21 stud motor

1

1937pickup

Well-known member
Hey all flathead folks,

Is the 21 stud more or less prone to cracks from valves to water jacket or other areas than later flatheads? I have a lead on a 21 stud that the heads have not been remove and thinking about buying, but concerned about cracks.

Thanks.
 
I don't feel that they are any more susceptible to cracking than the later 24 stud engines are but they are an earlier design. Later designs incorporated changes that improved maintainability and reliability. Excessive heat due to engine overheating and freezing of coolant due to lack of sufficient anti freeze are the most common causes of cracking other than plain old operator mistreatment. Those are all more of an operator error situation than a common design problem. They used the same engine in trucks as they did in cars with only minor adjustments to compression. They could take a lickin & keep on tickin.
 
I'll stick my head out and say that a 21 stud engine is far less prone to cracking than an 8BA series
 
Brian. while most of the folks on here would agree with you, I personally have had very good luck finding good 8BA's. I have purchased 5 so far. One was stuck (which I resold), and two have passed formal crack testing with flying colors and the other two have passed a preliminary visual inspection. I have a '51 Merc that didn't even have "Part Number" cracks! Maybe I should go to the casino.
 
Really? I thought you guys would lynch me for that statement! However, here in New Zealand, it is damn hard to find an 8BA that isn't cracked; they seem to have a propensity to cracking, mainly from valvepockets into #6 cylinder. Why?- I dunno, but that is the general pattern. Our stuff is Canadian sourced, but I stand by my statement that 8BA's are notorious for cracking!
 
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Ugg....how many people are tearing down 21 stud engines to build up? How many looking to build a 8BA? And why do you think you hear more about 8BA's being cracked?
You are dealing with engines that are 70 to 80 years old....Lots of thermal cycles are on them as well as many many mis haps.
A 1940 flathead may have over heated in 1943 and cracked the block, but was kept running (unknowingly) until it was replaced with a new car. Now we are looking to rebuild these motors and finding them they way they were left to us.
 
1937pickup, Are you able to pull the heads before purchase? Bit of a clean up around valve areas should show any cracks, but I doubt you'll find them. But, I'd exercise due diligence and certainly lift the heads. It'll give you an idea of condition of cylinders and state of water jackets too.
 
aonemarine, why do you think you hear more about 8BA's being cracked?
Because, in my experience, they have more of a tendency to do so than the earlier engines; particularly the pre war blocks. The prewar blocks were certainly a better grade of cast iron [nickel content?], dunno, but I'm of the opinion that after the war there was a shortage of some material, consequently, the cast iron is different. It certainly welds differently to the early blocks. And, the blocks cast in that stuff seem to crack easier. Or- maybe it's [the cracking] because the valve angles are changed??
My opinion, based on my experience, in answer to the original poster.
 
Brian said:
aonemarine, why do you think you hear more about 8BA's being cracked?
Because, in my experience, they have more of a tendency to do so than the earlier engines; particularly the pre war blocks. The prewar blocks were certainly a better grade of cast iron [nickel content?], dunno, but I'm of the opinion that after the war there was a shortage of some material, consequently, the cast iron is different. It certainly welds differently to the early blocks. And, the blocks cast in that stuff seem to crack easier. Or- maybe it's [the cracking] because the valve angles are changed??
My opinion, based on my experience, in answer to the original poster.
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Because more 8ba's are being rebuilt than the earlier 21 stud motors. Also engines that have hardened seats seem to crack less than those without.
I care not to speculate about the composition of the iron as there is so many variables when casting iron that with out a proper assay of the block who is to say?
 
You can debate this issue 'till the cows come home and both opinions can be right or wrong. In my case, I like the the early 21 stud engines. All of the cars I own came with a 21 stud engine from the factory. They can be built to run with the Big Boys if you know how to build 'em, and Brian knows how to build 'em. You might be surprised how well my Avatar '35 fordor runs with its 0.030" over bored cylinders and higher compression cast iron heads. I don't feel the need for a 59a or an 8ba in my '35 drivers.
 
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Right on John, My Avatar 35 has it's original Babbit bearing block (repoured and bored in 1970) reringed and valve job in 1996, it will run 80 MPH and run 55-60 all day long. That is pretty good considering it is almost as old as me and thats dammed old. Keith Oh.
 
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