Inliners International Forums General Discussion Engines Offset Dowel Pins For Cylinder Head Alignment

I have not seen any discussion concerning offset dowel pins and cylinder head alignment. This topic is mentioned in the Chevrolet Inline Six Cylinder Power Manual, 2nd Edition, pp 113, by Glen Rarick of Bow Tie Speed and Reproduction. His telephone number is now longer in service.

What size are the dowel pins, and where are offset pins available? Rarick states offsets of 0.030" to 0.090". Can you completely align the combustion chambers with the cylinder bores? Will the current overhang of the combustion chamber beyond the cylinder bore be alleviated? How much power is gained?

A Lot of speed shops sell them.Another thing that has been done in the Past was to angle cut the head (more off the passanger side) and redrill the head bolt holes.

Winter, the dowels are the same size as SBC, and Moroso and Mr. Gasket did/still do offer them.

I am curious as to how this gets done. Do you start at the valve cover side and end up with an elongated opening on the head gasket side or do you start boring from the head gasket side and end up with elongated holes on the valve cover side? I presume the head bolt bosses need to me milled square too, no?

Thanks for the replies guys. I searched the Moroso website some time ago and only saw a few offset distances, none close to 0.090". So I was wondering was there another source.

How about my other questions:

Can you completely align the combustion chambers with the cylinder bores? Will the current overhang of the combustion chamber beyond the cylinder bore be alleviated? How much power is gained?

I would say that several conditions would have to be met first, one being a large enough bore size to begin with to eliminate the overhang, and second, having to do with core shift, you might not be able to correct this problem all the time with every head by offsetting the head since the chambers are only cast and not machined, and their location is going to vary from head to head as well as chamber to chamber within the same head. So I would say that with bore sizes of .060 and larger for the 230-292's you would have a greater success rate of accomplishing this.

Greg, you can probably get by without having to slot the gasket or bolt bosses with a .030 offset, especially if you still are just using head bolts, but anything offset more/and or using head studs will require you to elongate the holes in the head and gasket to some degree.

I'm not sure it's going to help much. The 250 etc. head has its valves in this order:
Exh Int Int Exh Exh Int Int Exh Exh Int Int Exh
The overhang is in the crankshaft axis, but because the intake valves face in opposite directions, motion front to rear will be limited to averaging out the error - not improving all chambers.
To move all of them, the chambers would all have to be alike, such as:
Exh Int Exh Int Exh Int Exh Int Exh Int Exh Int
Like some modern heads (and 12 ports?).
The cross axis (left to right) may benefit from minor tweaking to bring the plugs closer to the bore edge.

I have not seen one Off a motor first hand Only mounted,But yes you would have to redo the head bolt landing. As for the bolt hole itself I'm sure both ends would show being elongated.I think? Leo may have some photo's on that Or maybe a little more info.