Here's the old thread.

https://www.camaroz28.com/forums/sho...scraping+noise

Now for some background info. Last April I did a H/C/LT swap and also replaced the stock timing set with a LT4 HD set. Once the engine heated up I could hear gear noise through an automotive stethoscope coming from the back of the opti. So I did some searching and found the above thread. In the mean time the stock opti died and I foolishly replaced it with an Allignition ripoff which didn't work worth crap and threw codes. The Allignition opti, however, did not make any noise after the engine was warm. So, I figured there must be some issue with the opti pressing against the timing set after the engine heated and expanded. Long story short, I replaced the junk opti with GM unit and lived with the noise until now.

Recently I had to pull the opti and crank hub to replace the seals (chasing an oil leak), and decided to place a set of 3 - 0.010" thick shims (http://www.mcmaster.com/ pn 3088A758) behind the opti where the bolts go through. Problem solved - the noise is gone .

 

Did you check cam pin length??

 

Yeah - it was 0.615", 0.005" shorter than GM spec. I checked it before I installed the cam .

 

Good deal...keep us posted if the noise returns....seems like anything I fix noise wise returns a few thousand miles later and I just ignore it then or turn the radio up louder Mine still makes the noise only at idle, especially when shifting from Drive to Park then it quitens down again...been that way since my original post back in the end of 2006. Even after the cam swap I did this last fall of 2007..you can hear the opti noise better now since this cam isn't as loud/big as the old one.


So you went with 0.010" thick shims and not the 0.005" shims mentioned in the OP?? basically just pulling the opti out 0.010" from its original location again the timing cover.

 

Yeah - 0.010" from the timing cover. I'm kinda shooting in the dark since there no way to measure accurately. Basically I put the opti on and noticed that it was slightly displaced from the timing cover. 0.010" took up just the right amount of slack.

 

Well I sprung a oil leak from the wp gear drive so I tore the front down Sunday night and got it all back together Monday night after work...I used some washers I found at the hardware store that were .035 thick, then measured the length of the dow and the depth of the opti and with those washers I had .234" of the dowl inside the opti end so I thought that would be enough...put it all back together and YES!! no more plastic grinding noise!!!