Clearance

[Schiada76]

Does anyone know the clearance for crank counterbalance to piston skirt in a blower application?
^&^&*&(%$## crank is rubbing a skirt!

[MikeF]

I can't be of much help, but I see some grinding and a rebalancing of rotating assys in your future .

[Schiada76]

Thanks Mike! I'm looking forward to another disassembly myself! Hopefully the balancer will be able to just do the pistons w/o doing the whole magila. The pistons are custom JE's speced for a stroker too. Anyone know the minimum clearance? Would it be the same as the crank to block or do you get lots more thermal expansion in the AL pistons?
I guess I could just keep putting it back together and win 76crusaders prize for first motor to break on that other thread.
I've got an idea! I'll just keep turning it over by hand until it laps itself in with zero clearance!
[ November 16, 2002, 05:32 PM: Message edited by: BradP ]

[Kurtis500]

Brad, I run my forged pistons at .008 - .009 under the bore. I also have 8 buttons in each piston to guide the skirt on the wall. I think cast pistons are closer i.e. 4.030 bore, the pistons should mic at 4.027 give ot take. On this scale mine would be 4.021 for a 4.030 bore in forged on a blown gas deal. I run a gapless on the top and moly for a second ring. What did you mean by crank counterbalance clearance?

[Snowboat]

What did you mean by-----I also have 8 buttons in each piston to guide the skirt on the wall.

[Fiat48]

Crank counterweight to piston clearance should not be a problem. Evidently your counterweights on the crank are quite large. If you haven't balanced yet, consider turning the counterweights down on a lathe to reduce rotating weight. Otherwise, you may have to run a differnt rod length/piston pin location combination. .060 is a good number for anything rotating to clear whether it be crank to block, rods to block, etc.

[Schiada76]

Kurtis500:
Brad, I run my forged pistons at .008 - .009 under the bore. I also have 8 buttons in each piston to guide the skirt on the wall. I think cast pistons are closer i.e. 4.030 bore, the pistons should mic at 4.027 give ot take. On this scale mine would be 4.021 for a 4.030 bore in forged on a blown gas deal. I run a gapless on the top and moly for a second ring. What did you mean by crank counterbalance clearance?The crank counter balance is rubbing a piston skirt when the piston is at BDC. The block is fine on clearance for the stroke but the %$&&&skirt is rubbing on the crank. It's a scat crank with JE custom fabbed pistons. Shoudn't this be a fairley "stock" after market setup?
I'll find out on Monaday I guess.
[ November 17, 2002, 01:13 AM: Message edited by: BradP ]

[Schiada76]

Fiat48:
Crank counterweight to piston clearance should not be a problem. Evidently your counterweights on the crank are quite large. If you haven't balanced yet, consider turning the counterweights down on a lathe to reduce rotating weight. Otherwise, you may have to run a differnt rod length/piston pin location combination. .060 is a good number for anything rotating to clear whether it be crank to block, rods to block, etc.Everything has been machined and balanced. I know it's not the machinists fault, he didn't preassemble to check clearance. JE knew the pistons were being made for a stroker it's on their spec sheet. Don't they know the size of a Scat crank? WTF?
I'm hoping the whole rotating assembly doesn't have to go back.
On the bright side.....It's not my fault this time.
Fiat can I just take out the ole die grinder and lean on everything and just hope for the best? LOL

[Fiat48]

I've seen all this before, usually 12 hours before the next racing event. It goes without saying "always mock up" before any balance work.
Anyway: I don't like taking weight off the crank without a rebalance. I would rather you take weight off the piston (creates overbalance..very slight..no problem.) But I don't know how much we are talking here. Not much I hope.
I bought a Cola crank once and it wouldn't even fit in the block and clear the main webs! Makes you wonder what this crank was going to fit in!
If it were me, I would disassemble it, make the clearance by dies grinder or lathe on the crank, then have the balance rechecked. I gotta know it's as right as I can get it before I put my foot in it. Rather than worry at the starting line.

[Fiat48]

Uh oh. I am missing a star. I musta pissed somebody off!