LT1 knocking help. Video Inside!
Just start with the basics. If it ends up being a lifter, you can fix that and yes if your possitive it's the lifter replace them all and look at the push rods really good to make sure there straight. I will say this, my brother had a rod bearing go and it would stop knocking at above 1500rpms. I have never heard one stop at idle before but thats just my experiance. It may be hope and pray time that it is a lifter but if you don't find anything don't waist the money and throw parts at it. just pull it and build what you want at that point. even with the knock the crank and rod should still be ok as long as it has not wiped out the crank and rod journals. You have to pull it at that point and take it to a machine shop for them to spec it.
TECH Veteran
Joined: Dec 2008
Posts: 4,147
Likes: 62
From: Little Rock, AR
If the sound sometimes disappears as you feather the throttle (loading and unloading stress on the rod/piston), it is probably a rod bearing. A lifter is always under tension.
You should be able to "feel" a bad lifter by letting it idle and holding a long screwdriver to the pushrod end of the rocker. Lean on the screwdriver (so contact remains constant) as it rocks and sense how it feels.
You should be able to "feel" a bad lifter by letting it idle and holding a long screwdriver to the pushrod end of the rocker. Lean on the screwdriver (so contact remains constant) as it rocks and sense how it feels.
If the sound sometimes disappears as you feather the throttle (loading and unloading stress on the rod/piston), it is probably a rod bearing. A lifter is always under tension.
You should be able to "feel" a bad lifter by letting it idle and holding a long screwdriver to the pushrod end of the rocker. Lean on the screwdriver (so contact remains constant) as it rocks and sense how it feels.
You should be able to "feel" a bad lifter by letting it idle and holding a long screwdriver to the pushrod end of the rocker. Lean on the screwdriver (so contact remains constant) as it rocks and sense how it feels.
Agreed, start taking things apart.
Not going to be a main making that noise, has to be something reciprocating like a rod or valvetrain.
Far as spun rod bearings knocking I have never seen number 2 spin, usually further back in the motor. So based on someone else saying always front and me seeing usually rear I would say it could be any one.
Not going to be a main making that noise, has to be something reciprocating like a rod or valvetrain.
Far as spun rod bearings knocking I have never seen number 2 spin, usually further back in the motor. So based on someone else saying always front and me seeing usually rear I would say it could be any one.
well what ever it turns out to be keep us posted it would be nice to know. I really don't think its a main it would sound different. My money is on a rod bearing, could be a lifter but i don't think u will be that lucky. Haha i never am anyways.
TECH Veteran
Joined: Dec 2008
Posts: 4,147
Likes: 62
From: Little Rock, AR
LOL, the guy is already running it. A little more idling is not going to make much difference. Of course if it was me, I would already be taking it apart, because it sounds like a rod.
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Teching In
Joined: Apr 2010
Posts: 12
Likes: 0
From: Collinsville, Il
I agree with not running the motor anymore. If you do decide to start it I read that you can check the rod bearings by unplugging the fuel injectors one at a time and listen for a double tap instead of that constant thud. I've never personally tried it but it seems possible since you are taking the load or stress of that piston/rod.
Thread Starter
Teching In
Joined: Mar 2009
Posts: 47
Likes: 0
Well guys, I had the motor pulled and i replaced it with a donor motor from a 94 z28 with 80k miles on it... The rod actualy hit my block so the motor was completely done for! I will try to get some pictures up later tonight for everyone to see. Thanks for the advice on everything i really appreciate everyone who followed this thread and posted to try and help me. Now you can laugh about being right 
I have $900 in the donor motor and $400 in the labor ( i did a few free custom laser and waterjet jobs for the engine guy) I don't think that's too bad considering he had to pull the donor motor, my old one, and put the new one back in and recharge the a/c and change plugs and oil ect. Anyone interested in a beautiful z28 with fresh paint, brand new rear end, built tranny, and fresh 80k engine? I have decided to pursue finding my dream car (77 t/a) and start working on it. I have no idea how much to ask for the car yet, any ideas? Also it won't let me post anything in the for sale section for some reason?? PM me or post back for more details. Thanks again to everyone!!
I have $900 in the donor motor and $400 in the labor ( i did a few free custom laser and waterjet jobs for the engine guy) I don't think that's too bad considering he had to pull the donor motor, my old one, and put the new one back in and recharge the a/c and change plugs and oil ect. Anyone interested in a beautiful z28 with fresh paint, brand new rear end, built tranny, and fresh 80k engine? I have decided to pursue finding my dream car (77 t/a) and start working on it. I have no idea how much to ask for the car yet, any ideas? Also it won't let me post anything in the for sale section for some reason?? PM me or post back for more details. Thanks again to everyone!! 