BSA Owners' Club Forum

The BSA Workshop => Singles => Topic started by: Starphil on 17 December, 2017, 20:37:32

Title: B25.Starfire - Tachometer Question
Post by: Starphil on 17 December, 2017, 20:37:32
Hi,
I recently  bought a 1970 starfire. It's in pretty good condition but has enough things to do to keep  me busy over winter.
 
The model I have has a single speed but I have noticed that some Starfire's also have a tachometer.  I thought this might be a nice addition but when checked my bike there is no connection point. 

Looking at some pictures of Starfires online I can see a connection  point just above to the right of the oil pressure relief valve but on mine there's nothing (see attached  picture).

My question  is,  should  there be one or was it only on some models?

Cheers
Phil
Title: Re: B25.Starfire - Tachometer Question
Post by: Starphil on 17 December, 2017, 22:29:01
Oops forgot  the picture
Title: Re: B25.Starfire - Tachometer Question
Post by: JulianS on 17 December, 2017, 22:38:22
There should be a little diamond shaped cover sealing the hole into which the drive spindle and its housing fits, on bikes suppled less a tachometer.

Maybe yours has the wrong cover fitted.
Title: Re: B25.Starfire - Tachometer Question
Post by: Starphil on 18 December, 2017, 08:14:52
Mine doesn't have one of those. From  the pictures I've  seen  it is part of the engine casing.  I've  since found pictures of  others  that are like  mine so wondered why some have feature and some don't.

Didn't know if it was something added or removed at some point in the manufacturing run.
According to the engine number my bike was made in May  1970.

Phil
Title: Re: B25.Starfire - Tachometer Question
Post by: AWJDThumper on 18 December, 2017, 08:16:10
Hi Starphil.

The earlier Starfires didn't have the tacho drive facility but a 1970 should have it fitted into the RH crankcase. What is your engine number?
Title: Re: B25.Starfire - Tachometer Question
Post by: JulianS on 18 December, 2017, 08:50:43
One of the new Smiths electronic tachos would do the job, look about the same as the magnetic original. No need for mechanical drive.

 http://shop.srmclassicbikes.com/product-category/smiths-genuine-instruments
Title: Re: B25.Starfire - Tachometer Question
Post by: Starphil on 18 December, 2017, 09:10:40
The engine number is ED11089B25s

I'll  check  out the electronic option.  Thanks.
Title: Re: B25.Starfire - Tachometer Question
Post by: JulianS on 18 December, 2017, 09:28:16
The engine decodes as May 1970 build,  E = May, D= 1970 season.

Quite late in the season,  so would have expected it to have the port for the drive, but who knows!
Title: Re: B25.Starfire - Tachometer Question
Post by: Starphil on 18 December, 2017, 09:58:13
Yes would have thought that.

Also, If you look at that part of the engine in the picture there's a seam just above where the port would  be.  I'm not sure if this is a normal part of the casting or indicates that there's been  a repair.  Not been able to look up close at another one to tell.

I suppose it's part of the fun of owning an old bike. I'm certainly enjoying it so.  Plenty to fiddle with but nothing too major so far.

Thanks for responding.

Cheers
Phil

Title: Re: B25.Starfire - Tachometer Question
Post by: JulianS on 18 December, 2017, 10:21:25
Phil

Not sure about your crankcase.

The 1970 engine would have had a pressure valve with enclosed spring and plunger and 2 parts, the outer hex being domed. Yours looks like the much simpler up to and including 1969 type which had a small diameter thread just one part plus a ball and spring.

Above your PRV looks like the poishing may be covering some weld repair caused by an engine blow up where the rod went into the cases - which happened to Starfires when thrashed by riders when they were new.

First photo is from the 1970 parts book.

Second from the 1969 book.
Title: Re: B25.Starfire - Tachometer Question
Post by: AWJDThumper on 18 December, 2017, 10:45:53
Yes would have thought that.

Also, If you look at that part of the engine in the picture there's a seam just above where the port would  be.  I'm not sure if this is a normal part of the casting or indicates that there's been  a repair.  Not been able to look up close at another one to tell.
The casting looks perfectly normal as is the horizontal seam above where the tacho output would be. Since the engine number appears to be legit, it looks as though you have a set of crankcases fitted from the previous year's model. It may be that a spare set of crankcases had to be fitted because the previous engine had blown up and the crankcases available where from the previous year. If new, they might well have been able to stamp the original number back on to them.
Title: Re: B25.Starfire - Tachometer Question
Post by: MICKREEVES on 21 December, 2017, 09:11:56
There are very cheap electronic tachos available.  about 2 inch long box. A single wire wraps around you HT lead for the signal.
Work perfectly, cost about 5 on ebay.
Mick
Title: Re: B25.Starfire - Tachometer Question
Post by: Starphil on 28 December, 2017, 00:06:36
I've  ordered  a cheapy from  China to try out. I'll let you know how i get on.
Title: Re: B25.Starfire - Tachometer Question
Post by: Starphil on 02 January, 2018, 11:58:18
Well it came very  quickly  and matches the after market speedo that's on my bike already.
I tried setting it up but with no luck so far. I found a set of instructions on the net which shows the contact signal wire connected to the positive side of the coil but this doesn't seem correct  because that side of the coil on my bike connects to ground (+ve) .
I also  tried  the -ve  side of the coil but that didn't work  either.
The bike has Boyer ignition but didn't think that should make any  difference.

The earlier reply mentioned wrapping it round the ht lead. Won't that  deliver too much voltage?

Cheers
Phil

Title: Re: B25.Starfire - Tachometer Question
Post by: AWJDThumper on 02 January, 2018, 12:39:51
This tacho is probably designed for a -ve ground wiring system rather than the standard one on a B25 which is +ve ground. You need to connect the supply wires the correct way round. What I don't know is whether the signal wire will detect the ignition pulses correctly (wrong polarity) but you may have use the HT cable as the source.