tip: changing valve seals in the 350 engine

[buickwagon]

This may or may not apply to these vehicles, but the 350 in my son's 1991 Sierra appears to be pretty much identical with the engine in my old 1992 RMW, so I'm going to pass this on here just in case.

His engine exhibited the signs of deteriorated valve seals -- blue smoke out the exhaust, but good compression and no knocks from the lower end. Seals are cheap and comparatively easy so we decided to try replacing those before tearing things down or replacing the motor. Compressed air in the sparkplug hole kept the valves up while the springs and seals were removed and replaced.

There are two seals per valve and two grooves in the valve stem. The upper groove of the valve stem holds the keepers, the lower groove of the valve stem holds the upper square-ring style seal and the lower seal (positive seals for the intake valves, umbrella seals for the exhaust valves). When assembled, the retainer is sealed to the stem by the upper seal. We assembled them all in accordance with the manual and the abbreviated directions that came with the replacement seals, set the valve lash and buttoned down the rocker covers.

Initially, this seemed to eliminate the blue smoke, but things quickly deteriorated and became worse than ever! I assumed this meant something else was wrong -- oil rings, bearing clearance, etc. and we started to track down a replacement engine. However, he and his brother were bored and decided to have another look at the valve seals, just in case.

They discovered that in all cases, the upper valve seals were dislodged -- no longer trapped in place by the retainers. They had been pushed down and were simply floating on the valve stems, doing nothing to seal the retainers to the stem. It is very difficult or impossible to detect this with the springs installed.

After much research and experimentation, the boys came up with their own procedure: Install the lower seal as before, but instead of installing the upper seal then the springs, they installed the springs and retainer, compressed the springs far enough that the retainer was actually below the lower groove, then installed the upper seal in the lower groove and released the spring compressor enough to push the retainer back up over the seals before finally installing the keepers and removing the valve spring compressor completely.

Where the square lower lip of the retainer caught on the seals and pushed them out of the grooves, the chamfered upper surface of the keeper slid over the seals without dislodging them.

So far, so good: no more blue smoke!

NOTE: I have never been inside an LT1, so I will not even hazard a guess if this might apply to that engine!

 

[MrBuick (Magnum)]

On the LT1, both valves use the umbrella style seals. You can also let the valves rest on the piston when it is at TDC on the LT1. I've done it that way on about 5 of them now.

Great post!