help...engine knock

[fenrir]

i just replaced the head gaskets, intake gaskets, put new rockers and rods in, new plugs wires and distributor, and cleaned all the grime off of my 94 4.3 vortec tbi. while driving it home which is about a mile it started knocking. the oil is new and filled correctly and timing is right. the knock im 99 percent sure its coming from the bottom part of the engine. ive only drove it maybe 10 miles since the rebuild and its parked untill i fix it. what are the chances the rod bearings cant handle the rebuilt top end and need replaced without having to get the crank machined? dont have alot of money and miss my truck. thanks very much for any input.

[Blue Bowtie]

Check oil pressure. Gasket fragments, loosened sludge, and debris may have affected the oil pump pickup and/or pump. Sludge may have entered bearings if the filter got slugged with debris and clogged. The filter will go to bypass if the differential pressure is more than 10-15 PSI.

I've had about a 75% success rate replacing bearings (with stock shells) in the vehicle and not having to grind the crank. Of course, you'll want to mic the journals. If clearance is more than 0.0015 you are wasting your time with new bearings. The rear main bearing cannot be replaced without removing the transmission since the rear main seal retainer will hold the rear cap in place.

While the pan is off, you should really check the oil pump. It may be prudent to replace the pump with a high volume unit since the factory pumps have barely adequate volume to maintain decent pressure at idle. Oil pumps are cheap.

[MagicRat]

Why did you change the head gaskets?

If a gasket blew in such a way that coolant got in the oil, your bearings may have already been damaged. Good bearings, even if they are fairly worn will still cope with a new top end.

I agree with Blue that debris in the oil system may also have wiped out a bearing.
In my experience, a badly-knocking bearing is too far gone to fix without machining the crank. Usually, if I am replacing bearings without machining the crank, I polish the journal with #400 grit emery paper. This can fix the roughness caused from normal wear only... it does nothing for actual damage.

Finally, check your flexplate for cracks and tight bolts. Sometimes, a loose or bad flexplate can thump just like a bad bearing.

[fenrir]

well the thing has about 170k miles and i started getting water in the oil after i changed it. its been awhile since it was driven while i was in iraq and as soon as i noticed the white smoke i pretty much figured it was the intake gasket... but if im gonna have it broke down that far might as well throw in a new head gasket just incase. the knock starts after it warms up about 5 minutes or so, and there was a bunch of sludge below the intake manifold. i got as much as i could out and cleaned the heads, intake, rocker covers the best i could which was pretty damn good. but i have driven it MAYBE 10 miles i would say more around 6 and just hope i dont have to break it down again. since the new parts the oil pressure stays at about 50 which is alot better than before i did the work. cant work on it in onpost housing parking areas have to take it to a garage that costs 8 bucks an hour and it gets kinda expensive. i orded new bearings today and im gonna put them in on friday more than likely. thanx for the input and the advise just have to cross my fingers now and hope the crank and main bearings are ok.