Can anyone tell me if the Tacho for a 69 Starfire is 3:1 or 4:1?
4:1 for B25/B44/B50
Twins are 3:1
Unless my memory is starting to fail...
Thanks Rupert. Much appreciated
I see previous old replies re the Starfire tacho ratio query that also refer to the B44. According to the Smiths application chart for 1966 through 1970 etc the tachos are 3003 series rev counters, the 3003/06 and 3003/14 and are both 3:1 ratio, sharing the same model with the BSA A50/A65. Some models (and oddly several singles in '69) used a 2001 series 4:1 and the original Victor Special I think used this ratio.
Rupert Ratio (no pun intended) in his Unit Singles Manual quotes 4:1 across the board.
The reason I am posting is because I am fitting a tacho to my 1970 B44 and finding it impossible to get a definitive answer as to what ratio to buy. I think Smiths probably knew what they were printing and as this has been repeated through the years it seems that 3:1 may correct, but a very odd ratio, though because these models used the oil pump drive rather than taking off the camshaft, this gear does not (necessarily) rotate at 1/2 engine speed like on Triumph twin etc. All very confusing.
Can anyone confirm an actual original fitment Smiths tacho drive number for the 1970 BSA B44 please AS FITTED and verified for actual revs? If fitting a 4:1 when a 3:1 was specified this will read ~1.32 x HIGH or vice versa 0.75 x LOW. so rather important if you want to know your actual engine revs ( a bit hard to get your head around how those ratios work?). Any help gratefully receieved.
I can't help you with the detail I'm afraid, but ai got mine from here. I'm sure they will kniw
https://www.classic-speedometers.com/fully-refurbished.html
Really pleased with it, recommended them.
Hi,
thanks for the link - may chat to them.
The 1970 manual says the tacho is an RSM 3003/01 which is a 4:1, while the 1966/67 (according to the BSA parts book) etc use the 3:1 3003/06, so how com,e the ratio is different between the years?
Ought to chat with these guys anyway.
Thanks again
Can't you just work it out by winding the engine over a few times ?
Looking at the genuine spare parts books and Smiths application charts, the mechanical engine drive parts all carry the same part numbers (though I gather this does not necessarily guarantee 100% identical parts) so in theory all years should give the same drive revs per engine revolution, so maybe not definitively different when just turning over and counting (?), but a good idea to try this and see what happens. Engine not together yet so will have to wait until built to do this. Was trying to get all rebuild parts together before assy. Thanks for the sensible suggestion though.
Attached is the comparison year by year (where I could find the data) that shows how oddly documented this is. I have included some T25/B25 data as they all used the same rev counter drive. In 1969 the Victor Special used the same drive but had different ratio instrument heads ! Back in storage I have an old Advance Instruments Nixie tube lab bench digital rev counter, so will be able to test/calibrate when all up and running, but this will be a couple of months away.
What would help me and others (though not necessarily for this issue) would be a key to Smiths part numbers - what attributes carry what assigned numbers/suffixes - or perhaps they were just sequentially assigned so not useful to know? Does anyone have clue?