engine knock

**67ls6** · 05-13-2011, 08:03 AM

i bought a take out ls6 that "supposably" only 6,000 mile on it before the car was wrecked. i replaced the heads with a pair of AFR's and a comp cam, installed in my project car and now it knocks very loud. any sugestions or places to look? any help would be greatly appreciated

**mark21742** · 05-20-2011, 01:44 AM

Are you sure it knock, and not mis adjusted valves? What lifters, rockers, pushrods and preload are you running? Maybe your valves kissing the top of the piston?

What cam, valve size and are your heads milled and do you have valve reliefs cut in the pistons?

Do you know what your total timing is?

**izzhemp** · 05-20-2011, 02:27 AM

Originally Posted by mark21742

Are you sure it knock, and not mis adjusted valves? What lifters, rockers, pushrods and preload are you running? Maybe your valves kissing the top of the piston?

What cam, valve size and are your heads milled and do you have valve reliefs cut in the pistons?

Do you know what your total timing is?

Wow i think you pretty much covered it with that man kudos to you for knowing your s**t

**bills98ta** · 05-20-2011, 02:31 AM

LOL... Mark does know his knocks...

**mark21742** · 05-20-2011, 09:56 AM

Originally Posted by bills98ta

LOL... Mark does know his knocks...

Don't forget the pops, chunks, bangs and that noise that fluids make when they burst into flames under the car lol

**67ls6** · 05-23-2011, 06:44 AM

they are afr heads and yes they have been milled i think .010 but cant remeber and the stamp it on the under side of the deck so you have to pull the head to see. the rocker arms are crane gold and i followed the instructions from crane at two full turns of preload and they are stud mounted. stock pistons no relief cuts and a comp .621 cam

**bills98ta** · 05-23-2011, 03:09 PM

Ouch. Two full turns. A cam that big, I'd go 1/4 to 1/2 a turn max. What lifters ?

**67ls6** · 05-31-2011, 06:24 AM

stock lifters. i think i found the noise i pulled the rocker arms and found a few witness marks on them and on the head. they appear to be hitting on the head closest to the intake

**mark21742** · 05-31-2011, 07:34 AM

Originally Posted by 67ls6

stock lifters. i think i found the noise i pulled the rocker arms and found a few witness marks on them and on the head. they appear to be hitting on the head closest to the intake

I had the same problem with my Chinese adjustable rockers...I ended up pulling each one off and hitting the back of the pushrod side with the bench grinder to give me some more clearance....then saw how much flex and movement the setup had and in the end I shimmer my stock rocker assembly and used it.

You might be able to use a prybar and put just a little pressure on the the rockets pulling them towards the valve springs ad you tighten them...if there is any play this "might" help...but don't pry hard, just use alittle pressure.

Also shot some black spray paint on the inside of your valvecover down by the gasket lip...re assemble and turn the engine over a few timed by hand...then look to see if the rockers rubbed any of the paint off

**bills98ta** · 06-01-2011, 03:37 AM

You would think crane's would fit.... But....
Make sure you bring each cylinder up to TDC, and once you get the push rod lash out, only go a 1/4 turn. Try and look down at the lifters to make sure none of them are collapsed.