17prospective buyer

But would you feel resistance when hitting a valve? I would think you'd have to put alot of effort into it to bend a valve by hand, especially with just a ratchet.

Ian S4

78-80 don't show as interference.

ROG100

However 81 to 84 do say interference and we know that the US 4.5L and 4.7L 81 to 84 are none interference so treat the information as suspect.

Bigfoot928

they all interfere with your wallet... that is all that counts.....

Dennis Wilson

Weak valve springs can also increase valve lash enough to cause contact.

Dennis

James Bailey

sorry but that is just bull**** ....if your valves are bouncing you already have problems... maybe on other cars/engines but 928s I do not think so ...but then again what do I know thousands of customers millions of $$$ in parts !

the old very brown 1980 after years of track use abuse it finally jumped time at idle in the pits at Willow after being just fine in the high speed sweeper of turn 8 at 5,500 or so and no valve problems at all.....

Dennis Wilson

Jim, guess Porsche put the valve tension spec's in the manual for nothing. Just because your very old brown has been well maintained doesn't mean all the 928's have been. Running too hot for too long can and will reduce the valve tension. This in turn increases valve lash and may cause contact. Just plain automechanics 101.

Dennis

Lizard928

If the piston and valves touch at all you will know when rotating with a ratchet. It will be like hitting a wall. Especially using a ratchet.

And Dennis, I have yet to see a 16V 928 with the valve springs being weak enough to float the valves higher than max lift. You are correct that the heat could make them softer. But the amount of heat would also cause numerous other problems inside the engine. Even cars that see 260f oil temps on the track have no spring failures/valve float.

dr bob

If the valves were hitting at the middle of piston travel, you'd be right. At the top of the stroke, you have a lot of crank rotation relative to the piston movement, translates to "mechanical advantage". Remember that there are seven other pistons at various points in their rotation in the block, so it's very easy to confuse the impacts with a valve edge four times in a rotation with normal compression and friction loading while rotating the crank.

It doesn't take much force on the edge of a valve to bend it slightly. Most 'bent valves' are only slightly noticeable to the eye when sitting in the heads. Pour a little fluid in the chambers and with the head face-up and it falls through. Leakdown testing before disassembly does the same thing with air.


I'm not suggesting that you shouldn't gently turn the crank to test for interference and/or debris in the chambers as you reassemble things. Do that with the plugs out, so that any sudden changes in effort will be more noticeable.

Doug_B_928

Hi Jeff and welcome to rennlist. I recognize your name from 914World. These are a great bunch of folks on this forum and, as you can see, very knowledgeable. For those who don't visit "the World," Jeff is very knowledgeable about 914s and manufactures/repairs wiring harnesses for 914s (and some early 911s and VWs).

Dennis Wilson

Colin,

On my 78 euro the machine shop found 2 valve springs below spec. There was no indication of valves hitting the pistons but with the heads being milled and a potential for carbon buildup, we had them replaced.

Dennis

17prospective buyer

Well when i was turning it, the effort was the same the whole time. I'm fine tuned enough to notice any irregularity. I hope i'm fine. Makes sense, any time you get a speed decrease you have mechanical advantage or a torque increase.

Jeff Bowlsby

Thanks Doug! :wavy:

stuartbrs

My 16V Australian delivered 1981S is definitely interference

danglerb

Anybody try clay on an 84/86 Euro S?

Is failure to notice valve tick on start up a valid way to assume the lifter didn't compress?