I used one years ago replacing valve stem seals with the head on. It worked but sometimes the valve would open even though the cylinder was pressurized with compressed air. For me, the tool worked better installing the keepers rather than removing them.
I plan to use rope down the cylinder to prevent the valve from dropping.
My main concern is how effective it is in getting the keepers back in and if there is a risk of damage?
I want to take on the task in a 24 valve V6 (Mitsubishi Diamante) where space within the head is very limited and if this tool worked well it would make the whole process much easier
Yeah, it's good for installing keepers. You just put the retainer on, the keepers in above then push on them with the tool. Much faster than using a valve spring compressor type of tool.
For removal of the keepers, I'll use a magnet on top of the valve stem and bang on the retainer with a hammer and copper pipe.
I think the pilot, on the portion of the tool that is black, is spring loaded. As I recall, the keepers are placed around that pilot and the pilot and the keepers retract into the tool's body when you press down on the retainer. A sharp blow on the end of the tool compresses the valve spring and the spring loaded pilot pushes the keepers into place in the retainer. I thought the tool was better at installing than removing.
Flanso is this from personal experience?
Does anyone think that there is a chance of damage to the valve stem and guide from applying sideways force by accident?
I've watched videos online and if this tool works it will make the job a lot easier
Yes, from personal experience on a Ford 427 and 289s. The stems on 4 valve engines are smaller diameter than the engines on which I used this tool so I suppose one could bend a valve stem with an errant hammer blow on the tool. But the tool sits squarely on the retainer and it's a pretty good size target for the hammer. I do not think it probable that you'll bend a stem. Those engines I worked on had very stout dual valve springs. I do not think I could have pushed hard enough to make the tool work unless I used a hammer.
I think you will be pleased with it. Take your time inserting the rope to make sure the valve is well supported near its center when the valve pops open after you strike the tool. I hope you will post about your experience using the tool.