Got a 1970 cutlass s with the original 350 in it, car runs great but im starting to hear a slight knock apon start up.. The knock gose away as soon as the engine is fully running but when it first turns over there are a couple of knocks that go with it. Any ideas on what im hearing or things to be checked ? Engine was rebuilt about 6 yrs ago

 

Knocks or ticking?

 

Could be piston skirt slap. Kinda hard to diagnose without hearing it. How’s your oil psi when cranking (without the engine firing, about 20 seconds worth of crank time (pull coil wire)), when cold and at op temp?
Is it a slap or a knock? Does it sound deep or up high?
Audible shirt slap usually happens on the first few revolutions after its fired up at ambient temp. Rod and or Mains can make noise on cranking and the first few revs or all the time depending on the state of failure. So...it’s anyone’s guess without standing next to it or tearing it down to inspect.
Timing chain and fuel pump shafts can make noises as well.
Read oil pressures and get back to us.

 

Consider lifter bleed down. Start simple and then work to the expensive stuff. Have you checked your oil level?

 

Oh, how I like knock, knock jokes!

 

Well......... Does it go like this????

I know a great knock-knock joke.
Ok, tell me.
All right. You start.
Ok, knock, knock!
Who's there?

 

Its fo sure a knock, not a tick.. The cars always had low oil pressure, i used to have digital gauges and it always read real low like 8psi at hot idle! iv since then swith to a thick diesel oil and change out to mechanical gauges and now get a reading of 50 something at cold idle and 15-20 hot idle.. now this car has been driving like this for a while, like years and not one issue.. ive pulled the valve covers and oil is deff getting up there things look clean and oiled under the manifold so ive been driving the car and no issues.

iv also heard from some old olds fans haha that the motor might be working under perfect pressure, and it is in fact the psi sender plumbing making it seem as if its low pressure. In order to fit dakotas oil pressure sender unit for the old gauges someone had to extend a littl piece of tubing up and out to a 90 degree elbow perhaps something can be cloged there?

Ive heard of ppl having this issue and tapping into the oil filter housing and getting normal readings, perhaps there is low pressure and the damage is finaly starting to kill the old girl!!! i hope not!!

 

The reading your getting with the mechanical gauges is normal, so no pressure issues. Is the knock just when it first starts, or is it constant. Is it coming from the upper lifter and valve area, or below?

 

Well thats great news, the knock only happens the first few seconds between the turnning over of the engine to the starting of it. If i had to guess id say it sounds like its comeing from the upper area of my 350. thanks!

 

Install a kill switch to the ignition and throw it when you get oil pressure.
Kinda acts as a 'pre-oiler' and makes the engine last longer!

 

Im not sure i get what your saying.. can you explain that for me again please?

 

If it is an automatic transmission check that the torque converter bolts (3) are tight. Listen closely to try to hear the same noise upon the last turns of the engine when you turn the ignition off, if you can hear it then too it is likely that they are loose.

Check that the starter is tight, the exhaust isn't hitting the chassis anywhere and with the engine off check that all of the pulleys are tight. It is good to confirm whether or not a noise is actually in a motor and not an accessory before going into the motor.

Listen to the fuel pump with a mechanics stethoscope as mentioned by droldsmorland, they can make a knocking noise. X2 on what oldscutlass said about the oil pressure, it sounds good.

 

just thinking when your checking the pulleys also check the water pump make sure there is no play in the bearing etc, I believe this also makes a knocking sound... just thinking out loud

 

If you crank the motor with the starter with the coil wire off, you'll acheive oil pressure.
Plugging in the wire, you'll achieve ignition.
If you wire in a toggle switch to your hot lead on the coil, when turned off, the engine will crank, but not start.
Watch the oil pressure guage - when you get pressure, flip the switch, and it'll start!! Pre-oiled!!
Had many guys doing that 'back in the day' with clearanced motors, and the kill switch is a handy 'anti-theft' device, if hidden - noone's going anywhere!
Also worked if you wanted to get stuck at the 'submarine races'!

 

The oil psi sounds ok. You state that the noise "happens the first few seconds between the turning over of the engine to the starting of it". That would point towards other items being suspect vs. piston slap though I won’t rule it out. As mentioned above it could be almost anything. Hard to give concise info on trouble shooting this without actually hearing it. The best advice I can lend is to do a systematic tbl-shooting approach. Remove all belts...crank it over. Noise gone there is the area of interest. Noise still present? Put the belts back on and pull something else such as the fuel pump. Noise still there reinstall pump. Un bolt the converter and push it back at the trans. Crank it up (briefly). Noise there or not? Pull the valve covers and release all the rocker trunions & push rods (careful here...install these parts exactly where they were removed from). Crank it over with spark disconned. Noise still there? Don’t rule out timing chain and or sprockets either.
You get the deal. Start with the simple work towards the complex. By investigating one thing at a time and putting it back to its original state and going to the next is the best way of finding things. You will eventually exhaust all the external removable items to disconnect. Obviously that points to "its time to have a look at the rotating assembly" (crank pistons bearings).

 

it could possibly be the starter.. i recently had to remove it to change out some valve covers hopefully thats it.

 

that engine is not long for this world, been there done that! i'd be willing to bet that hot & in gear you have no oil pressure... you need to start gathering parts...

 

455 block gose to the machine shop next week

 

that is a good call! the small blocks may not be as desireable but it'd still be a shame to trash a '70 350 when it can be avoided!!

 

True, if it happens it happens but id like to have the 455 ready before anything happens to the 350. Because of funds and the fact that this car is my daily driver its a long shot but not out of reach. Im babying the heck out of it right now. Lucky for me i dont work or go to school far from home..

Not sure wht im gunna do with the block im getting it cleaned and decked and bored to .030. Not sure what parts im going to use but its in the makes, ive for some reason gravitated towards mark princes 455 build as a out line i believe thats his name..