[drewm]

I decided to get a bore scope camera to look at the cylinders of the motor that came with my car. Its a 66 YF 389, but I believe has been rebuilt at some point in the past. To what extent, I do not know. Anyway, I was hoping that the pistons might be marked with an indication of what kind of overbore this has. The motor has been sitting for 25+ years. It does turn over by hand, and I put some marvel in the cylinders to let it soak. Anyway, heres the pics. Crosshatching is still visible. Any thoughts? Do those look like stock pontiac pistons?

[steve25]

The pistons look like stock cast to me and the bore finish looks ok if there’s no ridge at the top?
Hopefully they check out with little to no taper!

[Joe's Garage]

And the cross-hatch is kind of light - what you'd see from using a 'ball hone' on a drill.

Plenty of these motors were 'rebuilt' in the 1970s and 1980s by installing new rings, new bearings, timing chain and having the heads redone.

See how it runs before you tear it down. If it's already in the car, you might as well drive it for a while and put together the funds to go thru it right.

Good luck!

[steve25]

Just keep in mind that if they are stock cast pistons that they where prone to cracking out the ring lands even with just part throttle pinging if you had too much timing dialed in !

[drewm]

Thanks guys, its not in the car, and the car is in the beginning stages of resto. Unfortunately, I have no history of the car, and when I bought it, it was in pieces. Im really not sure if I am going to keep this motor. If it were a numbers matching block, then I would. But at this point, I am not sure.

[geeteeohguy]

Originally Posted by Joe's Garage

And the cross-hatch is kind of light - what you'd see from using a 'ball hone' on a drill.

Plenty of these motors were 'rebuilt' in the 1970s and 1980s by installing new rings, new bearings, timing chain and having the heads redone.

See how it runs before you tear it down. If it's already in the car, you might as well drive it for a while and put together the funds to go thru it right.

Good luck!

I agree. Engine has been honed with a ball hone, not factory cross-hatch. Stock cast pistons. Likely it was 'ring and bearinged' back in the day and placed back in service. The upside is that you have a nice core to rebuild with a minimal, if any overbore needed. If you need to bore, go as small as possible and have a set of dished pistons made (Ross, etc. ). The '65-'66 389's can be thin walled if there is any significant core shift, and you don't want to bore it over to .060" if you can help it. Go .020" if you can. The custom dished pistons will allow you to use todays pump gas with the stock heads.

[steve25]

Actually talking about the Ball hone look, closer inspection looks like it was ball honed with the 120 grit one, and not the needed 320 grit if Moly face rings where used!

[drewm]

Thanks again for your thoughts guys. I still am on the fence about keeping this motor. Regardless, I am going to rebuild whatever motor I put back in the car, so I am not sure I want to put the time and money into a non-original 389. If this was the original motor, then its a no-brainer to keep it, but at this point I just dont know. I still have a long while to think about that though. I know someone with a running (though badly) X4 400 out of a 73 catalina 2 barrel. He wants 700 bucks for it.

[steve25]

700 bucks is a lot for what might only be a usable short block due to the fact that so many of those 4X are cracked!
You could use that 700 towards rebuild that 389 into a nice stock bore 400 !

[drewm]

Originally Posted by steve25

700 bucks is a lot for what might only be a usable short block due to the fact that so many of those 4X are cracked!
You could use that 700 towards rebuild that 389 into a nice stock bore 400 !

I did not know that about 4X blocks. Good info to know, and might explain why it is barely running.

[1968GTO421]

To me the only reason to go with a 400 block over a 389 is displacement and availability of stroker kits. If stroking your engine is in your plans, Butler has what you need to make a beast out of your 389. Check this out. Also aftermarket aluminum heads will fit your 389, not just 400, 428, and 455's.

https://butlerperformance.com/c-1234...480-cu-in.html

[77 TRASHCAN]

The top of that piston sure looks ugly, to me! I wonder what’s going on there?

[jonmachota78]

Originally Posted by drewm

I did not know that about 4X blocks. Good info to know, and might explain why it is barely running.

Correct me if I'm wrong, Steve but it believe you were referring to the 4X heads not the block

[steve25]

Yes, the heads!
The block has no type of 4X designation on it.

[dirtybird400]

Originally Posted by 77 TRASHCAN

The top of that piston sure looks ugly, to me! I wonder what’s going on there?

Yeah, Oil burning in that cylinder. Wonder what the plug looked like?

[drewm]

Originally Posted by steve25

Yes, the heads!
The block has no type of 4X designation on it.

My mistake, typo, I meant X4. A 1973 400 2 barrel catalina.

[drewm]

So the plot thickens on this motor. The heads are 76, casting date of April of 65. The block is a 389 with a casting date of K55, which if they skip the letter "I", that is October. I would think that is early model year 1966. It does have another stamping on the front of the motor, near the YF code. I assumed that this was a machine shop stamping. So I wanted to see what the motor looked like on the inside, so I popped the intake and valley pan off and it is super clean. No sludge at all. The lobes of the cam look pretty good. The lifters all look intact. So now I need to see what the crank and bottom end looks like. Drop the pan and other than a little sludge in the pan, the bottom end is as clean as the top end. The crank, however, is a 9773383 Arma-steel crank, which the google-machine says is a 64-65 389 crank. So, if this block is an early 66 model year block, the heads and rotating assembly are from 65. The heads date code is 6+ months prior to the engine date code. I guess this is possible, but I would not think that they would have heads sitting around for 6 months before using them on an engine. So, was this a service replacement block? Would they take the entire rotating assembly and heads and put them in/on a new block?

[drewm]

Stamping on motor and crank

[steve25]

The stampings above the YF code tell you it was not a service replacement block.

The number stamping on the Rods tell you it was rebuilt.

The motor has 60 psi thick bottom plate oil pump which I do not think it would have been built with from the factory, also the motor should have had a full lenght windage try, did it?

Anyway it looks like you have a nice block with a great Crank to rebuild if nothing got hot Bearing wise!

[johnta1]

I agree with Steve.

I would say that the original engine (your block) had a problem, maybe overheated and ruined the crank/rods and valves. Easy to find prior year parts (1965) in junkyard to replace the original parts.

That 66367 number on block is probably the machine shop ID number they used when they did the work.