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Aug 24th, 2023
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Joined: Jul 2011
Posts: 836
Talk Morgan Regular
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Talk Morgan Regular
Joined: Jul 2011
Posts: 836 |
as soon as I saw the shot, I thought about a rubber mallet as well, scrolled down and found comments thinking the same...heck, I could design this...
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Joined: Sep 2016
Posts: 996 Likes: 23
Talk Morgan Regular
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Talk Morgan Regular
Joined: Sep 2016
Posts: 996 Likes: 23 |
as soon as I saw the shot, I thought about a rubber mallet as well, scrolled down and found comments thinking the same...heck, I could design this... I've seen literally hundreds of this type of coupling. Some have individual "buffers", like the M3W type, and others have a type of "spider" arrangement where the resilient elements are joined together. They're a perfectly good device and generally give good service. Unfortunately the one in the M3W is inadequate. It would be interesting if someone could advise the overall dimensions and we could then see if alternative resilient couplings are available. This is surely better than retaining the current setup which is patently not up to the job and is also a PIA to change. It may be that the current coupling is the only one that MMC could find that fitted, although I doubt it.
Last edited by mph; 01/08/17 10:11 PM.
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Joined: Apr 2013
Posts: 1,363 Likes: 11
Has a lot to Say!
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Has a lot to Say!
Joined: Apr 2013
Posts: 1,363 Likes: 11 |
Have watched this thread with trepidation. My Centa unit installed 16,550 miles ago has failed. I am getting a horrible metal to metal knocking from it which tells me that the neoprene barrels have given up the ghost. This happened quite quickly from being well behaved to totally obnoxious, as in one day.
I have gotten the ball rolling with my dealer but parts will have to be ordered and time scheduled.
This could eat up the rest of summer!
What's your mileage? Who cares. Is it practical? See #1. What happens when it rains? You get wet.
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Joined: Oct 2012
Posts: 2,776 Likes: 59
Talk Morgan Expert
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Talk Morgan Expert
Joined: Oct 2012
Posts: 2,776 Likes: 59 |
I'll take a guess that losing one barrel is barely noticeable, losing two gives a bit of slop but probably isn't that bad (especially if like mine a chunk of it wedges in the gap between the outer and inner parts of the Centa) but when the third barrel goes it will all get messy and the fourth one won't stand a chance with lots of slop until the debris wedges in the corners to transmit some drive.
The rubber barrels are at least cheap, it's the hours of work to get at them that is the problem. Best of luck with it.
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Joined: Jan 2014
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Has a lot to Say!
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Has a lot to Say!
Joined: Jan 2014
Posts: 1,075 |
I thought the new Centa was metal safe. In that if there were no rubber rods, the inner and outer halves could rotate around each other without any metal hitting.
If that's the case, if the rubber rods are being digested by the Centa, you should have no clanking or metal noise. In the case of the old Harley compensator going bad, it was ALL metal to metal, as that was the design with steel ramps etc.
Also if you lose one rubber rod completely, it has to throw the driveline out of balance. The more you lose the worse the vibration should be. Maybe there's just so much weight flinging around that the light weight of the rubber rods does not add up to much of a vibration. But when you consider when they balance the rotor on the motor, they drill very small holes in it, maybe only 1mm deep, you would guess that a rubber rod would be a significant balance issue.
I wish you all good luck with your Centas.
Dan
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Joined: Oct 2012
Posts: 2,776 Likes: 59
Talk Morgan Expert
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Talk Morgan Expert
Joined: Oct 2012
Posts: 2,776 Likes: 59 |
You're right Dan, with the rubbers removed the inner part spins without touching the outer. I'd suspect that the out of balance effects cause the "metallic sounds" rather than metal actually hitting metal. As far as I could see the two failed rollers in mine were opposite each other which may well have kept things balanced; if they'd been side by side it could have been a different story.
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Joined: Apr 2008
Posts: 11,854 Likes: 137
Scruffy Oik Member of the Inner Circle
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Scruffy Oik Member of the Inner Circle
Joined: Apr 2008
Posts: 11,854 Likes: 137 |
You're right Dan, with the rubbers removed the inner part spins without touching the outer. I'm about as far from a materials engineer as it's possible to get, but wouldn't this arrangement mean that the Centa drive rubbers are constantly suffering from shear forces? No wonder they break up. I wonder why they didn't use a simple cush-drive arrangement of interleaving plates separated by rubber blocks, like in the final drive sprocket of motorcycles? Then the blocks would only be exposed to compressive forces and would presumably last a lot longer (I've never heard of a cush drive wearing out in a few thousand miles). There must be a reason, maybe they couldn't find one of small enough diameter.
Tim H.
1986 4/4 VVTi Sport, 2002 LR Defender, 2022 Mini Cooper SE
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Joined: Jan 2014
Posts: 1,075
Has a lot to Say!
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Has a lot to Say!
Joined: Jan 2014
Posts: 1,075 |
You're right Dan, with the rubbers removed the inner part spins without touching the outer. I'm about as far from a materials engineer as it's possible to get, but wouldn't this arrangement mean that the Centa drive rubbers are constantly suffering from shear forces? No wonder they break up. I wonder why they didn't use a simple cush-drive arrangement of interleaving plates separated by rubber blocks, like in the final drive sprocket of motorcycles? Then the blocks would only be exposed to compressive forces and would presumably last a lot longer (I've never heard of a cush drive wearing out in a few thousand miles). There must be a reason, maybe they couldn't find one of small enough diameter. Tim, The design of the pockets in each half allow a tapered squeezing effect on the rubber rods. So they're not really in a shear as we would think. A true shear would be slots in the inner and outer housings with rubber flat pads inserted, kind of like a vane compressor. This would be a true shear. At some point though, as you've said, the pinch points would begin together at the far end of each windup and fatigue the rubber rods.  I posted this in another thread about drilling the compensator to grease it. Something like this could be adapted quite easily. The axial mounting could bolt to a splined plate that attaches to the S&S rotor and the radial mounting could bolt to an extension of the flywheel mounting shaft in the adapter plate for the trans. The LF22 is actually a four bolt, not three. They don't have a picture of the LF22 though. The LF22 would have enough MAX torque to cover even the 128" high output motors and it will allow up to 7.5 degrees of windup at max torque in both directions. At max torque it is rated at 553.3 lb/ft. It's also rated at 6000 rpms. So it has some safety factor built into it I'm sure. It only weighs 1.4 lb. This type of coupling is always under pressure as it gets a slight preload when being bolted into place. So there would be no loose spots and it would probably offer more dampening than what Phil ended up with his elliptical urethane inserts. The model I have shown is for studs on the radial mounting, but they make it with counterbores for the bolts as well. Again, just food for thought.
Dan
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Joined: Feb 2014
Posts: 368 Likes: 1
Learner Plates Off!
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Learner Plates Off!
Joined: Feb 2014
Posts: 368 Likes: 1 |
I had a Centa unit go into the "horrible clanking" mode. It turned out that the nut which held the outer housing to the crankshaft had loosened. It sounded ok while under power but at idle, it was like a Ducati dry clutch on steroids. Fortunately, the crank splines are much harder then the Centa housing and a new, properly torqued, Centa unit cured the problem. It was painfully expensive as we were on the road at the time and had to resort to Uhaul rental to get the rig to the nearest dealer. I have the old Centa unit on the work bench with about 6,000 miles on it, the rubber rods look pristine. My present Centa has about 11,000 miles on it and I'm keeping my fingers crossed.
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Joined: Jun 2016
Posts: 430
Learner Plates Off!
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Learner Plates Off!
Joined: Jun 2016
Posts: 430 |
You're right Dan, with the rubbers removed the inner part spins without touching the outer. I'm about as far from a materials engineer as it's possible to get, but wouldn't this arrangement mean that the Centa drive rubbers are constantly suffering from shear forces? No wonder they break up. I wonder why they didn't use a simple cush-drive arrangement of interleaving plates separated by rubber blocks, like in the final drive sprocket of motorcycles? Then the blocks would only be exposed to compressive forces and would presumably last a lot longer (I've never heard of a cush drive wearing out in a few thousand miles). There must be a reason, maybe they couldn't find one of small enough diameter. Tim, The design of the pockets in each half allow a tapered squeezing effect on the rubber rods. So they're not really in a shear as we would think. A true shear would be slots in the inner and outer housings with rubber flat pads inserted, kind of like a vane compressor. This would be a true shear. At some point though, as you've said, the pinch points would begin together at the far end of each windup and fatigue the rubber rods. I posted this in another thread about drilling the compensator to grease it. Something like this could be adapted quite easily. The axial mounting could bolt to a splined plate that attaches to the S&S rotor and the radial mounting could bolt to an extension of the flywheel mounting shaft in the adapter plate for the trans. The LF22 is actually a four bolt, not three. They don't have a picture of the LF22 though. The LF22 would have enough MAX torque to cover even the 128" high output motors and it will allow up to 7.5 degrees of windup at max torque in both directions. At max torque it is rated at 553.3 lb/ft. It's also rated at 6000 rpms. So it has some safety factor built into it I'm sure. It only weighs 1.4 lb. This type of coupling is always under pressure as it gets a slight preload when being bolted into place. So there would be no loose spots and it would probably offer more dampening than what Phil ended up with his elliptical urethane inserts. The model I have shown is for studs on the radial mounting, but they make it with counterbores for the bolts as well. Again, just food for thought. Good thought! This looks a lot like the rotoflex coupler, used on the rear axle half-shafts of the Triumph GT6 and Lotus Elan. They have their problems, mostly with age, and can be dramatic if they fail at speed in that application. I think they were used as a "cheap" way to accommodate universal joint action along with lateral axle movement due to suspension geometry challenges. The torsional "wind-up" affect of them was always a problem with the minor but noticable induced driveline snatch.
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