Cylinder head

Cylinder head:

Right, there are 4 valves, each valve goes in and out through a guide and is controlled by springs. The valves and guides wear and the springs get "tired" so we need to take this lot apart and replace anything worn. I acquired this bike in parts and judging by the state of the rest of it I expect to have to replace everything.

First you need to use a valve spring compressor to push the springs down allowing you to release the little half moon shaped collets that hold the top cover to the valve:
The threaded bit of the compressor goes up against the face of the valve and the other end is shaped to sit over the top of the valve. In this shot you can see the collets coming loose from the top of the valve stem,, You dont have to compress the springs much, use a magnet to catch the collets:



You can then pull off the springs and retaining caps and push the valves out. Put each set of valves and springs etc in seperate, labelled bags so you can put them back in the same place if required. I measured the springs and they are a millimetre outside of service limits, they are too short. In other words they have taken a "set" and are not as "springy" as they should be. The valves themselves look OK but with a lot of carbon on the back of the inlet valves suggesting worn guides.

Here is the head with no springs or valves but with the guides still in. The guides are a tight press fit in the head and therefore need a blend of science and violence to get them out. On the left you can see the special drift that is used to get them out:  (the funny lookin tool next to the drift is for putting guides in, ignore it)
First heat the cylinder head with a blowtorch to around 100 deg C. This will take several minutes and it will become too hot to handle. Wear gloves, turn the head upside down and insert the drift. You will need to put the head on a couple of bits of wood to raise it off the bench. If not you will be trying to hammer the guides into the bench... in this shot I have already got one guide out and it is lying on the bench. Keep the head secure and whack the drift quite hard. I used a 2lb club hammer, it seems quite brutal but 2-3 blows and it should come out. You may need to re-heat after getting two out.
Here's the head with all valves and guides out. You can now really clean it up. A previous owner has made an attempt at cleaning  and has scratched the mating surface a bit, im hoping it will still be usable.

24 May 2009
Here is the head back from vapour blasting at Tim Walker Restorations near Aylesbury:


The new valve guides are visible bottom left.

This is the tool for inserting the new valve guides:


Put the end that looks like a Trebor Swizzle up against the valve seat, the rod goes up through the valve guide hole and the new guide:

Put the new guide over the rod and slide it into position, one or two spacers depending on whether its inlet or exhaust slide over the rod, a nut is then tightened down pushing the new guide into place. Easy.

Like this:

Grinding in the valves, you put a smear of fine grinding paste on the back of each valve and spin it round back and forth with the stick with a sucker thingy on it. This removes any bumps and pits and makes the valves seal properly, once you have an even light grey band around valve and seat, clean it up but dont mix the valves up.


The lower valve seat in the next shot shows the effect you are looking for:

Ready to fit valves and springs:

Valve with inner and outer springs, bottom cup, top collar and split collets:

The bottom cup goes in first:


Followed by springs and top collar:


Use the valve spring compressor to squash them down:

Then put the split collets in place, a small screwdriver is useful for this:


Release the spring compressor, job done, only 3 more to do....


1st Aug 2009, made a shopping list the few bits I need to get the head finished, top and bottom collars and collets for one valve, two inner studs.

15th Aug 2009:
Here is the completed rebuilt cylinder head: