Just wanted to chime in with yet another left side header crack between 3 and 5 sounded like piston slap. The 87 GN has 68000 miles.If it wasnt for this site and the help of guys on it
I would have still been scratching my head.
Well I'm stiil scratching my head. Removed header and welded up put back on the car and still knocking. Stethascope points to center of int.man. or right at upper radiator hose outlet.Checked cam sensor I dont think thats it. Tonight I will remove valve covers and check valve train.This Is my first GN and have owned less than two weeks. Any ideas from you guys would be appreciated. Thanks.
I chased a slight knock noise myself for awhile. It actually turned out to be my cam sensor. Try to see how much you can lift the ring piece. I know there is a spec on it somewhere, I'm sure somebody that knows it will chime in. I put a new one in and no more knock. I'm pretty sure though you can have the cam sensor shimmed just like a distibutor, just didn't think of that and wasn't in an area where I was familiar with the local shops. Good luck hunting it down, I hope it's something simple.
Take the scope and probe around the top of both valve covers if the noise gets louder you may have upper valvetrain trouble. It's happen to me twice broken rocker shaft.
Thanks for the ideas. I didnt get to the car last night but this weekend I will run down the check list and the noise does seem to be more noticable
at the upper side of the valve cover and maybe even the intake man. towards the front.
Thanks for the input Scott,Frank.
I've had the belt tensioner make a similar noise. While the car is running, put a socket on the nut of the tensioner and move it with a breaker bar. See if that changes the noise.
Patrick '87GN
Well I removed valve covers and preformed inspection my findings were that right side forward most pushrod was clearly not spinning at the same rate as the others.The pushrods are marked with paint so the rotation is clearly noticed.Is this a sign of lazy lifter,bent pushrod,camshaft lobe being eaten or nothing to worry about? The oil in the motor looks clean no metal.The knock does sound to be coming from the front.If needed i will remove valve train and check if pushrod is straight.I did use scan tool and the knock sensor is not picking up the noise.Tonight I plan to spend some time on the car should know more tomorow.
Steve, The cam is tapered front to rear, to make the lifter turn. If the cam is out of spec, this could cause the lifter turn slowly. The crown on the bottom of the lifter could be out of spec. Yes, there is a slight spherical radius on the contact face. I seem to remember .0005" nominal. I figured it out once and it equated to a 9.0"R or something near it. You could have a problem with bore wear. You could get a line contact instead of a broad surface. It could be a frictional problem with that lifter not being lubed properly.
If your knock sensor is not picking up the knock, it could be in too tight. I think the spec is 14 ft/lbs. It could be a bad sensor. Get that fixed! It's under the coil pak. It's a critical piece on Turbo Buicks.
How about the rocker arm is it moving at the same rate as the others. If not maybe a wiped cam lobe.
A wiped lobe should give a high blm.
I got the chance to spend some time with the car and my findings are the following.When removing the belt from the motor the knock gets much more pronounced{louder}.After removing the cam sensor and inspecting, the cover has no signs of damage but when pulling up on the ring I do notice a substantial amount of play.What is normal? Tonight I will check the balancer and prepare to remove pan and check bearings as the car needs a main seal anyway.I will report findings at earliest convience. Thanks again for the ideas.
Well I removed the pan and checked the rod and main bearings all looks good.One thing I did notice was when removing the pan the front right side bolt that has the stud to hold the trans line is missing the clamp and the line is rubbing or vibrating on the mounting bracket for the intercooler.This noise might be the one that I have been chasen.I will let you know for sure after I get the motor back together.
With the new seal inplace and the motor back together the good news is the oil leak is fixed.The bad news is I still cant find this knock.Drove the car and noticed after warming up the noise decreases.Maybe lazy lifter? maybe timing chain?With the pan off you can do a visual inspection of camshaft nothing that looked liked it was being ground down and oil looks clean as do all the bearings.