Author Topic: 87 2wd 6 cylinder rough at idle  (Read 1395 times)

Offline 80HD

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Re: 87 2wd 6 cylinder rough at idle
« Reply #15 on: February 23, 2019, 09:27:03 AM »
These paragraphs are taken from Doug Anderson's article regarding the 4.3:

BALANCE SHAFTS

"Any 90° V6 creates some strong, primary imbalance forces, especially in the vertical mode. The 262 is no exception. Chevy originally underbalanced these engines by putting about 46% on the bobweights instead of the usual 50%. This reduced the vertical imbalance that was trying to lift the engine up off the mounts, but created a strong horizontal imbalance that shook the engine from side-to-side instead. So, in order to eliminate a lot of the "noise, vibration and harshness" in the engine and make it into a world-class motor, Chevy added a balance shaft to the premium engines in ’92 and included it in all of them by ’95.

There are two balance shafts, a light one and a heavy one, and two versions of the light one. See photo. The light one is either a 10224542 or a 10172748 casting that comes with or without a metal wear sleeve installed on the back journal, depending on the application. The wear sleeve was used on the lightweight balance shaft when it was installed in a ’92 "first design" engine with the needle bearings in the back, but it wasn’t used when the lightweight shaft was installed in the "second design" engine that had a bushing in the back of the block.

This "first design" shaft should not be used in a "second design" engine because the wear sleeve shortens the surface area needed for the bushing. These lightweight shafts were installed in all of the engines that had the light pistons including the ’92-’98 VIN "W," the ’96-’98 VIN "X" engines and the "first design" VIN "Z" engines in ’95 that were built with the lightweight pistons.

The heavy balance shaft is either a 10224541, a 10105902 or a 12550286 casting. It can be visually identified by the raised identification band around the middle of the shaft. It was used in all the ’93-’94 VIN "Z" balancer engines and in the ’95 "second design" VIN "Z" balancer engines with the heavy pistons. The heavy balance shaft weighs about 125 grams more than the light one, so it shouldn’t be interchanged with the lighter one.

The balance shafts rotate at engine speed and are gear driven off the front of the cam. There are two different gear sets, one with "wide" teeth and one with "narrow" teeth. The ones with the "wide" teeth were used in the "first design" engines along with the needle bearing balance shaft. Some of these early balance shaft engines had a whine to them, so the gears were modified at the same time the block was changed over to the "second design" version with the sleeve bearing in the back. We recommend using only the "second design" gears to help avoid any possible noise problems. "

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Not just my dash shakes.  Really, the whole truck shakes and when people ride in my truck at traffic lights, they are like, "Are we going to make it?"  This got old fast.   Fortunately, i don't do a whole lot of city driving.

i think the best way i can describe it is, if you took a regular v-8 and took off one, maybe two spark plug wires and ran it like that;  At idle it's not going to be smooth, but as you increase rpm's it smooths out.

Like i said, you may just have to get use to it........
That’s incredibly interesting, the motor actually smooths out 90% when rpm is raised just a little. I mean A LITTLE.
Thanks for your response, one of GM’s not-so-brilliant engineering accomplishments!


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Kim Burke