Don Terrill’s Speed-Talk

Has anyone ever run an Icon 2618 BBC piston in a street engine with .007 to .008 piston to wall clearance? I believe the pistons rock in the bore about .025 too. Top ring gap is about .021.

Icon recommends PtW .0045-.0055 for street NA.

Will the engine beat itself up or just be a little noisy until it warms up?

492 BBC with 10:1 compression

Thanks

The shorter the piston, the bigger the problem will be with excessive bore clearance...

Been several discussions here recently about using custom coatings to take up the slop.

Thank you for your replies. I will check into coatings.

You had better run a Barrel face second ring if your having less then pefect PTB issues , as all the coatings in the world will not help the rings seal better!

Line2Line claims their coating will fill up the sloppy clearance between the piston and bore. Sounds like magic to me. I wonder if anyone has successfully done this on Speedtalk. From Line2Line's website:

ADVANTAGES:
Restores and Holds Clearances
Highly Wear Resistant
NHRA Pro-Mod Tested

AND
Piston Skirt Coating reduces operational clearances, protects piston skirts from scuffing, retains oil, and reduces friction. Recommended when piston and bore dimensions are providing stock clearances. Reduces slap and ring flutter compared to uncoated pistons, effectively improving ring seal and reducing wear on the pistons and rings. Also protects the interface from foreign particle wear. During a short break-in cycle (5-15 min), excess coating thickness will wear away where contact stresses are highest. Where there is room, lower contact stresses allow the thickness to remain and reduce operating clearances.

ADVANTAGES:
Reduces Stock Clearance for Best Fit
Reduces Slap for Better Ring Seal
Protects Against Scuffing
Retains Oil Film
Promotes Hydrodynamic Sliding
Reduces Friction
2 Strokes Run Quieter Crisper

Bishop540 wrote:I wonder if anyone has successfully done this on Speedtalk.

Yes.

Recommended when piston and bore dimensions are providing stock clearances.
Reduces Stock Clearance for Best Fit

Anyone else having difficulty translating this?

PackardV8 wrote:

Recommended when piston and bore dimensions are providing stock clearances.
Reduces Stock Clearance for Best Fit

Anyone else having difficulty translating this?

I guess stock clearances are too loose for them and need to be tightened up.....

Yes, I think they are saying that stock clearances are designed to live long and prosper under worst case conditions, so coating them up to/near zero allows it to open up only where and how much required for your app. Under this scenario, the worst that could happen if a rare extreme arose would be self-clearance a tad more.

MadBill wrote:Yes, I think they are saying that stock clearances are designed to live long and prosper under worst case conditions, so coating them up to/near zero allows it to open up only where and how much required for your app. Under this scenario, the worst that could happen if a rare extreme arose would be self-clearance a tad more.

Yes Sir, I think it is my best option at this point.

Pistons off to Line2Line. They said they will coat them to .002 PtW, and then let the 2618 do its magic for the rest of the clearance needed. I hope this is a big step in the right direction.

(gonna start another thread about bearing clearance)....

Just for future reference, at .008, the thing would sound like a diesel at idle. Temperature wouldn't have mattered. It wouldn't kill the motor, it would just be noisy.

We once did a 283 Chevy at .006 and it was still noisy, but fine. We did a Chrysler "A" motor at .004. It ran great, but don't stop at the donut shop unless you have time to lose the heat soak, because it wasn't going to start until it was cold.

This was back in the day when we were still grinding pistons. The skirt designs we use now can still be run at or above .008, but they're not optimum.

I have to ask why??
The piston is inexpensive to start with so I got to ask why would you not just go to the next oversize??

ProPower engines wrote:I have to ask why??
The piston is inexpensive to start with so I got to ask why would you not just go to the next oversize??

They may be "inexpensive" in Canada but not in the USA.