Why does my 350 knock for 3 seconds when I start it? Oil pump or worse?

Oh i see. So have the ignition on a toggle and then just crank the engine until the gage shows pressure, then flip the ignition toggle to on while cranking to start. Not a bad idea if everything else fails. Normal or not, it cant be good for the engine to make that sound at every start.

The irony of it all is that ever since we have been talking about this in this thread the noise has now stopped and I havent changed the oil yet.

 

Oil is changed and new filter. When I started it up it made the sound. The true test will be tomorrow morning on a cold start. When I say cold I mean maybe 55 degrees since Im in Florida. I used Quaker State 10w 30 and a NAPA gold (wicks) filter. Im going to try that and see if it makes a difference. If not, Im going to wait until the oil is dirty and then replace the filter and oil with Fox Dens formula.

 

Before pumping the gas pedal & setting the choke let it crank for 5-10 seconds then pump the gas. This way oil will have started to flow & the noise should be less or not there at all. It's a lack of oil on start-up. Continue doing this "Dry" start & it WILL harm the bearings if they haven't already been damaged. The MOST WEAR on ANY engine is the initial start. Some give me a hard time about this but it's much easier & MUCH less expensive to replace/rebuild a starter than it is to replace engine bearings.
Just my thoughts on the subject.


Tom T.

 

Don't try and clean it out you could knock something loose and plug up the screen in the pan. Is there that much crap in the motor?

You do not have to go with my exact formula I do this to hold more oil pressure when hot. This was when I had the 350 trans in it and I was spinning 3 grand on the highway to drive to the track which was an hour away. The mix kept my oil pressure at 50 lbs at 3 grand. 10-30 may be enough for you since you are more stock on the motor. At least the synthetic will be on the parts and it will keep it from being beat up as much.

 

I drove the car for 30 minutes. Temp gage was at 190 which is where it likes to be. Oil pressure at idle in drive 600rpm was exactly 20psi. I would like to check the screen but I dont want to go through the trouble of jacking up the engine to pull the pan. I wish I had some kind of lighted scope I could insert into the oil drain hole and visually inspect the pickup tube screen. That would be awesome. Be nice to look in the heads too.

 

Hey Gary, it's Gary. :grin:

I have a theory:

Loose clearances somewhere, either the oil pump itself or bearing(s) or a combination of all the above.

You seem to have adequate oil pressure at ambient operating temperature, but oil pressure won't go up past a certain amount no matter how much higher you rev it.

Oil blow-by. It retains up to a point, then bleeds off through the loose clearances when it tries to go past that point. This also explains the knock early on before oil pressure is established.

It takes it a few seconds to build pressure after the oil has drained out of the bearings/journals.

Without having to rebuild the entire thing to put tighter bearings in it, you may want to pull the oil pump cover off and check to see if it's scored...maybe use a TA oil pump girdle and oil pump gear replacement?

If it looks scored up pretty bad, this may fix or alleviate your issue. It may be a good idea to do this anyway for good insurance.

Otherwise, it's not going to kill your engine to leave it as is and just live with it unless or until it gets worse as the miles accumulate.

Just be sure to use a synthetic oil like the Mobil 1 high mileage oil, which has a higher zddp content (1050 ppm or something like that) and use a good high mileage oil filter.


Gary

 

my 79 had a bypass valve in the stock pick up screen, so it could still suck oil with gunk in it. And gunk does collect right under the screen, and is impossible to flush out due to how they designed the pan. The drain plug screws into a giant nut, welded to the inside, with just two tiny holes half way up the side. Enough to let oil out fine but nothing else. They need built backwards so you can really flush the pan on oil change and that stuff wouldn't be able build up over time. [ why so many of the "flushes" are a solvent for the most part as that stuff won't leave the engine unless liquid. ]

 

I think you should pullvalve coveroff driver side of engine.check if you have aluminum rockers,if so take off rockers and pull rockers off shaft .shafts will probably have 2 grooves worn in shaft from each rocker.
see how some grooves are deeper than others. that's loss of preload on lifters.rocker is moving around until lifter pumps up. this is what I believe you have wrong. could be either bank. left side more wear usually.

 

I would bet, based on my experience, your pick up screen is not the issue, nor is your oil pump, if they were, you would have issues across the whole engine operating range, from idle to wot, such as low oil press. at hot idle, and reluctance for the pressure to climb with rpm.
I would say, again based on my experience, your main bearing clearence is right on the edge of being tight enough to indicate sufficient oil pressure, and operate fine, BUT just loose enough for the crank to slam the lower bearing shells at start up before the oil has a chance to get between the bearing and journal.
Try this: after you drive it on the highway for half an hour, go home, jack the front end up, put jack stands under the frame for SAFETY, start engine, slide under the car and listen closely at the oil pan, you may be able to hear the crank, banging or knocking, maybe not.
Try this and report back:TU:

 

Sounds like I was half right then.

Without completely rebuilding the engine, the only real option would be to run synthetic to help retain some oil on the surface of the bearings when the oil runs out of the journals and takes a few seconds to build back up after shutting off a while.

I think that (contrary to intuitive belief) a thinner oil may be the answer here since he's got good oil pressure. This will help the oil pressure build up faster than thicker oil would.

Say, a 0w30 or 5w30 fully synthetic.

Correct?

Gary

 

That's a possible issue but as Gary said before, keep it simple. And these are common for noise and as I posted with a pic of what aluminum rockers do to rocker shafts. Simple and cheaper fix. But as mentioned it could be like this for another 10 years and not change. With the low mileage I would believe car sat for long periods with no oil movement so a lot of dryer startups. And rockers will wear the most as they are last thing to get oil.

 

Good point on the low mileage/dry start issue:TU:

 

not to muddle the waters but I tried syn oil a few years back, my noise at start up happened more often. I went back to dino oil and it took several days of sitting to get more noise on start up. with syn it was every day.

 

Remove the valve covers and do a cold start so you can check out the top end for noise as it starts...

 

but it dosnt sound like small metal parts clicking together it sound like big metal parts knocking together and it sounds low down in the block not up high. Besides, now my choke pull off has finally given up the ghost after 41 years of service and I cant evaluate the sound at start up because it starts rough now without the choke working properly. I do not hear that noise anymore on cold start up or at any other start but ike I said I cannot hear cleary the start up noises because it starts rough now due to choke pulloff being broken. Ill have a new part in a few days when my Rockauto order arrives.

Im getting choke pulloff, fuel filter, Id like to get a fuel pump but dont know what brand to get and nobody mentioned a preference. Id like to find some Kendall blue EP grease but cant find it in the small tubes for my small grease gun.. Id like a nice USA made lever cap for the radiator. Ball joints, control arm bushings. But I need to know brands. I hate to buy some chinese parts. I know Moog for the suspension but I dont know for the other stuff. Can anyone please advise?

 

Odds are it's just your oil filter causing this... years ago I too listened to all the big talk about why you must use a wix filter. So poped one in the very next oil change. What do ya know sounded like someone was knocking on wood. Took off the wix and put on the fram tough guard and no m more knocking.Think I started a thread about it Idk, but I'm positive there were others. I know everyone's all about proven products... but slap on a fram tough guard. Bet that knock will disappear.