piston order

[Bri7man]

So I have a block that has been bored/honed .020 over, a crank that was polished, stock rods that were balanced and npr pistons that were balanced.

The machine shop says the cylinders were all bored the same and that my npr pistons were all mic'd the same and therefore the order does not matter.

Some convo's in flash chat last night thought otherwise and so this morning I brought my block and pistons to the machine shop only for them to explain the above to me and how it would be different with an engine that was not an inline 6.

Who to trust?

 

[Bri7man]

God damnit!! Mods PLEASE move this to the gte section... 2nd time this week..

 

[IJ.]

Muppet

If they say all 6 are the same then no it won't matter, just make sure you assemble the Pistons and Rods facing the right way.

Ring gap stagger is also very important, there's a diagram in the TRSM you DON'T want any gaps in the same place as others..

 

[Bri7man]

lol whats muppet mean?

Yeah I read up on the ring gap angles in adjusters thread and some other places so I should be good on that

 

[IJ.]

Google Muppet,

End gaps are very important and worth taking the time to get right, too much and you'll have blow by not enough and you'll close up a gap at high boost and trash that cylinder.

 

[Bri7man]

Ahhh urban dictionary definition, Muppet;"Someone who is useless until you shove your fist up them"

Hey I'll try anything once!! Make sure I bleed and is extremely excruciatingly painful because only once!


Yeah I measured each end gap with a feeler gauge per tsrm, only one needed to be lightly filed. Did that then taped them up and smoothed out all the sharp edges on the piston heads, should be plug and play now after a brake klean blast and 30wt dino oil lube I believe.

 

[CyFi6]

Should be good to go, line up the gaps properly and make sure the top ring is on top, second ring is second, as well as making sure the markings face UP, dont want to put a ring in upside down! If you didnt file your rings to each cylinder, check the rings in the cylinder they are going into, just to make sure. Lube it up good and make sure if the piston stops as you are tapping it in, START OVER do not force it or you could break your new pistons/rings

 

[hvyman]

doesnt usually the machine shop bore the pistons to the cylinders and mark the pistons to the cylinders? why would this make a difference just because its a i6? from my under standing just because its .020 over piston doesnt mean there all going to be the exact same size and that the machine shop should measure the piston and then bore that cylinder to that piston.

can anyone explain this for me?

 

[CyFi6]

The machine shop measured the pistons and they were all the same dimensions, therefore the bores are all the same dimensions, therefore theres no need to match anything as they are all exactly the same.

 

[Bri7man]

doesnt usually the machine shop bore the pistons to the cylinders and mark the pistons to the cylinders? why would this make a difference just because its a i6? from my under standing just because its .020 over piston doesnt mean there all going to be the exact same size and that the machine shop should measure the piston and then bore that cylinder to that piston.

can anyone explain this for me?

The machinist told me they were all mic'd the same. They waited to bore the block until I brought the pistons in so they must have all been the same.

I'm going back tomorrow and having them install the pistons because the harbor freight ring compressor I used scratched the fuck out of the first piston skirt I attempted. Although I did tighten it around the piston with it in my lap and that was a bad idea because the compressor walls did not overlap evenly.. Regardless I can't afford to experiment better ways at the expense of a new set of pistons

 

[hvyman]

i got that. the only thing i dont get is how ALL the pistons were the EXACT same size. if it were a v8 and ALL the pistons were the same size why should you bring the pistons to the machine shop to get the cylinders bored to the pistons. they are all going to be somewhat different whether it be .0000009 or .0001. what is the point of having the cylinders bored to the pistons if all the pistons are the same? why shouldnt you just measure the pistons and tell the machine shop this is what i want the cylinders to be measured to? why bring the pistons at all?

 

[Bri7man]

My cyls needed the bore, they determined it needed.020 off and then I ordered the pistons. They told me the pistons were all mic'd the same but that doesn't mean they actually were. Tomorrow I'm going to talk to them further about it.

 

[hvyman]

^thats what i mean. the machine shop should not bore your cylinders with out the pistons and should bore the cylinder to the piston. if they bore 1 cylinder to one piston they should mark it so it goes in that cylinder. etc. not o i measured all the pistons and they were roughly the same so i bored them all the same and you can mix match. i want to blue print my motor and have exact measurements and thats what im paying you to do. you get?

 

[Bri7man]

Exactly but I didn't know all this before I came to them, they made the sizing decisions for me and now that I look back on it it seems they led me in the wrong order... God knows what they really did.

Hopefully they will explain clearly tomorrow.

 

[IJ.]

Probably work to + - 1 thou kind of shop.... :nono:

Not too many shops chase tenths unless instructed to.

 

[BrandonW]

the machine shop i used did the machining with the pistons i gave them

they balanced the rotating assembly and bored each cylinder to each piston (i also used npr pistons .020 over)

 

[CyFi6]

When i measured my Probe pistons they were all the same to the .0001" place.. so yes it is possible. No they are not going to be the same to the .xxxxxx" place but nobody measures that precisely. You could technically measure all your pistons and tell them what to make each bore in the engine too, but most people leave it up to the machinist, not to mention a machinist isn't going to trust your measurements and put their name on it.

Trust me if machine shops were not so hung up on their ways i would have given them every dimension i wanted for everything and they never would have touched my pistons or crank.

 

[hvyman]

yes but the proper way to blue print an engine is to bore each cylinder to 1 piston and then balance the whole assembly. not take the pistons measurements and then bore and say you can put them in any order.

 

[IJ.]

yes but the proper way to blue print an engine is to bore each cylinder to 1 piston and then balance the whole assembly. not take the pistons measurements and then bore and say you can put them in any order.

"proper" and what happens in the vast majority of machine shop are 2 totally different things, ever wonder why good "race shops" can charge so much more than the local machine shop....

 

[Bri7man]

Okay they actually were all the same. .00175 piston to bore clearance, .002 rod bearing clearance, and .005 rod thrust clearance.

They even offered to come back and help with the last 2 pistons but I didn't make it in time as I had just got out of class.

I have to say I'm pretty impressed. They even printed out the above clearances for me on a specifications sheet. :love: