Here is the picture of my number 1 piston.
Is this normal or did I dodge a bullet?
It's not normal to see that scuffing. I think your pistons are fitted without sufficient clearance. It should be about 0.006" at room temperature. The pistons are cam ground so they are not round at room temperature but expand to round at operating temperature. You might check with Royce or Nolan about how to measure the piston.
You are going to need to pretty up the pistons and hone the cylinders to get a little more clearance. My " guess" is you need to take out about 0.002".
I am putting in new pistons. Same .040 over.
The piston clearance was checked and they have right at .002 clearance. I can try to get a more accurate clearance tomorrow evening. I plan on doing number 3 on Tuesday.
Aluminum pistons with .002 clearance will stick in the cylinders.
What should the clearance be?
It might be running a bit warm. Aluminum expands at a higher rate than steel and if it gets hot will get tighter. Since you are going to install new pistons, you should hone the cylinders. Hone it good and it should be fine. You need .005-.006 inch clearance on the side perpendicular to the wrist pin toward the skirt of the piston. This will assure that the piston will not get too tight as it expands.
.005 to .006 is my vote. That's where I am now after tearing apart a fresh rebuild that was badly scuffing all four pistons. The rebuilder had set it up with .0025 clearance as specified. That might do it for a parade car, but not one that sees daily use.
I was honing just enough to take the color off and give it a new cross hatch. I was getting more depressed, but Norman and Dave gave me hope.
The silly car is so much fun to drive.
I am about to soak the water passages in vinegar.
The radiator has been to the shop to get cleaned out.
What would you'll think if I put the head back on with the old head gasket and fill the block and head with vinegar. Let it sit for one or two days? Then flush the heck out of it. Pull the head and replace it with the new gasket.
I am trying to get it to run a cool as it can.
Of coarse all the vinegar after the pistons are with in specks.
You don't need new pistons.
You can remove the scuff marks and put in new rings with .017" ring gap on the top ring, a little less on the second ring and 10 on the oil ring.
You also need to hone the cylinders out with a good hone that keeps the stones parallel with each other at all times. They are costly.
Hone them to AT LEAST .005" as recommended above.
I have borrowed a hone from my machine shop owner. Use an electric drill on the hone and constantly move it to the bottom of the cylinder and the up to the top without stopping the hone and have a helper shoot mineral spirits or cleaning solvent into the cylinder as you hone. Can also use acetone or spray carb cleaner or Brake & Parts Cleaner.
When you are finished and have .005" clearance wash the cylinder walls with hot soapy water.
This is important. HOT SOAPY water.
Oil the cylinder walls with motor oil or gear oil before putting the pistons back in.
5-30 or 10-30 oil will get up there between the pistons and cylinder walls to keep that from happening again.
If you set the piston clearance at .0025
(2 1/2 thousandths) use 20W-50 or roofing tar you risk getting piston scuff.
When the pistons get hot they expand enough so the heavy oil can not get up there.
Unfortunately I have yet to find a rad shop that can clean out the accumulated scale from hard water in a T rad. 12 hours of vinegar in a T rad is a good start. Lay it face down. Seal the rad cap (a O ring can work well). A couple of gallons of cheap vinegar to fill the core. Save your money as far as rad shops go
I completely agree with the advice on piston clearance and Aaron on motor oil
I was able to check the piston clearance through the inspection plate. I checked at the bottom and top of the stroke. It depends on the direction of the stroke. The clearance was at .005 or .006 pending on where in the bore the piston was. I did check all four. They seem to be pretty consistent. I didn't check the top of the piston because the clearance seems to be a little larger.
I am soaking the water hose connection that holds the fan in vinegar. The bearings are not in the vinegar. I just want to see how well the vinegar will do or if I need to get the CLR.
The reason that I am swapping out the old pistons to the new one is because I know the new ones are almost dead on even weight.
I wonder if anybody has ever added an extra thousandth or two clearance,....say maybe 6 thousandths or so, and then knurled the aluminum pistons to lessen any chance of piston slap? Would this make sense? Just a thought,......harold
I have one with the old Jahn's pistons 0.030 that was knurled.30+ years ago,it is still runable
I have added a knurl to reduce excessive clearance on many occasions. Used to be a common job at the shop where I worked. Dave in Bellingham, WA
Knurling a piston gives a brief bit of extra life to a worn bore. It's a job that has little benefit beyond a couple thousand miles. You don't want to start out with worn bores Harold, and knurling pistons is only going to give you brief relief from piston slap.
I am not planning on knurling the pistons, but it is interesting.