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429 Rod Failure: Why is it ALWAYS #6

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429 Rod Failure: Why is it ALWAYS #6 Empty 429 Rod Failure: Why is it ALWAYS #6

Post  gcj April 19th 2021, 5:27 am

Hi, thanks for input on my SCJ build, but here is a new question:

I have three 429 engines on the table all have one thing in common: They all have had catastrophic rod failure. #6 always seems to let go first, followed by nr. 1. By case here is what I have found:

1. 1970 D0VE-A, two bolt main CJ with 2YABC crank, CJ rods, ARP bolts and L2404F60 pistons. Melling 84 oil pump, ARP oil drive shaft. Shaft broke because of a broken lifter plunger clip getting loose. Got sucked up in the pump which seized up. Engine ran for about 20 minutes, but seized up. Upon disassembly two rods were frozen; nr 1 and 6. Rod nr. 6 was blackened, blued and burned from heat, while all others were light grey and showing no sign of overheating. Crank is fine and bearings are not severely damaged.

2. 1970 DOVE -A block, std. D0OE 4V rods. I built this engine many years ago. First it was used with a C-6 in a heavy car with no problems. Later installed in a ´71 Mach 1 4-speed. Always had oil pressure in the 60 - 80 lbs range. (C6AZ-6600-A oil pump) During a drag race a rod broke at the 90° cut on rod for original square head rod bolts. It was rod #6. Cylinder shattered, block was junked.

3. Current build: 1971 SCJ with original D0OE football head bolts. All rods are matching, numerically except rods nr. 1 and nr 6. Both have been replaced. Additionally I see that cylinder nr. 6 has a sleeve in it. This engine was originally built for ´71 Drag Pack Mustang w. 3.91 gears and 4 speed. It shows signs of serious abuse in racing or street stomping. Took the original L2366F pistons out. They don´t have a scratch on them and the engine is not severely worn in any sense. Again, rod nr. 6 takes the kick. Rods nr. 1 and nr 6 have been replaced, others are original to the engine going by the numerical markings on them.

Question: Has aynone here noticed this? Any particular reason why nr. 6 seems to be at the greatest risk? This is hardly a coincidence ......



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Post  stanger68 April 19th 2021, 8:48 am

The only rod bearing failure I've ever had was on #2. It chewed ip the side of #6 rod in the process though. I think this was a combination of my own mistakes, not necessarily design flaw of the engine. Cheap oil pan, thick oil, methanol.

About 2 races before this happened. I made a test pass off the trailer before I realized I hadn't changed the oil. It was bad milky. I have always wondered if that one pass washed out that rod bearing? I never had any warning signs of metal in oil. It just seemingly chewed a rod bearing to nothing in one pass.


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429 Rod Failure: Why is it ALWAYS #6 Empty Re: 429 Rod Failure: Why is it ALWAYS #6

Post  enginetech April 30th 2021, 3:13 pm

My experience is that 4&8 show oil starvation signs first as they are the last to see oil.


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