Tuesday, March 13, 2012


It's no secret I’m a JAP engine addict.  In fact I belong to a Facebook group which is dedicated to the JAP engine.  And as such members will post photos and info and just general goings on regarding JAP.  And of course notes regarding JAP engines that pop up from time to time being for sale.  Well I saw this 1936 JAP engine for auction and was a bit stunned to see a buy it now price of $17,900.00.  That price makes my race engine seem cheap in comparison.  But as of now there had been no sale.  We shall see what happens.  It is a fine engine which is supposed to be complete and rebuilt 30 years ago.

This is the history part.  The same guy that is selling the JAP also is selling a Harley Davidson 500 cc single race engine which is one of the prototype engine built to run against the JAP.  The buy it now price is $199,000.00.  Yes I read and typed that correctly.  This is what the seller says about the engine.
Circa 1933 one-off Harley Davidson Over Head Valve 500cc, 30.50 cubic inch single cylinder racing engine.  This experimental engine is the predecessor of the Harley Davidson CAC 500cc Speedway single racers.  This engine is a virtual copy of the J.A. Prestwich, also known as J.A.P. Speedway 500cc, 4 stud racing engine manufactured in Tottenham, England from the teens to the 1960's.  The J.A.P. Speedway machines were beating all comers including Harley Speedway racers.  The Harley racing department decided it was time to even the score.  A brand new J.A.P. 4 stud Speedway machine was purchased by the Harley race department.  Their express purpose was to dismantle and reverse engineer the OHV J.A.P. engine to improve Harley's raing performance by incorporating some of the J.A.P. designs.
William Harley and Joe Petrali, scratch built this one-off Harley Speedway engine copying a J.A.P. single in the Harley race department.  William Harley told Petrali to discard the J.A.P. parts. but soon realized they could reuse the carburetor and magneto off the J.A.P. engine.  He asked Joe what became of the carb and mag?  Joe replied he threw them in the trash as instructed.  Harley told him to go retrieve them, which he did.  The original Amal racing carburetor and the Lucas racing magneto were found and installed on this Harley one-off racing engine.  They remain in use on it today.
The Harley Davidson engine turns over and has  good compression.  This is the original untouched engine as given to Joe Petrali by William Harley at the end of their project.  At the base of the cylinder, "EX 1320" is cast indicating it is an experimental item.  The brand name, "Harley Davidson"  is in bas relief on the rocker box cover similar to where the J.A.P. engine has J.A.P. in bas relief.  Other than "EX 1320" cast on the cylinder and "Harley Davidson" in bas relief on the cover, there are no VIN , line bore, or date code numbers.  The engine case castings are rough and crude where reinforced around the crankpin.  The compensating sprocket is on the sprocket shaft.  Use as a show engine or build a truly one of a kind Speedway racing machine.

I have always read bits and pieces which suggested that Crocker, Indian and Harley copied the JAP with apparently no shame at all from the looks of it.  But what I don’t understand is for how simple the JAP really is and if Crocker, Indian and Harley used in hand examples of the JAP to copy why couldn’t they beat the JAP engines?  Or at least build an engine as good as the JAP?  That may be a mystery of the universe questions I’m thinking.
Be that as it may, if I had some big lotto winnings in my pocket I would have the Harley engine winging it’s way to the Kiotee Garage along with a Crocker single and an Indian if I could prey one out of somebody’s fingers.

Memory refresher for all and a bit of engine porn tossed in for good measure.
                                                    1928 Indian

                                          500 OHV Crocker

So I guess nothing left to do but go out to the Kiotee Garage and fondle my superior JAP race engines.


  1. Some good info there Roy, i have one of those Harley single bottom ends, you've got me wondering if i can fit a JAP top end on it now, if i can find one that is.

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