Crank, rods, mains for '71 400? - Pontiac GTO Forum
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post #1 of 7 (permalink) Old 10-11-2011, 08:29 PM Thread Starter
 
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Crank, rods, mains for '71 400?

I'm having to replace my bottom end in my '71 400. Is there a specific crank kit or brand I should be shopping for? I don't drag race, just want something tough and last. What is the most reliable? What else should I look at replacing while we are in there besides crank, mains, rods? I'm also interested in changing gears from a 283 due to it being a turd on low end!!! Any suggestions on this subject as well.
Thanks, Neil
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post #2 of 7 (permalink) Old 10-11-2011, 08:51 PM
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You shouldn't need to buy a crank, just have the one you have machined. Rods should be reworked, cam bearings and cam replaced, block boiled out and re bored and line bored if needed, new high volume oil pump and pick up screen (welded to the pump), new frost plugs and oil galley plugs, new positions and rings. Have the rotating assembly balanced and you should be good to go.
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post #3 of 7 (permalink) Old 10-11-2011, 10:24 PM
 
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3.55 gears will make it quicker out of the hole. But, the best bet is a 461 crank, rod, piston kit for about $2K, corrected compresion to 9.5 to 1, and a nice cam. That low gear will haul ass, and still get down the highway at 80 mph. We, many of us put the 3.36 to 4.11s in our cars and regret it now, I removed and sold my old rear end for a 3.36, now for a cruiser, wish I left it alone. Keep it, and go for torque and it will be killer on the top end and torquey out of the hole.

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post #4 of 7 (permalink) Old 10-12-2011, 05:34 PM
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Do you NEED to replace the crank or just want to? Did something break?

If you're looking for strength/reliability - first thing to address would be the factory rods. The are 'the weakest link', so to speak. By the time you have a set of factory rods thorougly checked and reconditioned, you'll spend very close to what a good set of forged rods would cost you - and you'll still have "weak" rods. If your crank is still usable there's no reason to replace it for what you say you plan to do with the car. "Pontiacs ain't chevys" and the Pontiac factory iron cranks are very strong - more than adequate ujp to around 550hp and 5500rpm.

Now if you just want to make things a little more interesting, as others have said it's hard to beat a 461 stroker "kit". That's what I built for myself. Have the block bored plus 0.035 (to 4.155) and get one of the kits that comes with forged 6.800" rods, cast 4.250 stroke crank, and forged pistons (which heads do you have?). Build it targeting a static compression ratio around 9.3:1, sit back and enjoy all that lovely Pontiac torque.


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post #5 of 7 (permalink) Old 10-13-2011, 03:37 PM Thread Starter
 
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Hey Bear,
I've got a pretty consistant knock in lower end. We disconnected from tranny to ensure it was motor. Pretty sure a bearing came loose. I live in Indiana and know it would be a haul, but I'm seriously thinking of just getting this motor to you and let you set me up if possible. If you could give me some contact info, I would love to talk to ya. Thanks, Neil.
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post #6 of 7 (permalink) Old 10-13-2011, 05:53 PM
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Hey Neil, thanks for the vote of confidence but I'm just a hobbyist like you I'm just a little farther along on my project is all. If you want someone to build you a killer motor that'll last forever, I highly recommend Jim Lehart at Central Virginia Machine Sevice. He's one of the best (in my humble opinion -the- best) there is. A little over a year ago when I was getting ready to put my engine together, I spent a lot of time consulting with him and he helped a lot - and that was -before- I made the decision to purchase any parts or services from him. Nice guy. Give him a call.

Central Virginia Machine Service - Home of the Injun Engine!

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post #7 of 7 (permalink) Old 10-14-2011, 05:24 PM
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X2 on Bear's recommendations/referrals. Can't go wrong...especially with the con rod upgrade.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO General Discussion

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