390 FE rebuild question
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Laughing Gas
Joined: Apr 2018
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390 FE rebuild question
I have a Ford FE block here I'd like to use for my rebuild. If I can get away without having to machine and just use honing stones, I'd like to ($$$).
With my little dial bore guage set to 4.050 here is what I have... (So all my measurements here are 4.050 + the measured amount over)
In the middle of the cylinders I measure a 0.0016 difference from the dial gauge being at centerline and then 90 degrees turned
From top, to center, to bottom 0.0050, 0.0035, 0.0040, so the greatest difference being 0.0015.
That seems like it might not be too bad out of round to me and might just even out with the stones, but... I've never done this, so...
With my little dial bore guage set to 4.050 here is what I have... (So all my measurements here are 4.050 + the measured amount over)
In the middle of the cylinders I measure a 0.0016 difference from the dial gauge being at centerline and then 90 degrees turned
From top, to center, to bottom 0.0050, 0.0035, 0.0040, so the greatest difference being 0.0015.
That seems like it might not be too bad out of round to me and might just even out with the stones, but... I've never done this, so...
Tuned
Joined: Sep 2024
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I'm going thru much the same thing right now. I think ovality will always be a reality on these blocks. Short of having a machine shop sleeve each cylinder it'll be what it is.
For my case we've just at the stage of confirming the new piston rings are within spec.. which I believe they'll be.. and we're going to rebuild the engine.
I doubt it's your stones and that your bore gauge is telling the truth.
As for what to do - you call. I am rebuilding ours in 2 weekends so if you want I can share what we find
For my case we've just at the stage of confirming the new piston rings are within spec.. which I believe they'll be.. and we're going to rebuild the engine.
I doubt it's your stones and that your bore gauge is telling the truth.
As for what to do - you call. I am rebuilding ours in 2 weekends so if you want I can share what we find
Cargo Master
Joined: Oct 2020
Posts: 2,675
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Out of round conditions are something that I see from time to time in blocks and I'm not always sure what causes that to happen. I've seen it in Chevy LS blocks where the bore might be worn .001 or so, very little yet the bore will be out of round .003 or .004. There may be more than one in a block too but not all of the bores. It makes me wonder if they just got like that over time or if they were always out of round from brand new. I had one of those crappy late model Ford Coyote blocks last year that was out about .006 and there was not enough cylinder liner in the block to clean it up. .25mm is the largest overbore size.
Last edited by DaveMcLain; Apr 12, 2026 at 04:08 PM.
Cargo Master
Joined: Oct 2020
Posts: 2,675
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LS blocks are not prepped using a torque plate at the factory. I'm not sure about the Coyote but either way a torque plate doesn't distort the cylinder in the way I'm seeing. And it isn't on every cylinder, just a few and not in every block.
Cargo Master
Joined: Mar 2002
Posts: 3,132
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From: W (BY GOD) V
LS blocks are not prepped using a torque plate at the factory.
I THOUGHT THIS WAS A FORD FORUM, I'm Sorry.
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Cargo Master
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I was just talking about blocks in general.
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Laughing Gas
Joined: Feb 2011
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Ovality under .002 isn't bad IMO for stock build. Variation top to bottom isn't that bad either. I assume there is barely any discenable ridge at top of cylinder?
Unless you are building a performance enhanced engine, or one you'll expect to get another 50 or 60,000 miles out of, you'll be OK with honing. Not many of us drive these trucks like we used to back in the day so the mileage you plan to put on it over the years is a factor in the equation.
Unless you are building a performance enhanced engine, or one you'll expect to get another 50 or 60,000 miles out of, you'll be OK with honing. Not many of us drive these trucks like we used to back in the day so the mileage you plan to put on it over the years is a factor in the equation.
Cargo Master
Joined: Mar 2002
Posts: 3,132
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From: W (BY GOD) V
What you are attempting to do is akin to an old-style (1940's - 50's) IN-FRAME. You wouldn't even have to remove the engine.
Remove the crank and hone away. Put a set of rings, main and rod inserts, re-seal it and ride.
Remove the crank and hone away. Put a set of rings, main and rod inserts, re-seal it and ride.
Logistics Pro
Joined: Jun 2004
Posts: 4,763
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From: South Central Utah
This is a factory piston out of my 410. It was a low mileage engine out of a totalled 1966 Mercury.
It was rebuilt back in 1972 and I have to assume that the rebuilder didn't bore the block because possibly he didn't feel that it neded to be bored.
Instead he had the pistions knurled. I've been told this was a common practice back then and could malke up for around 0.002".
If you want it perfect and want to put a 100,000+ miles on it have it bored, line-bored, deck the block and heads, do everything you can to make it as good as it can be.
I've seen a lot of engines get rebuilt with close to 100k miles on them and never get bored, just a good hone and new rings.
And depending on the bearing wear I've seen them skip machining the crank too.
Rings, bearings, heads, cam and timing gears and hit the road with no oil buring or any other issues.
If I was rebuilding something like a 401HP 390, 352 PI, 289 HP, any of the 3 Boss or any CJ engines, you bet I'd havethe best work done I could find.
A 352, 360, 390... probably not.
Last edited by Rubiranch; Apr 14, 2026 at 09:39 PM.
Cargo Master
Joined: Oct 2020
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Cargo Master
Joined: Mar 2002
Posts: 3,132
Likes: 218
From: W (BY GOD) V