Norton comm 750 1972 valves springs shim or washer?
- Thread starter chiccogarz
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I would have to guess that the factory didn't put those shims in there so the springs might be aftermarket needing those particular shims. You probably don't want to separate them till you know what's up. Don't know where you live but you might be able to get in touch with other Norton enthusiasts in a INOA chapter near you. They may have spring measuring equipment. Here's a list.
http://inoanorton.com/Chapters/
Go over this thread on Combat valves/springs. I just found it.
combat-valve-springs-t10438.html#p116881
http://inoanorton.com/Chapters/
Go over this thread on Combat valves/springs. I just found it.
combat-valve-springs-t10438.html#p116881
rvich
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Before you go out shopping for shims ask yourself if you have faith that the previous builder knew what they were doing. You were smart enough to wonder about the shims, so trust yourself to decide if you need them at all.
When I assembled my head, I followed the procedure in the video for the most part. I checked the assembled height. I then put the bathroom scale on the drill press and used it to measure the pressure at the assembled height. Then I checked to make sure I had enough spring left for the required valve lift. Since it is a stock bike and stock rider I didn't sweat it more than that.
Of course I am more of a beginner than an advanced student, but my advice to myself is not to worry about stuff like whether my valves will hold up at 10K RPM when I didn't address the crank.
Russ
When I assembled my head, I followed the procedure in the video for the most part. I checked the assembled height. I then put the bathroom scale on the drill press and used it to measure the pressure at the assembled height. Then I checked to make sure I had enough spring left for the required valve lift. Since it is a stock bike and stock rider I didn't sweat it more than that.
Of course I am more of a beginner than an advanced student, but my advice to myself is not to worry about stuff like whether my valves will hold up at 10K RPM when I didn't address the crank.
Russ
- Joined
- Mar 2, 2009
- Messages
- 135
All valve springs have a recommended installed spring height to get the correct seat pressure.
If you buy aftermarket valve springs, almost all have recommended installed spring height. And to do this you use shims under the bottom spring seat. Because the valve seat has probbably been ground several times or replaced. The valves may not be the same length as the originals. There are many variables.
To measure spring height I use a small spring that will just fit over the guide, assemble the valve assembly, valve, spring seat, top retainer and collets. Then measure the distance from the spring seat to the bottom of the retainer and adjust with shims.
Later Norton twins came with a insulating shim under the exhaust spring seat. You can get valve spring shims from any auto parts store.
If you buy aftermarket valve springs, almost all have recommended installed spring height. And to do this you use shims under the bottom spring seat. Because the valve seat has probbably been ground several times or replaced. The valves may not be the same length as the originals. There are many variables.
To measure spring height I use a small spring that will just fit over the guide, assemble the valve assembly, valve, spring seat, top retainer and collets. Then measure the distance from the spring seat to the bottom of the retainer and adjust with shims.
Later Norton twins came with a insulating shim under the exhaust spring seat. You can get valve spring shims from any auto parts store.
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