Engine Builders - Hyper Piston Question

[80fbody]

My fresh block got a couple long, vertical scratches in a couple cylinders. Apparently the oil expanders are wrong. Of course I didn't catch it until I knocked a couple pistons in & they were too tight. Everything looked good but the oil expanders don't even fit the bore nevermind the piston.

My question is, what could a get away with for side clearance with KB hypers in a race only 451? Right now 4-5 thou. If I honed it to 7-8 thou to try & clear up the scratches in those two cylinders am I asking for issues? Or should I just slam it together & see if how it leak downs. Going to order a new set of rings.

On a budget of course or I'd just prep a spare block. Bought the shortblock on a deal & luckily tore it down to verify everything.

 

[Baxter61]

i read an article where the ran hypers everywhere from .0015 up to .010 piston to wall clearance and noticed no issues except for a little piston slap as they went up in clearance. you could always try it and let us know the results

 

[Darter6]

I'm not trying to be a D*&k but a old saying from the 60's went,"Build them loose,,they'll take the revs." I did a small block that was at least .010. was noisey when cold but after a few minutes quieted down and is still running today.

 

[Dcuda69]

Hard to tell. Ring seal may have been better with a tighter bore clearance (even with the scratches) But then again..loose is fast..lol. I'd feel a little more comfortable with forged pistons being loose as they grow more with heat than a hyper. My vote?? Put her together and give her!!!!

 

[69 Cuda 440]

We have run KB Hypereutectic {4.30 and Larger} Pistons at .0065" Clearance, and no issues whatsoever.

We don't run them at the recommended clearance of .002" to .0035" for the bigger bores either.

We always aim for .004" at a 'Minimum' in Street/Strip Applications.

Maybe you can get away with using a Brush Research 'Flex Hone' which will clean up
the scratches, with minimal material removed.

 

[moper]

Can you post pictures of the scratches? A big part of why hypers work so well is the lack of expansion which allows for the tighter piston to wall, less piston rock and loss of ring seal. If the engine was never run, and you feel safe thinking it would clean up with another .0015-.002 off the wall surface - I'd just take the sharp edges off it and run it as is. This means some minor work but not with a flex hone. Nothing that will remove any material - but rather smooth out the tears in the surface. Have your shop duplicate the final wall hone which should have been a fine brush. Then remember you have to clean the entire block again - so new cam bearings and remove the oil plugs and plan to get out the cleaning brushes again.

 

[80fbody]

Thanks guys, I lightly took the sharp edges off & ordered a new set of rings last night. Plan to file-fit, clean everything again & put it together. I'll give a leakdown check once it's up & running. Hopefully it will run ok. I've got a spare block that I'll have prepped if need be.