I had to move some stuff around in the garage today so started up The Fire Bike to temporarily move it outside. I had the choke on and noticed smoke coming out of the RH cylinder when I revved it. I had to look twice but, yes, It was definitely coming from the cylinder barrel to head joint. Occasionally I had noticed a black drip from the head gasket onto the leg shield but had thought it was just a little “weep” and it didn’t always seem to do it. Today it was chuffing out of there like a steam engine. Something had to be done! This is where the leak was.
I took the rocker cover off and put a spanner on the three head nuts you can reach while the rocker gear is still fitted. They were loose! I had a choice. I could just remove the rocker gear and re-tighten the nuts to the correct torque or pull the cylinder head off to take a look. I decided that, if the head had been so loose that combustion gasses could get past then the gasket should probably be changed. So, off with its head!
My first concern was whether I would be able to get the exhaust header nut undone. My experience with these had been that some will never stay tight while others will become stuck fast. This one had never loosened by itself so I feared the worst. However, it was OK. It took just one tap on the C-spanner with a soft-faced hammer and we were away.
To remove the exhaust header pipe I loosened the clamp to the silencer and the frame-to-exhaust clamp. I could just get to this with the leg shield in place.
I disconnected the carburettor, complete with manifold, from the cylinder head.
The next job is to remove the oil-feed pipe from the head by undoing the banjo bolt. There is a crush washer on each side of the pipe.
I removed the generator belt cover from the front of the engine (3 screws) and turned the engine with a socket on the crankshaft nut to take the pressure off the rockers. I then removed the rocker gear from its bracket (remove locking bolt and push the spindle out) and put the parts to one side so they can’t get interchanged. The pushrods were then removed and joined the rocker components.
The cylinder head (and cylinder barrel) are held down by nuts on four long and two short studs. The four long ones also hold down the bracket for the rocker gear. The short ones are top and bottom. The bottom one is by the spark plug. To get to the top one you remove a blanking plate in the cylinder head. There’s a crush washer under this.
It hides a sleeve-nut which takes a 10mm Allen key.
The six head securing nuts should be slackened in a diagonal sequence to avoid distortion to components although, in my case, they were already pretty loose. There is a heavy washer under each of the five ordinary nuts and a slightly different one under the sleeve nut.
Once the nuts are removed the bracket for the rocker gear can be lifted off. There are O-rings fitted to the four long studs under the rocker bracket. These were age hardened and have to be replaced anyway. I picked the rings out to make it easier to get the cylinder head free. Only one came off in one piece.
Now it’s time to lift the cylinder head. It didn’t want to move at first but, little by little, I managed to get it loose without resorting to hitting anything with a hammer. Hurt my fingers though.
It was easy to see how the gasket had been leaking and there was signs of pitting to the surface of the gasket but, I might have been able to get away with just tightening everything up. It’s difficult to tell.
I’ll put in an order for parts tomorrow but, I’m not sure whether to change the base gasket and two O-rings below the cylinder barrel while I’m in here. It wouldn’t be hard to lift and replace the barrel. I’ll buy parts for both cylinders though. I might have some of this list in the garage already.
- Head gaskets (2)
- Base gaskets (2)?
- Rocker cover gaskets (2). I like thick ones if I can get them.
- O-rings (12)
- Exhaust gaskets (2)
- Crush washers for under blanking plugs (2)
- Crush washers for oil feed lines (4)
I took a look at the coating on the cylinder bore. It’s still a hard chromed barrel. There are those who say bikes with these should not be run as the chrome will flake off causing all sorts of damage. Instead replacement nikasil coated barrels should be fitted. I do know what happens if it all goes wrong. It happened to the Racing Rhino many years ago. Nikasil cylinder barrels for the old 700s just aren’t made. I could have mine stripped of their chrome and replated but it’s expensive and these seem to still be in very good condition with no thin spots or blisters. I could fit barrels from a 750 but don’t want to do this.
I took a look at the rocker gear on the bench. It’s in very good condition. No wear on the spindles or in the pads that contact the top of the valves. It makes me think that some work has been done here not many miles ago and could be why the head was loose. I didn’t know that it needed to be re-torqued. It could also be that the cylinder barrels aren’t 45-year old originals. Old stock chrome ones still come to light from time to time.
I haven’t examined the valves yet but I’ll have a poke around everything else soon.