I'm trying to change my valve springs so I hooked up the cylinder to the air compressor through the spark plaug hole and what not. Well, when its hooked up, I can hear this fairly loud and consistent hissing, like none of the air is staying in the cylinder. I have the timing cover off an the noise is the loudest coming from that area near the oil pump. I tried both cylinders 1 and 3 and both gave the same exact results. The air compressor was set at about 30-40psi. What's wrong?!?!

 

Take the rockers off -- one of the valves is open...

-OR-

You have a bent valve or worse...

 

I used 90-100 psi, and yes it will make a hissing noise the whole time.

 

The rockers and pushrods are out obviously.... The air is leaking into the crankcase, no air is running through the intake or the headers. I'm very worried

 

pull up your dipstick and feel for air. Sounds like you have some bad rings

 

Well the timing cover is off right now so that won't work at the moment. Guess I will have to do some tricky work with my magnet pens...

 

more air pressure, either that if the springs are all still on you have some leaky rings, try turning the crank over

 

I agree.
Try more pressure. We used 80 psi

 

It will hiss alittle bit past the rings.It will be real loud in the intake or exhaust if a valve is bent.I do them at 100 psi and check the tank pressure after each valve to make sure there is enough for the next.The valve will hold up there until 40psi,no problem.

 

If your front cover is off, this is a no brainer. Use the OTHER method listed on my site, and use the dot on the gear to tell you which pistons are up top. This method is about 10x easier than the air method anyway!

Its all detailed here
http://www.ls1howto.com/index.php?article=23

 

The TDC method is safer too,The only way to go IMO

 

I agree with Jmx. I switched from the air compressor method to the TDC method after changing two springs. It's faster and easier, make sure to take the plugs out before so you can spin the engine over easier.

 

Yea, I did my by TDC and it worked great, just keep track of where your at.

 

TDC method is the best!!

 

I did mine with the air compressor and it was over 100 on all of them. It make the same hissing or leaking noise you described. Mine seemed loudest on the intake valves and the air would come out the TB. It worked and now it runs that is all we can hope for when working on one!

 

i highly agree!!!

 

Well, I upped the pressure to 95 psi and tried again and it worked! It is time consuming but what the hey... I got em all changed. Two or three were stuck really well and I had to gently tap the retainer to get the valve stem and locks off the retainer. The hissing on all the cylinders sounded the same so I guess nothing was wrong with the rings. Thanks a lot guys!

 

I always smack my retainers with a rubber mallet before I try to change the springs. It will loosen the keepers in the retainers and you wont have to fight with them.