Hi: I am not sure about what type of c/s bearings these engines have, but it would be a good idea to find out what type of fuel was used. My discussions with Dar Zeelon was that FAI fuels were normal. A 5% nitro fuel was ok without adding a head shim. Higher nitro content could do damage. I have a .45, and two .49 engines, and have added two head shims for using 10% nitro all castor fuels. The .45 runs very well. The others are still in their boxes having been pre-oiled.
I'll let you know once I receive them. I've never seen a HB .45 or a .49.
I read the manual(s) that comes with my engines...
NOT the conjecture posted on internet forums.
I've got several HB's and I've used SIG Champion 15% without any problems. Any "good quality" fuel with some castor oil works fine.
To quote the manual;
3. To break in the engine, any commercial glow fuel to which 20% oil have been added may be used.
Break-in time: 1 to 2 hours
After the engine is fully broken in, any commercially availabe glow fuel, including racing fuel, may be used.
I've used 40-61 sized HB engines for years.
PS: HB was Dar Zeelons first REAL RC engine........