The Stovebolt Site Forums The Shop Area Engine Shop 235 head bolts

Guys,
I busted down my '58 235 engine to determine what parts can be used between it and my '59 235, for my '59 truck.
In my '58 parts cleaning process, I noticed that 2 of the head bolts have an oil hole provision at the end of the bolt. The hole is drilled on centerline with the bolt about an inch or so deep, and another hole is drilled perpendicular to intersect the first hole.
oddly, one bolt head is crowned... the other has a slotted head (both heads are hex though).
I didn't catch the location of these and thought I'd ask if anyone knew their correct location and... why they're like that.

Jerry

It allows the oil to flow up to the rockers,it's important to put it in the right location.I believe there is only one drilled bolt used,but not for sure.
head bolt
If you do a search,you'll find plenty to read.


Thanks,Tim

the bolt goes in the hole that has the oil passage (vertical) from the lifter galley to the head. if your head is like mine then its the same location as the 1/8" plug that is under the side cover. as for where the other one goes i dont have a clue because mine only had one bolt with a drilled passage. Tim has pics that he might be able to link from when i did mine.

Thanks for the feedback guys.
I am looking at some previous readings on this subject and it seems so far, there are more questions than answers.
The drilled bolt hole is at the threaded end of the bolts and is only slightly more than the bolt thread in depth before it is intersected. One of the bolts even has a groove ground down the length of the threads to allow oil to travel.
I reckon I should look at the engine block inside the tapped hole areas, and see what oil supply holes might come into play. It makes sense that the oil provision would be on the center oil tube area of the vertical passage hole. I'll focus on that.
Any other thoughts or comments are certainly appreciated.

Jerry

The drilled head bolt is only needed when you are using 1958 or earlier rockers on a 1959-62 engine.

Up through 1958 there is a 1/16" orifice restricting the oil flow to the rockers.
Starting in 1959 they increased this orifice to 11/32"(the same size of the valve stem). At this same time the overflow tube on the rocker connector was pinched off putting all the oil to the shafts. Also at this time the groove inside each rocker was offset 1/4" so it did not line up with the hole in the shaft. This was done to pressurize the shaft.

If you use the rockers and rocker connector tube made for 1958 or earlier engines on a 1959-62 engine you will get too much oil from the rocker bleed holes.
The drilled head bolt was designed to cure this problem.

If you lay a head gasket on your block you will see a triangle cutout around the center head bolt on the lifter side. In this triangle you will also see another hole. This is the rocker oil supply hole. Oil came from this hole, through the triangle area over to the head bolt, up around the head bolt, through a horizontal drilled path over to the rocker connector tube.

If you are using 1958 or earlier rocker parts, Chev supplied a plug to be put in the supply hole in the triangle spot you see in the head gasket. This blocked the original oil path. Then the drilled head bolt is used in the center bolt hole, the same hole that is in the gaskets triangle area. This bolt is drilled with a 1/16" hole. This was then the new path for the oil, and the same matching restriction that the rockers were designed for.