Valve clearance = none

[loch]

Hello Everyone,

Yesterday I began the process of setting up for a manifold pressure test. One of the steps, if I recall correctly, is to set the pistons at so that they are BDC. Or rather, at a position where all the valves are closed. So I'm turning over the '32 VL engine by hand and I noticed after several attempts that the rear exhaust valve isn't quite close yet when the front intake valve begins to open. So played with it a bit before loosening the tappet adjustment nuts on all the valves. I did this to provide visible clearance, peace of mind that the valve is in fact closed. I backed off the front intake nut as much as it will go. Still, there is no clearance between the valve stem and tappet. I mean to say that the minimum gauge for tappet spacing is 0.004. And it would not slide between the stem and the tappet. All of the other tappets have lots of clearance.

As I contemplate this issue I realize it could be; incorrect valve installed. Or the valve seat was ground to the point that the valve stem rides lower in the closed, or nearly closed position.

That's all I can come with. Anyone else have any ideas, or things I should check?

Cheers,
Lochlain

[T. Cotten]

It seemed like Chiefs' intakes never closed completely, Lochlain!

So I just turned the motor through until pressure showed on the regulator, and set it to 15psi.

Please remember its not about holding pressure, its about the differential.

.....Cotten

[loch]

Okay, Tom.

I'm a little lost on your comment,

its about the differential.

I thought it was about holding pressure - looking for leaks in the manifold. What differential am I analyzing?

Lochlain

[T. Cotten]

More pressure inside than outside makes the bubbles, Lochlain,...

I was taught that was a differential.

Since we are looking for fissures that would leak under vacuum, a difference of one atmosphere is needed to be thorough;

Total vacuum should equal ~14.7 psi at sea level, so fifteen is a skosh of overkill.

.....Cotten

[loch]

Yes, exactly your definition of differential, a.k.a. delta, for those who tend toward a more scientific articulation.

We're thinking exactly the same thing regarding the manifold pressure test. Despite not achieving a complete seal at the manifold I was able to detect a leak at the front manifold nut. This pressure test procedure has been the bane on my existence since September. I believe I have a good solution now for the blanking plate. I crafted one out some old 1 inch thick oak. Cut a gasket out of rubber gasket material from the plumbing section of the hardware store - again, remnants found in the garage. It still leaks from around the bolt holes. My solution will be to apply some gasket compound to the surface between the oak and the rubber - retest. If that still fails then I'm thinking of putting gasket compound between the rubber and the manifold. Alternatively I do have a new gasket that came with the carburetor rebuild kit. I suppose I could just use that. But it seems to me the rubber gasket should form a seal. Especially considering 15 psi isn't that much.

Lochlain

[T. Cotten]

Once again, Lochlain,

It doesn't matter if there is leakage at the testplate as long as the regulator keeps up with it.

My testplates are simple ABS with a solenoid gasket, but often I just use a rubber stopper, particularly to test inlet nipples separately.

TESTKIT.jpg

NPPLTSTR.jpg

,,,,,Cotten

[loch]

Nice, Tom!

Is that first picture a manufactured kit?

And I've tried the stopper method but was unable ( or unwilling to strike it hard enough ) to get it to seat and stay seated when pressure is applied.

I'm connecting it to the compressor I use for the motorcycle lift - with the regulator dialed down to 25 psi and the painters regulator opened enough to register something on the gauge - some indication that engine is being pressurized. The latter has a 50 psi gauge. Not exactly the first choice, I would prefer a 25 psi gauge but I don't want to spend $$ or time looking for one. We're just ball-parking it anyway - to create that differential.

I think I'm good with the air set up. It's just the manifold connection arrangement I'm having difficulty with.

Lochlain

[T. Cotten]

"Manufactured" is pretty lofty for my conjurings, Lochlain!

And yes, the stoppers must be held in manually, but there is no other way to test the nipples.

I don't sweat the accuracy of the regulator gauge, as long as we can be certain of a constant twelve to fifteen psi;
You could always fill a tank, and regulate out of it.

The whole point is to avoid false negative results. Just like a buddy who burnt a hole in his piston after spraying WD-40 on his running motor and decided it was fine, tire pumps, shop vacs, air mattress inflators, etc. can only give a false sense of security.

....Cotten

[Rubone]

The valves are closed at top dead center on the compression stroke, not bottom.

[T. Cotten]

The most common confusion to avoid, Folks,...

..Is that testing the manifold is somehow like a 'leak-down' test, and that the manifold should somehow hold pressure.

Even if the intake valves sealed perfectly, with no 'over-lap' at all, the valve stem to guide clearances are orders of magnitude larger than the leaks we seek. ("Uh Oh, I've got leaks at my valve covers!")

So a constant, regulated air supply is critical.

....Cotten

[otis71]

I’m not sure if your VL manifold is similar to my ULH manifold but mine has a recessed area at the flange that a O ring fits in perfectly. Using the O ring and a simple homemade plate I get a nice seal.

[dukekleman]

Loch,
IF I'm reading correctly, it's sounds like your on the valve overlap cycle of the camshaft which occurs at TDC , rotate the engine another 360 degree's and your at the compression stroke of the next TDC . In order to insure that your valves are both closed and ready for tappet clearance verification, make sure your on the compression stroke TDC. Hope this helps...