How do I "preload" a dial indicator for cam timing?

[H.G.P.]

How does one adjust .."so that the indicator arm is depressed at least 10mm."...p 165 How to Build and Modifiy Porsche 911 Engines 1965-1989

Thanks

[ChrisBennet]

You just push the indicator body down, compressing the indicator shaft before you tighten the screw that holds the dial indicator in the holder.
You need to do this because the valve is going to be going down - away from the indicator so the shaft needs to be compressed initially. To put it another way, if you were using a digital dial indicator and set the "zero"/0.0 when you started, as you turned the cams the indicator reading would go negative i.e. -2.4mm or whatever.
-Chris

[al lkosmal]

It appears, from the pix on that page, that the dial indicator is held into the Z-block by tightening a thumbscrew. With the Z-block in place and the thumb screw loose you can slide the dial indicator until it just touches the valve spring retatining collar. I.E. no preload. Now slide the indicator .4" farther to preload the plunger spring. That way the spring pressure will keep the plunger tip pressed against the retaining collar through the travel of the valve movement. If this is not done the tip can come away from the collar at the lowest point of travel, for example, and give you a false reading.

[al lkosmal]

Oh yeah,
Once you've preloaded the plunger, tighten the thumbscrew to hold the indicator in place.

[5axis]

I went and grabbed my book.

FIG 7-7 you would slide the indicator down through the Z block and tighten it in place when you have the "preload" set. It does not have to be exactly 10mm. You need to be sure that it is in continous contact with the valve as the cam rotates.
It's probably easier to do than explain.

good luck
david

[Grady Clay]

Boy, I take one look at the 24 and ....

OK,

Before you install any rockers, make sure the engine turns over freely and note the resistance. If during the cam timing process, you encounter any additional resistance STOP and find out why. With mild cam engines it is possible to bend a valve just turning with a wrench.

If you want add a safety factor, do your initial set-up & test measuring with the valve adjust screw backed out a few turns and then reset it to 0,004” for the actual measuring.

Get the engine where you have valve clearance in that intake valve. Remember, if this is an initial set-up you only want one intake rocker installed – 11 others out.

Set up the dial indication and holding fixture as indicated in illustration 7-7 and 7-8 with the indicator just touching the retainer.

Loosen the thumb screw and push down the dial indicator gauge 10 mm, counting the revolutions. Make sure the spindle of the indicator can’t contact the rocker at any position.

During the process, repeat the measurements many times. Don’t rely on a single measurement. The process is easy and should also be done again just prior to putting the valve covers on.

I think most else in Wayne’s instructions are pretty clear. Ask if you have questions.


Best,
Grady

[H.G.P.]

Originally posted by Grady Clay
Boy, I take one look at the 24 and ....

OK,

Before you install any rockers, make sure the engine turns over freely and note the resistance. If during the cam timing process, you encounter any additional resistance STOP and find out why. With mild cam engines it is possible to bend a valve just turning with a wrench.

If you want add a safety factor, do your initial set-up & test measuring with the valve adjust screw backed out a few turns and then reset it to 0,004” for the actual measuring.

Get the engine where you have valve clearance in that intake valve. Remember, if this is an initial set-up you only want one intake rocker installed – 11 others out.

Set up the dial indication and holding fixture as indicated in illustration 7-7 and 7-8 with the indicator just touching the retainer.

Loosen the thumb screw and push down the dial indicator gauge 10 mm, counting the revolutions. Make sure the spindle of the indicator can’t contact the rocker at any position.

During the process, repeat the measurements many times. Don’t rely on a single measurement. The process is easy and should also be done again just prior to putting the valve covers on.

I think most else in Wayne’s instructions are pretty clear. Ask if you have questions.


Best,
Grady

Thanks for the advice. I have turned over the engine without any rockers installed. It seemed to turn over without any "resistance." However, being the first time, I do not know really what "resistance" means (no objective reference).

Now I have one rocker installed, the intake rocker as in the book.
The cams (before intalling the first (only one at this stage) rocker also turned smoothly.

(Another book mentions to use a "spanner" when turning the pulley for cam timimg, so I assume this can't be done by hand.) Also, can a valve get bent without the rockers installed?