Hello Everyone, i am pretty puzzled by the cylinder head bolt lengths of pre unit 650 triumphs with alloy head. i ordered head bolts as listed in a 1961 650 parts book. the head bolts i ordered were 4 outer domed head bolts 70-2873 they have a under head length of 3 inch 3/4 long. also 2 cylinder head inner bolts with threaded extension for head steadies 70-1596A under head length 5 inch 7/8 long and two inner head bolts with no extension also under head length 5 inch 7/8 long. when the parts arrived the long inner head bolts has written on the label cyl-head bolt p/unit TR5 T100. i think this is a parts book mistake. it lists the iron cyl head with outer domed head bolts as 70-0327 which is the same as unit 650 triumphs. also the long inner bolts for the iron head are 2 cylinder head inner bolts with threaded extension for head steadies as 70-1596 which is the same as unit 650 triumph. and two inner head bolts as 70-1484 with no extension, the book quotes 5 inch 3/8 under head length but they are 5 inch 5/8 long which is probably another parts book mistake. which ones are correct for the 650 pre unit with a single carb alloy head fitted. does anyone have a bike apart where they can measure the under head lengths of the bolts and please let me know. this is battering my head. just as a note, i have a 500 close pitch fin alloy cyl head plus a alloy 650 single carb 8 stud cyl head and a unit 650 9 stud cyl head to compare with and the depth of outer head bolt hole is the same on all 3 cyl heads. i am pretty good on triumph knowledge but today might be a learning day and i am always finding something new even though i am approaching 60 years old. as stated above, any info gratefully received. cheers. billy.
Last edited by billy banger; 02/03/17 4:48 am.