vintage chainring question

[bassboy64]

Hi,

I have a 70s Galaxy and the front inner chainring is a Sakae 40T ( outer is 52) . I'd like to swop it to a 36 or 34, as the hills are starting to make me blow a bit, but I'm not sure what would fit!
It has 5 inner bolt holes and they are 7cm apart, and the distance they are from the crank is about 50mm. I've had the rear rebuild and have 7 sprockets on the rear. I bought something I thought would fit used from ebay ( yes, I know) but the holes were in a diffent place.
Any suggestions where I might find one would be gratefully received

Regards,

Sean

 

[midlife]

You need to measure the BCD. Pics ?


http://www.sheldonbrown.com/cribsheet-bcd.html

 

[bassboy64]

Thank you! I will

 

[midlife]

BITD the touring SR crankset was this one....

86mm BCD

 

[bassboy64]

Thanks. I've measured the distance between 2 of the 5 bolts and its 69mm, which according to the SB link you kindly sent is a BCD of 122mm. My smallerst ring is a 40, so looks like its been changed at some point
Anyone know where I can get a 36T?

 

[davidphilips]

If its a square tapper bottom bracket ( more than likely) it may be as cheap and easy to buy a Fsa velo compact chainset/chrankset from ebay they some times go for less than £20 second hand.

You could then of set the cost a bit by selling your old chainset on ebay, good luck.

 

[biggs682]

Sure i have a "motobecane " branded triple crankset in the garage store if it's of interest let me know and i will get some pics @bassboy64

 

[PpPete]

122 BCD rings are somewhat rarer than hen's teeth these days.
Best selection of rings (and replacement chainsets) is probably Spa Cycles.
Bear in mind that the 130mm BCD - which used to be the standard for Shimano and many other copies will not take any less than a 38 teeth ring.
You'll need a 'compact' with a 110 BCD which will go down to 34 teeth,

 

[Ajax Bay]

the front inner chainring is a Sakae 40T ( outer is 52) . I'd like to swop it to a 36 or 34, as the hills are starting to make me blow a bit, but I'm not sure what would fit! It has 5 inner bolt holes and they are 7cm apart,

I have a chainset like the one @midlife offered an image of, which started as a 'touring' 50-40 (in 1981) and I now have a 54-40 (with a 14-28 freewheel on the rear).
The markings on the ring are a little SR inside an ellipse, "SAKAE" and - 50 -.

Checking on Sheldon's
Bicycle Crank/Chainring Bolt Circle Diameter Crib Sheet (which @midlife shared earlier)
Think it very likely that your chainset is "SR (Obsolete)"
NB: SR = Sakae Ringyo Company
Between adjacent holes - 69.4mm
Between non-adjacent holes 112.2mm
BCD=118
min ring=36
I've measured the two distances (on my 50t ring which is not fitted) and that matches (and OP's original measurement of "7mm" matches that too).
To be quite sure the OP needs to measure between adjacent holes and between non-adjacent holes accurately.
As @PpPete says (about rings with a different BCD) very hard to find (I only got the 54t because someone advertised it on another forum as something else and I recognised it). I looked a few years ago for a 38t but found zilch. Real men didn't use anything less than 40t bitd with these sort of cranks, partly, I surmise, because you needed at least a 52t to get a decent high gear (with a 14t sprocket) and the front derailleur would not like a jump of more than 12.
Hope that informs, even if it doesn't help you get a shorter gear. Might be worth asking about chainrings smaller than 40t with this BCD (with this additional knowledge) in the 'Vintage Bikes' forum. The crankset and rings will have resale value. But the idea of putting an FSA Velo on . . .

 

[bassboy64]

Thanks for all your help. Sorry I could not reply earlier...dragged off the pc by the other half.
I'll keep an eye out for a smaller chainring. Best bet, as suggested, looks like a new chainset from Spa

 

[Ajax Bay]

looks like a new chainset from Spa

You need to look / find out what sort of BB you have. Very likely it will be square taper and JIS. You need to measure the length of the spindle which might be OK for the Spa Cycles touring doubles (need 107mm).

If it's the original (mine is: a SAKAE (1.37 x 24) but is complaining of old age even after a thorough service), I would be very tempted to replace with a UN-55.
Assuming this was a genuine sale (in 2013), the 36t BCD 118mm rings do exist:
Bay/SR-Chainring-118-bcd-36-T-NOS