Discussion Starter #4
I was able to press the pins out after a little PB Blaster...must have been a slight bit of corrosion.
I have one piston where the pin will only go through one way...will not completely fit through the pin bore.
The instructions state to keep the pins with the piston...would you swap the pin with another piston that has more clearance?
Some pistons have more of the area removed under the piston...I'm guessing these pistons have a more dense area in the piston head?
The cylinders with the shortest intake runners should run richer than the cylinders with long runners?
Use the denser pistons on these leaner cylinders?
Thanks.

 

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Discussion Starter #5
You'll notice one piston has a very small rough area on the crown and will need to be smoothed out...you can hardly see it,but it's there.

 

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Discussion Starter #7
 

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take all of the rough surface off. it takes time and patiance but smooth them out,on those i do the entire top. i would not press the pins in with a press ,its way too easy to gaul the pins and ruin it and the piston. the machine shops have a heater that warms the rod end and alows the pin to slide in easily without the rist of damage.you should have it balanced if you are changing pistons or it will vibrate at speed and eat itself up or break something.do all of the piston dressing first and make sure to take the sharp edge of the dome down a little,consintrate on just the machined edges itself.
 

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Looking at the pictures of the underside of those pistons make me think they are not the same at all. Weigh them before you waste anymore time on them. they should be within a few grams of each other right out of the box. If there is more than 5 or 6 grams difference between the different styles you got a mismatched set. that might explain why the tops are a little different also. Maybe it is not as different as the pictures make them look.
X2 on heating the rod ends. Don't press them in cold if you use them!
 

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Discussion Starter #11
I'm guessing after forging,they shave the undersize to get the correct weight...almost like they do with connecting rods.
The pads on the little end are all different...some are heavily ground to get the correct weight...some are only slightly shaved showing most of the weight is in the rod,rather in the small end.
Piston forgings should be the same.
I'll buy a scale and weigh each piston and let you guys know what I find,although I have full faith in the old TRW.
 
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