Valve seal replacement

I haven't done it on a Commando and haven't done it using the rope idea. However, I have done it on a Ford crossflow engine in an XR2 using the compressed cylinder method. I used an old spark plug and brazed a tyre valve into the centre of it to use an airline to pressurise the cylinder to hold the valves shut. I squirted a bit of oil into the cylinder first to help it seal. I made myself a device to compress the valve spring. I used a long lever with a pivot that bolted somewhere on top of the engine and had a forked bit that pressed the valve spring down. You may have to give the valve cap a tap to start it off.

It worked fine and I thought it was safer than the rope method as the only thing you put inside the combustion chamber is oil and air. I don't see why it wouldn't work on a Commando.

Ian

I have the PDF of the thread with the pictures included. I have sent a message to you Roger as I thought I needed an email address to send it too but it has attached to this thread so no need to reply.

The rope trick worked well on my Commando engine. You need about 30cm of 10mm thick rope .......although it does not matter too much if it is a little thicker/thinner and longer. As long as it goes through the plug hole.

You need to ensure that the piston is coming up on the compression stroke until about 40mm from the top. Generally this is when you can see the piston top appear. Then start to feed the rope through the plug hole twisting the end as you do this. This helps the rope to coil inside the cavity to spread the load. Don't forget to hang onto the end of the rope or you will have a problem. Wind the piston up more until it stops moving. I usually leave my bike in gear to help stop any chance of the piston going back down.

All should be ready now to get at the valve ends. Getting the top hats/caps off will need a tool of some kind as a normal valve spring compressor is not going to fit. I made mine out of a long metal flat bar with some legs welded in place that would fit over the valve spring cap but not cover the collets. The end was then tucked inside the rocker openings as a fulcrum for this lever. It took me several attempts and adaptations as the rocker arm got in the way to start with.

Be very careful if you are going down this rope trick road as the springs have a lot of energy in them and will cause damage if mis-handled.

Phew! After reading the suggestions above it seems easier to just get on with and take the head off ... or am I missing something?

Previously Phil Hannam wrote:

The rope trick worked well on my Commando engine. You need about 30cm of 10mm thick rope .......although it does not matter too much if it is a little thicker/thinner and longer. As long as it goes through the plug hole.

You need to ensure that the piston is coming up on the compression stroke until about 40mm from the top. Generally this is when you can see the piston top appear. Then start to feed the rope through the plug hole twisting the end as you do this. This helps the rope to coil inside the cavity to spread the load. Don't forget to hang onto the end of the rope or you will have a problem. Wind the piston up more until it stops moving. I usually leave my bike in gear to help stop any chance of the piston going back down.

All should be ready now to get at the valve ends. Getting the top hats/caps off will need a tool of some kind as a normal valve spring compressor is not going to fit. I made mine out of a long metal flat bar with some legs welded in place that would fit over the valve spring cap but not cover the collets. The end was then tucked inside the rocker openings as a fulcrum for this lever. It took me several attempts and adaptations as the rocker arm got in the way to start with.

Be very careful if you are going down this rope trick road as the springs have a lot of energy in them and will cause damage if mis-handled.