Learning Rocker Geometry

[SkrapMetal]

n00b here when it comes to this stuff, but I've been reading all I can, and I'm ready to get this thing back together finally. For the record, 1915, engle 120, Scat 1.25 rockers, chromoly pushrods.

Ok first off, I had a head stud break on me, so I sent my heads out to Jeff Denham to go through them and check them out for me. He had to flycut them, but he said that I might still be able to use the same pushrods, but I want to be 100% sure.

I know at half lift, the adjuster should be parallel to the pushrod, but how do I know when I'm at half lift?

I have a dial indicator, but how do I read it? I'm pretty sure I have it set up correctly... parallel with the valve from all angles.

Zero lift

Full lift

How do I read this little bugger?

_________________
oo9less since 2007
-72 Ghia-

[Mongo63]

One full circle of the needle is 100 thousandths of an inch. Start at 0 lift and rotate face of dial indicator so pointer is at 0. Rotate engine and count the number of revolutions of the indicator needle as the valve opens, the point when the needle reverses direction of travel is just past full lift. For example if the needle makes exactly 5 full revolutions that's .500 lift. Take the number you found to be full lift and divide by 2, that's half lift that you use to set rocker geometry. The other option you have is to take your cam card and multiply the specified lift by your rocker arm ratio, in your case that's 1.25 then divide that by 2. Hope it helps.
_________________
Southside Buggistas VW & kit car club
www.southsidebuggistas.com

Mongo only pawn in game of life...

[Sigurd]

I just dealt with this and I too have a 120 with Scat 1.25s. Here's a hint...they aren't 1.25. More like 1.31. I got around 0.520" lift at the valve. Don't go by cards and paper specs; actually do it. When you find full lift, divide by 2...that's half lift. Then rotate the engine so that the pointer reads that half lift number. Once you are at half lift, you can check the pushrod/rocker alignment. Also have to check the wipe pattern on the lash caps with this type of rocker. Hope that helps.

[Mongo63]

[Sigurd]

If I had assumed the advertised 0.496", there would have been a problem. To further complicate things, the exhausts were about 0.508". I had 4 different pushrod lengths; intake and exhaust for each side.

[Hophead]

Read the Bob Hoover Blog about dialing in your cam. It was also in VwTrends three or four years ago. Did you find TDC first? Is your degree wheel dialed into TDC. On my 2110 the keyway on the crank for the fan pulley and cam gear was cut 1 degree retarded. You need to read where half lift is directly from the cam/lifter for best accuracy. If you can find a way to read the lift from the push rod side of the rocker that would be better but no where near as accurate as if it was read back when the motor was a shortblock and it could have been determined directly from the lifter. My FK-8 had .001 more lift on the 2-4 exhaust lobe.
It needed to be advanced 2 degrees. It was no big deal to find half lift at the lifter and mark the actual point on the degree wheel instead of trying to sort through it at the head.
_________________
70' Beetle Pan off Resto
2110cc
82 X 90.5
P&P 043 40x35.5
9.6-1 comp
FK-8
48 IDA

[SkrapMetal]

Alright, after measuring, I came up with 0.5089 at full lift, hard to tell from the picture, but I'm hoping I did that right? The needle passed 0, 5 times.

Then, I took .5089/2 and came up with 0.25445, so again.. the needle passed by 0, 2 times, and ended up here, correct?

Here is the angle of the adjuster to the angle of the pushrod

And this shows the wiper pad to the lash cap

How is this looking?
_________________
oo9less since 2007
-72 Ghia-

[Max Welton]

[chrisflstf]

I dont think having 4 different P/R lengths would be good for valve train balance either. Better to fix that problem at the source.

[sturgeongeneral]

[SkrapMetal]

[sturgeongeneral]

[Sigurd]

[SkrapMetal]

Not sure what to look at now. I know I'm supposed to go through and check all the valves. What's next?
_________________
oo9less since 2007
-72 Ghia-

[Sigurd]

Check them all for pushrod to adjuster alignment and also for wipe pattern on the lash cap. Add shims/shave bases. Check again. Then measure the pushrod. Cut new pushrods to match.