Thread: Coolant in cylinders; fresh 400 sbc build

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Originally Posted by glennsexton

Unfortunately, the 624 casting are probably the worst of the GM castings for cracking. They are prone to cracking across the exhaust seats and thru to the heat crossover. They’re not good candidates for any decking either.

Mortec says they are from a 75-86 350 or 400, 76cc chamber. They were manufactured with 1.72/1.5, 1.94/1.5 or 2.02/1.6 valves

If they have the 1.72/1.5 or the 2.02/1.6 valves and they are perfect – they may be worth drilling steam holes. If they are the small valves or (as is very likely) show any cracks, I’d start looking for new heads.

If you have any budget, the Vortecs are a good way to go. This means a new intake manifold as well, but will definitely bring the 400 alive. GM Part Number 25534421 ($1100 a set or less on ebay) is a great head, 185cc runners and 66cc chambers. They’ll need steam holes drilled.

Good Luck!
Glenn

I made another post but I guess it evaporated. Anyway, all I know about the heads is that they have been machined and have new valves so there should not be any cracks. I'll measure the valves tomorrow when I drill the holes. Thankx

Originally Posted by Bigbzc

I made another post but I guess it evaporated. Anyway, all I know about the heads is that they have been machined and have new valves so there should not be any cracks. I'll measure the valves tomorrow when I drill the holes. Thankx

STOP! Don't do anything else until you have read and understood post #45.

Yup - what Tech said - I was a bit premature in a head recommendation. It was my mistake to "assume" stock pistons and deck height. We might still get to the same place (i.e., Vortec heads) but it is really important to get the details of the PDH and squish.

I don't plan on using different heads as I am out of money for this project. I will drill the 350 heads I have tomorrow and hope to have them in by the weekend depending on the weather

make sure you use the 400 gaskets

Originally Posted by cffisher

make sure you use the 400 gaskets

Yes sir! lol Gottem loaded in the truck to take to work tomorrow. I was hoping to see "paths" on the head or gasket from where the water leaking but there were none. I guess this could be because they were not on there very long. I do see the point that it CAN leak because there is not much of a seal in the steam holes of the gasket

after looking at the gaskets carefully I noticed that there were no traces of water from the steam holes. What I did discover is that the cylinder seal of my gaskets are overlapping the coolant ports that are just beneath the spark plugs. So, now what?

I think I figured it out. Measured the diameter of the bore on the gaskets and it measures 4.180" This block has NOT been bored and it's diameter is still 4.125" Looks like they gave me the wrong gaskets. Let me know if I am correct

No--gaskets are correct---the heads are wrong

Can you take a couple close ups of the head and post them? Is either a bad picture or something nasty happened in the machine shop.

Originally Posted by glennsexton

Can you take a couple close ups of the head and post them? Is either a bad picture or something nasty happened in the machine shop.

I was thinking that they shaved to much off the heads. The pics I posted are not bad, what yo see is what it is. See the notch in the coolant port in the 1st pic? That is where the biggest leak is but ports on other cylinders over lap the compression ring on the gasket and leak into the cylinder.

Ok I had my personal guru (who just happens to be a Master Machinist and Master tech) look at the heads and he said they have been angle milled and too much. That they would make great boat anchors. He also looked at my 305 heads and told me that he would use those since I am looking to make more torque. They cam off a 86 transam and are the H.O. heads with 68cc chambers and 1.84" valves. Casting number is 14014416. Looks like this will be the rout I am going to try

There are two schools of thought in regard to using 305 heads on a 400 – one says “with a ton of work, they can be used”. The other school says, “don’t use them..”

I’m in the second school – The steam holes are the least of your problems. The heads you have (14014416) are 58cc (not 68cc) and that’s a big factor. With your all stock engine and a .040” head gasket you’ll be pushing close to 12:1 compression ratio with these heads. Couple that with the small valves and relatively short runners (165cc/59cc) and you will end up with a dog that will only run on premium fuel - anything over 10:1 starts to be touchy with pump gas.

The 400 was designed for torque, but it still needs to breathe. Remember that an engine is really just a big ol’ air pump and the 400 was designed to move a lot more air through its stock heads than even HO 305 heads can supply.

Your “stock” bore 400 is 4.125” and a 305 is 3.766” – do the math and you’ll have .359” of cast iron hanging over the cylinder area. You’ll play hob trying to get 400 gaskets to seal so you’d have to use 305 gaskets and they do not have provisions for steam holes.

Probably not what you want to hear – but I think your frustration will be compounded if you bolt those heads on your 400.

Check out this thread from several years back:

using 305 heads on a 400 sbc

We really do want to help you here –go back to Tech’s post #45 and get the measurements let us help you determine what a good head would be for your engine.

Regards,
Glenn

Bigbzc------

When angle milling cylinder heads was a more or less common thing to do to raise compression so as not to need a large piston dome sticking up blocking the flame front---on a sbc they welded up those slots in the heads and then redrilled a hole to line up with the one in the block.

Now , shortly , since you seem to have a blockage of anything any of us have posted, I will be deleting my posts later tonight, and I would highly recommend that others do the same thing>

Ok, in regards to what you have all told me, we did a little more research and found that you are correct. A race engine builder told me that I would have to use racing fuel if I use those heads because of the high compression. Sorry that I have been stubborn about this. I just am over my budget and really can't afford new heads. I will get those measurements Tech wants tonight