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Old 08-15-2005, 02:38 PM   #8491
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Originally Posted by Rapid Roy
The only reason I could think of is that there might be issues at your track with chunking tires. Maybe the boards are hard on foams and prople are having to toss tires with good foam left because of damage. I have found that you can run rubber a good deal longer then foam tires as long as the rubber doesn't overheat. Also rubber tires do loose grip as they wear. So you don't really NEED new tires every race unless everybody else is playing the "gotta run new tires in the mains" game. If thats the case, rubber tires are NOT cheaper.
we have some pretty sweet lookin new red and white curbing made of concrete and i suspect these are well aggressive on foam tyres. so your probably right Roy. not had much of a problem myself though, but I tend to not grab to much curb when i apex the corners.

oh yeah, check out our new track dryer
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Old 08-15-2005, 03:38 PM   #8492
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we have some pretty sweet lookin new red and white curbing made of concrete and i suspect these are well aggressive on foam tyres. so your probably right Roy. not had much of a problem myself though, but I tend to not grab to much curb when i apex the corners.

oh yeah, check out our new track dryer

Thats really funny!!

Nice looking track too!!
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Old 08-15-2005, 03:56 PM   #8493
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"oh yeah, check out our new track dryer"

Is that for de-icing planes or what?
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Old 08-15-2005, 05:02 PM   #8494
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a-i: you need to get pro4 rear body mounts!
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Old 08-15-2005, 05:13 PM   #8495
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"oh yeah, check out our new track dryer"

Is that for de-icing planes or what?
I'm not really sure tbh, the airplane guys were just playing around with them outside our track. Think they were setting the green one up to race the yellow one
Its pretty funny havin an rc track on an airfield your standin on the rostrum and the next minute your gettin distracted by a low flying old MIG jet fighter lol
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Old 08-15-2005, 05:34 PM   #8496
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a-i: you need to get pro4 rear body mounts!
Yah, it'll save some weight too.
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Old 08-16-2005, 05:01 AM   #8497
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Default R40 Centax Clutch again

Hi All.
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.

Symptoms.
------------
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.

Questions.
------------
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?
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Old 08-16-2005, 05:30 AM   #8498
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Quote:
Originally Posted by rbridd
I took advantage of the 99UKP offer on the R40 in the UK. It seemed like a good deal at the time.
ditto, I jumped at that deal 2 but its cost me a good 70quid more just to rectify these inherent problems. I still need to throw a little more at it to get it upto pace with the mtx's and serpents at my local track. but I still think its a good car, just a pain to initially setup, if you follow the manual to the last word you wont get anywhere! persistence is the key, you sound like you know what your doing just keep experimenting. it really helps to completely understand how the clutch and 2 speed system works then you can keep improving it.

1, just initially a little less linear in engagement I've found

2, as far as I knew the ID's are the same, the manaul doesnt point this out, unlike the 710 manual.

3, no load should be placed on the flanged bearing, if the shims are forced against the bearing the bell housing will have no end play. the serpent setup is very much like the mugens, shims are placed behind the tb. I wouldnt have thought it matters whether the shims are in front or behind the tb though. you must have at least one to allow for a gap between the flanged bb and tb so they dont bind.

4, stick with the centax cluch, just keep messin with it.

Last edited by Hesky; 08-16-2005 at 06:05 AM.
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Old 08-16-2005, 06:35 AM   #8499
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Quote:
you sound like you know what your doing just keep experimenting.
Thanks.

Quote:
2, as far as I knew the ID's are the same, the manual doesnt point this out, unlike the 710 manual.
I measured them, they are different, Why?

Quote:
3, no load should be placed on the flanged bearing, if the shims are forced against the bearing the bell housing will have no end play. the serpent setup is very much like the mugens, shims are placed behind the tb. I wouldnt have thought it matters whether the shims are in front or behind the tb though. you must have at least one to allow for a gap between the flanged bb and tb so they dont bind.
I have end play of 0.2mm. But when the shoe engages the bell, it pushes it up the shaft, the shoe pushes the endball such that it bears on the flange of the outer bearing. i.e. there is no force supporting the center of the flange bearing. If there is a shim between the thrust bearing and the flange bearing, then the load will be transmitted through the center of the thrust bearing onto the shim, thereby puting an axial load on the flanged bearing. The load will make the bearing bind in and of itself. with no shim in place, the outer bearing housing of the flanged bearing will bear directly on the Thrust bearing inner race resulting in no axial load on the flange bearing. This seems more correct to me.


Quote:
4, stick with the centax cluch, just keep messin with it.
I've spent about 8 hours on it now and I'm losing patience. If I could only see what exactly the problem is, I could devise a strategy. Are you using the Mugen endbell?
I need options. I'm still leading my club championship but each time I fail to win, the gap gets smaller. The serpents get closer

More questions.
5. Will a softer spring give earlier engagement, or more bite?

6. What is the difference in clutch performance between 0.2mm of endbell float and 0.5mm of endbell float?

7. What is the purpose of the shim behind the flywheel? As far as I can see, it just shifts the entire assembly forwards a bit. Ah no. I've just worked that one out. On an SG crank, it would move the flywheel/shoe assemply closer to the bell. but with the convertor part 87093, it makes no difference as the convertor will maintain a constant distance between the flywheel and the end of the shaft.

It sounds like I'm nearly there, but I need to control the initial slip of the clutch to stop the engine revs rising to max straight away.
Should I try more endbell float? but then the shoe will have further to travel, meaning that I must adjust the preload nut to match the extra float... and I'm already at the limit of adjustment!

Still confused.
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Old 08-16-2005, 06:48 AM   #8500
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Not sure the hardness of the mugen gold spring. But if its softer than the stock hpi. Go with that or whatever is of course the softest.

Try to loosen the spring as well as much as possible.

Check the inside of your clutchbell. Is there a perfect circle on the inside, towards the middle. If so this is your flywheel pins. Which are a major problem with the hpi flywheel.

They stick out too far and keep the bell away. I sanded mine down and tapped them inward as far as possible. If you look from the otherside you can normally see that they arent in as far as they should be.

I personally think they are to far out, even tapped in so I sand them down a bit. Just place a piece of hard sandpaper on the ground , turn the flywheel pins down and scrap away. Youll get a nice perfect flat and shorter pin.

Then go from there. I think your engagement might get a bit better after that. Take care. Otherwise the full mugen mtx setup will work. The links were just posted to where you can purchase this a few posts back.

Last edited by Artificial-I; 08-16-2005 at 08:39 AM.
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Old 08-16-2005, 07:06 AM   #8501
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I'd give the mugen setup a go, thats the only setup that worked for me
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Old 08-16-2005, 08:14 AM   #8502
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I used a dremel to sand down the pins, or you can just simply tap them in a bit further. Also the adjuster nut shouldn't be tightened far down. Turn it so you can see about 2 or so threads on the engine shaft. After that it all has to do with your low end settings on the engine. If the engine is running a lil rich and you're having some acceleration problems like what you described, when it doubt lean it out an 8th of a turn or so. Then readjust the clutch. Some blue loctite on the shaft can keep the adjusternut from moving since some people have experienced this.
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Old 08-16-2005, 08:51 AM   #8503
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Quote:
Originally Posted by tranced
a-i: you need to get pro4 rear body mounts!
I need to trim a body for it, all of my bodies were trimmed for a racer2, fits the standard r40 perfect. But I might do it. I have a pro4 so I just need to borrow the mounts.

One thing I like about it though it semi acts as a rear bumper and kinda protects the upper portion of the shocks more.
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Old 08-16-2005, 09:13 AM   #8504
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Quote:
Originally Posted by rbridd
Thanks.


I measured them, they are different, Why?



I have end play of 0.2mm. But when the shoe engages the bell, it pushes it up the shaft, the shoe pushes the endball such that it bears on the flange of the outer bearing. i.e. there is no force supporting the center of the flange bearing. If there is a shim between the thrust bearing and the flange bearing, then the load will be transmitted through the center of the thrust bearing onto the shim, thereby puting an axial load on the flanged bearing. The load will make the bearing bind in and of itself. with no shim in place, the outer bearing housing of the flanged bearing will bear directly on the Thrust bearing inner race resulting in no axial load on the flange bearing. This seems more correct to me.



I've spent about 8 hours on it now and I'm losing patience. If I could only see what exactly the problem is, I could devise a strategy. Are you using the Mugen endbell?
I need options. I'm still leading my club championship but each time I fail to win, the gap gets smaller. The serpents get closer

More questions.
5. Will a softer spring give earlier engagement, or more bite?

6. What is the difference in clutch performance between 0.2mm of endbell float and 0.5mm of endbell float?

7. What is the purpose of the shim behind the flywheel? As far as I can see, it just shifts the entire assembly forwards a bit. Ah no. I've just worked that one out. On an SG crank, it would move the flywheel/shoe assemply closer to the bell. but with the convertor part 87093, it makes no difference as the convertor will maintain a constant distance between the flywheel and the end of the shaft.

It sounds like I'm nearly there, but I need to control the initial slip of the clutch to stop the engine revs rising to max straight away.
Should I try more endbell float? but then the shoe will have further to travel, meaning that I must adjust the preload nut to match the extra float... and I'm already at the limit of adjustment!

Still confused.
It sounds like you understand the basic principle of the clutch. Here is what I did.

Make sure that the pins that locate the clutch shoes are not hitting the inside of the clutch bell. Your clutch bell will have a nice line in it if they are. Next, you want to run as little end play as possible.

You might be setting up the clutch bell to far away from the clutch shoes. If you shim the wrong places you will have too much gap between the clutch bell and clutch shoes. If this happens, you will never be able to get the clutch to engage early enough. What I did was to assemble the clutch weights, shoes and clutch nut on the flywheel. Then I test fit the clutchbell without any bearings or spacers. When I did this, I discovered the pins were keeping the clutch bell from comming into contact with the clutch shoes and I had to do my mod. Once you get good contact between the shoes and bell, you can now see the correct position of the clutch bell to the clutch shoes. You want a very small gap between the shoes and bell. Now take off the clutchbell, install the bearings, and adjust the spacers so you get the gap you want. Now add spacers at the end, just under the screw that holds the whole mess together so the is almost no wiggle (end play).

Once I figured this out, I built both clutches (I have 2 R40's) in 20 minutes and was able to adjust them both easily. The manual tries to give you a cookie cutter or simplified method of setting up the clutch, but I have found too many variables between engine shafts, flywheels, and the various clutch parts to get things to work the way the instructions show. This was not my first experiance with a centax clutch, but I was forced to throughly understand how to properly setup and adjust one to get mine to work. I use completly stock clutch components and haven't had any problems yet. I have bought the grey mugen shoes to try but havent' intsalled it yet.
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Old 08-16-2005, 09:17 AM   #8505
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Quote:
Originally Posted by Artificial-I
I need to trim a body for it, all of my bodies were trimmed for a racer2, fits the standard r40 perfect. But I might do it. I have a pro4 so I just need to borrow the mounts.

One thing I like about it though it semi acts as a rear bumper and kinda protects the upper portion of the shocks more.

Just suck it up and put some new mouting holes in your bodies. Its not nearly as bad as you think it will be. I do understand why you don't do it though. I still run that funky rear mount with me CF rear shock tower. The reason I do it, is that my son's car still has the stock rear tower on it, and I want the bodies to be interchangable.
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