Howdy.
So, here's the story so far: A couple of months ago I decided to take on the task of figuring out why my friend's 96 3.8L Caravan was knocking. As she tells it, after the knocking began she noticed the oil was very low, so she took it to a mechanic. The mechanic told her that her remaining oil was clear and that he didn't think she had spun a bearing, but thought maybe it was a damaged pushrod. Running with this information, I located the sound (more of a tapping) at the center of the back valve cover (no knocking/tapping anywhere else). After removing the cover, I found that the pushrods were fine, but the left-most (passenger side) rocker shaft support had snapped. I did some research and found that such a break is either commonly rare or rarely common, and that it could be repaired through welding, a helicoil or replacement, though the former two aren't guaranteed to work especially if the vehicle has been driven with such a break, as aluminum pieces likely fell into the engine. My friend had driven somewhere between 25 and 50 miles with the noise, so I drained the oil and filtered it but found no metal. I pulled the oil pan, and that was clear (I checked the crankshaft, too, which has no visible damage). So, I pulled the cylinder head. The cylinders and valves have a bit of soot but no apparent damage, and the lifters are clear.
First off, does anyone know what causes a rocker support break? I haven't been able to find info on a cause anywhere, and I sure as hell don't want to fix a symptom when there is a bigger problem.
Secondly, can anyone offer advice on the best fix for this break? My friend is financially limited, so my most accessible option for fixing the support is to have a friend of mine who is a professional machinist both weld it and insert a helicoil. That is considering that the engine appears to not have any aluminum bits in it... as far as I can tell, anyway.
Also, any advice on areas of the engine that I should check (timing chain maybe?) would be very welcome. I'm no expert...just a guy working toward a mechanical engineering degree and willing to help a friend out. I'd really like to get this van back on the road for her, so I'd be grateful for any suggestions on how to most effectively do that.

 

Drill and tap a deeper hole. Get some compressed air to get out the drilling debris. Get a longer bolt. Take out one of the adjacent ones and go match up the thread pitch and size. I haven't done one in a while so I can't remember the length and all that. I would say try to get at least 3/8" past the break in depth to have enough meat to be able to torque it down. Use the broken off piece to line up your drill bit angle.

On the reman heads, this issue is addressed....they have a deeper hole and longer bolt..lol. In place of the broken piece they used a milled steel insert and ground the old tower flat.

 

So, I wanted to follow-up on the Caravan.
I had the broken support TIG welded back on, tapped a deeper hole and used a longer bolt. The bolt was rather difficult to find -- even going to a fastener distributor only turned up a bolt that I had to modify myself.
Everything buttoned up well, and the van has been running strong for about two months now. The total cost consisted mainly of the gaskets, but included fluids, o-rings, and an oil filter, which all came to about $180 (not including some minor tooling).
I'd like to thank this forum for the information: Thank you!