Don Terrill’s Speed-Talk

A builder buddy of mine has this 1935 Packard I8 block/crank/rods/etc. in his shop. He sent me this picture, of a small hole on the back side of each cylinder.



They are about 1/8" in diameter and lead from inside the cylinder to out where the lifters/pushrods are.

We're all curious....what in the world are those holes for?

Wow Brent, never heard of that....
damfino, maybe old Jack V. Will know ?? Mark H

compression release for easier starting. lot of big bore 2 strokes did that with a small hole into the exhaust port area

These were to aid in valve/guide lubrication. The hole is below ring sealing area so no compression leakage. Some flatheads had the tappets and lower guide/spring in a section not communicating with the crankcase so any lubrication had to be provided not by splash. I have seen this in K series Kohler engines and it is discussed as a help for "Big Twin" Indian guide lubrication, although they would be drilled between crankcase cavity and the cam cavity. Their oil normally should be breathed around the lifter body, usually with a spiral groove. Indian valves have a .375 stem and when new are fitted with .0045 clearance so some negative pressure helps the intake--but that doesn't provide for the exhaust. A top end job was expected by 20,000 miles.

Some old motorcycle engines had holes from cylinder out into atmosphere
On the packard are the holes above or below compression ring level?

CJ, Search youtube for Indian 1915 8 valve and we see an indian like the one you pictured running (stationary). The holes uncovered at the BOTTOM of stroke were an early attempt at speed tuning by enhanced breathing-this was "porting" in their terminology. Later replaced by the art of tuning the inlet and exhaust tracts for extracting the spent gases by managing the gas columns. I think the early racing motorcycles provided a lot of crowd pleasing with the fire and noise of open exhausts. I suspect leathers provided some needed protection from crotch cooking as well as pavement rash.We also see porting in some of our old "farm engines" from the factory to improve breathing and to improve cooling by dumping the hot expanding gases at the end of power stroke---used more on early air cooled engines than water cooled but Patton Brothers oil field engines were water cooled and used it a lot. You can spot the ported engines from a distance by the exhaust note--you just can't make them sound good as most of the exhaust sound comes from the cylinder ports. In the case of the Packard pictured you couldn't tolerate exhausting into the tappet chamber.

Hi yes i have seen many vids of the old board trackers running, i think in the old bike engines etc venting to atmosphere was an attempt to (as you pointed to) expel all the exhaust gas pressure at bdc possibly the thinking was to use less power from pumping exhaust out toward tdc !?
For the Packard, i recon the amswer came in the post right before mine. That hole will be below comp ring height and in allowing oil into the tappet area.
Really cool seeing and hearing some of those old engines running.