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400SB 4 bolt or 2 bolt

TracStr400

LawnSite Member
I may be buying a complete 400 that was running the last time it was in a vehicle. It has been in storage for a year. I believe it came out of a '72 chevy truck. I haven't found out yet if it has a 2 or 4 bolt main. I know with 350s that you always want a 4 bolt main if you're going to build a strong motor. I have been told by several people that with a 400, the journals are big enough that it is not necessary to have a 4 bolt. I am going to completely rebuild it so I know nothing is wrong. My question is, should I stay away from it if I find out it is a 2 bolt? He is only asking $400 for it. Any info would be greatly appreciated.
 

northeast

LawnSite Member
Location
maine
the 2 bolt main will be plenty stout.I am pretty sure the 400 small block only had the 4-bolt block in 1970.built a few 400 strokers with 2-bolt mains for my drag 65 vette,never had any lower end failures.you will have to use the 400 heads becouse of the steam holes.
anyways go for it. Nick
 

BUSHMASTER

LawnSite Senior Member
Location
Columbus Ga
well drag engine you waant a 4 blot main no douht.....street well a 4 bolt main block will not stress in the bottom end. when i worked in the machine shop just about all 4 bolt main blocks that came in had stress cracks that showed up with magnafluxing in the liffter area why .... because the stress has to go somewhere and that is the first weak link in the block....have built many 383. with 2 bolt main and have had no problem at all ....
 

# 1 PLOWTECH WES/MEYER

LawnSite Member
Location
IL
The way to tell if a 400 is a 4-bolt w/o taking the pan off is to look at the block freeze plugs. 2 bolts only used 2 freeze plugs on each side.(you can see there is a boss for the third but is not machined out)The 4- bolt block used three freeze plugs on each side.4- bolts are prone to cracking in the main web area. ***CAUTION*** If you plan to put into 87, you need the flexplate/flywheel,harmonic balancer,(they balanced different than a 350),oilpan,and you need to check your knock sensor location,re-drill your inner intake manifold holes (they are at a different angle). The 87 has a one piece rear main seal which uses a different flywheel, and oil pan .You dont have to re-drill your 87 intake if your going to use the 87 heads.You can use 87 350 heads but drill the 6 steam holes. its easy use your 400 head gasket as a template.Any ? let me know. I do these swaps all the time. Good luck #1 PT.
 

BUSHMASTER

LawnSite Senior Member
Location
Columbus Ga
400 OR 350? the haromnic balancer on the 400 look like someone cut a chunk out of it .. about 1-2" the 350 is solid and a 305 is hollow inside .
 

# 1 PLOWTECH WES/MEYER

LawnSite Member
Location
IL
You must use a 400 Balancer with the "CHUNK" missing.The 350 is internallly balanced, thats why it is full round,the 400 is externally balanced,the flywheel/flexplate is counterbalanced and so is the balancer with the "chunk" cut out.Good luck #1 PT.
 
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