The Petruzzi Water Cooled Knucklehead
By C.L. Cake

Petruzzi Knucklehead

Were you aware that Harley Davidson had, at one time, filed for a patent on a water cooled V-Twin engine? Well, they did, but nothing ever came of their efforts until the V-Rod came along many decades later. Harley-Davidson, however, wasn’t the first to build a water cooled V-Twin engine; A racer and machinist named Joe Petruzzi built a water cooled version of Harley’s Knucklehead back in 1940!

Before World War II, Midget race cars were big on the national racing scene, and men like Billy Vukovich, the Gerhardts, and others were making Fresno a household word among racers and race fans. At that time, the Midgets were being powered with whatever was available, including motorcycle and outboard boat engines. With little in the way of safety equipment, racing them was a glory or death proposition.

Joe Petruzzi started going to the races around 1938, and crewed for other racers before he started racing his own midget. At the time, a company named Drake made a water-cooled V-Twin for midgets, but it had several critical design flaws; one being that it leaked water like a sieve, and another being the one piece head and cylinder that prevented “CCing” the motor during tech inspection. Petruzzi, being a very astute and talented machinist, thought he could improve on the design, and set out to build his own engine back in 1939. He started with his own handmade wooden patterns, and cast his heads and cylinders out of raw steel that he machined into finished units. He even cast his own flywheels for the experimental motor. Only a few of these steel castings were ever made, and all have been lost or destroyed over the ensuing years.


Originally, Petruzzi had used a Linkert carburetor, but it couldn’t provide enough fuel for the alcohol burning midgets, so he eventually cast his own “barrel valve” type carburetors with more fuel and air flow for more power.

In 1942, all racing was stopped for the war effort, but by that time, Joe Petruzzi, running his water cooled engine, was a national points champion. By the time racing resumed after the war, Ford flathead 60 and Offenhauser engines had become the standard for midgets, and the Petruzzi Knucklehead disappeared except in the memories of old race fans and racers alike.

In 2007, Ron Weber, of Cap’s Bright Hot Coatings, found pieces of an old carburetor with “Petruzzi, Fresno” cast into it, and his curiosity led him to learn as much as he could about the history behind such a rare piece. An internet search finally led him to Joe Petruzzi’s grandson, Mike. Mike gave Ron more information about his grandfather’s racing, and the origin of the carb, and then informed Ron that his grandfather, Joe, was still alive and well! A phone number was provided, and Ron contacted Joe Petruzzi Jr., the son of the 98 year old legend himself. Joe Jr. told him that the carburetors worked well on the water cooled engine his father made. This was the first mention of an engine, and led to yet another search!

Joe Junior was happy to tell Ron more about his father’s racing career, and the water cooled Petruzzi engines, and during their conversation, he revealed that back in 1970, his father loaned the original wooden casting patterns to his nephew, Vince, who is also a machinist, and was living in Oakland, California at the time.


Luck was again with Ron, and after tracking Vince down, Vince was able to find the pieces to cast the engine components, and after extensive questioning about his motives, and his assurances that he was, indeed, going to build a running Petruzzi water cooled Knucklehead engine, Vince and the Petruzzi family agreed to loan Ron the casting patterns, which were then taken to Bob Kearney, at Kearney Foundry in Fresno for the casting process. In a snit-fit, Lady Luck had thrown Ron one last curve, as one of the pieces was missing from the old casting patterns. Fortunately, the foundry that cast the original parts for Joe Petruzzi back in 1939 is still in business, and in a one-in-a-million stroke of luck, a search of the attic turned up the missing piece! Ron decided to have the engines cast in aluminum rather than steel to save weight and improve cooling over the original steel.

Ron had help in his quest to build a water cooled Petruzzi engine from friends, including John Dove, Ray Barella, Wayne Sumner, Marsh Runyon, Pancho Vincent and others who have forgotten more about Harley engines than most of us will ever know, and as a result, the first Petruzzi Knucklehead engine to serenade us with its staccato rumble on 70 years is now a reality.

Ron is currently restoring a midget that was powered by the original Petruzzi Knucklehead engine, and driven by Edgar Elder. It’s powered by the first Petruzzi engine Ron built.

The second engine is in a rigid Harley frame, with the right side fat bob tank converted to a radiator, as well as a fan and cooling tube built into the rear wheel. The power these engines make is legendary, and Ron, along with the Petruzzi family has brought that legacy home to Fresno where it started from Joe Petruzzi’s quest to go faster. Unfortunately, Joe Sr. passed away shortly before the first engine was running, but his legend lives on.

Ron told me “these are not Ron Weber engines. They were, and always will be, Joe Petruzzi’s engines. I’m just glad that I could bring them home where they were born, and where they belong.”

Petruzzi Knucklehead Tech Sheet:
C.I.D.: 105
Bore: 3 5/8”
Stroke: 5”
Rod length: 8”
Cam: Leinweber, .565 lift, 340 degrees duration.
Compression: 8-1