Why do Flathead V8 Blocks Crack?

J

JAKEFORD

Senior Member
I have owned many flathead engines over the years. Some were perfect with no cracks and some had cracks. Sometimes the cracks caused problems and other times not and didn't even know about them until rebuild time came around.

The cracking I remember was mostly in the area of the valves. Seat to seat and seat to cylinder bore. Sometimes the cracking was due to coolant freezing but this should be expected if you don't keep proper strength anti-freeze in the engine.

I was under the impression that the non freezing cracks were due to some casting flaws or temperature overheating and cooling but I was never sure. I know I threw more than one block away due to excessive non repairable cracks.


Can anyone provide a better explanation?
 
Well, the cracks from the center head studs to the water jacket actually were part of the design process. They were put in to relieve stress between the cylinder walls.
The other cracks, I'm sure, were a result of the way these engines were treated, back in the day. Too many overheat cycles, and or freezing in the winter contributed to most.
 
Other cracks probably came about from overheating issues. The earlier blocks had plenty of sand left in them once they left the factory, resulting in some overheating. The treatment or inadequate treatment of the overheating issues were probably more cause for cracking than anything else. If you ever talk to H&H flathead they will tell you they have never come across a cracked flathead block they could not fix. I certainly would not pay for their rebuilt engine prices knowing that but I am sure there are many who have and had no issues.

In my limited experience I have dug out a gallon pail or more of sand out of several 59ab blocks. These blicjsca a were relatively crack free and have severed me well since their rebuilds.

I guess, in the end, it's a bit if luck, acquired knowledge about overheating, and how you drive and build them that really determined whether you have a really good block or not that will not overheat. Sorry to have rambled a bit ...
 
Well if you take a perfect block of cast metal and you heat and cool it for 80 yrs, let's say at least 200 times a yr. that's 16,000 heat cycles. Well you have a used flathead. Kind of amazing they hold up as well as they do.
 
Ralph Moore said:
Well, the cracks from the center head studs to the water jacket actually were part of the design process. They were put in to relieve stress between the cylinder walls.
The other cracks, I'm sure, were a result of the way these engines were treated, back in the day. Too many overheat cycles, and or freezing in the winter contributed to most.
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Come on Ralph, you're not serious, are you?! I have heard this comment made many times as a joke, because this type of crack is so common-such as "Ford assigned a part number to these cracks", etc. I seriously doubt, though, that they "were part of the design process"!!!
 
I have thought about the idea of heat threating a block to releave the stress and then throwing it in the dark hiding to sit and age....
Thats what you do with a new cast iron piece but should it add something to an old block and how much ?
Have any of you guys some of the valvepocket sleeves left ?
I still have the kit but im not shure if i have any sleeves.
 
Don't know why, but in my experience the later (8BA) type blocks seem to more likely crack from valve to bore than the prewar blocks. Anybody else found this? Or am I lucky on the prewar blocks?
Martin.
 
All the exhaust created by the engine gets routed to the outside of the block through the water jackets. The center exhaust port handles 2 cylinders and concentrates more heat there. I believe this fact contributes more to the non freeze cracks then anything else.
 
40 Deluxe said:
Come on Ralph, you're not serious, are you?! I have heard this comment made many times as a joke, because this type of crack is so common-such as "Ford assigned a part number to these cracks", etc. I seriously doubt, though, that they "were part of the design process"!!!
Click to expand...

I was joking, of course :), but I have rarely seen a block that didn't have those cracks.
 
Scooder, I'm with you on that...the prewar blocks had better [in my opinion] metallurgy than the stuff cast post war. Definitely different composition of iron. [Less nickel?]
 
scooder said:
Don't know why, but in my experience the later (8BA) type blocks seem to more likely crack from valve to bore than the prewar blocks. Anybody else found this? Or am I lucky on the prewar blocks?
Martin.
Click to expand...

I was told that the 8BA blocks for the 1953 model year did not have hardened valve seats - that the block itself was used as the valve seat and that rotary valves were used to compensate for wear. Could this be the cause of "valve to bore" cracks in 8BA blocks?
 
Flathead design has caused the cracking, very poor design. If you have flathead you will have the problem sooner or later. Block repair is a good answer, I had one repaired few years ago no problem(cracked from no 2 cylinder to valve seat). My recommendation keep as cool as possible, I am always looking for ways to keep engine cooler. I have a Model A that has been overheated to where it would hardly run no cracking, but look how the exhaust valve is next to the manifold.
 
There is a big difference between overheating and running an engine to cool! All engines need to run at as high a temperature as is practical.
 
The problem with overheating (to the point of boiling over) is the steam pockets that form from the loss of coolant. The pockets can allow superheating conditions to occur and the hottest spots in a flathead block are the Siamese exhaust passages. This is why a lot of flatheads have cracks in the middle cylinder exhaust ports up to the valve seats.

The moral of the story is to never allow your flathead to boil over. It's one thing to get hot, it's entirely another when it gets so hot that it blows out the coolant like a geyser.
 
I figured it sounded more technical than the Ford assigned part number. One of these days I may get lucky and get to see a NOS V8 block!
 
scooder said:
Don't know why, but in my experience the later (8BA) type blocks seem to more likely crack from valve to bore than the prewar blocks. Anybody else found this? Or am I lucky on the prewar blocks?
Martin.
Click to expand...

This is something that I have also wondered about. I'm thinking back to the 50's, when I worked in a small independent garage. We saw mostly 'abused' cars, usually not ones that looked well cared for. I'm pretty sure I can't recall an 8BA that didn't have a crack. I saw 59 & earlier with cracks, too, but it seemed a lot less frequent. Coincidence? Imagination?
I'm sure guys like Pete, Ron, John, and other builders that see lots of engines, would have a better 'take' on this.
 
It's easy to look back and say poor design, but look at the times: V engines up until then were multi-piece castings with much room for tolerance stack-up and leak points. The crankcase was cast and machined, the cylinder blocks were cast and machined top and bottom with lots of bolt holes to drill and tap, and the heads had to be cast and machined, plus other bits adding to the complexity and cost. Ford's engineers decided to put the complexity into a one-piece block/crankcase assembly so once they had the design down and the molds figured out, they began saving money by doing far less machining. Plus, money was scarce-depression years.
 
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