Where Have All The XAs Gone?

[Perry Ruiter]

I think Moto Cuzzi copied Indian ... Perry

[23JDCA 808]

Re: W-Opposed

Originally posted by petri
I am rereading Hatfield's book on Harley flatheads and just read about the W's. They had a displacement of 35.6 cu in (584cc) not 37 nor 30. A rather odd displacement. And I photographed one of those at Wheels thru Time last weekend so here it is. Hatfield's book has some nice pics.

Howard

WJ Sport Twin was about 36ci or 600cc. Claimed 6hp.

[petri]

XA Pics

Clearly, the W's have no similarity to XA's. The W's were made from 1919-1923, long before the XA was in 1942. The W was a Harley Davidson design, the XA apparently was not.

Hatfield's book, Harley Davidson Flatheads, states that the XA was "basically" a copy of the German BMW. The book also claims that Harley Davidson did nothing more than convert the drawings from metric into british units. It surprises and puzzles me how they would even have such drawings in the first place. Especially after the war started. If it's really a copy then one would think you could swap parts with the old BMW's. So can any of the XA experts tell us if an XA is a flathead german BMW made here, or just a similar design. And it's not really clear to me why more weren't built.

Howard

[darrylri]

I'm not sure how accurate it is to say that Guzzi copied Indian, but Indian did build the transverse V layout before Guzzi did.

From what I've read, Harley believed that the Army specs for a new bike reflected the Army's experience seeing the BMW R71 in action. Harley obtained an R71, which had been sold in Europe since 1937, and reverse engineered it. There is no question that the two bikes bear a striking similarity in many features of the drivetrain.

On the XA mailing list it is said that an R71 crank will fit perfectly into an XA's case. There are differences, however. The XA had a one piece crank and split big ends on the conrods, while the R71 had a built up crank with one piece conrods. And as soon as you get away from the motor and transmission, it doesn't look so much like a BMW any more. Harley spec'ed 4x18" tires, while BMW had been using 3.5x19" tires. The narrower tires allowed BMW to have a straight shot from the transmission output to the final drive input, but Harley had to add a U joint into the driveshaft to compensate. BMW had been using oil damped telescopic forks for 7 years by the time Harley made the XA, but they put a springer fork on it. And so on.

Compare these images of the XA...





... with these images of a BMW R71




The way I see it, Harley made use of the BMW drivetrain design and adapted it to their existing designs and production techniques. They did this as an expediency in meeting the Army's requirements for a bike they didn't actually believe in, and therefore, didn't want to invest a lot of money into it.

[HarleyCreation]

Re: XA Pics

Originally posted by petri


Hatfield's book, Harley Davidson Flatheads, states that the XA was "basically" a copy of the German BMW. The book also claims that Harley Davidson did nothing more than convert the drawings from metric into british units. It surprises and puzzles me how they would even have such drawings in the first place. Especially after the war started.

[and]

And it's not really clear to me why more weren't built.

Howard

If you mean that Harley had actual BMW drawings, I don't think that's the way it happened. I believe that Harley obtained an actual BMW motorcycle thru a neutral country and then dismantled it and measured the parts. From those actual parts and measurements Harley then made their own drawings and at that point converted the metric dimensions to U.S. units.

Initial plans called for a LOT of XAs. In fact, Harley hoped the XA was going to be the standard U.S. motorcycle to replace the WLA. But then the Jeep came along and the motorcycle as a military vehicle fell on hard times. Plus the African Campaign with all that sand was just about over by then so the need for a shaft-drive MC was less anyway so they finished up the war with the venerable old 45.

[VPH-D]

The 'reverse engineering' idea of the BMW makes sense. The Russians did it with B-29 bombers they refused to return to the US.
VPH-D

[HarleyCreation]

Originally posted by darrylri
I'm not sure how accurate it is to say that Guzzi copied Indian, but Indian did build the transverse V layout before Guzzi did.

From what I've read, Harley believed that the Army specs for a new bike reflected the Army's experience seeing the BMW R71 in action. Harley obtained an R71, which had been sold in Europe since 1937, and reverse engineered it. There is no question that the two bikes bear a striking similarity in many features of the drivetrain.

On the XA mailing list it is said that an R71 crank will fit perfectly into an XA's case. There are differences, however. The XA had a one piece crank and split big ends on the conrods, while the R71 had a built up crank with one piece conrods. And as soon as you get away from the motor and transmission, it doesn't look so much like a BMW any more. Harley spec'ed 4x18" tires, while BMW had been using 3.5x19" tires. The narrower tires allowed BMW to have a straight shot from the transmission output to the final drive input, but Harley had to add a U joint into the driveshaft to compensate. BMW had been using oil damped telescopic forks for 7 years by the time Harley made the XA, but they put a springer fork on it. And so on.

Compare these images of the XA...

... with these images of a BMW R71

The way I see it, Harley made use of the BMW drivetrain design and adapted it to their existing designs and production techniques. They did this as an expediency in meeting the Army's requirements for a bike they didn't actually believe in, and therefore, didn't want to invest a lot of money into it.

Nice pix!

The XA is indeed a "loose" copy of the BMW. They copied as much of the core bike as they needed and then hung their own bits and pieces onto it: carbs, generator, fork, tanks, fenders, etc. I didn't know that a R71 crank fits the XA (will it also work?) and never thought about the tire size and the U-joint business. Interesting....

I wonder if the bore and stroke are the same?

While the XA wasn't Harley's machine (as one old guy put it) they did have post-war plans for it. Big plans. They got very far along with an XA powered shaft-drive Servi-Car project. Well into the prototype stage and were close to producing it. (That was supposed to be Model K and then Model H.) But then the market fell off and they dropped it.

About the same time Harley had other plans for a shaft-drive solo model and I think they may have built a tool-room running example of that job too. That may have been the one that was near 61-ci and OHV.

Well into the 1950s Harley had XA motor projects for air-compressors and utility engines but couldn't interest anybody in them. Sad.

I always asked old guys about the XA because that bike interested me. I remember one guy who had dyno tested it said they couldn't get the same level of horsepower from XA as from the orig. BMW motor. Another old guy used an XA tranny in his garden tractor.

A person could write an interesting story about the XA. Yes indeed!

[darrylri]

Originally posted by HarleyCreation
Nice pix!

Thanks. The XA shots are of a bike that was in the vintage display at the BMW MOA national rally last July in VT. The R71 pictures are stolen from the BMW online historical archives (hence the watermark).

The XA is indeed a "loose" copy of the BMW. They copied as much of the core bike as they needed and then hung their own bits and pieces onto it: carbs, generator, fork, tanks, fenders, etc. I didn't know that a R71 crank fits the XA (will it also work?) and never thought about the tire size and the U-joint business. Interesting....

I can't claim to know how well these pieces fit, but one of the members of the XA mailing list claimed that it worked and that the R71 crank was a stronger piece.

I wonder if the bore and stroke are the same?

They are, to within a couple decimal places. For example, the nominal bore on the XA was 3 1/16" (77.78mm) and the R71 had a nominal 78mm bore.

While the XA wasn't Harley's machine (as one old guy put it) they did have post-war plans for it. Big plans.

They weren't alone. The R71 served as a basis for a lot of countries' motorcycles. Because production of aero motors took priority at BMW's Munich factory, they moved the motorcycle line to their Eisenach plant. That ended up in the Soviet zone after the war, and they carried the line off to Russia, where they produced the M72. In the 60s, the Soviets sold the line to the Chinese, and you can buy a Chang Jiang CJ-750 today that looks very much like the R71 (but with 12V electrics and a car alternator, among other things). One must be very careful when looking to buy an R71, because a lot of the Chinese bits will fit right in.

[HarleyCreation]

That bore & stroke is close enough for Govt. work!

Can you imagine that if Harley had produced post-war XA/BMW type bikes as the Soviets did/do and then the Chinese did/do and also the Germans that bike would have literally gone around the entire planet! Came very close.....

Sort of like the German Model 98 Mauser rifle actually did go around the entire world!

Are the Chinese still producing a side-valve BMW type motor today?????

[mmoore]

lots of god theorys here a few points I want to add. first we all know a fat tire works better in sand so I believe H-D wanted better flotation in the sand. oil filled forks would require field maintence and be prone to failure from heat and sand so a springer would be nearly trouble free. also I work for magna who is the leading supplier to the automotive ind. (magna.com) and am familiar with a new product launch. This is not a fast or easy task! building from the ground up involves a lot of testing and training. Time was crucial here as lives depended on getting this job done. by reverse engineering a lot of time would be saved getting these bikes into the war effort also a cost savings would be realized. A reminder what started this thread, ronnie's book is more about the personel history of specific bikes from day one to now, a angle that would be interesting to me (I do plan to add it to my library). so any info in this area would be helpful to him. much as I would like to prove the alleged xla I think ive been on a wild goose chase. still waiting on H-D to respond (and they will) maybe I'll help ronnie look this weekend again. I also have been enjoying this thread!

[Rockin Ronny O]

Well, I must agree. This is a very entertaining, enlightening and interesting thread.

My book is about where the XAs are now and how they got there. However, some of the info in it will be gleened from what has been written here (and other places). The book needs it!

The XA had been tested as Servi-Car (I've seen official H-D photos). It looked awesome.

Last year, in the AMCA magazine, there was a photo of a race car with an XA engine. The car was called the Molenear Special. Please don't quote me on this but it's possible that was built by Mr. Molenear, a now-deceased H-D dealer from Calumet City.

It is rumored that he and Dudley Perkins of San Francisco bought up a bunch of XAs and/or parts just after the War. Where they are now is anyone's guess. I can tell you that I visited Mr. Molenear's dealership in 1978 and asked if he had any XA footboards. He replied, "I'll be right back." He wasn't gone for more than three minutes and he came back with several sets of them and said "Pick a set." Dopey me, at the time I didn't have any cash on me as I was just in the inquiring mode. It was a Saturday, banks were closed, I was travelling through, etc., anyway, he only wanted $20 a set then. I never went back because I thought for sure that if he had a lot of them, then others would as well. I was 19 years old then. Ah, youth is wasted on the young.

[mmoore]

I will post the reply when I get it. I think my wife is catching up to why i have been looking for a XA!!! If she reads this thread im busted

[darrylri]

Originally posted by HarleyCreation
Are the Chinese still producing a side-valve BMW type motor today?????

Yes, they are, as well as an OHV version. Check it out:

http://www.chang-jiang.com/cj750/

The R71 was BMW's last sidevalve model. After the war they went exclusively to OHV motors.

Originally posted by mmoore
lots of god theorys here a few points I want to add. first we all know a fat tire works better in sand so I believe H-D wanted better flotation in the sand. oil filled forks would require field maintence and be prone to failure from heat and sand so a springer would be nearly trouble free.

Well, I can only make guesses as to why each company used what, but I suspect that they both, BMW and HD, used technology that they were already making where possible.

But I suspect that the BMW forks didn't have problems, for whatever reasons, in the sand; in 1942 BMW came out with a purpose built war machine, the R75M, an OHV 750cc machine, with similar forks to the R71. (The oil damped forks BMW was producing were already on their third generation by this time.) In comparison, BMW developed a fairly extensive system to keep sand out of the intake tract on the R75M, so they were still concerned about it.

The R71 was a relatively light machine, and this fact weighed against it with the Wehrmacht. When the Wehrmacht started equipping for the war, BMW wanted to sell them the R71, but the army liked the robustly built R12, with its pressed steel frame. It wasn't until after the war started that the german army started buying R71s. As a solo bike, it weighed a bit under 400 lbs.

[HarleyCreation]

I wonder if a Chinese BMW side-valve unit would drop into a R50/2 chassis?

That would be a cool bike, but I wouldn't be that lucky....

I was told that Harry Molenaar indeed bought up much of the leftover XA stuff from Harley-Davidson. I never heard that Dud Perkins got any that I can remember, but he certainly might have. Tom Perkins is still around I believe.

I was looking thru my old notes for something else and found where I had written down that somebody at H-D had an XA with a Panhead top on it. I never saw it and was told that second hand and don't know how true it is/was, but the guy who told me worked there and claimed to know the fellow who had/built it. Nor do I know if it was a factory thing or somebody's homebuilt project.

And while the guy did say "Panhead" he might have meant or seen the standard OHV version of the XA which did exist. Hard to know.

[darrylri]

Originally posted by HarleyCreation
I wonder if a Chinese BMW side-valve unit would drop into a R50/2 chassis?

That would be a cool bike, but I wouldn't be that lucky....

I believe it will fit... however, you'll need to fabricate some kind of adapter to mate to the R50/2 transmission. You can't use the older transmission for two reasons: 1) the output of the transmission needs to mate to the U joint flange on the R50/2's enclosed shaft, which runs inside the right swingarm leg; and 2) the older transmission is a 2 shaft unit and turns clockwise (facing it from the rear), while the /2 transmission is a 3 shaft unit and turns counter clockwise.