Engine Inspection

Engine Inspection

March 2015 – 289 V8 Engine Inspection

When I bought the Disgustang, I was told it had a little over 100,000 miles on it, and nothing I’ve found so far has led me to believe any different.  The odometer showed a little over 8,000 miles when I took it out (if memory serves), the transmission fluid didn’t smell burnt when I drained it, the door hinges aren’t worn out, and the brake pedal rubber isn’t worn excessively.  With all that evidence, I firmly believe the reported mileage to be correct.

Why does the mileage matter if I’m going to restore the car anyway?  Great question!

With only 100,000 miles on the clock, my hope is that the engine hasn’t been rebuilt.  At that mileage I’d expect the engine to be in need of a rebuild, but again, the hope is that it hasn’t been done already.  Ford 289 V8 engines are thin-wall castings, making them both light and compact, but it also means they won’t tolerate much overbore before the block is considered useless.  Because the motion of the pistons up and down slowly wears the walls of the cylinders down, they get larger in an irregular fashion as the miles pile up.  Instead of being a perfect cylinder, they can become barrel-shaped, wider in the middle of the bore than at the top and bottom.  To remove the wear, at each successive rebuild you have to enlarge the cylinders slightly to get them back into the shape of a perfect circle.  Apart from the factory original “standard” bore of 4.000 inches, common overbore sizes are 4.020, 4.030, and 4.040.  According to much of the literature I’ve read, 40-over is pretty much all these blocks are good for, and sometimes even that’s a stretch.  And for reasons passing understanding, many mass-market rebuilders go straight to thirty thousandths (.030 overbore), so if my block has already been rebuilt, I may be better off finding another block than rebuilding this one.

Part of the fun of restoration is the forensic inspection of existing components.  I feel like a car detective!  How did this part perform in use?  What went wrong?  Did it just wear out or was it defective? How worn out is it?  Has someone else already messed with it?  Is this the way it’s supposed to be?  I love those questions!

So what did I find when I tore into the engine?  Disappointment and a ray of light.

The moment I pulled the valve covers, I started to fear the worst.  Engine inspection is a lot of measurement, but the first thing that matters is your gut reaction.  What did I see?  There was paint on the rocker arms and on the surfaces of the head.  I’m pretty sure Ford didn’t paint engines like that.  And then I saw it: the valve tips were wrong.  They’re the later, longer type intended for rail-style rocker arms (a common mistake).  My heart sank but I continued along and pulled the intake manifold and heads.  And then I got the irrefutable news.

Just as I’d feared, the block had already been bored.  I stink at micrometer measurements, but this block is at least .020 over, certainly not standard bore.  But from looking at the cylinder walls, it hasn’t seen much use since the rebuild.  It might actually be salvageable.

I pulled a main bearing cap and a connecting rod cap and measured the bearing clearances, they were both within spec.  Not wanting to blow the engine apart completely and possibly lose parts, I buttoned the block back up and put it back in the bag.  I’m a little ahead of myself anyway, since I haven’t even sent the car out for paint yet.  Ultimately I’ll leave it up to the rebuilder to see whether he thinks this block is salvageable or not.

Oh, and to cap it all off, I could’ve probably deduced the engine had been rebuilt had I paid more attention to the casting date on the block: 7A8 – January 8, 1967, 7 months after my car was built and 8 months after the heads were cast.