400 cracked block?
- Thread starter TBMG270
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An aftermarket balance job especially with an aftermarket crankshaft can fix a number of issues. Also costs a small heap of dollars.
How important is it to use your existing flywheel? The 2-piece seal crankshafts have a larger bolt circle than the one-piece seal cranks. Therefore a one-piece-seal flexplate is NOT going to work on an OEM two-piece-seal 400 crank.
How important is it to you to use a neutral-balanced torsional damper? If you're forced to use a Vortec front cover, do you have a timing pointer on that cover?
The 400 in my 'Camino has aftermarket rotating assembly. As it turned out, it was easier to use a neutral-balanced flexplate than to use a weighted "400"-style flexplate. I still have the weighted "400"-style torsional damper up front.
Having built one 400; I wouldn't do it again without sonic-testing the block (cylinder walls) for thickness.
How important is it to use your existing flywheel? The 2-piece seal crankshafts have a larger bolt circle than the one-piece seal cranks. Therefore a one-piece-seal flexplate is NOT going to work on an OEM two-piece-seal 400 crank.
How important is it to you to use a neutral-balanced torsional damper? If you're forced to use a Vortec front cover, do you have a timing pointer on that cover?
The 400 in my 'Camino has aftermarket rotating assembly. As it turned out, it was easier to use a neutral-balanced flexplate than to use a weighted "400"-style flexplate. I still have the weighted "400"-style torsional damper up front.
Having built one 400; I wouldn't do it again without sonic-testing the block (cylinder walls) for thickness.
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b454rat
I'm Awesome
A new balancer and flexplate for a 400 isn't that expensive. Nor is getting the rotating assembly balanced. Local shop charges $100 I think. He's doing my 406, so I can find out. Externally balanced is fine for a street motor. It's when go to higher RPM n exotic parts where intern comes to play. I had a healthy 406, used stock but new flex n balancer. Ran beyond good.
A 400 is not a motor for a budget build. Seriously consider the roller cam swap. Get the rollers, dogbone, and retainer from a junkyard motor and have your machinist tap the three bolt holes if you're not willing to. I'd skip the Vortec heads and buy some circle track iron heads with 2.02s.
+1 on the sonic check, especially since it's .060" over.
The Vortec reluctor wheel will not fit under the non-reluctor wheel timing covers. It barely fits under the plastic cover.View media item 32350
+1 on the sonic check, especially since it's .060" over.
The Vortec reluctor wheel will not fit under the non-reluctor wheel timing covers. It barely fits under the plastic cover.View media item 32350
b454rat
I'm Awesome
Uh, what 3 bosses are you talking about?? It's not as simple as just going to the junkyard. Need to get the retro fit roller set up, it's like a grand for everything. Also, can use the stock Vortec cover. Also no reason can't built one on a budget. Only thing that cost more, and not even that much is the pistons, IF using 5.7" rods, which is highly recommended.
Postmech
Newbie
4 bolt main 400 blocks crack next to the short outside bolts. 2 bolt blocks are pretty bulletproof. I would use the Holley cast aluminum cover as it has dowel holes and provision for crank sensor. Unless you keep it above 3000 rpm all the time, you must drill steam holes in heads. Use a 400 head gasket as a template. Unless you want to hot rod it, I would use stock 5.565 rods for low speed torque. A stock 5.7 TBI cam would also be a good choice for torque and cheap. You will need both a 400 flywheel and Harmonic balancer as both have counterweights. The balancer will need to be shortened the thickness of the reluctor to perfectly line up the serp belt. I would also use the Vortec heads for cheap. They flow better than any other production head. 'Course you could spend as much money on the engine as a new truck if that is what you want. lol Is the short block useable as is ?
If you're really on a short budget and you're clearly capable of swapping a short block - could you put new rod and main bearings in the second motor you got from the wrecker? Probably just worn out. Probably the cheapest way to get back on the road.
Ive owned over 20 400s and never ran a steam hole. I tap and plug the block even. I even tap and plug the water pump bypass hole in every sbc i do. The external balance flexplate and harmonic balancer is required on a stock crankshaft unless heavy metal added to crankshaft for balance but have more in it than a new already internal balance crank
That spot is common on later 400s after 74 mostly ones with two freeze plugs and a riser in center where 3rd plug goes. Wont hurt anything. The cam will be a issue due to it being a carb cam without enough lobe separation for the fuel injection to perform right. Retro lifters and a stock vortec cam, roller cam button, a double roller w torrington bearing timing set to make up not having thrust plate would be best. The stockish tune will run it but a 0411 swap with individual injectors only way it perform like you want.
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