1928 sunbeam 350cc motorcycle

[telford]

Hello all I am new to this forum,I have had the above ohv motorcycle for about a year now.Just before Christmas I took the engine down for a general overhaul.To my surprise the plug hole is 1.25 inches deep and the plug fitted was only a half inch reach.Questions amongst my sunbeam motorcycle friends confirm this is normal.I have aquired an NGK plug which has been turned down to provide a one inch reach but the spark will still be shrouded.Does anybody have any ideas to provide a solution to my problem?.The plug is originally an 18mm but I could change to 14mm if it was necessary.Ideally a one inch reach 18mm plug that could be turned down to provide the extra quarter inch reach would be the answer but I am unable to locate such a plug.Any suggestions will be much appreciated. telford

 

[pgarner]

hey and welcome to torquecars mate.
sorry most of us proberly wont be able to help as we're more into the cars than bikes.
but hopefully someone might know about them

 

[obi_waynne]

You need to look at the temperature rating of the plug as well as the depth. Surely this odd design has been done for a reason and it may well run less smoothly if you tried to "fix it".