I have a 1988 EVO with 71k miles on it. Suddenly yesterday, I started getting a loud knocking noise from the top end at around 1800rpm and it goes away after that. If I'm under good torque it doesn't do it. It sounds like heavy metal hitting something solid, like I would expect to hear if my rocker arm is very loose, but that can't be. So what can it be? I'm not going anywhere until I tear it down, I just don't know where to look. I've only torn down one engine, and that was an inline 6 with overhead cam. I don't know about these EVOs much. Thanks.

 

Before tearing into the top end, I would first pull the primary cover and check the compensating sprocket (front sprocket), they are a common source of noises like you explain here (under good torque) and it's a lot easier to do than to pull down the engine. Are you sure it's not coming from the foward primary area, noises sometimes travels and can be misleading.

 

Ain't that the truth.

I had a noise most heard when decellerating...had the shops test ride...none could locate it. I reluctantly dealt with it for a month. One day it sounded like the top-end...next the primary.

Then one day while riding on a quiet road I started really sticking my head down...grabbing different things. What was it??? The f^@k!n& jiffy stand occasionally rattling against the frame!!!! I pulled over to find the rubber bumper moved. Once rotated back into place, all was good once again!

 

Also check the primary chain adjustment, had a buddys that started knocking and the chain was slapping the case.

 

Check the gas cap if you have two. Think I'm kidding? I was riding in the mountains up and down with throdle at a certain rpm I seriously thought the engine was grande. I put my hand on the cap to lean to the side to hear better and it stopped, Gave a small twist and no more noise. I would never have never believed a loose cap could cause such a horrible engine like noise.