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Gary
Gary, Chevy Technician
Category: Chevy
Satisfied Customers: 16209
Experience:  15 years GM master tech
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Chevrolet Blazer 4x4 (Full Size): I got a 350 carb block. It

Customer Question

I got a 350 carb block. It has a very faint knock sounding like from the bottom of the block almost not noticeable
Submitted: 1 year ago.
Category: Chevy
Expert:  Gary replied 1 year ago.
Welcome! My name is ***** ***** I will do my best to assist you with this problem.Ask me about added features such as phone contact anytime if you wish !
I am sorry for the long wait
is it rear of the block near the starter or back lower of the oil pan ?
will it increase with engine speed ?
when did it start making this noise ?
Customer: replied 1 year ago.
I just bought it and noticed it. You cant hear it at all in gear and the very center pulley I think its the crank pulley has a wobble to it. But I can only hear it when its warm and in park
Expert:  Gary replied 1 year ago.
do you hear this from the front crank pulley ?
just hear it in park and neutral at idle ?
i really need to know the exact area you are hearing this noise from
Customer: replied 1 year ago.
It seems to increase with the rpm
Customer: replied 1 year ago.
It sounds from the very botto but I honestly cant tell exactly where
Customer: replied 1 year ago.
And its just park and neutral and goes aways when you rev past a certain rpm or so it sounds like
Expert:  Gary replied 1 year ago.
its odd you do NOT hear this noise in gear and just hear it in park and neutral
your sure its not there in drive and reverse ?
Customer: replied 1 year ago.
I got my wife to get in it and put it in gear and do a little power brake to get the rpms up and I couldnt hear it
Customer: replied 1 year ago.
Not sure what the idl oil pressure is supposed to be but its at about 10 to 15 psi at 750 rpm idle. Hoping its not a rod bearing but its weird I cant hear it in gear
Expert:  Gary replied 1 year ago.
this noise when it will NOT make it in drive or reverse is usually a sign of possibly a flex plate issue or possible transmission converter or front pump
is this noise near where the transmission meets the back of the engine ?
i am sorry for all the questions but i want to be sure to give you the right direction to go
Customer: replied 1 year ago.
Yea no problem man. It sounds like it is directly under the oil pan but its hard to tell exact. It doesnt have the flex plate dust cover on it now. But its weird cause it only does it when its hot.
Expert:  Gary replied 1 year ago.
any access to stethoscope ? or a long flat head screwdriver ?
what we need to do is duplicate this noise and listen starting at the front lower of the pan and listen with the screwdriver up to your ear and work your way back the oil pan when its making this noise can you hear where it sounds the loudest ? front or mid or rear of pan ?
pan area or up the block a little bit ?
that kind of pinpointing on the noise
Customer: replied 1 year ago.
Ok ill do that and get back with you
Expert:  Gary replied 1 year ago.
ok let me know
we want to be sure if this is a crank area noise or not to see which direction to go next here
Customer: replied 1 year ago.
Its loudest at the front of the oil pan
Expert:  Gary replied 1 year ago.
ok if its front of the oil pan lower and NOT from the timing cover area at all then this issue will more than likely be a rod or main bearing causing this noise which would also account for the low oil pressure
the next step will be to drop the oil pan to inspect and possibly plastic gauge the bearings all the main and rods to see if any are out of spec
there is nothing more than the crank bearings in that area to make this noise
but in a nut shell tear down needs to be done next and if you leave it alone and do nothing the odds are the noise will get worse and could possibly damage things that are not damaged yet inside the engine and are cheaper to fix now
Customer: replied 1 year ago.
Well looks like I need to just order a new block
Expert:  Gary replied 1 year ago.
I am real sorry i wish there was something else it could be or another direction to go here but like i said the noise from that area there is nothing there but bearings
i would pull the pan to check them next before you buy anything to confirm this
don't forget you can always get me back through this post any time for any follow up with this question anytime even after you rate us here at Justanswer !
Customer: replied 1 year ago.
Thanks man
Expert:  Gary replied 1 year ago.
anytime
dont forget to rate us here at Justanswer !
Customer: replied 1 year ago.
Will do and one more question. If its just the rod bearings could I just order a new block and bolt everything to it?
Expert:  Gary replied 1 year ago.
yes if you order a shot block ( without heads ) or a long block ( with heads ) everything from the old engine will bolts right up to it