I have also found this I was sent it from graces guide uk. They have updated the history and I've sent them pictures of the engine. of 27 Quinton Street, Earlsfield, London and of Henley
1907 Advertising castings for small engines
1909 Producing their H and S single and twin petrol engines
1909 Model Engineer Exhibition, London. 'Messrs. H. Heckman and Co. of Henley were also exhibitors, their chief items being petrol engines and castings, and a coupled set of their two-cylinder engines suitable for yachts, houseboats, bungalows, charging accumulators, etc. Another feature was the coal or coke fired model steam boiler. The firm also make a speciality of vertical centre tube boilers which are of mild steel throughout.
1912 Advertisement. Heckman's, General and Motor engineers, Smiths and Cycle Repairers, Henley upon Thames. 'We repaired the first Petrol Motor, brought into Henley in 1897.
Possible Connections
1901 Advertisement. W. Heckman and Sons, General Engineers, Smiths and Cycle Engineers, 41 Market Place, Henley-on-Thames.
1911 Living at 41 Market Place Henley Oxon: William Heckman (age 77 born Odiham), Engineer's Smith - Employer. With his wife Elinas Heckman (age 71 born London) and their three sons Albert Heckman (age 41 born Henley), Electrical Engineer; Arthur Heckman (age 31 born Henley), Engineer Fitter; and Alfred Heckman (age 28 born Henley), Motor and Cycle Repairer. Also grandchildren. William had a total of ten children all living.