Should my piston go into my block?

[djharr]

I am working on my new engine, and today I was getting things cleaned up ready to put the pistons and rods together and start the reassembly process. I have had the pieces for years, after having gotten sidetracked after I bought them but before I had a chance to do the build. So, I was just playing around trying to see how things would fit with the machined block and the various pieces. As part of it, I attempted to slide the piston into the cylinder...and it wouldn't go! This is a forged TRW piston, casting number 255-98, which theoretically means that it is an 0.030" over piston for a 302. My machinist bored the cylinders of my 302 out to 0.030" over, so I am certain that the dimensions of the cylinder walls are correct. Also, I have an old 302 A4 four bolt main block that is bored 0.060" over, and the piston won't easily slide into that cylinder, either.

Are forged pistons just larger than normal pistons? Do they run tighter clearances? I already put a small scratch in one cylinder wall, and I don't want to damage the block, since it is all set up and ready to go, so I am reluctant to try and force it in.

Frankly, I am mystified about the whole thing.

David

 

[dcurtis]

For starters never have a machine shop just bore a block to a certain size, always take the pistons to the machinist and have the bore finished to that specific piston. And if a .030 piston won't go into a .060 over hole then something is wrong. Verify the piston and the bore. And don't ever force a piston into the cylinder.

 

[blackened88lx]

What he said. .030" over isn't just .030" over. The machinist should have the pistons and match the bore to them. The pistons should go in pretty easily so something is definitely wrong. I'm guessing you got the wrong pistons somehow. Why aren't you building it with the A4 block anyway?

 

[djharr]

I got the A4 block several months after I started gathering parts for the buildup using the Mexican block. Then things got strange and I stopped working on the thing for several years. I guess I will just have to schlep the pistons and block over to a machinist and seewhat he has to say. If I have start over, I guess I will go ahead and use the A4 block. Anyone want a prepped Mexican block and DSS main support system?