When I want to hold a valve in place whilst removing the spring I use compressed air through the plug hole. Now I can see how a piece of rope might perform the same task but how does it allow you to remove the valve so you can ream/clean the guide and then re-install that valve?
That may or may not work with compressed air, depending on how much pressure you need to hold the valve and how leaky your rings are. The rope is much easier, you just fill the chamber with it (good sailing rope) and then turn the prop to push the piston and compress the rope. Once you have removed the wedges that hold the valve stem, you turn back the prop and pull out the rope. Then you let the valve fall into the cylinder and do your cleaning job. The tricky part is to get back the valve. You do this by fabricating some kind of holder that you insert through the lower spark plug whole while watching through the upper hole. Then you insert a magnet through the valve guide, position the valve stem, catch it with the magnet and then use your holder to align the valve horizontally so it slides back in through the valve guide by gently pulling back the magnet. Finally you put back in the rope, compress it with the propeller to hold the valve and install the springs.
That’s what’s called the “rope trick”.
I thought the purpose of the rope was to fill the cylinder chamber, to allow the valve to be pushed almost all the way out of its guide, have the guide cleaned, and then push the valve back in.
Once the valve drops out of the guide completely, you will have “some fun” getting it back in, surely?
thought the purpose of the rope was to fill the cylinder chamber, to allow the valve to be pushed almost all the way out of its guide, have the guide cleaned, and then push the valve back in.
No, you have to entirely remove the valve and let it fall into the cylinder. The crud is right at the entry of the valve guide as seen from inside the cylinder). You can see that on my pics.
Once the valve drops out of the guide completely, you will have “some fun” getting it back in, surely?
That’s indeed the most difficult part and I was in awe of it. However, it was easier than I thought, the first time it took me about 3 minutes, now less than a minute. It’s very much doable. You need a good magnet that fits through the valve guide.
I’ve never done it, nor ever seen it done, nor ever needed it done 
but I’m led to believe (matching what Achimha says) that you might use one of these to hold the valve stem through the spark plug hole. Then you pull it into place with a similar tool having a magnet on the end, inserted down the valve guide.
Or maybe instead of the mechanical ‘grabber’ use only a piece of wire bent into a hook at the end… (?)
I think this video shows the rope trick being used on car engine. Move to 5:00 to see him using the rope.
Car engines are so much harder to work on I stopped when I sold my 1982 Mercedes-Benz 190D. Only one spark plug hole in car gasoline engines and much more difficult to access. Nothing beats an air-cooled boxer when it comes to maintainability and accessibility.
Thanks, it was much as I imagined in that getting the valve back into the guide would be the tricky part.
I’ve been fixing cars for 35 years and have never heard of that trick!
A 1982 190D was a great car, especially if it was a 2.5.
A 1982 190D was a great car, especially if it was a 2.5.
No, it was a plain 2 liter with 72hp. After years of being overtaken by trucks on highways and the humiliation that came with it, I exchanged it for an Audi A8 4.2l quattro. That did solve the problem but it was no longer a car I could do interesting work on Now my mechanical ambition has entirely shifted to my low tech Cessna…
Reinstalling the valve in the guide is not as difficult as it would seem, I’ve done it a number of times on my O-200. You have the two spark plug holes to work through, but much more useful is the exhaust port, when the exhaust is removed. It’s quite easy to get the valve under control and into the guide with that access.
