Thread: bbc thrust problem

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I've built a 1977 chevy suburban 454 to a 496 using an eagle rotating assembly, all was well until stock chrome oil pan baffle spot welds let go and crank turned into a garbage compactor. After having crank turned, and totally dissassembling motor and cleaning wore out thrust in about 400 miles, had thrust welded, reassembled again grrr and now again thrust seems to be going i can move crank back and forth over the spec limit but still have good oil pressure..any ideas i did upgrade to the nitrous hole shot converter to eliminate converter ballooning im stumped and the block was line honed..

bbc thrust is not much of a problem .after welding the thrust was there
finsh good ? every time the crank gets turned the thust can get bumped alot of the cranks i see are at mild to big end of the end play new and thats fine .did you set the thurst ? and make sure your running on the upper and lower thrust bearing alot of guys not know this just bolt the cap on.some shop when they cut the rear main cap of line hone or line bore can tip the cap when cutting them for line bore or hone. this screws up the end play .i would be looking at this stuff . you can re work the rear thrust for more oil there is bearing s out there that put more oil on the thrust i have only seen one bbc that was hard on the back bearing and thats was when the trans busted car was a 565 cid and did big wheel stands.i would look at the trans converter line psi free play from converter to fly wheel it may had to long of a pump drive on it ? but i think it would eat the front pump up?? after checking the finsh on the crank .check the main cap .and if you running on the upper and lower thurst 1/2 s

You can also get oversize thrust bearing surfaces /undersize for shaft

Also what type of front drive/belt system/supercharger belr????

my front accessory is a simple march under driven 2 pulley set up, im wondering if the harmonic balancer would cause this, because the threads in the crank snout are on there last legs, too short of a bolt will not bite, if this were to wobble slighty could it take out the thrust

Originally Posted by bbc nova1

my front accessory is a simple march under driven 2 pulley set up, im wondering if the harmonic balancer would cause this, because the threads in the crank snout are on there last legs, too short of a bolt will not bite, if this were to wobble slighty could it take out the thrust

no... it would not you can drill and tap it to 9/16 bolt and drill the washer. the thrust only controls the back and forth of the crank and under a load and keeps the crank riding on the brearings and stops the counter weights from hittting the bulk heads of the block .damper is press on so it bettter not wobble and is on the front of the crank if bad it could in time beat the brearing out . not the thrust. .your fly wheel or trans is more at fault of a bad thrust or all things i listed to much load on thrust . to loose to start with? bad machine work? beating the thrust out? and every thing on other post not the crank damper bolt

i dont now how u have the time for all the reply's really appreciate the help, u need to be nominated for poster of the month.. anyway how would a person check for to much load on the thrust caused by the tranny. I know the tq coverters on correct i have small amount of play back and forth play on the converter, iguess next would be to be check line pressures on the cooling lines im not sure supply or return and what pressure specs are supposed to be, small not a local tranny shop gave me an inline check valve for the pressure line because i had drainback in my th400 i guess is a typical problem. They told me to check the dip stick hot should be at full mark, let sit overnight if its above the the full mark it was draining the tq coverter. Could this be a clue to a bad pump tranny etc. Tranny was rebuilt, not saying much i did not witness. Tranny seems to shift ok. How much crank movement is to much 1/8?

not much more then 010 end play that about it .as for your trans and converter .you need to talk to a good trans guy .i have built some race 400s that did work good but i am not a trans guy if you have 1/8 play some thing is way off .i am thinking your crank is junk ? for who did the welding of the thrust was the job done right? what did it have for end play when fixed? did you set the rear thrust ? like said this is over looked by shade tree builders .you need to go over evey thing i listed