Spring engine shock absorber

Peter Lecompte · Post by **Peter Lecompte** » Thu Jan 19, 2012 9:22 pm

What is the difference between the 2 parts (STD702 - 350cc and STD703 - 500cc) for the engine shock absorber springs used in the heavyweight singles? Are they interchangeable? Thanks Peter

Rob Harknett · Post by **Rob Harknett** » Thu Jan 19, 2012 10:36 pm

Thats 000702 & 000703 for the new parts numbers, both available from JSL 702 is for 350cc 703 for 500cc. That may help get an answer, but I would assume 500cc spring would be a bit stronger. So probaly OK using stronger 703 on a 350 but not 702 on a 500.

wilko · Post by **wilko** » Thu Jan 19, 2012 10:41 pm

Lord knows why they bothered with two different spring ratings?

Rob Harknett · Post by **Rob Harknett** » Thu Jan 19, 2012 10:56 pm

I guess if too weak, engine power could compress the spring enough to allow the cush drive to ride up and jump.

Peter Lecompte · Post by **Peter Lecompte** » Fri Jan 20, 2012 12:00 am

The reason why I asked "what is the difference" is so I can determine which ones I have in my box of bits? They look identical to me, so I probably have one type only. I am putting together a 1949 AJS 18. So it may be important not to fit the one for the 350cc. Thanks Peter

clive · Post by **clive** » Sun Jan 22, 2012 11:18 am

350 and 500 springs were different lengths and so different ratings. If the 350 one is fitted to a 500 then it will compress too quickly on acceleration(!) and tend to jar the drive making it harsh. (it would probably fail earlier too) A practical way to tell the difference is that the 350 one can be fitted relatively easily whilst the 500 requires lots of effort to get thread on the nut engaged. (I usually compress part of the spring using molegrips to help shorten it to prevent the swearing). Do remember to fit the "spacer, collar, for engine sprocket 35-G3-E124" or this method of telling the difference will not work and the dynamo chain will damage the crankcase. Off to the garage later and I will measure the lengths of the spares I have and let you know.

clive · Post by **clive** » Sun Jan 22, 2012 3:44 pm

from my stock 350 were 1 9/16 inches whilst the 500 were 1 3/4 inches

Peter Lecompte · Post by **Peter Lecompte** » Tue Jan 24, 2012 5:30 am

Hi Clive, measured the couple that i have and they are all around the 1 19/16" which indicates that they are for the 350, So it is back to JSL for part 000703. A couple of weeks for the post and then try it out. Thanks for the advice. Cheers Peter

strider · Post by **strider** » Fri Sep 21, 2012 8:11 pm

This seems to answer the question I was going to ask.
Taking the primary drive apart on my '47 G80 I was suprised to see the shock absorber cam standing "point to point" that is, ridden up its cam slopes, and stuck just before going over. Never seen that before. Having got it apart, measured the spring. Just about 1 1/2". A smidge less than the size given above for the 350. So that's one new bit i need.

cf160 · Post by **cf160** » Fri Sep 21, 2012 9:29 pm

Isn't it likely these springs will become permanently compressed after being stuck jammed up as Strider has described? Springs do fatugue and compress : witness
the clutch springs on the AMC and Burman clutches.
After a few years use , they are shorter by 20%.
The only shock absorber spring I have is 1+7/16" in length at the
longest point.Edited by - cf160 on 21 Sep 2012 8:33:14 PM