William Harley’s Aluminum Motor Experimental Machine

1Black-Betty-069Harley Davidson only built one.! 15 years ago, Patrick James acquired this Bill Harley’s 1939 experimental all aluminum motor Harley twin. It now sits in his garage parked next to Paul Bigsby 1936 #5 Crocker, 4 other Crockers and several Ace Fours , Cleveland, etc. Paul contacted me and was nice enough to tell me the exceptional story of this very unique experimental Harley. All true fans of  the brand are going to enjoy this feature. Read…

2Black-Betty-059“Two major events in 1937 altered Harley- Davidson history. William S. Harley suggested in June that the company should undertake design of a 45 ci overhead-valve twin by installing new cylinders and heads on the standard side-valve base. He felt this would be more worthwhile than trying to improve the Seventy-four and Eighty side valve twins.

3Black-Betty-059Harley followed up in August with more specific ideas on a Forty-five overhead. The Forty-five side-valve model’s frame would have to be altered and strengthened. The most powerful of the current Forty-five side-valve models was the WLDR, which produced up to 27 hp. Harley’s proposed Forty-five overhead was targeted for 30 hp in a mild state of tune that could be later revised for more power. Even in the 30 hp version, Harley reasoned, the performance would be on par with the Seventy-four side-valve due to the smaller motorcycle’s lighter weight. The manufacturing cost of the Forty-five overhead would be about the same as for the Seventy-four side-valve.

William S. Harley countered that at least two years of design lead time would be required for a completely new Forty-five, and that the company would save money by converting the side- valve Forty-five to the overhead-valve configuration. Walter Davidson entered the discussion by stating that the Forty-five side-valve transmission had never been thouroughly satisfactory to dealers and riders, and he doubted the transmission would hold up to the additional horsepower of a Forty-five overhead-valve motor.

The Forty-five side-valve powerplant had the primary chain on the left, a frame-mounted transmission and the rear chain on the right, subjecting the gearbox and frame to heavy twisting loads. Walter believed that an entirely new transmission would be required on an overhead and that the crossover feature would have to be eliminated on such a model. He was impressed by the Indian Sport Scout Forty-five side-valve, believing it had the advantages of light weight and economic production. Walter felt the Forty-five side-valve Harley- Davidson should be continued unchanged and that an entirely new Forty-five overhead- valve should be considered.

3bisBlack-Betty-059One of the reasons William S. Harley had been pushing for a Forty-five overhead-valve was a continual piston problem on the side-valve motors. Between 1914 and 1934, all Harley- Davidson motors had featured tapered cylinder bores. Heat distortion was caused by the normal temperature radiant between the top and bottom of s cylinder, as in any engine design, and was aggravated by the eccentric cylinder head porting of the F-head and side-valve layouts. The theory behind the tapered cylinder bore was that heat distortion would warp the barrels into the propper shape. But the theory was not working well in practice and had resulted in excessive piston failure. Effective with the 1934 models, the factory accordingly had been using a new piston design in conjunction with straight cylinder bores. Nevertheless, piston problems persisted until yet another redesign. The minutes of the September board of directors meeting are illuminating.

“At the time this Forty- five overhead- valve motor was suggested, we were apparently at our wit’s end in regard to pistons in our Seventy-four and Eighty motors, and it was felt we would have to come to an overhead- valve motor to replace these side- valve motors. Since that time, a new piston has been developed which seems to be the answer to our troubles. If this proves to be correct, the necessity for overhead- valve motors to replace the side- valve motors is not so great. The one outstanding difference between the overhead- valve motor and the side- valve motor is that the overhead costs considerably more to make.” The new piston design referenced here was the steel- strutted type. Steel- strutted pistons would be incorporated on Seventy- four and Eighty twins in the latter part of 1938 model production run and cataloged as new features of the 1939 model Seventy-four and Eighty.

6Black-Betty-059Discussions on the proposed Forty- five overhead- valve continued into November without producing a consensus. William S. Harley proposed the building of fifteen to twenty special Forty- five side- valve competition motorcycles in order to compete against the Indian Sport Scout. William H. Davidson brought up the idea of a lightweight motorcycle, which he believed should be subsidized in order to be offered at an attractive price. The board agreed that there was a demand for a lighter motorcycle; however, the design and fabrication of the tools to manufacture a lightweight were estimated to cost $75,000 to $100,000, so further study was deemed necessary.”

Three new board members attended the December board meeting. Robert P. Nortman, William J. Harley, and Gordon Davidson, all sons of directors, had entered the management ranks. The Forty- five overhead- valve dialogue continued with William S. Harley repeating his earlier rationale. A revival of the 30.50 ci side- valve single was discussed, but Arthur Davidson opposition ended this idea. William H. Davidson again suggested a subsidy program, this time intended for the Forty- five side- valve, which he believed too expensive. Arthur agreed this might be a good idea if the price of the projected Forty- five overhead- valve was kept up, thus ensuring a meaningful gap between the prices of the two different Forty- fives.

7Black-Betty-059In January 1938 deliberations over the Forty- five overhead- valve model, William H. Davidson sided with William S. Harley, favoring reconfiguration of the Forty-five side-valve into an overhead-valve model. Citing the cost advantages of sharing forks, frames, tanks, and transmissions, William H. Davidson’s statement drew agreement from Arthur Davidson. So Walter Davidson’s proposal for an entirely new Forty-five overhead-valve motor was dropped, and the engineering department began work on the development of a Forty- five overhead- valve derived from the existing side-valve design. However, no decision was reached on the transmission.

During February and March, the engineering department continued working on the Forty-five overhead-valve, and the general specifications on the motorcycle were worked out. However, continual engine problems resulted in a decision to cancel plans for a specific launch date for the Forty-five overhead-valve so that testing and problem solving could be accomplished at a measured pace. Management wanted to ensure the model would not be introduced until fully developed. Wooden patterns for the Forty-five overhead-valve cylinder heads were completed by April and were being studied for possible improvements.

4Black-Betty-059Also under consideration was the use of 10 to 14 mm spark plugs in lieu of the standard 18 mm plugs on all models. This idea could save costs on the some 100,000 spark plugs purchased annually. Furthermore, the smaller plugs were considered advantageous because they permitted more room on the cylinder heads for better cooling. From April through June the engineering department concentrated on shedding pounds from the Forty-five overhead-valve. William S. Harley still believed that the Forty-five overhead-valve could be built for about the same cost as the Seventy-four side-valve.

In April the Forty-five overhead-valve was canceled as a 1940 model. After working out the cost, the projected Forty-five overhead-valve would have been as expensive to build as the Seventy-four side-valve. Although Chief Engineer William S. Harley had been saying that all along, apparently the board at last decided that without any cost savings on the Forty-five overhead-valve, it would not be a marketable proposition. Instead of working on the Forty-five overhead-valve, the engineering department would be concentrating on the new 74 OHV. Other development attention would be given to aluminum cylinder heads for the Seventy-four and Eighty side-valve models; consideration was being given to offering the Eighty only with aluminum heads.

‘William S. Harley of the Harley-Davidson Motor Co. states that in regards to experimental work with other metals other than cast iron, he has tried aluminum, brass, and steel. In his experimental work with aluminum cylinders he has made new patterns, the cylinders with cast in bronze valve seats. Having tried them both with and without sleeves over a few month period decided to drop the matter. The cylinders not having satisfactory results, but he did realize there were many factors to the problem which they did not go into. The results he got from these tests were largely inclusive, but from his experience with other metals William S. Harley decided that cast iron was the best material for air cooled cylinders.’ (Automotive Industries Vol. XL VI Number 22)

5Black-Betty-059Here is BIll Harley Experimental “Second Generation” All Aluminum OHV 52 cubic inch 1938-39 Harley. Bill Harley’s dream of an over-head valve lightweight machine created experimentally by Harley- Davidson Motor Co. He only built one of these and four of the all iron models. This one has all aluminum heads and barrels with EX clearly marked to both. The lower end is OHV only with 1937 OHV oil pump. The Motor is proprietary to this machine using narrow cams and oversized cam cover. Notice where the lower pump area fits, this is for the Pressure Fed Crank on the OHV Bill Harley designed for this motor. The Iron head motors are similar.

The all aluminum one has the “A frame” style head and the Iron model is the “Gap type” with many differences in design as pictured. All are EX marked clearly and this motor is also marked #4. Note the oil return angle is straight instead of angled on the OHV, also the bearing is removable and not blind on the output shaft.

Also to note is the difference of the lifter blocks. They are drilled to the channel to vacuum the oil from the OHV heads. The wheels sport one off narrow stepped hubs with small spoke rims. There are many experimental parts on Bill Harley’s machine.

This Harley uses the “Dome Piston” mentioned in the Harley-Davidson Board Meetings in 1938-39. BIll Harley was so proud that this piston pictured would end his overheating problem. It was acquired by Egeberg from Bill Harley, as I was told by a family member, as it sat on his desk for many years. This piston bares the EX marks as well as Harley numbers.

This was purchased from Roy Egeberg in 1974 at his home by restorer Daniel Pugens well known as a specialist in Harley CAC’s, DAH’s, and OHV’s. He acquired 85% of this machine as a roller, missing very few parts. Roy Egeberg was the Harley dealer in St.Paul Minnesota. He was selling Henderson’s and Ace’s as a friend of William Henderson and of Andrew Strand of Cyclone Motorcycle.

The Motorcycle is mentioned extensively in well known author Herb Wagers book ” Harley Davidson 1930-41″ where he has a wonderful story about the “Second Generation” bike with an extensive history. It is also mentioned by Jerry Hatfield in his wonderful book “Inside Harley Davidson” in which he go’s in depth on all of the meetings and manufacturing of this motorcycle . William Harley’s one-off experimental machine.”

21 Responses to “William Harley’s Aluminum Motor Experimental Machine”

  1. 1 Greeko Apr 22nd, 2016 at 8:24 am


  2. 2 Woody's Apr 22nd, 2016 at 8:26 am

    Great stuff, will have to re-read a time or two to take it all in. Would be great to have it in the Museum in Milwaukee, in the gallery with the progressive line of major bike changes.

  3. 3 Steal Your Face Apr 22nd, 2016 at 9:53 am

    That is pretty impressive. And priceless. Some rich collector would pay big to own a one off with the kind of history this bike has.

  4. 4 burnout Apr 22nd, 2016 at 10:30 am

    Cool bike and great story. peace

  5. 5 Danny Ray Apr 22nd, 2016 at 10:34 am

    Love this piece. Thanks Cyril.

  6. 6 Chief Waldo Apr 22nd, 2016 at 11:14 am

    This motorcycle was up for auction at Mecum’s January, 2016 auctions in Las Vegas.

  7. 7 chopmonster66 Apr 22nd, 2016 at 11:20 am

    Great history lesson

  8. 8 JT Apr 22nd, 2016 at 12:10 pm

    The best article thats appeared here in a very long time !

  9. 9 KIrk Perry Apr 22nd, 2016 at 12:43 pm

    Does it run? A start-up and ride video would be another dimension to the story.
    4-cams though… 8-lobes wearing.

  10. 10 P. Hamilton Apr 22nd, 2016 at 12:48 pm

    Difficult to find such amazing stories every week, even every month…I learned a lot.

  11. 11 Greybeard Apr 22nd, 2016 at 1:46 pm

    And making as much HP as they do today!!

    jk,jk!! ;o)

  12. 12 Chris Apr 22nd, 2016 at 4:12 pm


    Perhaps I missed something in the article, but it looks like a standard 4 cam w/ one lobe per cam just like an XL set-up.

  13. 13 F. Petersen Apr 22nd, 2016 at 4:20 pm

    Amazing story.

  14. 14 Woody's Apr 22nd, 2016 at 4:31 pm

    @ greybeard, perhaps, but WAY more HP than the 1954 Indians ☺☺☺

  15. 15 nicker Apr 22nd, 2016 at 9:23 pm

    “…The manufacturing cost of the Forty-five overhead would be about the same as for the Seventy-four side-valve..”

    Logic like that could put lesser companies out of business


  16. 16 nicker Apr 22nd, 2016 at 9:30 pm

    “…The one outstanding difference between the overhead- valve motor and the side- valve motor is that the overhead costs considerably more to make…”



  17. 17 KIrk Perry Apr 22nd, 2016 at 10:02 pm

    ” it looks like a standard 4 cam w/ one lobe per cam just like an XL set-up.”… and not (4) valves per cylinder then. 🙂

  18. 18 Dale Apr 23rd, 2016 at 8:38 am

    I love this stuff. Great write up.

  19. 19 John Apr 23rd, 2016 at 1:12 pm

    Just an observation but that is not a 45 or UL cam cover it looks much larger and it has a different bolt pattern. I am assuming it is due to the oil channels it appears they are cast to the odd looking lifter blocks. that would mean the Cams are NOT standard I wonder what the lobes look like.

  20. 20 coma Apr 24th, 2016 at 7:28 am

    Looks like the direct forefather of the K/XL family to me.

  21. 21 Jay Horton's Private Shop Apr 25th, 2016 at 7:54 am

    What a thing of beauty! Later Jay

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Cyril Huze