Hi Twiggy, I have found that the way nick sugested to set up a clutch on the sirio pr pro will work very well. Here is my base settings for all 21 engines and then you can change slightly from there for outher engines and track condishions. I run an Evolva and i run 1mm to 1.3mm spring tention on the 4d spring, std unmodified fly weights and fmw 10 gray clutch shoe. I then place the bell on the shaft and shim it so the clutch bell just spins free from the shoe. Then i add 0.5mm worth of shims on top of that to get a Gap of 0.5mm between the clutch shoe and the clutch bell. I then put the bell guide on and thrust bearing and shim it so there is a max end float of 0.2mm and a min of 0.1mm end float for heat expantion. I use to blow thrust bearings like crazy when i set my clutches as the kyosho manual vagely explan's with 0.5mm end float. All your doing by shiming behind the bell is taking the slaping that the trust bearing gets when you set a clutch with big end float. By making reversing that 0.5mm from the thrust bearing side to the clutch shoe/ clutch bell side and 0.1mm end float for heat expantion you taking all the stress off the thrust bearing wile keeping the 0.5mm clutch shoe movement. Once i was showed this by A very good friend all my engines came to life and i have not blown a thrust bearing there after. A centax style clutch is any clutch the same as a mugen mrx 3 4 4r mtx 3 or 4 kyosho 3r all models and kyosho evolva and serpent from 705 up 10th and 8th. They use whats called Fly weights they are the white (on kyosho) nylon bits with holes in them that sit in the flywheel behind the preshure plate. If a clutch has fly weights I class it as a centax style of cluth most use 3 fly weights but mugen and the 4d kyosho optional clutch uses 4 fly weights and a 4 pin flywheel. I hope this helps you I would start at 1mm spring tention depending on what clutch you have and spring you use all the settings above are for an evolva clutch i sugest for a 3r or 3r evo clutch you drop the gap to around 0.3mm and see how that works. I don't run 10th scale so i can not say for shore that that is the best gap size. Also be very cearfull if you run more than 0.5mm gap it sometimes only takes an extra 0.1 or 0.2 mm of gap befor you can edject the fly weights from the clutch. Best Regards Jeremy.