Rocker stand shims and rocker arm geometry

[Antics]

Hey All- first time on the Samba in years; first time working on a VW in years.

Short version: Working on a ‘71 bus that I’m told has a high comp engine. Stock rocker assembly as far as I can tell/stock type adjusters and what look like aluminum, non-adjustable push rods.

Did a valve adjust when it came into my possession and one of the rocker adjusters was out of adjustability (#2 intake if I can recall, was all the way in and seized up on the nut), didn’t think much of it at the time, bought some new, stock style adjusters, replaced the offending one and slapped everything back together. About 3k miles later, on the next valve adjustment, the same thing, only this time with #3 exhaust. Knowing that #3 exhaust is most prone to failure, I pulled off the rocker assembly to find only one side of the rocker stand was shimmed (under #4 at 0.03"). Otherwise I rolled the #3 pushrod on a piece of glass and it seemed true.

Now I don’t know a whole lot about rocker arm geometry (I’ve tried to do my research), but aren’t both sides of the rocker assembly supposed to be shimmed evenly? I was running out of daylight by the time I got the shims so I threw a 0.03" shim under #3, bolted everything back up and went to work for the week.

Fast forward to the following weekend (60 miles later), I go to recheck my work. Everything stayed pretty much the same except this time I noticed the rocker stand shims under #1 & 2 aren’t shimmed evenly either, 0.045" under #1 and 0.03" under #2.

Like I said, did my best to learn a bit about rocker arm geo, and by this coming weekend, I’ll pick up a base for my dial gauge so I can eyeball whether everything lines up at half lift… of course doing this without the engine out might prove futile. On most all cylinders, before I went messing with the shims, most the adjusters are almost were all the way in. I guess my main questions are:

1) Are both sides of the rocker stand to be shimmed evenly? If they are not, was whoever built this engine trying to compensate for something?

2) If I can’t get a real eye on the geometry at half lift, I’m tempted to leave #1 & 2 shimmed as is and just put a .015" under #3 instead of a .03" and then bump the shim under #4 .015" to closer match what was originally in there. Or do I need to start looking at pushrod length? What do you all think?

For those who want to know: after making sure everything was still together some 60 miles later, I ran a comp test cold and got: #1 = 118, #2 = 121, #3 = 127, #4 = 142. This was cold but #4 is obviously the outlier and some 20% over #1.

Let me know if there is anything I’m leaving out and thanks for any input in advance!

[telford dorr]

Yes, if you use shims, both shims on a side should be identical. That said, for a stock engine (specifically, a stock cam, push rods, rocker arms, and rocker arm adjusting screws, turning stock RPMs), you shouldn't need ANY shims (VW built millions of engines without shims, and they work fine). On the other hand, if engine valve train customization has been done (cam, rockers) , then that's another story.

The fact that some of the adjusters are at their limit indicates something is wonky. If all the way in (as long as possible, and still loose), then maybe too much shim. If all the way out (as short as possible, and still tight), then check for valve stretch. Pull the rocker arm assemblies, then lay a straight edge across the valve tips. All should be at roughly the same height. If not, (exhaust) valves may be stretching (a common failure mode), and may warrant inspection / replacement. If not, adjust shims.
_________________
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[Starbucket]

Shims should be the same thickness. Shims are used when the head is fly cut where it seals to the cylinders and the shim thickness is the amount of material removed from the head.

[Antics]

Thanks guys! I’m told it’s a high comp engine which led me to believe that the heads were cut so I figured the shims were a necessity but if most adjusters are all the way in—maybe not! I did take a straight edge across the springs when the rocker assembly was off and everything lined up (forgot to mention that). Picked up a base for my dial gauge today and will probably remove all shims and check the geo at half lift to make sure. Keep y’all posted.