I got my engine kit last night...

I was weighing the pistons to see how much the matched up.
I swapped a few pins to make them a little more even.

Now, any recommendations for piston prep?

I have see recommendations of:
match the weight as close as possible. (except one, there +0, -0.5g)
remove sharp edges (on valve reliefs? and piston skirt?
polish top of piston.

Any others?

I'm going to get the rods redone and then will see about weight matching them.

BTW, they are speed pro hyper's H631CP (coated skirt pistons)

 

Leave the skirts alone.

RACE ON!!!

 

NO !!!!!!!!!!!!!!!!!!

Tell us you are kidding, PLEASE.

You "swapped" the wrist pins arounf from piston to piston????????
To even up the weight???????????????????????????

 

CFI, I think you better take over from here..............
May be better if I don't come back to this thread. You know how they want to shoot the messenger and all.....

 

 

THANKS ALOT!!!
I totally spaced out the pin swap part. All I really paid attention to was the "sand paper" work.

Adam,
When you take the rods for rebuilding and weight matching, take the pistons, too, and tell them what you've done. They can RE precision fit the pins to the pistons.

I'm ducking, now.

RACE ON!!!

 

Sorry CFI,

I didn't want to be the bearer of ill-tidings.

Adam:

Listen to CFI-EFI.
Him give heap good advice, quemosabi.

 

>When you take the rods for rebuilding and weight matching, take the pistons,
>too, and tell them what you've done. They can RE precision fit the pins to the
>pistons.

Hmmm, the pin + piston is a set - don't change the set?!

I swapped a wrist pin (piston A has piston B's pin, and vice versa).
I have my notes on the box.

Why is the wrist pin such a critical fit for a pressed in wrist pin?

 

The normal swap is the piston and rod. heavy rod with light piston

 

Unless you are having the pins pressed into the PISTONS (???) the pin still turns inside the pin bores of the piston.


CHICKEN!!!

RACE ON!!!

 

Chicken???


Adam: If you only swapped A & B then you are in good shape.
Swap back B-> A and you're good.

Long as you didn't swap C-F,G-D,E-H etc,etc. you'll be ok.
Just swap the wrist pins back to their original piston and no harm will be done.

The pins are, as CFI-EFI pointed out, a precision fit in the piston wrist pin bores.
This makes a piston/pin a matched set for the life of the parts.
Sort of like "married" together.
The piston mfg. does this match when they do the machining of the piston and fitting of the wrist pins.

Not to worry, everybody has to learn somehow. I can remember back when someone told me, I thought the same thing you did.

If you don't have a personal engine building advisor, check with these guys on here along the way.
There's a LOT of guys on here that REALLY know their stuff.

So ,don't be bashful about asking questions.

Regards

Jim

 

What about floating pins? If you are holding the pins in the pistons with spiral locks not pressed fit, why cant you swap the pins?

 

When JE sent me my custom made pistons with floating pins all the pins where packaged in their own box and wrapper from the pistons... took the assembly to be balanced and thought the machinist would have some fitting to do..nope he said floating pins are interchangable.

 

If anything, a floating pin turns MORE in the piston than a pressed pin, because it's rotation in the rod isn't limited. I can't imagine J&E or anybody else matching all 8 pistons to all 8 pins in one box to be interchangeable. Maybe. I would question whether the machinist really knew something, or was just lazy. Pin fitting IS a common machine shop operation. *I'D* be talking to J&E before I fired that thing up. *I* would err on the side of caution, because *I* don't KNOW.

RACE ON!!!

 

My SRP floating pins were the same way. All in one box. Its those $500,000 CNC machines that make it possible...But once the machine shop balanced everything I was told to keep the pins,pistons,rods all together and not to mix them up...

 

CFI-EFI thanks for the concern I always take your advice to heart but I really trust this machinist..he has absolutely no advertizing except word of mouth, he comes highly recomended by all the racers in my area and has been in business for 38years now... I bet this old guy has forgot more about machining and building motors than most of us combined..
anyway, I did pose that question to him when I dropped off the stuff for balancing and block prep/work... he didn't seem to concerned about it and did say just don't mix'em up afterwards and I'd be good..so as soon as AFR gets off their A$$ and sends me my new heads I'll be able to fab up my new headers and button up this project..

Gotta love these big cube small blocks!

 

You can check each pin with a micrometer to ten-thousanth's. and you will most likely see no measureable difference. Weight is a different story. My JE pins ranged from 130.3 to 130.6 gms, but all diameters were identical (within .0001).

 

Hey CFI-EFI,

Maybe we're getting too old for this stuff.
We've been outvoted on this about 6~7 to 2.

All the things we were taught simply don't apply anymore.

Actually they would "probably" be fine. Just throw'em in a bag, shake'em up throw it together and it'd probably run fine.

Same with honing cylinders for a particular piston.
I reckon that doesn't apply anymore either.
Those holes are all the same size anyway, right?
And the pistons are all the same size, right?

I'll admit I've built a few engines and didn't worry about piston/pin clearance, piston skirt clearance or even bearing clearances.
Most ran ok.
I remember one that didn't.
It had bearing clearances that were to SMALL. Spun 3 rod bearings and 2 mains.
Welded them right up to the crankshaft.
It still run ok even with the spun bearings. But it had a vibration in it that said it was pretty sick.
It would have been ok in a street car but I had it in a racecar and it saw WOT on it's first run on an old Alabama dirttrack.
Won my heat race with it but it was vibrating when I brought it in.

That was about the second one I built back around 1972.
Didn't have anybody to tell me all this stuff and was just doing the best I could with what I had, which wasn't much.

Time for new books for us maybe? Our old ones been preceded by computerized/CNC machine parts.
Maybe that's a good thing.
I still don't think we'll find a book that says it's hunky dory to mix pistons and pins. But that's JMHO I reckon.

Good luck with your engine, Adam.
And remember, "The Devil Is In The Detail".

 

KyRP2NITe Corvette,
I DID say maybe. I don't for a fact, KNOW. I do remember, and still see "pin fitting" offered. Your machinist seems to have all the right credentials.

VetNutJim,
No question, we've been out voted. Maybe you're right about "modern manufacturing" processes. As I said his machinist DOES seem to have excellent credentials. But I have to agree with your statement, "The Devil Is In The Detail". How often do you hear of engine problems caused by checking too many times. Since I admit I DON'T know for a fact, I would have at least made the phone call, just to ease my own mind. I'm being dragged, kicking and screaming, into the 21st century.

RACE ON!!!