Sorry...I think I posted this in the wrong forum the first time.
I have an 86GN. I have owned the car for about 6 months now. It has 90K on the motor. It has always made a tick/knock sound. Using a mechanics stethoscope it sounds like the noise is most pronounced on the exhaust header for the rear-most driver-side cylinder (and on the valve cover in this same general area).
Almost everyone who listened though it was a lifter not pumping-up. I just replaced all of the lifters and pushrods with stock pieces...and the sound went away for just a short while after I started the engine. Now it sounds exactly the same. The odd thing is that it comes and goes (mostly comes). Oil pressure is 20-25psi @ idle, 50psi+ on the go. No problems, it's just annoying!
I've thought about going to slightly longer-than-stock pushrods (+.060") to see if it is a "slop" issue.
Any thoughts would be very much appreciated.
The junction between the #3 and #5 cylinders on the driver's side exhaust header is notorious for cracking. And thus being a source of noise like you describe. If yours hasn't been repaired, chances are 100% that it is cracked. Before you go tearing into the motor further, I'd take it off and have a good look.
Double check your torque converter bolts while you're at it just to eliminate that as a possible cause.
Hi Scott,
I looked through the reciepts and the drivers side exhaust manifold was replaced about 10K miles ago. I did check it out, no cracks, all fastners are tight.
Also checks the TC bolts...all nice and snug.
A guy I work with thought it might be bent valve....but I'm not sure how that would have happened, and I'm not sure why it would come and go if it was a bent valve. I will check the cylinder pressure this weekend just to make sure it's seating.
It seems to me that this has to either be something in the rocker-arm or valve...or perhaps in the piston/rod area....although I've never had a rod piston problem come and go, nor have I ever noticed a rod/piston problem only make noise at idle (in my experience it gets much worse when revved).
Have any idea how to tell if a rocker arm is worn or if the nylon retainers (to the rocker shaft) are bad/worn?
Thanks,
Carl
i've heard that general motors had a recall involving the valves because they produced different sizes on one of the heads. I dont know if thats true or not, but just letting you know.
This could be a header leak. Do you have a gasket in place?. Try installing a new gasket and see what happens. What happened on my car and a friends after replacing the header soon after you could hear this tick noise sound like a lifter. I pulled the v-cover and things were tight.For some reason the gasket burned near the back cyl.
Frank, I could never get my headers to seal with gaskets, I just use a little high temp sealant and it works perfect.
Carl, I had the very same tick sound you are talking about and went through a lot of the things listed above and it turned out to be to be just a bad fuel pump.
Thanks for all of the good input. Sorry it's taken so long to get back with my findings.
I've thuroughlly checked everything posted here with no problems found.
I did remove the pan and I replaced the oil pick-up tube/screen...it was about 1/3 blocked with what appeared to be old gasket material. It appeared that someone did me the favor of replacing the rear main seal, but got a little "aggresive" with the RTV (this was most of the debris on the pick-up screen).
At any rate, nothing changed..still had the tick.
I once again used a stethoscope and found two specific areas making the tick noise (front and rear cyliners on the drivers side) at the rocker arm covers. I just removed the rocker arm cover and noticed that the intake vavle rocker (front cylinder) and exhaust valve rocker (rear cylinder) have very little oil in the rocker arm (in the cup formed above the valve stem side of the rocker arm). These rocker arms correspond to the tick noise areas. The rest of the rocker arm "cups" are drenched in oil.
What do you think, blockage in the oil path? I don't see any wear or discoloration that would indicate a lack of lube, but it seems like more than a coincidence. I suspect that the lifters are not fully pumping up, thus cuasing the tick noise.
I was going to install a couple of slightly longer push rods (+.030) on the questionable rockers to see if the noise goes away (or changes)...I figure that this will confirm my lack of pump-up on the lifters.
Any input is greatly appreciated.
Thanks,
Carl
Carl, I know I mentioned this above and I am going to say it again did you check the fuel pump? I know it sound dumb and that there is no way it could be that, I thought the same thing and was going to buy a couple of longer push rods when the fuel pump stopped working.Just my thoughts.
How about replacing the lifters and pushrods in question. Sometime the inj's make a ticking noise
if they are sticking.
Frank
Ok, here goes...
First, thanks for all the input...it's really nice to have other opinions and experiences!
When I originally heard the noise I figured it was a lifter gone flat, so I replaced all of the lifters and pushrods (I've also replaced the rocker arms in the area creating the noise). No diffence was detected when I installed the new components, the same noise still comes from the same area. I saw nothing wrong with any of the lifters or puchrods that I removed and the cam lobes looked fine and we very uniform amongst one-another.
I put my stethoscope on each injector and they all sound exactly the same, a light tick.
I don't know what to say about the fuel pump...I have good fuel pressure and I never get any (or very little) detonation under full boost (I have a knock counter). So, I'm wondering what led you to replacing the fuel pump on your car....did you have some other symptom (other than the ticking noise)?
More and more I'm thinking that I have a issue with the cam, or an oil starvation issue in the lifter gallery.
As always, I appreciate any input.
Carl
What type of cam in the car.
Frank
I have a non-turbo car, I had the same noise that you describe it would come and go, running down the road or at 1000 rpms. It sounded like it was coming from # 3 rocker arms. The fuel pump started pumping oil out of the vent and when I replace it the noise when away and I have not had anymore noise. Had to be the pump
Carl, after some thought this would only help you if you have a mechanical pump and that is not what you have is it? I am sorry if I have pointed you in the wrong direction. I was just so sure because your description of your problem is the same as my own.
Thanks Chriss,
I was really stumped by the fuel pump because the fuel pump on a GN is in the tank, not on the block.
At any rate, I appreciate the input.
I did install .030" over size pushrods and the while the tick is there it has been dramatically reduced...in fact it is all but gone. I still want to figure-out the true cause.
I'm al little puzzled by hydaulic lifters as I recall when I installed new lifters I could depress the lifter about .30". Granted they were not "pumped-up", but I thought that the idea behind hydraulic lifters was that they would only "pump-up" enough to remove valve lash, but not apply enough force to compress the valve spring (at least not until they are compressed to the point that they have no more "float" as would be the case when the cam lobe is compressing the lifter to force the valve open).
Anyone out there know much about the theory of hydraulic lifter operation?
Thanks again for all of the feedback.
Carl
Carl, You never said if your oiling problem to the rockers went away when you put in the new lifters. That info is critical for trouble shooting.
The perfect push rod length can be determined with an adjustable push rod. With the lifter on the heel of the cam, lengthen the P/R just to where you can't spin it with your fingers. Now you have all the slop out of the system. Remove the P/R by lifting off the rocker shaft. Measure the P/R and add 1.00mm (.040"). Do this with every lifter. Record the lengths and average them. This will put your lifter plunger in the proper location for optimum function.
The hydraulic lifter is a very forgiving mechanism, but you want to get it close. If the push rod is too long, you could bottom out your plunger and your oil cushion goes away. If it's too short, your plunger could bottom out on the top side which allows clearance and then noise.
Did you ever take a lifter apart to see what drives the oil up the push rod? Fasinating!
Hey carl, well I had the same problem with my gn. I replaced the lifters and what not just like you,and it still Ticked like crazy at idle. Then I started thinking, the cam lobe is not totally parallel to the face of the lifter, nor is the lifter totally flat. As the cam rotates, it forces the lifter to rotate in the bore so as the lifter doesn't produce a valley in the face of the lifter, and thus reducing preload and making noise. After I installed a poston gn107t cam with hi-rev lifters the noise went away for good. So take a look at your old lifters and look for a valley wore into them. Hope this helps.