EngineBuilding
Piston scoring on only one side
I have a customers Olds 350 that he tells me has been bored .068 over (I have yet to verify) with all sorts of fancy expensive forged parts & Howard’s roller conversion.
He paid some guy with a gold rattle can 4x what I typically charge for this thing & 1000 miles later it’s being torn down because he can’t find the knocking noise that he said was there from day one.
I am don’t see many Olds engines, but more importantly I don’t see many with scoring on just one side off the piston.
Tomorrow I will get the rest of it torn down & actually get some real measurements. (Only thing I measured so far is the rod & it is round)
Customer says it had 20 psi at idle & 60 driving, ran VR1 & hasn’t overheated.
The build has a real shade-tree vibe, no two bolts are the same, multiple washers on bolts instead of shortening one, painted with a dead chicken etc.
Anyone got any good bets on what the last guy screwed up to cause this?
Discussion
Ya had me at 'Painted with a dead chicken'..
Cylinder may be out of round
If it’s on the thrust side of the piston, lack of lubrication caused by fuel wash
ring gap to tight and butted
Are the pistons offset pin and installed in the wrong direction?
That’s a great thought, the pistons are DSS FX 1-6020-4125.
I will need to check what the rods are in the morning, but they did have A0 370 as a casting mark on the cap if it means anything to anyone.
The chamfers were similar size on both sides & the rods looked relatively symmetrical. They do have an oiler hole, because that’s in my notes to check for orientation.
Bingo, we had an LS come in like this. Guy bought 8x of a piston instead of the kit and they were .035 offset left side pistons. The dots on top not facing forward on the whole bank wasn't a dead giveaway......
Highly probable. Very old school used to be reverse the pistons to increase dwell at TDC.
Very old school indeed.
Exactly what I was thinking
Hey those pistons look familiar. They are DSS. If they are the 4032 version, they have centered pins and should have been installed with about .0035 piston to wall. They might have the metric rings, or the 1/16 compression rings.
Good eye, DSS 1-6020-4125, will check the rest in the morning.
Check to see if they did any of the goofy stuff people try on Oldsmobile engines, like restrictors in the oil hole to the cam bearings.
Looks like the "X-groove" technology didn't save this one.
Can't save it if there is negative clearance
"Negative Clearance" I'm using that in the future
Ok fine....why only on one side then? Because of the offset?
Edit: just saw they're centered pins.
Thrust, uneven temps, stuff like that
Gotcha
It's a stiff, rigid forging. It's not heavy, but has enough mass to make pistons for many bore sizes and comp heights. One side could well get hotter.