Hi. I have a 1991 Z28 305 TPI. It smokes rather heavily when starting cold in the morning. The smoke lasts about 10 seconds and then it stops. I believe that my valve seals are gone.

My question is this.. can I remove the spring assembly from the valves and hope that they will not fall in, if the piston is set at TDC? or do I need to put rope in the cylinder or compressed air thru the spark plug hole?

I have worked on engines where the piston being at TDC was enough to prevent the valve from disappearing into the cylinder, but I am not sure about this engine. By the way this engine is not in a Z28, but in a XJ6 Jaguar.

Also, can anybody tell me the best seals to get and where?

Appreciate any advise. Thanks
Rick

 

Get a "air hold" fitting. It screws into the spark plug hole, you attach a LP air line to it, and when you take off the rocker arm off, the valve snaps shut, letting you R/R the seal with the head on the eng. NAPA has them.

 

Continuing this thread, when I tried to order the valve seals I was asked if O-ring or umbrella type. I haven't yet taken apart my valve assembly to take a look, but it seems that the O-ring goes onto the stem towards the top in a cut provided for it in the stem in conjunction with the spring keeper. The umbrella goes on both the stem and guide boss . My question is this.. are both used at the same time or you only use one type-either or- thing.

Thanks
Rick
PS: the positive type of seals seem to require machining of the boss guide,to either .530 or .500 Diam. Are there any positive type that will fit a stock head?

 

you only use 1 type of seal,not both,usually its the maker of the head who decides.usually you se umbrellas on ford and o ring on chevys.drop a valve cover off and look at base of valve and see if you see any kind of seal,if not them its a o ring which will be on top of the valve and hard to see with the spring on.also air works fine,youll also need to rent or borrow a on car valve spring compressor,just you compres springs with heads installed.dont forget if you do air method dont let your air supply run out or loose the connection for what ever reason before you get spring on otherwise your screwed......the rope method works fine,just turn it over by hand to squish the rope in there.bbut mor elikely you have the o ring style which is a ****ty design fo rlong term contol,whichis why you see a lot of smoking chevys,including that 4.3...pc seals or teflons ones are the ticket but require machine work to install.but this is an easy job to do

 

So if I have the original O-rings style, could I get rid of them and install rubber umbrella types, which I assume need no machining of the bosses? Would they provide better oil control?
I am almost sure that you need to remove the heads and send them to a machine shop to machine the bosses.


Rick

 

rick,yes ideally going with a teflon pc seal the best way to go.but for a base 305 headed stock engine the time and effort aint worth it.replace your o rings and youll get 50k plus more smoke free miles.pribablyy will outlast the engine itself.dont make it harder than it is.fix it and engine your ride.dont beat yourself up for nothing

 

There are umbrella type seals that fit without machining for SBCs. BUT you have to make sure they are specifically for SBCs. I've seen engines with the Ford type umbrellas installed. These are too big and will hit the inside of the spring, causing them to ride up. The ones specifically for SBCs won't. The red ones are made from a superior material that resists heat.

Teflon types are positively retained on the valve guide, but they are not recommended for street use. They tend not to allow enough oil to the guidesat lower rpms. The Ford and aftermarket umbrellas for SBCs actually ride up and down with the stem.

The stock type o rings work fine, but you have to be careful not to damage them as you uncompress the spring and the retainer comes up over them. Easier for this to happen when doing the seals with the heads still installed.

Don't be tempted to toss the outer metal shield that goes under the retainer if you stick with the o rings. These work with the o rings to allow only a small amount of oil to get to the stem to lube it. This is also why you don't use umbrellas on the stems with o rings. It would starve the guides of oil and burn them up. You can get rid of the metal shield if you go with umbrellas, but the spring pressure will drop a bit cause it isn't compressed as much without them there. I use umbrellas with stiffer springs and no shield, just my preference.

Heads up: the keepers tend to stick to the retainers. So when you compress the spring, the keepers stay on the retainer and won't let you take the springs off. I like to take a socket almost the size of the outer diameter of the retainer and give it a sharp rap with a hammer to unstick them. Then use the compressor. I recommend the thin rope technique for 1st timers. Less chance of getting into problems than with compressed air. But for sure, pull all the spark plugs 1st. Makes it easier to spin the engine going from cylinder to cylinder by hand.

 

I also use a small magnet to get them out once they are loose.

 

the type that i bought were Fel-pro and they came with an o-ring as well as a plastic umbrella to put on top of the ring. don't remember the p/n though its been a few years.