March 2000 Tech Feature   
    Home / Features / Ace Engine page 1
 Inside the Ace Engine,
 Part 1 - A 1926 Example.
  By Rohan Bradney
  To Page 2 of 2
Ace and Henderson – some History.  

When William Henderson, the designer of the Henderson Motorcycle, parted company with Excelsior Manufacturing in early 1920, the announcement of the Ace Motorcycle followed shortly afterwards. So soon afterwards that there was speculation that much of the design of the Ace must have been done prior to the public parting of the ways. It is the elements of the design of the Ace 4 cylinder motorcycle engine that will be briefly outlined here.  

The Henderson brothers had formed the Henderson Motorcycle Co in late 1911 to manufacture the Henderson 4 cylinder motorcycle for the 1912 season. It was aimed at the luxury market, and promoted smoothness and quietness of operation . The Co struggled financially until Excelsior purchased the ailing company in the years around 1917/1918. Both brothers stayed on board after the buy-out. William as Plant Manager, and brother Tom (former President of Henderson Motorcycle) eventually took a position as a Sales Agent in Europe.  

The story goes that William Henderson was not happy with Excelsiors’ proposal to built his beloved Henderson as a much heavier sidevalve powered design for 1920. Sidevalve designs were becoming popular in other motorcycles of the time. Reading Standard had utilised a sidevalve design of v-twin for some years, and the very successful sidevalve Indian Powerplus v-twin had been announced in 1916.  The Henderson prior to 1920 had previously always been built as an inlet-over-exhaust (ioe) engine design – see later explanation of ioe.  

With a large amount of financial backing, the Ace Motor Co with William Henderson as designer of the Ace  was announced in early 1920. A factory in Philadelphia, MA was very rapidly established, and production commenced  a few short months later.  

Not surprisingly, William Hendersons’  design of the Ace 4 cylinder was similar to his earlier design of the Henderson 4 cylinder. Very similar looking designs indeed, but it was said that nothing was interchangeable, a feature confirmed by Henderson and Ace owners alike. This was to prevent any claims of infringement of design from Excelsior, the new owners of the Henderson Motorcycle – Will Henderson had broken his employment contract with them, to leave and start up the Ace Motorcycle Co.  
Ace Design Overview.  

The Ace design philosophy of the 1920s was embodied in the advertising slogan adopted – “THE FINEST THING ON TWO WHEELS”.  A  powerful lightweight 4 cylinder motorcycle to give smooth comfortable riding with effortless performance was the design brief.  

Was this achieved ?  The answer, on the rough stony roads of the early 1920s, was a qualified “Yes”.  The Ace4 was popular with local Police authorities (as was the Henderson4 and the Excelsior, Harley Davidson and Indian v-twins). To reinforce the performance aspect of the bike, the Ace factory built a pair of  modified speedsters. In 1923 the Ace XP4 claimed an unofficial world solo speed record of 129.6 mph, and XP3 claimed the world sidecar record at over 100mph. The road-going models were not capable of this sort of speed – indeed who would wish to on the rough unkept roads of the time ?  

At a glance, the Ace motorcycle in the years of manufacture 1920 to 1927 all look very similar - to the casual observer  they probably all look the same. Close inspection reveals a very large number of minor changes and improvements. Some were for performance reasons, to keep ahead of the pack, and some were reliability based, to give better service.  

The engine the subject of this article is a 1926 example. Surprisingly very little of the 1926 engine is exactly the same as the first Ace engine of the 1920 model. Many parts are also quite different to the later Indian 4 models based on this design. Many of the 1926 engine parts will physically interchange with earlier and later models, but would not be correct for any other year – a fact restorers need to be constantly aware of.  

The Engine.  

The motor was an in-line four (along the frame), with a bevel gearset in the intregal 3 speed gearbox to turn the power through 90 degrees to provide chain drive to the rear wheel. A large crankshaft-mounted clutch with heavy flywheel was interposed between crankshaft and gearbox.  

The 1920 motor was an inlet-over-exhaust 75 cu in 4 cylinder, with 2.7” bore x 3.25” stroke. This was soon changed, so that the motor became 77 ci in, using a 2.750” x 3.25” bore and stroke. The slight increase was to keep up in the advertising war being waged in the motoring press of the time – Henderson and Ace were seemingly engaged in a battle over supremacy on the roads and in the dealers salesrooms.  

Engine Bottom End.   

The crankshaft, camshaft, clutch and gearbox internals were all fitted or clamped into the upper crankcase casting, with a large and handsome finned alloy lower crankcase sealing the bottom of the motor (or sump cover in automotive terminology). The lower crankcase is not a structural part of the motor assembly. The drive to the camshaft, oil pump and magneto and generator is through a train of gears at the front of the motor (see picture 2).  

Engine Top End.  

Four separate iron cylinders bolt vertically on top of the crankcase.  The exhaust valves are mounted in the cylinders, very similar to the layout employed in sidevalve designs. An iron combined one-piece inlet manifold and valve cages for all 4 inlet valves bolted across the tops of the 4 separate cylinders (picture 3). 

Each cylinder has a circular opening of approx 1 ¾” diameter at the top, for the inlet valve cage to mount the inlet valve directly above the exhaust valve – whence comes the engine type known as inlet-over-exhaust.  

The combined inlet manifold and 4 inlet valve cages was a new part for 1926, and continued until late 1927. In late 1927, Indian (new owners of the Ace) announced a new combined inlet manifold and inlet cage assembly, part number VF-2300. It was claimed that it gave improved power and low speed running – and gave details of fitting it to earlier motors as an update. Restorers note well!!!  
In all previous years of the Ace engine, the inlet cages consisted of 2 separate “heads” each serving 2 cylinders, and a separate alloy manifold connecting the carburettor to the ports.

“Dad, look at them funny things jiggling up and down on that old motorbike “.  

“That motorcycle is an Ace, son, once the fastest motorcycle on earth. And those things are pushrods. They are usually inside the engine”.  

“Why, dad ?”  
 Click on pictures to enlarge.  
As in almost all VI articles. 
   Above - An unrestored 1926 Ace engine. Note the traces of blue-black paint on upper and lower crankcases, with some traces of red paint over the top of that (this Ace engine is known to have been used in an Indian 4 at some stage in its life). Also note the remains of dull nickel on the combined inlet manifold and inlet valve cages. The iron cylinders appear to have been painted black at some stage, but the undersides of the fins (where the black didn’t reach) show the original gray (?) finish   
Picture 2. 1926 Ace gear train.  

Picture 3. 1926 Ace cylinder head.
 To Page 2: Inside the Timing Cover and Gearbox.