I know this subject has been cussed and discussed half to death in this forum, but back when I first started to think about putting 307 V8 pistons in my 250 inline I heard two different stories about modifications. Some said they didn't do anything to the new pistons, but others said they had to trim the bottoms of the skirts. no one could seem to remember how much they trimmed off.

Well I just came from the machine shop a few hours ago, and here is what I learned. The 307 pistons are .060 longer from the bottom of the wrist pin to the bottom of the skirt compared to the 250 pistons. I do not know if this would create a clearance issue or not, but I opted to have the machinist trim them before installing the pistons and wrist pins on the rods. Better safe than sorry I say

Boo Radley

It becomes a issue when the Piston is in the Bottom of the Bore. The main issue is the shirt hitting the crank counter weights. If I remember right Is what my machine shop told me about 20yrs ago when I had 12-1 307 pop-ups installed in my 250.But i could not remember how much they had to remove.

#3220 }[oooooo]

I put them in during my christmas break and didn't do anything to them. They cleared everything and haven't had any wierd noises yet.

It may also be a Brand issue Thing??
#3220 }[oooooo]

Dear Boo;

When building a "custom engine" do just that.

Go to Ross of someone like them and have the pistons you need made to order. This way there's no 'guess work' etc.

Leave the 'parts-mixing' to others.

Good luck, John M......

The pistons I have in my 250 are TRW forged flat tops w/four valve reliefs & I did not need to trim anything.
I did however take out 200 grams or so of weight inside the piston just to lighten them up.
They are kinda heavy as they come.
Hank

The stock pistons had two small oiling journals on each side to oil the wrist pins. The ones I gat from NAPA do not have those journals. should I have the machinist drill them? I think i should.

Boo

B;

Here on our BB all you can get is "general information".

Answers to specific questions (your NAPA pistons)must be answered by the part provider or a professional Automotive Machine Shop....that knows or can see what you have.

JM....

I've been thinking about this issue with the oiling journals, and I am going to have the machinist put them in. No sense installing something I know isn't going to work as well as original equipment when it's such a simple upgrade. Leaving those holes out looks like something the factory did to hold down manufacturing costs, and it is obvious that the wrist pins will oil better with the journals in there!

Boo

I need to post a correction here because when the machinist cleaned absolutely all the crud off the old piston and checked both with a height guage on a flat surface the V8 pistons turned out to be SHORTER!!!! Moreover, he called GM and the tech said do not drill for the oiling journals because there isn't enough material to remain structurally sound. This partcular tech had never heard of putting 307 pistons in a 250, so I don't now how much he can be trusted, but comparing the pistons the originals are a lot beefier.

Boo