Valve Seals

I plan on replacing my valve seals on my stock 304. In reading about how to do they mention turing the motor over so that the cylinder I'm working on is TDC.

I'm assuming I can just crank the key to turn over the motor, but how do I know when that piston is up all the way, to TDC?

thanks,

 

I would turn the crank with a wrench on the crank bolt. Not hard if the plugs are out.

Do the AMC V8s use valve seals? JMO - I'd be inclined to replace them with the head on the bench, or let the machine shop replace them. What's your reasoning for replacing (adding?) valve seals? I looked through the '72 shop manual and they don't mention seals. They do discuss replacing the springs, and the process should be the same - the manual suggests pressurizing the cylinder with compressed air to 90 psi.

If you really want to add/replace seals, having the cylinder exactly at TDC isn't critical - it just ensures that the valves are closed so that there's no pressure on the valves via the rocker arms. If you look in the plug hole and see the piston, and both valves are closed, that should be close to TDC for that cylinder. Also, the distributor rotor will point to the spark plug wire for that cylinder at TDC.

hth!

 

When initially starting after she has sat for a week or so I get loads of blue smoke out the exhaust pipes (it then goes away when warmed up), my mothers old 72 Cougar did the same thing so I am kind of assuming the valve seals are shot.

 

Compressed air to sparkplug hole, or a length of small rope shoved in to hole. rotate motor till piston will not move, remove keeper and spring. R and R valve seal and reassemble. Rotate by hhand or you can damage piston/valves. Turn crank backwards to free rope.

 

my73cj5, let me know how that goes if you do it. My 75' 304 always has some blue smoke for a minute or so after start-up and goes away after it gets a little warm. I've been told that it's weak valve-seals too. Also, I was told that you can rig up the fittings from a compression tester to an air compressor to keep the valves from falling into the cylinder while changing those. Was told to aim for 100-110 psi, does anyone know if thats correct?

 

timgr, now is see your 90psi, sorry I'll have to check my manual about having valve-seals... I would think that it does, but I've been wrong before

 

Timgr & guys,
I checked a parts manual which I got from this forum for years 74-76 and they show what looks to me an umbrella type valve seal. I'm not sure I can do this type of fix but when it warms up I may give it a try. Smokes like a bear especially right after changing the oil and the oil level is right up there.

Anyway, thanks for all the help and suggestions

 

I have never read the procedure for replacing valve stem seals but I have changed quite a few. In order to remove the valve springs you first have to remove both rocker arms on a cylinder (both valves are going to be closed) it isn't necessary to have the piston at TDC because reguardless of where the piston is when you apply air pressure to the cylinder it is going to be forced to BDC (keep your hands away from the fan blade and make sure the transmission is not in gear) air pressure holds the valves closed while you replace the seals.
Good luck

 

I guess if the piston isn't TDC when cahnging the seals then what alignes the valve? Or do thay all connect the same via the cam and no adjustments should be required?

 

The only reason I can see for going to TDC is that both valves will be closed before you start. The timing is unaffected by removing and replacing the rockers, retainers and springs. If not at TDC, when you remove the rockers they will be under compression, and you'll need to compress them again when you tighten the rocker bridges.

I'd just follow the factory manual instructions for replacing the valve springs - it's the same process, except you're changing a different part at the same location.

JMO - if it were mine, I'd ignore the blue smoke and feed the engine's oil habit (if it uses any oil). Seems like a cosmetic issue to me.

 

There are a couple reasons for the piston to be exactly at TDC. First, as mentioned, if the piston isn't exactly at TDC when you apply air, the engine will turn and put the piston at BDC. Second, if for some reason you lose your air pressure when the springs are out and the pistion is at BDC, you get to pull the head to retreive your valves which are now in the cylinder sitting on the piston.

The exact air pressure isn't critical, but it must be enough that you don't push the valve in when you compress the spring to remove the keepers. A very helpful hint is to put a socket about the size of the retainer over the spring and whack it with a hammer to loosen the keepers. Don't hit too hard or you may knock the keepers out which is a nasty surprise when the spring comes shooting off the head.

 

In some locations, my home state of Colorado being one of them, if the vehicle smokes the state can force you to take the car off the road until it's fixed. During emissions testing, any smoke, including the startup puff, is an automatic failure. Smoke failures do not have a dollar limit for repairs, so again, you're done driving it until it is fixed. Some of us don't have a choice but to make it right.

 

(edit) I should have read page 2 before posting , sorry

The reason for being at TDC is if you loose air pressure or you bump the valve to hard with no spring on it will fall down out of reach,then you will be taking the head off. You can get a hose from the parts store with sparkplug threads on one end and threads to hook up to your air line on the other. I like the rope better, remove the rockers so the valves are closed shove some white nylon rope in the plug hole and rotate the engine over by hand as said before. You will need a tool to compress the spring. Worn valve guides will also cause more oil to run down also. I drove a chev. pickup with this problem for about four years , never fouled a plug , never used more than a quart of oil in 3000 miles. Any questions please ask.
Thanks Paul

 

If you have an air supply that is questionable then it would be safer to put the piston at TDC. Cylinder #1 and it's companion cylinder probably won't be that difficult if your balancer and timing marks are on the money but the other 6 cylinders are going to take some time because if you are off by just a degree or 2 when you apply the compressed air it is still going to force the piston to BDC. I don't do engine repair at the dealership where I work anymore but some of the other technicians who do have even rigged up 4 air hoses into a junction so that they could apply air into all the cylinders on one side of a V8 at the same time then they just remove all the valve springs and replace all the valve seals on that side of the engine(I wouldn't try this with a 5 gallon compressor). I have never heard of the rope trick (it's not a bad idea) you wouldn't even need compressed air if you have a good spring compressor.