When I hear clicking under the hood on one of my OHC hondas, I adjust the valves - it doesn't take very long to do 16 valves, plus it will often restore a little performance. Porsches are a little different than Hondas. Tell me if I'm correct here... 951's have lifters, and lifters are located between the cam and the valves, right? Does this mean the cam turns, pushing down on the lifter, which in turn pushes down on the valve? Do lifters automatically take up the slack, meaning there is no way (and no reason) to adjust the valve clearance?

I'm a little confused in the way that it works. Can someone clear it up for me please? If there is a way to adjust the valves, does anyone have a procedure with clearance numbers for intake & exhaust valves?

Thanks!!

 

Jax951 -

The way the lifters work...

The cam turns and depresses on the hydraulic lifter which in turn depresses the valve spring thereby opening the valve.

As the lifters are hydraulic, they automatically take up all the slack, and are non-adjustable.

If you have a tick, or a louder noise, you may have a collapsed lifter. Easy to test them when they are out of the car, almost impossible to test with them installed.

HTH!

 

Am I correct in saying a collapsed lifter would cause a valve to not open up all the way? If an intake valve doesn't open properly, then not enough fuel would get in, possible causing a lean condition, am I right? You say they're easy to test? I'm not afraid to pull out my cam - how do I test a hydraulic lifter?

Thanks!!

p.s. what does HTH mean?

 

Jax -

A failed lifter would prevent the valve from opening all the way. To test - you remove the cam tower, and the lifters literally fall out.

Depress the button in the lifter in the middle of it - and if it's solid the lifter is good. If it's soft, it's not, and needs to be replaced.

You need to pull the cam tower though to get at them, and that means tensioning the timing belt correctly.

HTH! (Hope that helps!)

 

Forgive my ignorance - I'm new to porsche engines. Isn't the cam tower just a valve cover in essence? Do I have to be careful of the lifters falling out once I pull the cam tower? Will oil drip down onto the exhaust manifold?

After all that, why does the timing belt need to be retensioned? If I don't have to pull the cam, why would the tension change?

Thanks again...

 

The cam is inside the housing with the lifters protruding out the bottom. Very little oil if any should drip out when you pull the cam houing off. The cam sprocket is on the front of the cam housing so you must remove the timing belt to get the housing off the engine. A Haynes manual for under $20 was very helpful to me when I had to remove the housing.
It isn't written for turbo's but removing the cam housing isn't much different between any of the 8 valve engines.

Jim Cooper
'84 944

 

There is no "valve cover" per sey on these cars. To get at the lifters, you will have to remove the timing belt and the cam housing. The lifters will fall out of the cam housing as you lift it. The fun part is reinstalling it since the lifters will want to fall out as you put the housing back in place. To diagnose which lifter is bad, go to an auto parts store and buy a mechanic's stethescope (about $12). Start you engine and listen to the top of the cam housing about where each valve would be. That will help you localize the problem. Good luck.

Dave

 

"Depress the button in the lifter in the middle of it - and if it's solid the lifter is good. If it's soft, it's not, and needs to be replaced."

So how soft is soft? I can push in the button on mine, but how much pressure? I have two sets and they seem to be fairly consistent except for one that is locked up solid. A litle help is always appreciated as I am getting ready to reinstall.

 

If the button pushes in easily, try this.

Fill a small container with oil, and immerse the suspect lifter. UNDER oil, depress the button a couple times.

If the lifter stiffens up, then it's ok. If it doesn't - it's bad.

there's a small hole on the side of the lifter that allows it to pump up - the lifters you have might be bled down. Re-Prime them as I described, and see.

If you can push the little button without getting white knuckles, then it's bad. If you're replacing one - you may want to replace them all... Chances are they're the same age.

HTH!