badgta

iTrader: (4)

i am in the process of cleaning my engine parts on the 383.. i am now at the piston rod assemblys and notice that the skirts on the pistons have alot of scuffing on them..... what would make them have this much with only 100 miles on the bottom end? maybe due to the longer stroke and side loading?

DartByU

A longer stroke with short rods will increase side loading some, what length rods do you have? If it overheated some that could cause it also, also too much piston to bore clearance is another cause, what type pistons do you have, and what clearance do they have? Why did it only run 100 miles?

ede

excessive thrust clearance will too, but my guess is heat or piston to bore clearance.

badgta

iTrader: (4)

well the machine shop asked me about the pistons when they bored it.... there was a measurment that he had to have to properly bore the block.. he said it was already built in with the numbers i gave him.....

it never overheated....... it would barely hit 160, and when it did the thermostat opened and it would go down below 160....

the motor went down due to burrs in the scat crank that broke off and found there way to the bearings... then a sort of chain reaction occured and eat more of them up..... the place i bought it from is paying to have the crank turned and sending me new bearings.......

i am pretty sure the measurment was broe vs piton size clearence.... i think some need 4.035 for 4.030 PISTON...

the piston is speedpro l2491f30

ede

i've had a lot of blocks bored and no one has ever asked me what pistons i'm using. i'm no machinest but i believe the over bore is standard, any sort of special needs or clearances is built into the piston. if i'm right that may be your problem, someone added a few thousandths to allow for something they didn't have to. i guess there's no chance you measured anything before you put it together is there? that might tell you something if you knew the numbers.

badgta

iTrader: (4)

thats what he was wanting to know.. if it was built in or not.. i gave him the numbers and he said it was.. i guess he was wondering since they ere fordged.. i think some forged need more clearence....

the rods are 5.7's.......i could probably take some emery cloth to the pistons and smooth them out alot......

Vader

Anything you remove from teh pistons will never get put back on them, only making the clearances unnecesarily wider. If you have sharp risers in the scuffing, I'd suggest roller burnishing the high spots, not sanding them off. You can roll the high spots back down into the grain of the metal without removing any material. If the scuffing is only cosmetic, I wouldn't even touch them.

Forged slugs do operate with a little higher initial clearance, but tend to expand a bit more when heated. If the pistons were not cam ground to accept this expansion, you may have to live with teh sloppy fit on cold starting, and understand that you'll have to warm the engine a bit longer before loading it. That's never a bad idea anyway, unless you're the EPA or really into generating good CAFE numbers for the boys at GM.