Clearance for Ross pistons?

[nickrule99]

Hey guys-

I dropped my stuff off at the machine shop the other day, and they told me my block was bored out to much... there was 6.5 thousandths between the piston and the wall. So I called up Ross to check with them, and they guy I spoke to said 6.5 was to large, it would work, but it would be noisy, and 4 thousandths clearance would be better. So, I ended up buying another block for the machine shop to bore out to waht they said should only be 2 thousands, but I told them 4 since thats what Ross told me.

Well, the shop called againt today, asking what side of the piston was intake and which was exhaust. I didnt know so I called up ross again. The told me the logo was towards the intake side (is this true?) and then I asked about what they recomended for clearance. He asked what boost I was planning to run (I said 15-25) and he said I should go with something between 5.5 and 6.5 thousands of clearance.

So now I dont know what to tell the shop. They say I should have it bored to 2 thousands clearance between the piston and wall, and ross is telling me both 4 thousandths and 5.5-6.5 thousandths.

Im supposed to call the machine shop back and let them know what side of the piston is which, but turns out it doent matter because an Eagle rod can be mounted either way?

So... Im going to call the machine shop back and tell them to not touch the block yet, but if any of you can help me out I'd GREATLY appreciate it.

The pistons have 8.5:1 compression
and Im using Eagle rods.

Thanks guys.
-Nick

EDIT:
Did a search and found .003 to .0065 to be ok...

Anyone care to chime in about what their clearances were, and if they get much/any piston slap?

I think right now I'll tell the Machine shop to make the clearance .0045, sound good?

[johnnytsi]

I got the same runaround between Ross and my machine shop. I finally told the machine shop to use .0055

The engine has 5000+ miles on it now with 24psi as my low boost setting.

Still no piston slap noises!

Good Luck,

[NDgsx]

Take your stuff to another machine shop. Anyone that is trying to put a ross piston in at .002 and then can't figure out which side of the piston is the intake side based off the valve relief doesn't know what's going on.
.0045-.005"
Big valve relief = intake side

[blue1]

Piston companies will usually specify your piston to bore clearence with paperwork supplied with the pistons and where to take the measurement from eg: opposite the gudgeon pin or .500 below the gudgeon centreline. i have found in a number of years of using forged pistons (27 of them) go up .001 on manufacturers specs and you will be fine. and they do face a certain way inlet reliefs ( bigger ones) to the inlet valve side is usually a good indication, if not do as NDgsx says find someone where you are confident!
My 2 cents.

[TSIfreek]

.045 on mine. Get another machnine shop. I would stay as far away from them as you can. You need to trust your machinest just like you are a marrired coupple. If you cant dont use him.

[nickrule99]

I guess the confusion they had was they thought it was a N/A engine, so they were looking at the wrong set of numbers. I told them it was turbo, and they said, Oh.. we'll set it up for .004 -.0045.

Well, I went down there today to pick it up and they ended up boring it for .004 clearance between the piston and the wall.

Is that too little? Its not really going to be used as a race engine, more of a daily driver with a little kick in the ass when needed.

Im just scared of it seazing up on me now.

[johnnytsi]

Take it back and make them do it right!

.004 is to tight for Ross pistons in a Turbo engine!!

The Ross instruction sheet specifically states to use .006 for small bore Turbo engines.

I told my machine shop to set my clearance to .0055. I "fudged" a little on mine with the same thought that the engine will be a daily driver and would never see huge amounts of boost.

HA! Here I am a year later running a td06-20g with 24psi on my low boost setting.

frankly, the only reason for going to the expense of a forged lower end is so you can "crank the boost up"

Now is the time to "do it right the first time"

[nickrule99]

I called and talked to an engine builder at a reputable DSM shop, and he said they use a .004 clearance for boosted engines with no plans for nitrous.

And If this shop is doing it, then I'll sure as hell trust what they're telling me. Not that I dont trust you, but these guys build engines for a living, and its working so far for them.

We'll see what happens when I finailly get this thing together.

Thanks for all the advice, I'm sure I'll need more in the coming weeks.
-Nick

[swordfish]

I run my long rod 2.4 at .004. Big boost, and for this summer big nitrous too.

jeff

[NDgsx]

Originally Posted by swordfish

I run my long rod 2.4 at .004. Big boost, and for this summer big nitrous too.

jeff

Jeff the clearance on the long rod 2.4s is tighter, I'm not sure if it is because of skirt profile or material mass, but 150 rod 2.4s are run at .0055-.006".
When in doubt run a little looser, it's much better than scuffing the walls.

[Colossus]

On forged pistons, at least my wiseco's, look at the notches for the valves. The intake side ones are slightly larger than the exhaust side. This can tell you which side the pistons should be facing. I put mine in backwards one time not knowing :-\

[swordfish]

Originally Posted by NDgsx

Jeff the clearance on the long rod 2.4s is tighter, I'm not sure if it is because of skirt profile or material mass, but 150 rod 2.4s are run at .0055-.006".
When in doubt run a little looser, it's much better than scuffing the walls.

Yes. That's what Marco was telling me when I built this motor. Wrist pin location (6mm up + the offset) allows for the tighter clearances. Long rod = big sex. :laugh:

jeff

[spoolamatic]

Mine are at .006 in. good compresion and very little blow by under boost but they sure
are noisy till you run it a good while .I wish the machine shop would have put them at 4 to 5 like I told them .