Cylinder Head & Valves

My cylinder head turned out to be a lot of work. First, the original hairpin valve springs had been replaced by more modern double coil springs. Apparently, this was a common modification. Not being able to locate any hairpin springs in a reasonable amount of time and wanting to retain some traces of everyday, practical modifications that owners made, I kept the coil springs. Since these were non-standard, I do not have any specifications for them nor do I know their origin. Table 1 above from the manual shows the specs for the standard hairpin springs.

Valve Guides

I did not need to do it but the manual says that if you need to replace the intake valve guide punch the guide out from the inside (there is a retainer step on the outside); presumably, heating the head will make this easier. For the exhaust valve guide, the manual warns that the end inside the combustion chamber can get deformed making punching from the inside out difficult. The recommended process is to chisel off the retainer step on the outside and then punch it into the combustion chamber. A new intake guide needs to be reamed with a 10mm reamer while the exhaust needs a 11mm reamer. Though I did not need to do it for my coil springs, the original hairpin springs when compressed to 16.5mm, must be able to hold a weight of 21kg to 23kg. If they hold less than 20kg replace the springs. Finally, check the edge of the upper plate where it supports the spring - if heavily grooved, replace it.



One thing to note in the drawing in Table 1 is the oil passage drilled into the inlet valve (B) guide (E). This is an approximately 3mm dia hole that aligns with a corresponding hole in the cylinder head and allows oil to lubricate the inlet valve stem. The head and valve guide did not have the hole drilled (for whatever reason) and so with a 2mm drill bit I drilled down carefully at an angle, making sure my drill bit did not break off. Sure enough it did, but luckily there was enough sticking out for me to extract it and restart. Once I had the 2mm hole, I used a 3mm bit to get it to the right size. A little bit of fiddling with a small file to deburr the intake valve guide and I was done. The photo above shows the hole leading to the inlet valve and the waisted stud that holds the rocker box. The narrow waist of the stud allows oil mist to travel past it to the hole and then into the valve guide. This setup allows intake suction to pull oil from the rocker chamber, along the intake rocker surface, and up into the intake valve guide area. It then blows out to lubricate the exhaust guide. It's a dead loss system. But you won't get any rocker or valve lubrication without it. The rocker boxes rest on the spacers, one of which is shown next to the narrow stud.



Valves

My valves were within the specs shown on the Table. With the head upside down on my bench, I poured some acetone into the combustion chamber with the valves resting on their seats without their springs. I left the acetone for a while to see if there was any leakage. None after a half hour or so which meant that the valve mating surfaces were fine - no need for lapping. If I had to, starting with coarse Clover compound and then finishing with fine would do the trick.
he brass bushes that the rockers run in have a number of oil passage grooves that someone has carved.One thing missing from my engine and the photo below are the caps that fit on to the valve stems on which the rocker tips act. Mine were missing and I could not locate a pair anywhere. I doubt there is going to be serious wear of the valve tips given my usage. If I find some, I will retrofit it.

Rockers
I was running my finger along the rocker shaft (the part that lies in the bush) and felt a small ridge that seems to correspond with the oil groove in the bush. This must have happened as the rocker bushes must have been too tight or the machine not used for a while. According to jerry Kimberlin, that is just the way the rockers wear, common on all older machines. Probably the rocker shafts were oval to some extent too. Jerry' s solution is to put the rockers in his lathe and grind them with the tool post grinder until they are round. That might take more grinding than you have bushing so you have to be really careful how much is taken off. With new bushings it might be possible to skim 0.20 mm and still be able to bore the bushes to fit. But a little too much and both the rockers and the bushes are useless! Filing down the ridges is a no-no. I ran a smooth oilstone around them till I could not feel much of a ridge but stopped fairly quickly as I did not want it to get out of round or remove too much from the rockers. I replaced the cups that the pushrod ballends act on. The tips that act on the valves were in good condition as were the locking threads.

Rocker Bushes

The rocker bushes were a different story - they had clearly seen better days and. They were clearly mismatched and had a number of gashes in the bearing surface. I got a new set from Stucchi. The picture shows the oil grooves and the threaded hole which is used to retain the bottom half to the rocker box. There is an oil groove that intersects this hole with one end of the groove running all the way to the end of the bush and other end of the groove stopping a few mm before the radial groove. They are installed so that the end where the groove extends all the way to the end of the bush is closest to the pushrod tube. There is a bevel at each end of the bearing ID also. This allows the vacuum to suck oil from the pushrod tube into the intake rocker guide. The exhaust rocker guide is lubricated by drip from the intake guide area. If those grooves went clear out to the felt seal and washer, it would break the vacuum effect and result in a poorly lubricated intake rocker. The inlet rocker bush has a hole that aligns with the lubrication hole in the intake valve guide and the hole in the rocker box and the bush obviously need to align.

The rocker bushes are clamped between the halves of the rocker box. The bottom half of the bearing is attached with a bolt, the top half just sits there and is held by the edges of the rocker. This results in no float of the rocker. The diameter of the bearings is supposed to fit the rocker box without any space. If it is all nice and tight, you don't have to worry about any misalignment since any misalignment is taken care of by the ball and socket on the pushrod and the valve adjuster on the rocker arm.

Rocker Boxes

The rocker boxes needed a lot of work. First, I had to remachine the oil seal grooves - these had closed up. The ends of the boxes also had modern oil seals - fine for keeping oil in if in good condition but they were not! So, with my Dremel I carefully opened up the half moon grooves in each half of the boxes to the width of the endplates that I got from Stucchi.

Next, I had to get the felt oil seals from Stucchi - the ATHENA felt kits which are labeled for SuperAlce are too thick and can't be inserted. The ATHENA kits labeled for Sport-14 fit nicely but the kit seems to have only one rocker felt and so you need two of these kits and you cannot use the remaining Sport-14 seals. You can, of course, make your own if you have the right dimensions. I needed new rocker bushes and these again came from Stucchi. The rocker bushes are retained by bolts that thread into them.



Rocker Box Mounts

Once I bolted the boxes together I found that I need three mounts for the rocker box to rest - there was a motley collection of nuts and washers that supported the box in the unrestored bike. Patrick Hayes had his head open at that time and so the dimensions came back for the three rocker box mounts - the inlet having different dimensions from the other two. This larger spacer also has a flat side so it is shaped like a "D". This flat side goes up against the rubber accordion seal at the top of the push rod tube. If you used a fully round spacer, it would crush and distort this seal. The drawing above shows the specs.

The last thing to check was the threads, rocker shafts, rocker adjusters, and rocker tips. These seemed to be in good condition and nothing needed to be done. I bolted the two halves of the rocker box together and then mounted it on the head and that was that!

Broken fins: One of the fins on the head had broken off and I wanted to try my hand at fixing it. I cut out a piece of thin cast iron from some scrap at the local dump and beveled one edge of the broken fin and the other edge of the shaped piece of scrap. I held the piece in place with a magnet tilting it down slightly. The reason for tilting is that as a cast iron weld cools it shrinks and, in this case, would pull the added piece up at an incorrect angle to the rest of the fin. I tack welded the corners, removed the magnet and then filled in the bevel. Luckily, my estimated angle of tilt worked out fine as it came level to the old fin when cool. A run with the grinder over the weld brought it to a smooth finish. Viola!

Now, onto mounting the head, the pushrods and valve timing.