Locomobile Model L Piston Information Needed

Has anyone here been involved with a full rebuild of a 4.5" bore Locomobile engine? I will be going through my engine and would like to do some homework before I start. I am interested in the compression height of a stock 4.5" cast iron piston, the weight if possible, wrist pin OD and the total height of the piston. Also, how much additional compression will the "T" head design tolerate without problems.

Thanks,

Alan

Alan,

I do not know the specific dimensions you ask about the Locomobile however I can tell you something about the issue of additional compression.

Since the vast majority of the head space in a T head engine is not over the piston, it is physically impossible to greatly affect the compression ratio by altering the piston top. The only T head engine that I know of that has had the compression ratio changed to any appreciable degree is a Lozier that had new cylinders cast with redesigned combustion chambers. Even replacing the valve plugs over the valves with new plugs that reach down to just above an open valve do not have much/any effect on the ratio.

Hello Layden, I have the same basic thoughts that you share, with regards to compression and the "T" head design. I would like to have a good feel for what Mercer did with the small cube "T" head engine, as it was a proven performer that could compete favorably with Stutz and others in the day. During the time, of engine rebuilding, is the window to consider anything that would be a performance/mechanical improvement. My engine has the left overs/remains of the original make and break system that effectively reduces, yet further, the end compression ratio. Does anyone else have reasonable ideas for consideration as I contemplate the Locomobile engine OH.

Al

The late Phil Hill had a 1925 Locomobile Sportif with a T-head engine that was probably not unlike the one in your much earlier model car, since Locomobiles didn't change much. He told me that he raised the compression ratio by installing taller pistons, but had to cut a groove in the piston head to link the combustion chamber on each side. You might also consider converting to dual ignition if your car does not have it already. It makes a big difference in power and smoothness. Further, Phil equipped his car with multiple carburetors (presumably three) that undoubtedly improved engine air flow. Pictured below is my '19 Sportif. Do you have the speedster?

If it was mine I would leave it alone. I doubt you will suffer from lack of power with 4.5" bore cylinders.

You might consider running it on a mixture of kerosene and gasoline, to replicate the very low octane fuel available when it was built. Others who have done this report cooler, smoother running and more power.

Rusty has a good point with just what are you trying to achieve.

You can try fuel mixes and along with that is always efficiency. I think Mercers raced well because they had large carburetors as was all the rest of the intake system. The chassis was not too light but certainly not a heavy weight like many of the others.