differance between two and 4 bolt main caps

grumpyvette

Administrator
Staff member
TWO BOLT MAIN CAP BLOCK
2boltcapbn.jpg

4 bolt SBC block


3504bolt.JPG

typical2bolt350.jpg

typical two bolt cast crank 350

24502503a.jpg

splayed 4 bolt
SPLAYEDCAPS-1.jpg

keep in mind that once you exceed about 450hp the O.E.M. blocks strength becomes a limitation and you should be thinking of upgrading the the much thicker castings of the aftermarket DART or similar blocks.

blockcrack.jpg

preparation+mag-check.jpg

mag check for cracks in the block

NOT A TA said:
For those who never witnessed Magnafluxing this is how its done. Electromagnet is located so the area you want to test is located between the posts. Then some "magic dust" (in my best Cheech impersonation) is puffed ofer the area to be checked and the dust jumps right to the crack. Even if the crack is very small (like the one on my head) it will show right up. The crack in this pic was easily seen by the naked eye but it made for a nice easy pic to display the process. The lightweight head in the pic had been sleeved for the bolt hole previously so thats why theres a circle of magic dust around it. The dust knows it as a crack. This head will be pinned to repair the crack. If the opportunity arises to get pics of "pinning" sometime I'll get some.
DSCN0004-2.jpg

brokemaincap.jpg

main%20web%20crack.jpg


the crank or block can have the correct bearing clearance but still be slightly bent or the block may be warped and result in the bearing wear



http://webtools.delmarlearning.com/samp ... _ch139.pdf

http://www.thirskauto.net/BearingPics.html


Neither plastigage or a full set of micrometers or other ways of checking crank to bearing clearances will detect a bad align bore or a crankshaft with runout.

But there are some simple ways to check both.

http://www.herboldracing.com/2010/02/19 ... ank-runout

173207.jpg

Here are a set of main bearings that 400 miles o them and you can see there was an alignment issues the rear main bearing is missing but was in good shape.



BADMAINLINE.jpg

bblock.jpg


failure to check for cracks or use of a O.E.M. block at power levels its not designed for can and frequently does result in engine failure, most O.E.M. SBC blocks are rated at no more than 400hp, we all know guys pushing them to 500hp but much beyond that its a crap shoot and the blocks eventually going to flex and fail.

rollerspider.jpg


hydraulic_roller_cams+one_piece_rear_main_seal_truck.jpg


roller blocks have taller lifter bores, because roller lifters are taller, and a provision to bolt the lifter retainer spring, but they can be very easily used for the earlier flat tappet lifters if desired by simply removing the spider(SPRING RETAINER), keep in mind most roller blocks use one piece rear seals
 
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