Hi everybody,

I would need some help from all out there!

I'm rebuilding my Corvette (2002) LS1 engine and got 0,0035 inch in the piston to wall (cylinder) clearance with the stock piston (Hypereutectic), after honing. The piston sould have a maximum clearance at 0.002 inch from what I have read. Is there anyone out there that have experience of this big clearance on stock piston (Hypereutectic) or should I go with forge piston that needs 0.0035 inch minimun clearance? Like JE forge pistons (2618) or can I go with the stock pistons without problems?

The engine is supposed to make 500+ HP with Trick Flow top end kit, 228/230 cam, edlebrook pro flow intake ect.

/Alex J

 

You'll lose compression/power, burn more oil, and increase engine wear if you keep the stock pistons with tolerances that out of spec. Replace the pistons.

 

You have the option of coating the pistons. Places like Calico or PolyDyn can apply about .001" to each side to reduce the piston-wall clearance a total of .002". I've used PolyDyn since they're local to me and they charged $150 IIRC.

 

.035 PTW clearance?

replace the pistons.

Sure you didn't "hone" out a little TOO much?

 

you mean .0035 right?
Not .035.

Bigggggg difference between the two.

 

^^ what that guy said.

 

That's about 10x too much for even 2618 forged pistons, so looks like you went WAYYY to far with the honing. If you run that car like that it's going to knock so bad your ears will bleed. And won't last long either.

 

Thats down right boring at that point to go .035 over the pistons. Can the ls1 being sleeved even get bored that far? I was under the impression no. I really think he meant .0035

 

I´m sorry! I meant 0.00355 inch (0.09 mm). Do I need to change the pistons to forge pistons that work with that kind of piston to wall clearance?

 

Sorry, I meant 0.0035 in.

 

That's still huge, hypers usually call for 0.0007 or so PTW clearance. So that's 2618 forged piston territory.

 

That's still huge, hypers usually call for 0.0007 or so PTW clearance. So that's 2618 forged piston territory.

 

Thanks for the answer!

 

First, How did you determine clearance?
A. did you measure your piston with a micrometer? Where? Are they all the same?
B. Use a snap gauge or dial bore gauge for the cylinder? Where?
C. What was the bore before honing? Out of round and taper specs?

Getting them coated is the most economical way the regain spec, shoot for around .0015. If you can justify forged pistons, you may have to re-hone the block, unless the piston maunfacturer can supply pistons that are clearanced to your specific bore.

Some more information is needed before you go out and spend cash for parts that might not make things any better or easier on yourself.

 

The block was honed at an engine machinist so I could use some new piston rings (total seal rings). Unfortunately he honed the block without torque plate and the cambearings was bad mounted (this engine machinist/builder have a good reputation here in Sweden, thats why I went to him...). I got the money back for the bearings but made me suspicious so I went to another engine machinist/builder to make sure that all the otther things was done at a proper way.

Here is the resault after the honing, measured with a cylinder dial gage.

Top 3.8988 - 3.8992 inch
Middle 3.8988 - 3.899 inch
Lower 3.8980 - 3.8984

All piston is at 3.8962 inch

The machinist that have the enginge now is going to mount an torque plate and se what the value is with the plates on next week.
I now have a cambearings tool that i´m going to use and that´s not a problem for me anymore.

/Alex

 

I'd either get the pistons coated, or even possibly knurled.

 

It's cheaper to buy new pistons (http://www.summitracing.com/dom/part...view/year/2002) than coating the used ones here in Sweden.

If the clearance is bigger than 0.0039 inch I will go with forge Wiseco piston (3.903 bore) and if the clearance is under 0.0039 inch I will go with new Speed-Pro Hypereutectic Pistons H868CP. If the clearance is 0.0039 inch and gett new Pistons with coating skirts I will get a reduced clearance with about 0.001-0.0015 inch that will get me to 0.0029-0.0024 inch piston to wall clearance. Is 0.0029-0.0024 inch a good clearance for a 500+ hp engine?

Is there anyone that have any experience about Speed-Pro Hypereutectic Pistons?

/Alex

 

very curious to see the results, keep us posted

 

Hi everybody!

Well folks, I got the result today... With the torque plate mounted on the block the value on cyl. 1 and 2 went far away from out of round. 0.0023 inch in different between top and lower measurment points in the cylinders. If the machinist would fix the out of round in the cylinder, the piston to wall clarance would be 0.0051 inch (TOOOOO BIG!).

I will go with aftermarked forged piston and rods... Any recommendations?

if anyone is going to rebuild the engine and reuse the stock piston, use torque plate and Cylinder Hone Tool 600 Grit for the rings!!!

/Alex