An axe, eh - do you have any Viking relatives?
Water in Cylinders, Blown Head Gasket
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sigpic Whiskeyjack a '68 Columbia 36 rebuilt A-4 with 2:1
"Since when is napping doing nothing?"
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Causes of a cracked block
I'm curious as to the likely ways in which a block cracks. i have a particular theory in my case, but I'd like to hear what others think or know.
I can only think of three ways:
- Severe localized overheating (clogged passage?)
- Freeze damage
- Mechanical impact (say, with a framing axe )
Any others? And which, if any, of these are unlikely or impossible?
Questions, questions!@(^.^)@ Ed
1977 Pearson P-323 "Dolce Vita"
with rebuilt Atomic-4
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I once had a piston wall fail where the wrist pin attached, essentially a thrown rod. The destruction of the block was massive, looked like someone dropped a hand grenade in there.
I like the extreme temperature theory, either heat or cold and I'm leaning more toward cold.Neil
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others
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Originally posted by ndutton View PostI like the extreme temperature theory, either heat or cold and I'm leaning more toward cold.
But now I'm not so sure. How succeptable is the block to freeze damage? Won't the freeze plugs pop out first? (they didn't)
I'm beginning to lean towards the theory that some local obstruction in the block's cooling passages caused the region around the #3 exhaust valve to be starved of coolant, causing it to overheat and crack.
But I don't know the layout of the cooling passages in the block. Is this kind of blockage even possible? Maybe Don could weigh-in here.@(^.^)@ Ed
1977 Pearson P-323 "Dolce Vita"
with rebuilt Atomic-4
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Originally posted by edwardc View PostBut now I'm not so sure. How succeptable is the block to freeze damage? Won't the freeze plugs pop out first? (they didn't)
What are commonly called freeze plugs are actually core plugs, necessary in the block casting process to align and evacuate the internal sand form. While it's true the closing plugs may pop under freezing conditions, that's not their primary purpose and not a guaranty. The core plugs may be strategically located to take advantage of this side benefit however.
Anyway, that's my story and I'm stickin' to it.Last edited by ndutton; 10-01-2010, 11:35 PM.Neil
1977 Catalina 30
San Pedro, California
prior boats 1987 Westsail 32, 1970 Catalina 22
Had my hands in a few others
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Niel’s Merc mechanic friend is correct. The old auto and marine engines of the 50’s and 60’ were heavy walled and could withstand freeze expansion trauma dropping the plugs into the bilge. On those old set ups only the manifolds and oil coolers would blow. For the last 20 years Merc has only used GM engines. The 350 cracks on the outside and the 454 likes to crack on the inside push rod alley areas. The small GM 4cyl will some times survive a mushy salt water freeze. The v6 cracks inside and outside. A cooling jacket full of sand or sediment will sometimes not allow proper circulation of antifreeze causing isolated freeze damage.
Our motors tend to collect block sediment on the hot port side away from flow blast at the side plate inlet. That’s why Don has recommended the addition of a rear downward flow hole in the side plate fitting in an effort to direct some flow around the rear cylinder to combat this build up.
Many an a4 block has frozen and lived to run another day. Not so much for our manifolds and heads.
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