This seems to be the most populated and active R40 forum on the planet, so I'll post here.
I am relatively new to Nitro. I started racing an RS4 in February this year. Figuring I'd need to get a car more suited to racing sooner rather than later, I took advantage of the 99UKP offer on the R40 in the UK. It seemed like a good deal at the time.
I have fitted the HPI Nitrostar RXS motor an the HPI tuned aluminium pipe (A940), which I had successfully been running in the RS4.
As with so many other people, I have had problems with the R40 centax clutch.
The instructions are vague and in places misleading, or just wrong.
I have read all the responses in this thread and others and tried to apply what I have learned, but am still not able to get the clutch operating to my satisfaction.
1) When the car is first placed on the track, you need to rev the engine at full throttle for circa 3 seconds before the clutch engages and the car slowly creeps off the line.
2) Once going, the car goes quite rapidly, but when you open the throttle, the engine almost immediately reaches peak revs, then the clutch slowly engages, (Slipping i'm guessing) and the car speeds up. It sort of works acceptably, but drinks fuel so fast, that I can't finish a 5 minute race. Is this normal behaviour for a Centax? I have no reference point as everyone else at my track uses a traditional centrifugal clutch.
3) Last weekend I had some problems with the engine bogging down through the infield. This disapeared when I richened the main High Speed Needle. The interesting thing though, is that as the engine bogged down, i.e. lost power and revs, the centax appeared to be engaging properly. i.e. you could hear the revs match the car, then build as the car accelerated down the straight.
What I have tried.
The Centax is set up as far as possible to the instructions in the R40 manual.
There is a shim behind the flywheel collet, I have a matched flywheel and collet.
I have a standard shaft engine so am using part 87093.
I assembled and set up the clutch using the measurements as on page 37 of the R40 Manual.
i.e. a clutchbell float of between 0.2 and 0.5 mm, (actually 0.5);and the preload spring adjustor nut screwed down so that circa 0.5 to 0.8 mm of thread was showing.
With these settings the clutch failed to engage at all.
I reduced the clutchbell float to 0.2mm, and screwed out the preload nut til it wouldn't adjust any more, and achieved the barely acceptable results documented above.
Having read about the advantages of the Mugen parts, I swapped to a Mugen MTX-3 Gold Clutch Spring, Hard (MUGH0764), and a Mugen MTX-3 Gray Clutch Shoe (MUGH0765).
These seem to have made a marginal improvement in the speed at which the clutch builds up speed. i.e. it has improved the slip and therefore the acceleration a little bit.
I also have the Mugen red shoe, but haven't tried that yet as it seems I have a deeper problem to solve first.
1) Is this normal? Should a Centax clutch feel different to a traditional non-axial clutch?
2) There has been mention on other forums, of the difference in internal diameter of the two outer races of the thrust bearing, one being 4.0mm and the other being 4.2mm, with the slightly greater internal diameter having to face towards the engine. Why is this? What difference will it make?
I have measured the difference and ensured it is the right way round, but cannot see why it should matter.
3) The R40 Manual
shows the shims Z825 and Z695, fitted between the thrust bearing and the flanged clutchbell bearing. This seems counterproductive to me, because wheen the clutch engages, the bell is forced along the shaft against the thrust bearing. Won't there be an axial load placed on the center of the flanged bearing by the shims? If the flange bearing bore directly on the thrust bearing, (As in for instance the serpent design), then the load would be spread across the whole flange bearing and transfered correctly to the thrust bearing. Is the HPI Manual wrong? Should the shims go on the outside of the thrust bearing?
4) If I decide that the Centax is more trouble than it is worth, is there a traditional clutch option I can pursue? Will the 2 speed clutch from my RS4 fit (Part no 86038). I understand I'd have to use RS4 pinions, as the R40 1st and second gear pinions have different internal diameters. The pinion pitch looks similar, but HPI list different part numbers for the pinions, even though the first gear pinions have the same internal diameter and number of teeth.
I'm confused. Are there any other non-centax clutches that would fit? Serpent? Kyosho?