The BSA A7-A10 Forum

Technical => A7 & A10 Engine => Topic started by: Peter Gee on 16.06. 2017 10:08

Title: Thread Type for Restoring Amal Monobloc JET BLOCK?
Post by: Peter Gee on 16.06. 2017 10:08
Hi, am needing to chase the threads on my type 89 MONOBLOC  Jet Block ( the one the main jet holder screws into) but darned if I can imagine what tap they used, and they are not replying from AMAL itself. .the nearest size I seem to get is 19TPI measured on the main jet holder....which would be BSP thread, confusingly there are TWO BSP 19 TPI in tap list named 1/4 and 3/8 . 7/16 x 18 BSF seems close but not correct. The actual thred of the JETBLOCK seems between the diameters of  the two 19TPI  BSP taps..in fact I get about 0.430  dia when measuring the Jet Holder itself, which is neither one --1/4 BSP x 19 is too small, or the other 3/8 BSP x 18 is too large at over 0.500.... Anyone know?