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Old 10-09-2012, 10:01 AM   #1
94cobra69ss39694cobra69ss396 is offline
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Default Time For The Cobra To Get A New Engine - The 347 Build

What started this build is when I broke another rocker arm and bent another pushrod on the Cobra. With 90,000 hard miles I figured the cause was weak valve springs. So I pulled the heads and and while I had them off ported them. I then took them to Pacific Engine (well Guy did) and had them machined and a valve job done. While doing so Guy discovered that AFR had way too much spring pressure and that some of the springs only had .500 lift before going into coil bind. My cam with 1.7 rockers has .530 lift so surprising they lasted 90,000 miles.

While the heads were being done I started cleaning the carbon off the tops of the pistons and noticed a nick in one of the cylinder walls. With that discovery I really didn't want to just slap the heads back on so I started looking into the cost difference of rebuilding the 302 compared to buidling a 331. The cost diiference was going to be very little so I'm building a 331. I've been saving up to buy the stroker kit from Coast High Performance and will likely be ordering it this week.

This weekend I pulled the shortblock from the Cobra and disassembled it to see what caused the nick. What I found is that two studs that hold a splash shield on the intake manifold had come out and fell into the pan. They must have been in there for a long time. There were nicks on the bottom of the pistons, cylinder walls, crank, rods and one lobe on the cam. Here are some pictures of the worst piston.





Before I discovered the damage this weekend I was planning to sell the pistons and cam to help offset the rebuild but now I don't know. The threw the cam out but I'm still considering selling the pistons. They've obviosly held up fine in the Cobra pushing 11-12 psi and the only damage besides the nicks on the bottoms is the wear marks on the skirt of the one pictured above. What do you guys think? Would you buy pistons with nicks like that?
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Old 10-09-2012, 10:10 AM   #2
Shaolin CraneShaolin Crane is offline
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Oh sure, i've used pistons in worse shape then that. Those are cosmetic at best and wont effect longevity of the pistons. They're .030 over right? Those will sell no problem, hell if I didn't have 5 sets of forged pistons i'd probably grab them from you. Bring them down to the shop and i'll toss them in the washer, you'd be surprised at how little you'll be able to see them once clean.

Also dont toss that cam, it's still salvageable and can be refreshed for not too much money. Hell Joey might even buy it from you.

As far as 331, well, we've discussed that before
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Old 10-09-2012, 10:23 AM   #3
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I threw the cam in the trash and it was picked up yesterday. I do need to have Dick take a look at the block though to see if .030 will take care of the nicks. If not I have another block but the one that with the nicks is a much cleaner casting and I would really rather use it.
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Old 10-09-2012, 10:38 AM   #4
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I wouldn't care about nicks like that. Just put it in the ad and people can just choose for themselves.
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Old 10-09-2012, 11:22 AM   #5
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Pics of nicks?
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Forget about winning and losing; forget about pride and pain. Let your opponent graze your skin and you smash into his flesh; let him smash into your flesh and you fracture his bones; let him fracture your bones and you take his life. Do not be concerned with escaping safely lay your life before him

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Old 10-09-2012, 11:38 AM   #6
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They are all in the same cylinder which is number 4. The dark spot in the first picture half way up the cylinder wall isn't a nick, it's just a stain. The deepest nick is the lower one in the top picture but I don't think it's .015 deep.


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Old 10-09-2012, 01:19 PM   #7
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Are those at the bottom of the bore? If so those are no big deal.
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Forget about winning and losing; forget about pride and pain. Let your opponent graze your skin and you smash into his flesh; let him smash into your flesh and you fracture his bones; let him fracture your bones and you take his life. Do not be concerned with escaping safely lay your life before him

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Old 10-09-2012, 03:20 PM   #8
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Yes, they're at the bottom.
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Old 10-09-2012, 05:01 PM   #9
Shaolin CraneShaolin Crane is offline
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Dont even worry about them, the rings dont go that far so they arent a problem. Most aftermarket blocks dont even have material that deep. On my dart motor we removed a 1/2" piece at the bottom of each cylinder to clear the rods.
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Originally Posted by Bruce Lee
Forget about winning and losing; forget about pride and pain. Let your opponent graze your skin and you smash into his flesh; let him smash into your flesh and you fracture his bones; let him fracture your bones and you take his life. Do not be concerned with escaping safely lay your life before him

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Last edited by Shaolin Crane : 11-10-2014 at 10:56 PM.
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Old 10-11-2012, 08:52 PM   #10
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I ordered the kit today and as you can see from the change in the title I ordered the short rod 347 kit fro Coast High Performance. The original reason I was going to build a 331 instead of a 347 was because the 5.40 rod with the 3.40 stroke on the 347 puts the oil rings in the pin hole. This causes it to burn oil. With the short rod (5.315) it moves the pin lower to resolve that. So it won't burn oil and I'll have an additional 16 CI.
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