My brother just replaced the valveseals in his '87 TA with a 305 CCC quad. The intake seals had umbrella type seals with an o-ring on the stem. The exhaust valve only had the o-ring?

We replaced all the o-rings and the umbrella seals, along with a set of new stock springs (why not at this mileage). We talked about putting umbrella seals on the exhaust, (I've never seen a motor that didn't have umbrella or pos type seals on ALL valves?) but we decided to just replace what was there from the factory.

The car used to smoke blue on startup and now it puffs black smoke all the time. I did some searching and found a write up that states to put the spring on before the o-rings. We didn't do this. We used both a screw type and a lever type valve spring compressor, and put the o-rings on the shaft before installing the spring.

Is it possible the o-rings were knocked off during spring install and that would make it smoke this bad? How do those o-rings work to prevent oil getting down into the valve guide anyway? I'm just not understanding what those o-rings actually do?

Well, needless to say, the springs will be coming back off to see what's going on. Any advice before this happens is greatly appreciated!

Thomas.

 

without a doubt you assembled it wrong and the seals got moved off location and now are doing nothing or very little, not that the o ring seals ever did much. you need to do it again, and look for a set of positive seals.

 

Use positive seals on all 16. Sounds like you either used the wrong size seals or installed them wrong.

 

If you put the o-ring on first then the spring and retainer then you've knocked the o-rings off.

There's never any seals on the exhaust because the pressures will not suck oil down the exhaust stem. On the intake valve, there's a vacuum on the underside of the valve drawing in the air/fuel mixture. This vacuum can also pull oil down the valve stem. On the exhaust, there's only exhaust pressure pushing out so there's little chance of oil going down the exhaust valve stem.

I'd say pull the springs again and check the o-rings.

Blue smoke = oil burning
Black smoke = unburnt fuel (running rich)

 

Thanks guys. It seems we installed it wrong, and the o-rings probably fell off the stem.

I realize the exhaust valve has pressure pushing up instead of sucking in like the intake, but can't oil seep down the stem after the motor has been shut down? Especially if the exhaust valve is open after shutoff, wouldn't this cause smoke on startup?

Would it hurt anything to put umpbrella or pos type seals on the exhaust valve too?

Thanks again,
Thomas.

 

Oil can seep past exhust valves/guides. If the guides are sloppy, you'll get exhaust pressure pushing past them and pressurizing your crankcase. Seal them.

 

Yes, if you can, put umbrella seals on all of them. To use the PCV type seals, the guides need to be machined to accept those type of seals.

When using any kind of guide seal, clearance must be checked especially with a high lift cam. The bottom of the spring retainer can hit the valve seal if the guide isn't cut down enough. With a relatively stock cam, there's normally not a problem.