Piston to crank clearance

I am building 351w/393 stroker. My crank counter weights are contacting the skirts of three of my pistons. The question is, do I notch the piston skirts or shave the crank? If I notch the pistons, do I do all eight the same or do I match piston weights by taking it out of the back side of the remaining pistons? Do I need to keep the pistons symetric? What is the correct clearance for this situation? I have 0.050" in my head but I am not sure where I got this number from. This is my first build and I would rather not funk it up. It will not be my last, so I want to learn to do it right.
The crank is an Eagle cast steel and the pistons are full floating Sealed Power hypers. It will be balanced with a TCI Rattler and backed up with a five speed manual. I plan on spinning it to 6000rpm. The mill will be in a late Bronco and used as a trail/tow/blazer recovery rig.

If you take it off the crank you'll put it slightly off balance.. If you take it off the pistons the diffrence is much less...

I say take it from the skirts, but only enough to give safe clearance...

Maybe someone else will chime in with personal experience in this matter.


FE

Either way you do it, your going to need to rebalance. I suggest clearancing the pistons, its much simpler.

Question? have you had the crank index checked? Whos / What parts are you using? Have you checked the deck clerances?

Doing it to the pistons you will not necessarily need to re-balance...

I balanced my last set of 390 pistons by hand and it takes a hell of a lot of material to make one 10th of a gram... Notching the skirts a bit should not effect the piston enough to hurt it I think.
Especially if you do each piston the same amount in the same place....

Call a machine shop...

I have not had anything balanced yet. Crank is balanced from manufacturer but rotating assembly will be done after fitment.

Something doesn't add up. Why is it only doing it on 3 pistons? As many 393 Windsors as there are, you don't hear of this problem very much.

The counter weights are not all the same width and the cylinders are offset from one side of the block to the other.

You need .060 clearance on all pistons. You may not be able to remove all .060 from the pistons without compromising the pin boss. You may also require heavy metal it you remove all .060 from the counterweights if the pistons and rods are heavy.

So what do you do?...I can't help you completely because of my inexperience with a 393. My experience is with a 331 using 5.155 length rods. This setup required modification to the crank and pistons to obtain the .060 clearance. I removed .015 from the pistons and about .100 from the crank counterweights. I was able to do this and still have enough counterweight that heavy metal was not necessary...your case may be different. Heavy metal is not necessarily bad, but it raises the cost.

I would first remove as much material from the pistons without compromising their pin boss strength. Ask a professional how much can be removed. I doubt that all .060 can be removed, but some can probably removed.

After you lighten up the pistons as much as you can, take the rotating and reciprocating assembly to a balancer and have him check to determine if the counterweights have enough mass to obtain the total .060 clearance by removing metal from the counterweights only. Then you can have the counterweights turned down by a machine shop and then proceed. Otherwise, some heavy metal will come into play.

If you want to save money, you can cut down the counterweights yourself (after you find out if there is enough counterweight to do this). I have done this with a grinding wheel...it's not a big deal. You gotta be good with a grinder to do this or you may remove too much or worse yet hit a journal. You can knife edge while your at it.

Yep! Knife edge the crank clearance your pistons then get it balanced...
You really want' to stay away from needing heavy metal.. The balance shop in my area charges $100 per ounce....

Maybe JOE SHERMAN will chime in here. He's been building race engines and the like for about 4,500 years... Or since the advent of Oil I would guess...

i ran into this on my 427 build,speedomotive used a crank for 6.200 rods and i got the 6.125 rods to get the rings lower on the piston and not into a wrist pin,the wieghts hit/scraped 3 pistons at the pin boss,they had clearanced 1 piston boss,i knew it wasnt right esp since i spent 7500.00 with these idiots,i sent the rotating assy back and finally after convincing them wahat the problom was they cut the counter wieghts,had to rebalance the whole thing.went from 0/28oz balance to 28oz/50oz,damper/flywheel.what afreakin ordeal that was,i say send it all back and get the right stuff.