Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Centa spline failure

Hello everybody, has anyone experienced the Centa coupling coming loose on the crankshaft? The female splines in the coupling have worn on mine causing a horrible rumbling noise and I have had to re manufacture the thing.

Sorry to hear that Phil.

You've probably had yours off more than others here.

Just a Harley trick that may help you.

After '06 Harley changed their crankshaft to a full length spline on the crank for obvious reasons; read higher hp available. '06 and earlier have the same crank as the S&S Wedge motors used in the M3W's.

On both the old style, '06 pre, and new full spline, after '07 later, it's VERY IMPORTANT to run a tap into the crank on the new style and into the nut on the old style to clean he thread of any Loctite residue.

The Loctite will leave a residue on the threads and the nut on the old style and the bolt on the new style, will not seat all the way and this leaves the assembly a bit un-torqued.

On the Harleys it lets the compensator run a bit loose under the Belleville spring and eventually cause issues.

Likewise if there is a build up of Loctite in the nut and you keep adding Loctite to the male threads on the crank, you will get a false torque reading and turds will soon hit the rotisserie unit...

This may not be your issue, but it's important to always clean the nut threads and crank threads prior to reinstalling the Centa housing assembly.

Is yours bad enough that the crank AND Centa flange has to be replaced?

Hi Dan, thanks for your info. Mine had no loctite at all and a rather poor arrangement of shake proof washer on top of a plain washer but the problem comes from poor fitting of the splines which were fitted to the flanks but neither major nor minor diameters. This is fine if both items are hardened but not so good with the soft Centa hub. My crank shaft survived the mess and I replaced the Centa hub with a harder and tougher unit fitted on flanks and major / minor diameters. All is well now, I am just wondering if this is a common problem.

Your comments on cleaning of the old loctite are good - more people should be aware of this.

Thanks again,
Phil

Phil,

Thanks for the update.

I guess if I were to have anything fail in the coupling of the S&S crank to the Centa hub, having the hub spline go south would be my preference. Sacrificial part so to speak.

As you've asked, is this going to be a common thing? I'm wondering now with your firmer Centa pucks, is this creating the next in line failure, the spline hub adapter?

I do very much like the idea of the firmer pucks. But in the case of the Harley, people have removed their compensator and replace them with solid splined sprockets and the performance is better, but the bikes vibrated terribly. The other case is when they do a belt drive replacing the comp and chain setup. The front crank sprocket is solid, but the rubber belt tends to act as a shock/compensator and the bikes run fairly smooth without a comp.

When I get around to running a Centa, I'm sure I'll be in contact with you about the urethane pucks.

Keep us informed on your further durability testing.

Thanks and have a great day...

Hello again Dan.
I think there is something in the splines being the next weakest link. I am waiting trial some higher temperature resistant inserts. These are also a slightly different shape to reduce an annoying rattle from the gearbox on tickover and I am sure they will be kinder to the splines. My problem now is that my Centa has a good spline set up and so will not fail, making testing impossible from that point of view.
It seems that nothing is easy!

Hi Phil,
We were on a road trip several years ago and had the Centa unit become loose on the crank. It evidenced itself as a barely audible jingling sound while running and making a horrible jangling noise at idle. We finished the trip towing the Morgan to the LA dealer (some 600 miles).
Our Morgan had a Centa up grade while the engine was out for a frame swap. The mechanic in LA said the issue was the the nut which held the coupler to the crank shaft had been improperly torqued. He showed me a large crush washer that was not properly “crushed”. It was a very expensive fix and made question the sanity of extended road trips in the Morgan. I can handle cam belts, fuel pumps, regulators and the occasional broken valve spring but this left us dead in the water, so to speak.

Thanks for the info Rolsmith, sorry to hear that your confidence has been dented.

It is easy to say that torquing the nut up wrongly is the cause, but a well fitted spline should not rely on the securing nut to do any more than prevent longitudinal movement. For example the splines in a gearbox allow the selector dogs to move freely on the splined shafts and they survive well enough.

More thought required here methinks.

Phil

I've not heard of a "crush" sleeve/washer being used in this type of application before.

Yes on a pinion shaft in the differential for preload on the bearing with the appropriate resistance for the nut to stay tight.

In the case of the Centa, and the Harley compensator, having these parts tight to the crank is very important. Even more so on Harley comp as it has all the side load from the primary chain. But in the M3W it's an axial load, not radial.

I know what you're saying Phil about trans gears on shaft that literally just slide on the splines, but with all of the vibration and torque pulses on the V-twin, I'd rather have the flange super tight non the less.

How does your inner housing pilot bearing/bushing attach inside onto the hub? Could this have been part of the problem? I doubt it though as you are a "thinker" at a super level...

Hi Phil and Dan,
I still have the suspect Centa unit on the shelf. I took a hard look at splines on the portion that bolts to the crankshaft and they appear to be uniform (no obvious wear that would indicate rotational wear from rocking side to side due to the nut loosening up. The noise it made at idle was very much like a dry clutch Ducati makes but 4 or 5 times louder. The unit was installed at 7k miles and failed at 12k miles, the replacement is still quiet after an additional 13k miles.
In retrospect, had I known what the repair would cost and the apparent condition of the failed parts, I would have towed it home, pulled the motor, applied liberal amounts of loctite and motored on.
Best,
Roland

my history with Centa is as follows.

First Centa was installed by factory and they missed out tightening the centre nut enough. after 2000 miles the alternator shifted backward and seized with the Centa. Back to new Centa. Second one lasted 3000 miles and male female spline between crank and centa started rumbling horribly. Out it went and when checking crank splines they look ok, but centa splines are shot. Asked factory for advise. Answer was "install a new Centa" . New Centa does not sit tight with crank spline. So no way we will install this Centa as such. Question to factory. did S&S change any specs on crank between 2012 and 2016? No answer. You're out of warranty, you're out of luck