Re: valve train geometry: what is it?

Here's my take based on mainly what I've read:

Goes clear back to the cam/crank connection. The cam will not necessarilly be ground to the same TDC that the crank says is TDC.

So you have to check that when you put the puppy together.

If you have a fully adjustable cam you just move the gear around a tad till they line up with each other. If you have stock non-adjust, then you may elect to move it a tooth forward or backwards to get close. There's some play in the bolt holes where the gear bolts to the cam. You may use that.

This is all set up and then you mark the pulley with your true TDC.

Then you get to the push-rods which should all come out at the same height. The pushrods should all be checked for straightness, if not they will flex and be off the full lift under load.

Of course the valve stems also have to be at the same height.

You're checking all this with the dial indicator, right?

Then the valve springs have to all be the same height in closed position. The valve springs also have to have the same tension in open or closed postion.

How? On the Valve Spring Tester how else? :-)

These are checked outside the assembly and put aside for the moment.

You should be using dummy light springs for this setup until later in the assembly. Strong enough to hold the valves etc. but light enough to move by hand.

Then you get the rocker arm and set the adjuster screws to half-way.

Then you shim the rocker arm so that when the valve is half-open the center of the valve adjusting screw is in line with the center of the valve-stem.

Meaning the adjuster screw slides back and forth across the center of the valve stem while doing its thing.

A note here: in that if you dont have them tuercas mortas or in gringo, dead perfect, you will have unequal loads and unequal wear in valve guide and other bad things will happen to you.

You do this while the heads are off and on the work bench. What you mean you don't know how much is halfway? You checked the lift on the cam lobes, didn't you?

Since the rockers come off again to install the heads you keep the shims tied to the rocker for each stud.

Now if all is done right, the valves will all open the same amount at the proper time on all pistons.

Now you install the real springs and verify.

You put the Valve Stem Seals in before you installed the springs, didn't you?

That could be said to be all there is to VTG.

Can you say VGT 4500 times a minute? Your engine does.

Now the rest of the story:

Down on the other end is the cam/crank gear which have zero backlash, meaning no slop.

Note here: that 0 or +1 or 2 or -1 or 2 on the cam gear and gear on the crank refer to deviation from theoretical pitch diameter.

The numbers should match but the real criteria to you is no slop and no binding when installed in the case.

Beyond that is the dizzy timing gear which should also have zero slop.

This is then engaged to a nice tight distributor which is also set to the proper #1 plug.

If all this stuff gets there at the right time your engine goes "Vroom" if not—well...

In a race engine, I expect they spend weeks getting this all in order.

I have heard that some cams can be as much as 10 degrees off of true TDC. Of course you also have to check every lobe, not just #1.

If you're building the engine, then you can check a lot of this stuff and set to the best of your ability and instruments.

If the engine is already built, about all you can do is get the stuff in the rocker arm box as close as possible.

If you don't have unlimited patience and money just buy the chrome tin and let it go at that.

You would probably go thru dozens of cams etc, suppliers and so on.

Use VTG in bars when you're trying to blow smoke at the other guy.

Is it important? I think it's the most important.

I can't even get my FLAPS to stock new gears, he just sells them over and over. Of course a +2 will go with a 0, they've been in 3 engines!

Symptoms of poor VGT: Everything under the sun.

Sick as opposed to sweet, runs hot, no pep, no top end, stumbles, vibration, no bottom end! As in it's a brand new rebuilt and it's a piece of shit. It also won't last long.

"well, that's the name of that tune"

Bibliography:

• Tom Wilsons book "Rebuild your Engine"
• Bill Fishers book "Hotrod the VW engine"
• Probably some Hoover
• Some other dead people I don't recall

Smart ass remarks and incorrect statements are mine. west