odonnell

You can find more comprehensive information on the web (I think Van has a good video one cross-sectioned) but basically they are subjected to pressurized oil. That pressure acts on a small piston, that's the round button you see that presses the valve, so there's no slack between the lifter and the valve throughout the duration of the cam lobe. So you can see how it needs to "pump up" for proper valve operation.

You should see a little hole on the side of each lifter...that's how the oil gets in. Submerge the lifters in clean oil with the hole facing up for a day or two, not really sure how long you're supposed to wait. The goal is that the button should be firm...not easily depressed with your thumb. Before you do that though, see if you can depress any of the buttons easily for now. They should be pretty firm, if they're empty of oil, you should be able to depress them with firm thumb pressure.

CrookedRacer

I had actually just watched Van's video. Thanks, Van! Awesome.

I'll do some more web searches and noodling too.

I'll report back on the behavior of the lifters. I didn't actually touch them yet so I don't know their condition at all.

I'm looking forward to getting back into it tonight!

Van

I don't know if it's in that video, but I put them in a jar of oil, then pull a vacuum. The air gets sucked out and the oil gets pulled in.

For if the lifters are good, if they're right out of the engine, or out of oil, the button should be firm - a soft button means the check valve has failed (likely there's a bit of debris preventing that little ball to seal all the way).

The hydraulic pressure of the oil is meant to move the piston out to "take up the gap" between the cam and the valve stem, and the check valve is what provides the "holding resistance" while the cam lobe pushes down on the lifter to open the valve.

CrookedRacer

So, can a lifter fail by sticking out too far? That might make sense to me.

When the oil pressure is high, maybe one of these lifters is actually able to open the valve.

After a few seconds at idle, and when the oil is thinner when the engine is warmed up, the oil pressure in the lifter might be lower. So the lifter isn't pushing out as hard, and the valve can close.

Just a theory that might mimic the same symptoms of a broken spring.

To recap my symptoms:

The car purrs at idle.
If I rev the engine, it misses. And it continues to miss after it returns to idle for 4-5 seconds, and then it purrs again.

The exhaust has an ugly sound at certain RPM's. Like an unwanted resonance. A new muffler and tailpipe with no holes didn't fix that. Sounds like maybe I'm listening to the compression/power stroke coming out an exhaust valve.

Unburnt fuel is making it out the tailpipe. The muffler I replaced was expanded by a detonation at some point before I got the car. And other drivers tell me my car stinks on the track. (I get that a lot in any car... maybe that's just me)

Terrible hesitation on acceleration (misses badly until higher rpm's).

Van

No, a lifter can't fail by sticking out too far. The little button (piston) is staked in to limit it's travel outward.

I personally don't buy the theory of the broken spring and the hydraulic pressure in the lifter holding the valve open... The lifter piston is about 3/8" in diameter - at 60 psi of oil pressure (a good 4+ bar), that's only 26 lbs of force. Someone smarter than me can probably tell us the spring force at the installed height (partially compressed), but I'd have to believe we're talking about hundreds of lbs per inch (with the 2 springs).

If you really were getting that much "float", the piston would surely have hit the valve by now, and you'd have other running problems, too.

I'd first give your ignition system a very close investigation - rotor, cap, wires, rotor mount on cam, etc.

(The engine changes the timing as you accelerate - and then decelerate - if your rotor is out of alignment, or part of it is broken off, the spark might not be jumping right when the timing advance happens.)

Then I'd do a pressure test of your intake to check for leaks.

(There might be a tear in the intake boot or something, and under fast acceleration, it's pulling in extra air that hasn't been metered... Then, after going back to idle, the gap/rip/tear/hole closes back up. Does the problem happen when you accelerate gradually?)

StoogeMoe

Does the problem happen at WOT? If not, then it's your AFM.

If it still does then I'd check the spark plug wires as Van suggested.

If you think it's a pain with those lifters falling out on disassembly, wait till you try to put it back on! I used Vasoline on the lifters to hold them in a bit longer. You still have to be quick and not tear the new gasket. Have fun!

Hope you find the problem.

CrookedRacer

Tonight I replaced the valve springs on cylinders 1 and 4.

The tool worked well and my compression gauge adapter worked perfectly after I took out the little check valve in the end of it. I never did get used to the compressor kicking on as it was wont to do. Made me jump every time.

<img src="https://farm2.staticflickr.com/1465/24998054064_5cec1dd19a_z.jpg" width="360" height="640" alt="2016-03-08_08-14-25">

There was a chip of spring in the seat of the exhaust spring set on cylinder 1. Not enough to change the overall behavior.

<img src="https://farm2.staticflickr.com/1689/25001843783_bb431c1239_z.jpg" width="640" height="360" alt="2016-03-08_08-13-07">

The new springs seemed beefier than the old ones. And the old ones had shims underneath the spring seats.

<img src="https://farm2.staticflickr.com/1570/25602405546_5d5d38e950_z.jpg" width="640" height="360" alt="2016-03-08_08-13-27">

So after I removed each spring, I wound a pipe cleaner on the end of the valve stem and de-pressurized the cylinder. That way I could articulate the valve and feel it against the valve seat, spinning it, pushing it in and out, and listening to it as it hit the valve seat. Cylinder 1 was fine:

<img src="https://farm2.staticflickr.com/1689/25332942170_b282b28802_z.jpg" width="640" height="360" alt="2016-03-08_08-14-02">

Unfortunately, I was able to wiggle the valve in its guide on cylinder 4's exhaust valve more than I am comfortable with. When I pull it against the seat, it makes a cl-click feeling sound, not just a "tap". Like a sloppy/loose valve seat in the head? A chipped valve?

Also, that cylinder hissed a lot louder than Cylinder 1. I could hear it when I put my ear to the exhaust. I'll bet it wouldn't fare well on a compression test, which I should have done from the start.

I got this much done after work this evening, and putting the little keepers on is such a PITA. So I stopped after just half the valves. I was going to make mistakes if I continued tonight.

I have tomorrow off if I want it, a perfect day of weather-wise, and I have to decide whether to just finish the springs and wrap it back up, or go deeper and tear off the head to see what's going on. If the head comes off, I'm definitely not driving it this weekend. Too much to do and I'll want to have it taken care of at a machine shop, most likely.

Thoughts?

Also, thanks to everyone for your advice and suggestions. This is the deepest yogurt I've ever waded into, and without this community I think I'd just be broke instead.

Scott at Team Harco

Have you checked all of the valve springs? Based on the story I am reading (could be a comprehension problem, on this end) it sounds like a broken spring.

Unless it does, indeed, run well at high rpm. If that's the case, I will need to reanalyze. You're unlikely to overcome a broken spring at higher rpm. If anything it would run more poorly.

Edit: We must have been posting at about the same time. Get all the springs out and then reassess the situation. Yes - you should have performed a compression test and even a leak down test. Valve guides may be a problem here - be sure to check the rest, as you have the first ones. A valve and seat grind is in your future, for sure.

CrookedRacer

Oh, and the lifters are all rock solid except for the intake valve of Cylinder 1. It's soft, but it may also have drained itself of oil overnight. I'll have to fill it with oil and check it again. It was the only one whose cam lobe had positioned it all the way to the top of its travel (towards opening the valve).

The one that fell on the driveway is fine. It was the lifter for the exhaust valve on Cylinder 4, the valve that didn't feel right. It dropped right back into its cavity without drama.

CrookedRacer

Thanks, Scott.

It does run better at high rpm's.


here's what it sounds like. The engine is just about fully warmed up by the end of the video.

odonnell

Could you tell if the hissing was coming from the valve seat, or into the crankcase? That would determine your next move, I would think.

Van

I have a nice little magnet tool that makes taking the keepers in and out a cinch.

The little broken tails on the inner springs is somewhat common - I've found several on drain plug magnets over the years. That's not going to cause a valve not to seat, though.

The shims under the springs are to adjust the "installed height". Again, this will change how much spring pressure is being exerted on the valve to hold it closed. The thicker the shims, the more the spring is compressed, the higher the force.

There is a spec for this in the FSM.

951Dreams

Van is the expert here, so listen to him. But I sounds like to me, removing the head is almost a foregone conclusion with that one valve seating funny.

You might want to throw all the springs back on and do a compression or leak down test, but at this point, for me, I'd just pull the head.

You're so close now anyway. I'm sorry to say, I think your going to be running your Ford this weekend.

You're just a tad bit of work from pulling the head right where you sit. To not do it now, to ME, would be a waste.

Course then you really should have the head done. But if all you do is deck it and a valve job, shouldn't be that much. Just to deck a head is like $80 here. Maybe $150 with redoing the problem valve and/or seat.

But wait on others to chime in on the pull, but I'd still get on that comp/leak test. I think #4 is going to fail.

CrookedRacer

Holy cow, guys.

This morning I removed the springs from exhaust valve #2 cylinder, and voila...

<img src="https://farm2.staticflickr.com/1604/25525357872_55773ebe0e_z.jpg" width="640" height="360" alt="20160309_090333_HDR">

BAM! It was coiled in on itself, and wasn't doing much work apart from preventing the valve from actually hitting the piston face. At least, I hope it was keeping the valve from hitting the piston face.

The valve stems felt and sounded good in all the remaining four valves.

Unfortunately the broken spring did tear up the spring seat a little bit (not the hat which I had been concerned about)...

<img src="https://farm2.staticflickr.com/1442/25276453319_5df032c264_z.jpg" width="640" height="360" alt="20160309_090338_HDR">

<img src="https://farm2.staticflickr.com/1571/25525341112_b2cfd85978_z.jpg" width="640" height="360" alt="20160309_090355_HDR">

So... I don't have one of those. You guys are going to flame the crap out of me, but I'm thinking about putting that bad boy back in. I think there's enough lip left to keep the inner spring from going anywhere. Actually, it's already been put back in...

I'll make some calls, perhaps to the burtonsville place you've recommended, to see if anyone has one of those to spare.

As for the play in the one valve, based on this new evidence, I'm going to call it "marginal" as opposed to "out of my comfort zone" and put the car back together.

As for the hissing, after sitting overnight, it sounded a lot better on that cylinder. Subjectively speaking, of course.

V2Rocket

time for an upgrade...

http://www.ebay.com/itm/Porsche-951-...item3ab2d21dbf

I'm sure Lart has one or two loose ones laying around.