first off this isnt 3rd gen related. however, it is a 2nd gen firebird. u guys always provide info for my 3rd gen, so id rather get advise on here.

my neighbors pontiac 400ci in his 77 firebird is knocking rather loud. i thought "rod". just because thats what i generally hear in association with a knock like this. he was told that it was either bearing(s), or piston slap. then after explaining his loss of oil pressure, the fella told him it could be his oil pump knocking also.

so basically could a oil pump make that much racket and still be working somewhat? thanks

 

I'd like to see what part of an oil pump COULD make that much noise.

In short, no. Probably bearing related if I were to make a guess based on a semi-descriptive sound alone.

 

Wiped out bearings will lower oil pressure.

 

ok guys. thanks that kind of what i thought, because ive have a oil pump apart once and i just remember 2 gears so... ok well thanks.

 

Maybe the bolts holding the oil pump to the block came out and the "knock" is the distributor thrashing it around in the oil pan?

 

well we just dropped the pan and pulled the pump off. the pump wasnt grinding or anything when i turned it by hand. and the bolts were secure.

neither of us know much about diagnosing the internals of an engine. so ive got a few questions.

when we were just lookin and the crank and checkin that all the bolts were there and tight (because a missing bolt wouldnt suprise me on this car lol), we noticed that a few rods would move on the crank as we wiggled them. whereas others wouldnt.
is this normal, good, bad???

i dont know how many miles are on this engine since it was rebuilt. but i hope my info is enough to get a few answers... thanks again

daniel

 

You just found the problem. There should be no movement of the rod when bolted to the journal. BTW...the oil comment was just a tease. Get a mic or caliper and measure the crankshaft main and rod bearing diameters then you will have an idea of where to go next with the crankshaft and next time you seem movement like that you will have a reference value to estimate the wear.

 

ok ive gotta buddy who could rebuild a sbc blindfolded. ill get him over here to help us out. and about the oil pump coming out... i just kind of skimmed over it and i thought u said the pump might have the been loose against the block and banging around. lol.

 

yesterday we found out that the pickup was sitting right on the pan. starving it. there was a dark ring in the pan were the pickup sat. the pan had been dented, and beat out, just not enough. so we took some heat to it and a punch and we got it lookin better. also we moved the pickup up a little bit so not there good clearance. im almost positive his oil pressure will be better. as far as the knock we'll just have to see.

could better oil pressure fix a knock like this? or is it too late?

 

Too late. When shes knockin' shes knockin'.

You might get away with just installing new bearings if it isn't worn too badly. Have the SBC guy you mentioned to have a peek at it. Hopefully you won't need the crank turned.

 

Too right i'm afraid, once bearings have been starved of oil thats it, possibly it might knock a little less, but its time to pull the crank and get it re-ground and new shells.
Or get another motor.

 

we pulled the engine yesterday. we know this has been rebuilt, and we're hoping its just .30 over so he can go .60 over and he'll be set. the last i heard, he was checking rods 3 and 5. this is about were the knock was coming from when he used a stethoscope (aka: dowel rod). hes probably gonna go all out. full rebuild and we're paint the bay.

BTW he said he was getting up to 90 psi oil pressure after we knocked the pan out. i know the pump is a melling. i think the previous owner put in a high volume pump to fix the problem, instead of fixing the obviously dented pan.

we've got us a project now!!! thanks again fellas.

 

you dont necasarily need to bore it unless the cylinders are badly worn, just new bearings.

i have had an oil pump drive cause a knock that sounded like a rod before