By "The dry seal plugs, had a little different taper and that's why they don't go in as far." I was referring to the depth, not going so far.

Anyway you should use "Dry Seal" plugs for all gallery applications.

The type of pipe plug that you will need, is called a "Dry Seal". Edit: The dry seal plugs, had a little different taper and that's why they don't go in as far.

In a critical area, you need to use a pipe plug thread gauge to be sure that the thread is deep enough but, as shallow as possible. The gauge has a flat on it, across 3 threads. When you reach those threads, the first is min, next is nominal and the last is max thread depth.

You may not need to drill all the way threw if, you use a pipe reamer. It tapers the hole the proper length for the thread.

I hate to disappoint anyone

But, the serrated joint is stronger radially and on a new rod, I would go for it or if I could measure the big end and it be in tolerance but, they're not in hand. Though I could make a cutter to machine the serrations, to resize the cap, it would be way to much time involved to do that and machine the rod to resize it.

Regarding, " The small head limits the maximum clamp load too." It's my recollection that the underside bearing area is the same on hex head and socket head bolts but, I will check that out today.

Don't give up on me, Doug  

I'm a machinist and have used Socket Head Cap Screws (Allen bolts) for 50+ years. In my world there are only black oxide coated, steel bolts. For anything else I would add SS or Nylon and know that they are weak. Flat head and button head are also made to a different spec and are weaker and not in consideration.

If you look at the chart on bolt strength, there is only one spec for all SHCS, both min proof and min tensile strength. Both higher than grade 8 bolts. So, when any SHCS is manufactured, it has to meet those requirements, same as grade 8 bolts.

That is what I was going by and have always thought of them as quality fasteners and I would not hesitate using them as head bolts but, as rod bolts I'll be diligent if, I were to buy these. The reason I like them, is because of their design and I can see a strength advantage in the serrations,over dowels but, the offseting thing, is their age and unknown history. I suppose I could Xray and mag them.

I can remember that even using grade 8 bolts for bell housing bolts wasn't recommended, in the '60's and '70's because of their low elongation percentage.

Can anyone ID this 6.490, FE rod? It has a serrated cap joint, Allen bolts, lightened H beam and doweled rod bearings?

It looks like it might be a high end rod,out of the 70's? Carrillo?

It may not apply in your case but, check your motor mounts and/or restrict the engine movement with something as simple as a chain from the front face of the head to the chassis, on the drivers side.

I had that issue but, it was at over 5k.

One other thing you should check, is to make sure the bottom of the retainer isn't touching the top of the valve guild.