Temp variance between cylinders

[tbirdtbird]

Several of us in the past have stated that cyls 3&4 run hotter than 1&2.

Today I did startup on a clients A motor that we had to re-work extensively because the prev. shop had set the piston-wall clearance too tight ( We see this all the time). Piston 3 got real hot, then shrunk, giving him a knock. We had gone thru all the easy stuff before commiting to pulling the head and dropping the pan, which we do over a pit. While in there he wanted to change out for a Bill Stipe B profile with .330 lift

The piston is badly scored and I will post a pic later. Fortunately the walls were not bad at all, the bores needed to be honed anyway. He had done little driving once the knock appeared.

All cyls were honed in our shop to 3.955 which is 080 over. (these bores were .001-.002 too small). Pistons installed were custom 283 style (short skirt) from Pete's Auto Machine in Albuquerque NM. These custom pistons allow you to use the original A rods. (an extra 1/8" of meat has been added to the top of the basic 283 piston. The machining of the pistons is such that the clearance is built in; i.e. they are machined .0035 under the 3.955.

The startup and initial cam break in went even better than expected. After full warmup, I used my temp gun on the cyls from the driver's side of the engine. Please know that the motor spins freely whether cold or hot.

Here are the readings:

1- 210 degrees
2- 210 degrees
3- 240 degrees
4- 240 degrees.

This is why you cannot set piston to wall clearance to modern car standards (usually .0015); which happens all too often.

You must use .003-.004; else bad things will happen. You be the judge.