390 budget built with 4.112" bore
 

Good morning!

I am sitting here with a considerably rare 390 FE motor (by South African standards, and also due to budget constraints) and a bore size way past the limit, meaning not salvagable?

The block had erronoulsy been honed to 4.112" once instead of 4.11" which, according to my engine builder is too big for the corresponding 4.11" pistons. I don't have the actual piston diameter yet.

If it was 4.112” from wear at the top of the bore we all agree to assemble the motor with new rings (and bearings, which we don’t need to discuss now). This would be Option 1.


Option 2 is to bore the block further to 4.13" and get those pistons. This can just fit into my budget. There seems to be enough meat, which we can only find out by doing it.

If this fails, we can sleeve the block back to 4.05" for which I would have to buy pistons and rings, which makes this Option 3. The most costly version, which is actually out of budget.


Option 4 is to find another short block locally. Importing from overseas is too costly.
But then I may find that this is also not feasible. I suppose I can spend time on this thought after the bore.


I owe you the actual piston size, but I doubt they will be their nominal diameter plus 0.002” to fit perfectly into the bore.

Who would go for Option 1?

Or try option 2 using STD 406 cui pistons for $150, plus rings?
And which cylinder shall they bore first? Which one is prone to hit water the easist?

Don't bore to 4.130". 99% chance you'll lose a good block.

If it cleans up at 4.112", then I can supply you pistons at that exact bore size for about the price of an off the shelf forged piston. I can get them in any bore size, in .001" increments.

Don't bore that block anymore than you have to, and even at 4.112", I would sonic test it.

Thanks Brent!

I had that thought in the back of my mind to source pistons to fit. Never hoped they could be affordable at all. And they may not, but adding re-sleeving and cheap (cast) pistons together probably cost me the same, or similar.

This is Option 5 :-)

It's shows "cleaned up" at 4.112", because it must have been bored/honed to that size. Let me verify this.

What is the actual piston diameter (or bore clearance)?

The piston is made to fit the bore, so in this case, the piston will be about .003" smaller......

I mailed you just now. Let me do my homework about the dimensions.

Thanks!