'95 Buick Riviera Supercharged Engine Knocking

[Red-Z]

My wife has a '95 supercharged Riviera. The engine became overheated and blew a headgasket. After repairs, the engine has a loud knck with the frequency of a valve tap. Can anyone help me diagnose this?

[ralfwho]

Check to see if the harmonic balancer has failed. There should be no rotational play when you attempt to rotate the balancer by hand. Of course, you'll have to de-tension the belt (or remove it).

[Red-Z]

ralfwho:
Thanks for the tip. This is a mystery. Engine compression is normal within limits, however the car has lost its pep. The harmonic balancer would explain this. But what bogs my mind is the "toc, toc, toc" noise that seems to increase in intensity when starting up, or accelerating. This noise seems to be in synch with a piston.

[ralfwho]

It was the racket (like you describe) that led me to believe it was my timing chain. So I decided to take off the front cover and inspect it.

In the process I found that the harmonic balancer had come apart. When the rubber in the balancer disintegrates, the timing changes AND there is a terrible noise.

[Red-Z]

Is it a difficult job to replacethe harmonic balancer? Does the engine have to be pulled?

[ralfwho]

It's not terrible. If you're reasonably handy and have decent tools.

• Remove the serpentine belt. Once done, check the pully. If is rotates by hand, it is defective. If it doesn't, the balancer is not the problem.
• Put the car on jack stands and remove the remove passenger tire.
• Remove the plastic fender liner so you can see the balancer from the wheel well.
• Support the engine with a floor jack. (put a 2/4 between the oilpan and the jack) Raise up the engine to take the tension off the engine support that is on the passenger side, towards the front.
• Remove the support from the body of the car and lower the engine just enough so you can put a puller on the haromonic balancer.
• Remove the bolt from the balancer and then use the puller to remove the pulley. You may need to hold the balancer while removing the bolt. The book says you need to hold the flywheel but this is not necessary. By a big wrench strap and "freeze" the balancer while you un-bolt it. You'll need a second set of hands for this. KD makes a perfect tool for this, the flexible belt will fit the grooves in the pulley perfectly. Craftsman makes an OK one.
• Once off, inspect the seal on the front cover carefully. Replace if it looks crummy.
• Lube the crank and the new pulley and install it. Carefully align the key in the crank to the keyway in the balancer.
• Torque the bolt to the specified value.

[Red-Z]

Thanks for the tip, but it wasn't the harmonic balancer

[Steve R/S]

Have a 95 supercharged Riv. Had a knock--especially on startup and shutdown. Knock also noticeable as engine revved. Sluggish performance. Had to replace the supercharger. Bad front bearing in roots. Was an expensive fix.

[Rolanduo]

I am having the same exact issue with my 95 Supercharged. I believe that it may be due to a rocker arm tapping the valve cover. Since the pushrods will now come through the head further due to the milling that is done during a rebuild, they sit higher, which may effect the valves and might be messing up your fuel air ratio. I havn't had any issues with the power, but I am getting poor milage myself. I am currently trying to solve my issue as well, I will let you know if I find anything else. Hope one of us can find a solution.

[Rolanduo]

may have bad news for you unless you have found the problem for yourself. I gave up looking for the problem when I couldn't find anything that was visibly wrong and look it to my friends shop. He isn't sure, but he thinks during the rebuild, one of the lifter springs may have gotten damaged... meaning the valve in corresponance is not opening correctly dropping milages and efficiency, with a sound of a valve tap. The only way to fix this is pull it down to the block... and redo the entire head job. I am hoping that some other issue is the problem, but your case sounds the same as mine.

[Red-Z]

This one was piston slap. Rings eventually failed. Replaced engine for $1100.