67stang12

ok I am rebuilding a 302 and just found out tthat it is bored to .0040 thousandths and so the machine shop is going to go to .0060 oversize ... Is this a good thing because ive heard both sides. I dont drive the car everyday and it is basically a stock rebuild ... I would like to know as soon as possible and the options i have or if this is ok.

valley firearms

It shouldn't be a problem.

Starfury

I disagree. 289/302 blocks are not built to be bored that far out. They're thin sidewall blocks, and core shift is often an issue to consider. A little core shift and you run the risk of constantly overheating.

If it were my money, I'd go find a 5.0 to start with. They're easy to find, and much cheaper than having constant overheating issues in the future.

DenDen

Let me chime in on this one.I just had my 302 rebuilt last winter.By the time I was done at the machine shop,I could have bought a new short block 347.The boring of the cylinders,cleaning,deck height adjustment,new forged pistons(it's hard to find 302 pistons believe it or not)new rods,crank turning,ring gapping,cam bearing installation,balancing to 8000 rpm.All this came to over$2500.00 .I went all the way with it so it would last.Balancing is super important to lessen the strain on your main bearings.
Now,my point is,you have to decide what's better for you.You can go cheap and hope for the best,keep the machine shop busy for a week,or buy a new(assembled) short block.Prices vary but the new ones are cheaper than if the machine shop builds one.

Norm Peterson

I'd look long and hard at a 1980's/early 1990's 5.0 roller cam block that could be cleaned up with only 0.030" overbore. You can always drop a carb & aluminum manifold on it if it's an EFI motor.

Just getting the roller cam is good insurance for an engine that may go for longer periods of time without being started (more time for the oil to drain away from those valvetrain places where lubrication is really needed).


Norm

SuperHoss

Some people have had success with an 0.060 overbore but I caught hell keeping my 289 cool with a 0.030 over...but then again, when I got it the car the engine was rebuilt in the 80s and had set up for nearly 10 years.

Roller engines are an obvious upgrade but not always necessary...depends on the person. Rollers are more reliable and tend to last a long time when modestly built but some people just prefer flat tappets. Regardless, never cut corners when it comes to machining and balancing...if you do, you will pay for it in the end.

If you decide to go roller then go find a mid-to-late 90s Explorer with a 5.0 and pull the engine out of it...you will be a lot better off. I was lucky with mine, it was a low mileage engine that just needed the cylinders cleaned up; it did not even have to get bored (which made me feel bad about taking it apart).

DenDen probably has the best advice for the average person...order a short-block. This will save massive amounts of time and headache, and they generally come with some type of warranty. If I did not want to personally build my engine with my parts then this is the way I would have went.

JMD

If the machine shop can sonic check the block you will be one up on the whole thing, but if it was me (because I am lucky that way), especially on a more or less stock rebuild, I would let them bore the damn thing and move ahead.

Core shift can be an issue, but imo, it would be more of an exception than the rule (to the extent of causing bore issues anyway).

Overheating might be an issue due to thin cylinder walls, but in my mind this might be more a result of the marginal cooling systems that plague most Mustangs (unless addressed), even those with stock bores.

It shouldn't be a lot of money to bore, hone, and deck your block.