Hi John and Swarfy, (and anyone else who's listening!)
Well between us we've probably got one of everything it sounds like, unfortunately my set is the least compatible it seems. Clearly there are a lot of different parts out there in the mix but I will have to try and make this thing work. I have two basic issues as I see it ( I have other issues but we won't go there)...
1) I only have a maximum of 3.2mm of cush travel. This is probably not enough for a cushy cush although I've not seen any specs or requirements as regards what the max and min travel should be but I am aiming for a minimum of 5mm, lets say 5 - 8mm would be good, anything more than this probably isn't necessary unless you are a very mechanically unsympathetic pilot.
2) I am coil bound on the spring as soon as I tighten the nut in fact I would say, this is the biggest problem as we really need the nut to tighten hard onto the end of the sleeve bearing as has been very well covered already and the cush is therefore solid with no travel available.
Further to the above whatever I do to increase the travel is no good unless the spring is able to freely compress. If not the spring becomes the limitation on travel when the coils bind and this is undesirable for spring life. It also means the spring is working at maximum even excessive preload and I have an idea this also makes the cush less cushy and reduces spring life.
The way I see this I need to tackle both these issues to obtain some cushtyness so I can increase the travel on the sliding sleeve by putting in a spacer between the nut and the sleeve bearing. Without the spring this will allow more travel and increase the space for the spring by the same amount, however, it wont stop the spring binding as soon as the gap between the shoulders gets back to 24.
ie. In my set up a 5mm spacer gives theoretical cush travel of 8.2 (3.2+5) and a spring gap of 29 (24 +5) but the spring will bind again after 5mm travel.
This means I need to find at least another 4mm clearance between the shoulders say to ensure the spring never binds or remove 4mm off the overall height of the spring, or a combination of both.
At this stage I am reviewing my options as follows:
Change the nut, well this was a new one bought to replace the one that came with, which had been ground down by 3mm on the end by the PO. (He was using an incorrect Plunger drive sleeve bearing with a 5mm shoulder which put the sprocket 3mm out of line with the clutch) No John I don't have a 14.3 nut but if I did I would certainly use it! I could buy another nut say the SRM one but this doesn't give me much improvement so I think I will stick with modifying the one I have. I can pinch 1mm safely here I reckon.
The sliding collar is definitely a problem as you point out Swarfy (thanks for all those measurements by the way very useful). If I could pinch a mm out of the collar I would but it is really hard, carbide doesn't touch it and hard to hold to. If I can find a way I will try to grind 2 off the nose and at least 1 off the shoulder but workholding is the challenge.
The sprocket is a new 22 tooth from Feked and seems correct, at least similar to John's examples with a 1.6mm raised shoulder on the rear. I could grind this down but anything removed here puts the sprocket out of line with the clutch again...
So the only other option I'm left with as I see it is to grind the spring down. I bought a new spring as well which has 3 1/4 turns but is poorly made and the ends are nowhere near parrallel Also it is smaller on diameter and doesn't quite fit over my sliding collar. My previous spring is much better quality and although 3 1/2 turns squashes to 24 rather than 26! I intend to 'work' this to reduce its compressed length and reduce the likelyhood of binding up in use. (Grind the end faces down 2mm each end and cut the tails back a little, all to add extra clearance.
Then mostly I am going down the pub!
