The Stovebolt Site Forums The Shop Area Engine Shop Chevy 51 head to engine block bolts

I removed the head to engine block bolts from my truck and found a extrange one. It has a drill of about 1/32" from the bottom to just 1/8" over the tread. It looks like used for some kind of lubrication or maybe just a not original bolt installed on a previous repair for some reason.
At the same time, this bolt has been manually grinded to flatten it partially along up to 1/8" over the thread.
I have no idea what to do with it. Should I replace it for a solid one?, Was it designed that way?. What for?. I will apprecite your advice.
Thanks in advance bolters!

lazyduck15,

This could be the infamous 'mystery bolt' found on some of these engines. As you indicated, the passage would allow oil to flow to the center oiler to lubricate the rocker assembly.

I have never seen this bolt, and don't know how it works, but there has been many a heated discussion on this forum about its existence...guard it with your life.

Stuart

Atomarc
Thanks a lot for your note. I know what you mean, thanks again. Do you know, I mean, yourself or know of someone that can tell me what is the position on the head to install it. I have no idea. If installed wrong I will ruin the rocker assembly! I guess.

lazyduck15,

I have no first hand knowledge of this bolt, other than what I have read here.

I have enclosed a link to a thread that dealt with this subject. I don't know if your engine falls into this specific category or not.

The gentleman that answers the question in the post I linked is VERY accurate in his info.

I think they call out the head bolt location in this post. If you look at a head bolt torque sequence chart, it will show you where #1 head bolt is. I believe it is in the middle of the head near the center support for the rocker assembly. Good luck.

http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=2;t=011564#000000

Stuart

Hi,,,the deal on that bolt is,,it allows oil to pass up to the rocker assembly.
It MUST go back in the same hole it came from.
I went through this same ordeal abt. 20 years ago when rebuilding an engine,after asking many different old mechanics,and checking many old books,the answer was all the same.Plus,,it makes sense,its an oil passage route.
So,,please just put it back where it came from upon re-assembly.Youll be glad you did.
Marty

[img]http://1954advance-design.homeip.net//Stovebolt-engine/235-54-62.jpg[/img]

Be sure to look at the link that Stuart gives above. In that post, Pre '68 Dave explains how/when that special bolt is used. That bolt does not seem to be mentioned in any of Truck Shop Manual (but might be in a Service Bulletin).

The 1960 Truck Shop Manual notes other significant changes in blocks/heads/lifters/rocker-arms between 1958-1959 that are related to the need for the special head bolt:

1958: New style mechanical lifters were used in blocks from 1958-1962. Those blocks had an oil passage in the block from the camshaft bearings to the rocker arm assembly (I think earlier blocks had a thin tube inside the side cover for this purpose). I believe this oil system also allowed for the use of hydraulic lifters in these blocks. The new lifters had an indentation in the side (an annulus) that allowed oil to pass sideways towards the middle of the block and then up.

1959-1962(63): a new style rocker arm assembly was used to allow for better full-pressure oiling. There was a new oil connector and all rocker arms had a smaller oil groove than in earlier years.

It would seem to be a good idea to keep matching rocker arms assemblies with same style heads (59-62); and, it is imperative to use the correct style lifters in the 58-62 blocks.

Here is a page with a picture of the 58-62 block . This information comes from the Chevy site of the Old Car Manual Project (thank you, Keith Hardy).

I see the light at te end of the tunnel. After looking at the information and threads provided by you guys I am sure it goes to position #1 as per the thightenning secuence. The less I can say to you Atomarc, delux54panel,tclederman is; you bolters are gentlemen.Thanks a lot for your help.
I feel pretty sure on the next step to follow. Regards