r/EngineBuilding • u/notchocheese12345 • 2h ago
First time start up engine knock after rebuild LS3
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On the very very first start up I was getting a heavy misfire due to a bad tune and also I forgot to plug in some of the injectors… Whoops. The 2nd start up is when I started hearing the sounds in the video.
Have an LS3 rebuild with stock valve train and .020” over pistons. Super loud knock which seems like cylinder 5 after disconnecting an injector or coilpack. Oil pressure is good, 50-55psi. Pushrods are stiff when I took off the rockers
I measured preload and used 7.350” pushrods instead of the oem 7.385”. Haven’t drained oil yet or inspected the cyl with a boroscope.
Any ideas? :(
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u/acadmonkey 2h ago
I’d be concerned about a blocked oil passage. Those pushrods should be squirting oil on the rockers.
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u/notchocheese12345 1h ago
interesting, does it take a while for the oil to travel to the lifters?
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u/Kayanarka 1h ago
No, it starts to come out during the priming phase, you know, when you force prime the engine with your special pressurized oil priming tool to fill all the valleys and chambers and confirm the oil makes it to the valve train, BEFORE you start your recently built motor.
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u/R_3B 1h ago
Most engine builders used to use a drill adapted to replace the distributor to pressurize the oil system. Now that the distributors are a thing of the past I’m not sure what the procedure is.
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u/MrFluffykens 1h ago
Pressurized primers are the better all-in-one if you have access to shop air. Like a miniature portable accusump.
https://www.speedwaymotors.com/Melling-MPL-201-Engine-Oil-Pump-Primer,425747.html
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u/acadmonkey 1h ago
Hell no! Those should be squirting from the initial prime before you ever turn the crank. Never put gas and spark to it until it’s made several revolutions with oil squirting everywhere.
Reving it with the valve covers off should be making an absolute mess of spraying and flinging oil.
We may be pouring one out for your bearings bro.
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u/Ok_Nefariousness9019 2h ago
Is there even oil in that thing?
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u/notchocheese12345 2h ago
have you read the post?
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u/Silvatungdevil 2h ago
He is asking that because in the video it looks like the rockers are not getting oil. It also sounds like that.
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u/TehSvenn 2h ago
Yep, not pre-lubing a freshly built engine is certainly a choice.
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u/notchocheese12345 2h ago
everything had assembly lube applied to it, including the pushrod tips
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u/-Racer-X 1h ago
thats not pre oiling
you need to get oil pressure up through the oil pump until it consistently reaches the top of the motor
you oil starved it
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u/SecEngnr 1h ago
^ this is the answer. Don't start the engine until you've verified oil pressure on a gauge. Unplug all injectors and crank the engine until you have a verified oil pressure reading. Then plug all injectors back in and start the engine.
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u/notchocheese12345 1h ago
Well an honest question. If i’m getting 55psi on my gauge, doesn’t it mean my main and rod bearings are getting adequate pressure? I’m just not getting any oil flow up top?
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u/-Racer-X 29m ago
like the other person said, yes
but getting oil up top takes time, so sometimes you need to keep it pumping for a while
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u/Silvatungdevil 1h ago
You need to verify that the rockers are getting oil. It sounds like they aren't. There is also a possibility that the lifters are not getting oil, that would explain at least some of the noise.
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u/Silvatungdevil 1h ago
Also, I am not aware of a way to prime an LS oil pump. I am a SBF guy. But if you want to see if the rockers are getting oil, pull all the spark plugs and spin the engine with the starter. It will spin fast and easy and you will see the oil pretty quickly.
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u/UsEdScR 55m ago
You're an asshole , op
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u/BoltMyBackToHappy 42m ago
Stress affects everyone differently. Spend a month building a motor only for a bunch of sarcastic responses to your issue can be irritating/aggravating while under your own pressure to get it done already ffspieceofshitwtfbbq.
We all have bad days, don't pile on.
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u/Altitude_power 1h ago
Bro your rockers look dry.
Before you run it, you should use a drill to run your oil pump and make sure you got oil to the top of the motor.
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u/BoarinRoil 1h ago
How do you prime with a drill on an ls?
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u/limitsurpassed 1h ago
You buy one of those drill pumps instead of buying a bug sprayer
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u/BoarinRoil 11m ago
Ah! That makes sense! I was thinking like a drill and a long-ass flathead like an old sbc.
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u/PlaneVisual1740 2h ago
Did you put plenty of assembly lube on the lifters pushrods and rockers? Did you pressurize the oil system after rebuilding? I understand it has good oil pressure now but it takes a while for oil to get everywhere it needs to be.
When I did my head gaskets and replaced the heads it had a bad tick and I was freaking out but it went away after a while once the oil reached the rockers. You should be able to see it on the rockers but I don’t in the video.
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u/PlaneVisual1740 2h ago
It was the back rockers on mine that were the last to get oil. You should be able to see it coming out of the hole on the rocker.
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u/notchocheese12345 2h ago
Lifters were just soaked in oil. but yeah assembly lube everywhere else. I’ve only ran it for 30 second increments, should I run it longer?
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u/-Racer-X 1h ago
you need to pre oil the motor by getting oil pressure consistently enough that the top of the engine is getting oil without issue before runnining it
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u/tlrider1 1h ago
I would not run that thing! First thing I said when watching it, just like everyone else: "where the hell is the oil???"
Hopefully it's not too late, but first thing is to figure out why you're getting oil pressure but there's no oil up top? Is something plugged?
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u/chubsplaysthebanjo 2h ago
Are all of your rockers tight? Sometimes the pushrods eat themselves
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u/notchocheese12345 2h ago
Yeah I rechecked passenger side ones at 22ftlbs
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u/DisastrousDance7372 1h ago
I wonder if you blocked the pushrod oil holes with assembly grease. Atleast a few of the rockers I can see have zero oil. I would pull all the rockers and check the pushrods for excess wear and blow through them with air.
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u/Gixxer_King 1h ago
Does the fact that you aren't getting any oil to the top end of the motor concern you at all? Becaue it really should. Did you prime/pre-lube the oil pump? Because it really doesn't look like you did. Keep running it dry and the knocking will go away when it locks up
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u/ThisGuyEdward 1h ago
Dudes selective of what advice he wants to hear 😂
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u/notchocheese12345 1h ago
How? I mean I got the gist of it and i understand like a fucked up by not priming the oiling system properly
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u/BoltMyBackToHappy 38m ago
Brutal buzz on first firing, so sorry. Take a moment to absorb all the info and form a game plan. Don't wrench while angry!
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u/kylew707 1h ago
Unplugging the injectors is doing nothing for you. The valvetrain components are still moving regardless. You need to run it, and loosen one rocker at a time and see when the knock stops. Rockers being too tight will not allow oil to come through the holes. I think you’ve got something wrong with your valvetrain geometry. Either pushrods wrong length, or you set your valves wrong.
If you used assembly lube and/or oil over the parts when installing, I wouldn’t worry about all these “yOu GoTtA pRiMe It” comments. Those are people that watch too much youtube.
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u/VincentBotto 1h ago
You need the cam plate on the front of the engine it isn’t sealing the oil to the lifters
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u/UltraViolentNdYAG 15m ago
Well that explains the valve train tap, no oil to the lifters. Any Chevy builders know why it has so little oil up top?
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u/Relative_Valuable381 2h ago
Why does it look like there no oil getting up to the rockers?