Hi,
Pre '68 and '68 on valve springs have different lengths determined by a change in the bottom cup design. What are the differences in the bottom cups?
SRM list the same springs for all years.
Dave.
Whilst all springs can be used for all years. Originally I beleive the wire gauge of the spring changed to one much thicker on the later bikes.
I didn't know the bottom cups were different though.
Hi,
I didn't but there are two part numbers for the springs and the bottom cups. Pre '68 springs are longer but I cannot find images of both cups for comparison.
Dave.
hi dave,
i believe the bottom cups are the same as oif b50 or b25 but the people to ask are autocycle in dudley? who bought old bsa stock.
Hi Eddie,
I think that the B50/25 are the same as the later ones using the shorter springs. The earlier ones must be quite different to accommodate the longer earlier springs.
Dave.
Hi,
An update. Draganfly appear to show the same bottom cups for both part numbers and the later ones are not even in the '69, '71, '72 parts diagrams.
There is no difference in the diameter of the springs just the length so a shorter stiffer spring could be used but why have different bottom spring cups?
Dave.
Hi,
The later cup, part 68-0931 is 1/16" thinner.
Listed for the B44 B50 1968-1973 & A50 A65 1968-1970
OD: 1 11/32" ID: 9/16" Thickness: 1/8"
Best wishes...
Hi Bess,
Thanks for info. 1/16" difference is not a lot when compared to the springs with the outer being 1 3/4" for the later spec. and 2 1/32" for the earlier one.
Dave.
Hi Dave,
The outer spring wire diameter increased around 1966, perhaps spring bind was experienced so in 1968, -1/16" off the cups and change in spring length was a workaround.
Best wishes...
I have had trouble in the past getting some springs to sit in the bottom cups, so it is possible that the two springs also were of slightly different O.D.s
Maybe the bottom cups sold nowadays have a larger ID to cater for this.
Hi,
The spec. in the manual only refers to different lengths but I suspect that some pattern parts are not quite to spec. and use a heavier gauge wire or don't coil then quite right. I find that SRM ones fit so have ordered some from them.
Dave.
i have a set of replacement valve springs [hepolite ] and the wire diameter is thicker. increasing the bottom cup diameter would make sense as less chance of coil bound at high speed and spring breakage.
Hi,
I am not sure if the Hepolite name is the trusted one of years ago but rather a marketing tool. If Hepolite make bottom spring cups are they made to accommodate their springs and would the extra space be a problem if springs of the correct size were used. Could they move around a bit?
What ever happened to Terry's?
Dave.
The ones SRM used to sell did fit. Red paint for their race springs and green for std. I think they are using hep-o-shite now as they don't fit.
Hi,
I have just emailed SRM with a direct question re the valve springs they supply and if they fit the standard bottom cups.
Dave.
i recently bought some hepolite valve springs. they did fit the cups but the coils diameter is thicker. the problem with that is there is a chance of coil bound at high speed. a clearance check is in order when assembled.
The ones I bought last year don't fit very well at all. Ones I've bought historically have been fine.
Hi,
My springs have just arrived and they fit nicely in the bottom cups.
The springs lengths are roughly to the pre '68 spec but with 5 coils of approx. 3.75mm wire and 2.75 wire respectively.
Dave.
Quote from: DAVE BRADY on 20 Nov, 2023, 12:24
Hi,
My springs have just arrived and they fit nicely in the bottom cups.
The springs lengths are roughly to the pre '68 spec but with 5 coils of approx. 3.75mm wire and 2.75 wire respectively.
Dave.
do these have the green (or green and white, can't remember which) paint on them Dave?
Hi Allan,
No paint a tall. The last set did have green. These new ones are pretty much the same the earlier spec.
Dave.
Hi,
Having had a reply from SRM, I am re-assured that the springs are of top quality and the same as are used in staff bikes and SRM engine rebuilds.
I will be fitting them after the head has been in the dishwasher for a final clean and when my nasal cavity and sinuses stop over producing virus packed mucus.
Dave.