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Broken hairpin valve spring



billirwinnz

Well Known and Active Website User
VOC Member
#1
I've just discovered that one leg of an inlet spring on my TTR has broken at the coil and fallen out. It has done less than 500 running-in miles. I bought a set from the club a couple of years ago but have only recently got the bike going. Has anyone else experienced this problem? I'm going to replace the whole set from Neal Videan as I don't want to risk a dropped valve.

Bill IMG_2134 1.JPG IMG_2134 1.JPG
 

A_HRD

Well Known and Active Website User
VOC Member
#2
Eek! That's a good spot Bill before any further damage was done!

As a matter of interest, what is the wire diameter? Originally, TTRs and TTCs had a slightly thicker gauge from the rest because of the inevitable pounding they would get under racing conditions...

Peter B
 

Mike 40M

Well Known and Active Website User
VOC Member
#3
It has not happened to me, but one reason for having hairpin springs in the old days was that you could replace them quicker than filling petrol at the TT. So it must have been quite common.
 

billirwinnz

Well Known and Active Website User
VOC Member
#4
These are standard A springs. 4mm rather than 4.5 from memory. No evidence that my bike ever had the thicker ones. I certainly haven’t raced it yet.
 

mercurycrest

Well Known and Active Website User
VOC Member
#5
Now you're scaring me. I replaced my old springs that would float the valves at 70mph with new VOC ones. They were a right dog to put in because they were so stiff. Can anyone check how much seat pressure the new VOC ones have? I was thinking of using an old one and new one on each valve.
Thanks, John
 

billirwinnz

Well Known and Active Website User
VOC Member
#6
Hi John

Hairpin springs must be matched otherwise the guides wear unevenly and the valve ends up being canted over which eventually causes the valve head to fall off. It will happen quickly on a conventional single guide setup.

I learned this the hard way on a Guzzi single when I reused a pair of springs that were the same height but turned out to have different spring rates.

Bill
 


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