Worn valve guides vs. loose valves.

cygtoad · cygtoad's Garage

I have an 87 Carrera and I am getting ready to do a valve adjustment. It has about 110K on the clock and it has has been pretty chatty since the day I bought it at 100K.

I did a full tune up when I first got the car, before I really knew about the valve guide procedure, so with this tune up, I am going to take that plunge.

My question is: Is there an easy way to tell the difference between a loose valve and a worn valve guide? I thought I would ask, so that I could diagnose while I was doing the adjustment if that is possible.

Is there a little wiggle in the stem evident, or can you only tell if you adjust tight enough and the valve is still noisy.

Thanks.

ruf-porsche · ruf-porsche's Garage

Wiggle in the stem would indicate worn valve guides, Loose valve is a little noisy tapping, better to be a little loose than too tight, especially on the exhaust valves.

2.7RACER · 08-22-2006, 07:37 PM

cygtoad,
My approach to this is to check the valve gaps. If the valves haven't been adjusted recently, (more than a year or two, or more than 20,000 miles), I say the chances are good some of the valves need adjustment.
Checking the guides is tough with the motor in the car.
I've heard of putting air pressure to a cylinder to hold a valve in place while removing the keeper and springs.
I have no experience doing it that way.
It seems like a job where things could get bad quickly.
I don't know how you can check the guide with all the pressure on the valve from the springs.
My view is check and adjust your valves, carefully. Make certain they are at spec.
If the noise goes away, you know the noise was from the excessive gap.
I don't think guides make a lot of noise, if any.
Loose guides will show up with more smoke at startup, decelleration and increased oil consumption.
More than a quart every 1,000 miles.
Others may have a more precise method to determine valve guide condition without disassmbling the engine.

cygtoad · cygtoad's Garage

Thanks you guys.

stevepaa · 08-22-2006, 09:52 PM

Do a compression check, wet and dry. Do a blowdown/pressure/leak test. That's how we discovered 4 of six heads had very worn guides which the allowed the valve seat to get distorted because the valve kept hitting it at all sorts of angles.

afterburn 549 · 08-22-2006, 09:56 PM

do you have other symptoms?....and yes just grab the top of the spring wriggle it back and forth (piston tdc )......if you find A suspicious one get familiar with a air chuck and spring compressor and and then re check with no air in the cylinder....DO NOT LET THE VALVE Get AWAY from you. If you have one loose one you will a a bunch more........

ianc · 08-22-2006, 10:00 PM

A leakdown test per se won't show you anything about the valve guides. My car (the 87) had one valve guide that was so worn it was letting enough oil into the cylinder so it wouldn't fire anymore, but the compression figures were fine.

As 2.7Racer says, look for increased oil consumption and smoking on decel. I have about 1300 miles on my engine after doing the guides and I had a puff on startup today, so I don't think that's necessarily a good indication either.

If you're worried about the tappy noises, just adjust the valves and be done with it. 3-4 hours and you're done.

ianc

nhromyak · nhromyak's Garage

I run my valves a little tight. I adjust mine by feel. I was taught this by an old Swedish German auto-tech. I used the gauge many times, and then he asked me to show him what I was doing (in his broken english). Then he adjusted one, had me put my hand on it and try to wiggle it. I could barely wiggle it (up and down) off the valve stem. He said THAT was they way they are supposed to be!

I have done ALL my valves (73' 2.7 CIS - '80 SC - now '85 Carrera) that way since. Sometimes I wonder if they are too tight, but they have all sounded good, like excellent running sewing machines. If they clack now, I know they are too loose.

I have heard of people/mechanics using a Big A. screwdriver and pushing and pulling on the valve to make it wiggle to check on the guides. This seems rather scary to me, and I have not tried it. As if it moves (why wouldn't it when you break it?!?!?) then the valve guides are bad.

Good luck.

afterburn 549 · 08-22-2006, 10:05 PM

Hmmm ?? adj valves is one thing, not to be confused with id loose guides