# Safe to bore 400 60 over?



## keeperofthecode (Oct 10, 2017)

Recently learned my 67 I puchased has a 326 and not the 389 it was supposed to have which is just my normal luck. I trusted the guys word it was a 389 but who knows maybe he didn't know himself it was a 326, i understand it is a common mistake. Been doing some searching and found someone selling a 1974 Pontiac 400, .060 over bore, 6x heads, new oil pump, Ofenhoser intake, noisy gear drive for $850. Engine was rebuilt several years ago but never installed and looks in pristine condition. Is the engine being bored 60 a concern or pretty normal in these engines? Seems like a good deal but its just my luck for things to go wrong if they can.


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## bigD (Jul 21, 2016)

Many 400's have been safely bored .060 over, and some even more. But, on the other hand, some won't safely go .060. Core shift during casting, as well as corrosion over time, can reduce the mount a block can safely be bored. Most good shops can check the thickness of the cylinder walls, to determine how much the block can be bored. 

But, since the engine in question is already built. You'll just be taking a chance. So, I'd only buy it if I felt the other parts were worth pretty close to the purchase price. From your description, you should at least get a decent set of 6x heads, assuming the machine shop didn't ruin 'em. Then, even if the block is too thin, you have the rotating assembly & other parts, which could possibly be used in another block. But, it might have cast rods and pistons, which are practically worthless. 

How lucky do you feel ? Can you afford to lose most of the purchase price ? 

It seems that VERY few Pontiac guys will take a chance on anything these days. I tried to sell my 455 bracket engine recently. It was running good, in the car. But, our local tracks closed, and I never got to make a pass. I advertised it for a very reasonable price, in lots of different places. Never got one single offer for it. Not even a lowball cash offer. I suppose most nowadays think that all used stuff is junk, and everybody is a liar, out to swindle them. 

I took a chance on a 455 Ventura bracket car, which I'd never seen. Had it shipped from another state. It was exactly as the seller had described it. Ran 7.30's on our local 1/8 mile track. I still have the 455 from that car, which I've also tried to sell. Again, not one single offer. So, I've got two 455's, which I suppose I'll try to eventually come up with a couple of decent bodies for. Couldn't use the bodies they came out of because they had both been stripped down for racing. Will have to be street legal or close to it, in order to sell, here in my area. 

Hey, good luck with whatever you decide to do !


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## PontiacJim (Dec 29, 2012)

.060" can be OK, but it is basically the limit of the block. .060" would be best if it were sonic tested to ensure none of the walls are too thin due to core shift. You want to confirm it is a 1974 block as the later blocks were thin wall and will only take a .030" overbore at most. If you ever need it rebuilt, it will not take another overbore and it would be sleeved which is very pricey and not worth it when you can purchase another block for less.

The price is almost too good, in my opinion. A basically stock rebuild is going to run about $2,500 if properly done. If it was rebuilt a "few" years ago and never installed, who rebuilt it and what is the name of the local machine shop that did the machine work on the block & heads? You should be able to contact them and confirm. Otherwise, you don't really know what is inside the engine until you tear it down. You could use one of the hand held video camera's that you can snake down into each cylinder and look inside to see what is really going on. Don't let the clean outside fool you. 

Might have the "generic" rebuild kit which is inexpensive and comes with the low compression cast pistons which are not the best choice - it will be a low compression engine unless pistons were selected to raise compression. What are the cam specs? Connecting rods resized and new rod bolts installed? ARP? Heads rebuilt? Valves ground? 

So it is really your call. Could be a good deal or could be a bust. If you can chance $850 and not be concerned about losing it, you still could have some good parts to put on another engine. I would not assume the engine to be a "turn-key" deal until I brought it to a machine shop and had them disassemble the engine and check the block/heads for cracks, then check the bearing clearances, inspect crank, rods, pistons/rings, cylinder bore, etc. and reassemble with a new gasket set. OR, you can go through all the trouble of installing the engine and then find out you have a major problem and have to repeat your process. My machinist has seen 3 Pontiac engines this year that were purchased for rebuild that were bad and could not be rebuilt as had been hoped. Usually no guarantees when you buy used parts.

Just being honest with you as I too purchased a 455 that was supposedly purchased from _another guy_ who said it had "some lifter noise." The engine was stuck, but I figured this was from sitting over 10 years as the guy claimed - and under cover in a building he said. The only thing I was able to save was the block and it had to be bored .060" to save it, but my machinist would not guarantee he could even save the block when he first looked at it. The engine cylinders looked like they were under water the last 10 years and that was on top of the fact that the engine's oil pump had quit and had been driven and gotten so hot that it warped the crank and burned through all the bearing and was running meta-to-metal on a few of them. I guess that was the "lifter noise" as the lobes on the cam were rounded off and one lifter was just about worn through. I suspect the engine simply quit running when the valves no longer opened anymore. LOL So buyer beware. Many Pontiac engines being pulled and put up for sale are those left hanging around in junk piles because they were blown up or had some other major damage that was not worth repairing.


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