Norton CS1 Valve Guide Wear and Modification
Updated: Sep 1
After the valve guides on my 1928 Norton CS1 wore out in only a few thousand miles, I wanted to understand why before simply replacing them. After checking the rocker geometry and considering the effects of the exposed valve gear, I made a simple modification intended to protect the new Norton CS1 valve guides from road dirt and grit. This article explains what I found and how I modified the cylinder head.
Fitting New Valves and Guides
The first job was to get the worn items replaced. This was a job for a specialist so I stripped the bike and passed the head over. When it came back with new valves, guides and recut seats, it was ready for refitting, but I wanted to take my time and search for the cause of the rapid wear.
Valve to Rocker Angles
The first thing I checked was the angle between the rocker arms and the valves. This needs to be as close as possible to 90° when the valve is half open. If this isn't the case, the rocker arm puts a side load on the valve stem causing premature wear of the guides.
On the CS1 the cambox is bolted onto the cylinder head by means of an adaptor plate and spacers. These spacers had been remade by a previous owner and, if they were the wrong height, this could introduce the problem. However, it turns out whoever made them knew what they were doing and these angles were all correct - this clearly wasn't the cause of my rapid wear issues.
Issues Caused by Exposed Valve Gear
Exposed valve gear is inevitably more vulnerable to dust and grit from the surrounding environment, which could contribute to accelerated valve and guide wear. As you can see in this picture, my CS1 is fitted with a very small front mudguard and the front downtube is always covered in road dirt. The top end of the engine also takes a hammering and as it is quite oily, everything sticks! None of this can be helping matters.
Making Valve Guide Seals for the Norton CS1
With this in mind I decided to fit some form of valve guide seal. I don't need, or want, it to be oil tight but if it can help to keep the dirt and grit out it can't do any harm. The following photos show how I did this. I machined the bottom valve spring seat out to take a top hat shaped retainer which clamps a felt seal against the top of the valve guide.
Once assembled the seal and retainer are clamped in place by the valve springs.
There isn't a lot of space between the valve collets and the top of the guide when the valve is at maximum lift. I checked this and had to slim the whole assembly down more than once before the engine could turn freely without hitting the steel retainer.
Once assembled you can hardly see the modifications. My CS1 has been retrofitted with the copper pipes from the cambox to oil the valve guides as is found on the Internationals. This means the modification doesn't interfere with the existing lubrication supply to the valve guides.
Road Testing the Modification
Once reassembled, the bike started second kick but ran very rich. The worn valves and guides were obviously letting in more air than I realised. This led me to find problems with the carburettor which were probably being masked by the air leaks before.
I have now done around 1,000 miles since putting the bike back together, including a week in Wales, and I've experienced no problems with the modification. That's nowhere near enough mileage to know whether it has extended the life of the valve guides, but I'll continue to keep an eye on them as the mileage builds.
What Would You Like to Do Next?
Read more about my 1928 Norton CS1
Read about the AMAL Type 76 Carburettor Fault Finding and Repairs
See how the CS1 performed during a week in Wales
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