I am currently working on a numbers matching 1967 Firebird 400. I bought this project with the majority of the work done. the car was painted and the drive line was all rebuilt and sitting in the car. I have receipts for everything. After getting everything wired and plumbed we fired the car to break in the cam. After a few minutes of cam break in i noticed white milky foam coming out the dipstick tube. Yep, a considerable amount of water was getting in the oil. We pulled the engine and found about a 10" crack going from fore and aft along the main caps.

I have looked into getting it fixed, and have decided not to try it at this point. I will be keeping the original block, but i am going to build a new engine so we can enjoy this car. now for my question, I have a 1975 400 block, crank, rods, and pistons that are all machined and assembled. I have been researching this for about 2 weeks now, and i think that i can use this as a starting point and use all my parts from my 67 engine on this 75 block. Can anyone think of any road blocks i might run into.

Keep in mind that i understand this 75 block is not as strong as earlier blocks, but it will do for my mild street build. This car is going to be driven to ice cream shops, dinner and car shows. not raced.

Thank you so much for any help in advance.

I see you are from Dorr Township is that Michigan?

in regards to your cracked block, is it the original block? What research have you done to determine if it can be repaired? If you are going to build a new engine regardless I think the smartest starting point is with the original.

Yeah, the 500557 block is a simple bolt-in replacement block, if it has all 5 motor mount bolt holes on each side. It may have the small crank register, requiring a flywheel/flexplate with the smaller hole.

Its your car & your money. But, I personally would not spend a penny on a 557 block. Not worth the risk, to me.


"...I have a 1975 400 block, crank, rods, and pistons that are all machined and assembled..."

But, I suppose that if you already have it & it is ready to bolt in, you can give it a try. Hey, if you drive it easy & not very much, it may last for as long as you own the car.

Keep in mind that if you use the '67 670 heads, you may have more compression than current pump gas will support, without octane booster or race gas mixed in. Some get by with 10:1 CR by using a cam with more advertised duration to bleed off some cylinder pressure at lower rpm, and by backing off the timing advance some.

Also, if your 557 shortblock has the dreaded "8-eyebrow" rebuilder pistons, your engine will be even more likely to detonate, because of all the sharp edges on the piston top, and because these pistons are usually down in the holes enuff to create a large quench distance.

But hey, you may be able to bolt it together & have it run perfectly, with no problems at all, on straight pump gas. Most every time you post what problems many have experienced, there are some who will post that they did exactly the same thing & it all worked out perfectly for them.

I suppose you can't know whether it will work for you, unless you give it a try. Let us know how it works out.

If you paid big bucks for a numbers matching car without being told the block was cracked I’d go after the seller to get a substantial portion of your money back. The block is a boat anchor. It can’t be repaired.

Double check if the 75 400 block has the 5 mounting holes. If not, it will need adapters.

Yes, I am from Michigan.

and yes, it was the original block. Im being told that there is only a chance that it could be fixed. It would have to be furnace welded, and with it being .060 over already, i might have trouble still. Plus where the crack is im pretty sure that the 75 block will be stronger.

The crack is from red line to red line. across 2 main journals.

oldskool

The block has the 5 holes, and it is all ready to go, but it does have the crappy pistons.

As far as compression goes. I am going to check the CC's of everything i have here soon and come up with a plan. I have 6x-8 heads as well all rebuilt.

Is the 500557 block really that bad. I see several people that claim to be at 500hp with them. I dont plan to be do that. I am going to be doing a aftermarket cam to help with my compression.

The gentleman that i bought it from has paper work from the engine builder stating that the block was checked. This was a long time project for him, he started the project almost 20 years ago. The engine was built 15 years ago and never fired. He has been collecting NOS parts from around the country ever since. He ran into health problems and had to sell the car. I got a tremendous deal on the car for what it is.

Finding this engine problem is a big bummer and has caused a decent amount of anxiety, however i knew there was some risk and I dont believe he knew about it. He has tried to buy the car back twice.

It's probably not worth putting $ in the old block given the crack and 60 over. I would park the block and leave it for the future tech to fix it.

Have you put money into this 75 engine yet? There are built and rebuildable 67-69400 engines still available. I know of a 68 400 ready for a rebuild right now. It's for sale now I believe.

You need to properly design your build or expect trouble. You have to decide how your going to handle today's gas in your new engine as well as other issues.

Nice color! Love the blue!

"...I have 6x-8 heads as well all rebuilt..."

"...Is the 500557 block really that bad. I see several people that claim to be at 500hp with them..."

"...This car is going to be driven to ice cream shops, dinner and car shows. not raced..."

For the type of driving you say you're going to do, you may get by. I've already mentioned that no matter what you post, about a problem that some have had, some will say they did it without any problems.

The 6x-8 heads will probably produce less that 7.6 CR, with those pistons, unless the heads have been shaved some and/or the block decks have been machined, to bring the piston tops closer to the deck. But, from what you've posted, all you want is just an engine to get you from point A to point B & back. So, low CR may be a way to help the 557 block live longer. Another way might be to rig up the carb so that the secondaries will not work. I did this on a 350 sbc engine in a 2-ton truck. Ran just fine & got better fuel mileage than our trucks that had a 2-barrel carb, because the Q-jet primaries are smaller than the holes in the Roch 2-barrel.

Pontiac had so many problems with the 557 blocks cracking at the main cap dowel pins, they tried hollow roll pins for the dowels, for some of the 1977 W72 400's. These pins were supposed to cushion some of the shock load, to help prevent web cracking. For the '78 & '79 W72 engines, they cast some more 481988 blocks, adding an XX before the casting number.

Here are some pics of a cracked web, a hollow pin, a block with one broken web, and a block with 2 broken webs. The guy that had the 2 broken webs said that the engine was in a boat & they were just gonna freshen it up. Didn't know there was a problem, 'til they tore it down.

For the power level you want a 350 Pontiac engine would work just fine. There have been lots of Pontiac 350's for sale that were junked because nobody wanted 'em. Some guys couldn't even give 'em away. But, for your power level, a good 350 shortblock, with the 670 heads should make a a decent engine.

For the big valve heads, you'd need a block with 2 valve chamfers at the top of each cylinder, for valve clearance/unshrouding. I've read that many of the 350 blocks from the '60's & early '70's do have both chamfers. But, some blocks have only 1 & some blocks have none. Chamfers can be added by the machine shop, or anyone with a small hand grinder, who knows what to do. The only 350 blocks to avoid are the 500810 blocks. They have thin webs just like the 557 400 blocks have.

And, the cheap replacement pistons have only 4 valve reliefs, like the '68-'73 originals.

Without checking the numbers, most would not be able to tell whether you had a 350 or 400 block in your car. You may be able to find a 350 for a very reasonable price. I've actually seen ads offering 350's for free, with pick-up.

Hey, the 350 is just one option. You can even stroke a 350 block, if you want more power.

https://www.hotrod.com/articles/hppp-1102-350-ho-engine-build/

https://www.hotrod.com/articles/hppp-0712-small-bore-pontiac-engine-build/

So i apologize about switching gears like this, but I have another idea/question. I just found a 68 4 bolt main 428 with a crank and +18 dished forged pistons. (for a pretty fair price) I have to believe that it would be very strong and i believe that my rods will work. Then i will have a pretty good short block.

any issues?


Thanks again

There is certainly nothing wrong with a GOOD, properly built 428.

BUT, the question is: Are the parts you've mentioned all usable for a correct 428 build ?

(1) Are the pistons in good re-usable condition ?

(2) Will these pistons work in the block, or will the block need to be bored bigger, & larger pistons bought ?

(3) Is the crank in good condition and can it still be cleaned up at a size for which rod & main bearings are available.

(4) Are the cylinder walls thick enuff ? A good machine shop can check this, as well as check the block & crank for size & cracks.

A good 428 will have much more torque/hp than what you said you wanted.

If you go with the 428, I'd go with forged H-beam rods. RPM brand H-beams are $400. Eagle H-beams are about $475. Some say that the cast rods can be resized, using new ARP bolts for about $200 or a little more. BUT, you still have CAST rods that are over 40 years old. I think the extra $200 for H-beams is a very good $200 investment. Why put cast rods in an engine you'll spend thousands on, when for $200 more you could have much stronger & lighter H-beams ? Hey, that's just my opinion. There are lots of cast rods still in use every day. But, lots of engines have been destroyed by broken cast rods.

1. the pistons are brand new 6113X 4150; GSX 4.150" Forged Dish for Pontiac 428

2.block is already been machined and ready to go .030 over

3.crank is ready to go, .020 under and .010 under (my rods and bearings are for .010 under) they are cast, but they have been cleaned checked and balanced. And they are the same size as the 428 rods if I understand correctly.

i will have less money in this 428 then what i think i can sell my 557 block for.

This just my personal opinion.

I would not use cast rods with those nice pistons, in a 428.

The H-beams are stronger, lighter, & you can buy the floating pin version, so that no pin pressing is required. The pins will have to be fitted to the rods, by the machine shop, since most all rod pin holes are purposely made on the small side, due to the variation in actual pin diameters. The entire rotating assembly will have to be balaced together.

Here is a link to the RPM $400 H-beams.

http://www.racingpartsmaximum.com/sae4340steelhbeam-2.html

$468 is the best shipped price I can find right now for the Eagle CRS6625P3D H-beams.

https://www.ebay.com/p/Eagle-6-625-...ontiac-V8-8-PC-Part-CRS6625P3D/622056633


Just a word here about online parts prices. Many companies are now charging tax ! On a $400 purchase, this can make quite a difference in the total price. I know for sure that Jegs now charges tax. I've read that Summit does also. Amazon Prime also does. But, some Ebay & Amazon sellers don't. So, to find out the total price, you sometimes have to go thru the checkout process. Then if you don't like the total price, you can delete the item from your cart.