I built myself an engine for my 1990 Trans Am GTA. Its a 355 utilizing the stock TPI injection system and a Modified computer chip. It runs 11.2:1 compression ratio. Im right around 10,000 miles on it and just went from open headers to a full exhaust system. Now I am noticing a knock in the engine. I believe its been there for some time, but I just wasn't able to hear it over the headers.
With the help of a long screwdriver, I figure its coming from cylinder 1. It only knocks when the engine is at running temp (160F) and is equivalent to RPM, although it seems to stop at higher RPMs... I have noticed no power loss, nor do I feel a misfire of any sort.
I can only think of two possibilities. A wrist pin, or maybe a cracked rod? (They are stock rods, so I know they are being pushed to their limits.) Any ideas on other issues or maybe an easy diagnostic?

 

Is knocking the accurate word to describe it or could it be tapping? Different possible causes for each.

Jake

 

Its definitely knocking.... Before I inspected it further, I thought my new headers were hitting my sub-frame, but to my dismay, its coming from cylinder 1.

 

What makes you lean toward wrist pin? Not sure what you mean by "a cracked rod"; is there something you haven't mentioned?

You can do a couple of more tests before breaking out the heavy tools: Check the valve train up top by pulling the cover then crawl down under and listen at the oil pan.

If the valve train checks okay, next would be to remove the oil filter, cut it open and look for metal particles caught up deep in the pleats. Then drain the oil and look for the same thing: gold or silver glitter - that would be bearing material and is BAD news.

Based on what you find, you'll know what needs to be done.

Hope this helps.

Jake

 

There are no metal particles in the oil, and the valve train is in check... I mis-typed when I said cracked rod. I meant excess clearance. I have done a little more investigation and found that it was to much clearance between the rod and crankshaft. Thanks for the help.

 

Okay, then it looks like rebuild time. Sorry for your loss.

BTW, did you cut open the oil filter?

Jake