RXS100 suddenly afflicted with bizarre engine woes

[27cows]

OK, virtually every part of my old girl has done ridiculously high mileage. Yes, everything is bodged. Yes, my motor is a collection of less than perfect bits and bobbles. But normally she'll soldier on reliably no matter what.

I had a ring go on me for the first time ever on this bike a couple of weeks ago. Top end had done a ludicrously high mileage so it was to be expected. But coming home I suddenly had horrific metallic noises coming out of the bottom end. Seemed too loud for it to be the missing ring peg I discovered when giving top end a look over. No sign of shrapnel damage in the combustion chamber. Bottom ring had cracked but no pieces were missing. Replaced top end with slightly less worn out one. No further horrific noises...but something had made that racket.

Shortly after I had a clutch issue. With lever pulled in, bike started creeping forward. Couldn't be adjusted to behave. Whipped cover off - no sign of damage. But tightening up the clutch centre nut, the centre itself seems extremely reluctant to turn freely. Double checked that I hadn't missed something. Still the same. Tried a different centre and this one was OK. Clutch worked as normal...only now I had another bloody noise - an odd rhythmic sound. Not metallic. Kind of dull throb/knock/heavy tapping. Not what you'd get from big end, for example.

Now I've acquired an quite unpleasant rumble. Checked mains - fine. Which is to say, no movement at flywheel. I thought I knew these motors like the back of my hand but clearly not.

Performance is about the same as ever. A fair way from what you get with a sweet RXS motor, but still able to do 65 without any great trouble. Only now I'm getting duh-duh-duh-duh....horrible rumble FFS, am I going to have to gather assorted bits and make a bottom end to replace this one? Am I missing something stupidly obvious? Is the motor conspiring with the buggered frame to tell me that the party is finally over after 23 years?
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The RXS100: vehicle of choice for Chuck Norris

[SQL]

[27cows]

[cb1rocket]

Check piston/small end area? Top end bearing buggered?
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Honda H100S2 Rebuild - https://www.bikechatforums.com/viewtopic.php?t=253852

[cb1rocket]

Cows, are you still running on the same barrel just out of curiosity?
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Honda H100S2 Rebuild - https://www.bikechatforums.com/viewtopic.php?t=253852

[27cows]

Small end is fine. Never had one fail on the RXS but I do occasionally put a new one in - current one has done a couple of thousand miles at the most.

Noise is definitely coming from the bottom end, clutch side. Rumble could be a dodgy bearing, even without significant up and down play. But that doesn't explain the duh-duh-duh knock that appears to be coming from the clutch. These motors are normally entirely predictable.

Using a different barrel. This one has done about 25,000 miles and is standard, with original ART piston. No excessive wear.
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The RXS100: vehicle of choice for Chuck Norris

[stinkwheel]

I'd suggest taking the clutch cover off and having a look.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[27cows]

I have. Basket seems fine. Centre also seemed fine - but I swapped it for another anyway. Also swapped the centre spacer and both thrust washers, again to be on the safe side. I have a sneaking suspicious something has happened to the main bearing on that side. Gonna have to knock up another bottom and pull this one to bits. Would be nice to know what has caused the oddness though - it's not something I've ever experienced on any bike that I can remember.
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The RXS100: vehicle of choice for Chuck Norris

[bladerunner]

Aye maybe primary side mains on the way out....I can't remember if the rxs had a balancer shaft like the lc but might be worth a look. Also....has it done the other trick of breaking the clutch pushrods? I'm guessing yours gets an easy time as the motor in my lc has eaten 3 of them in the last 20k miles!
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[27cows]

No balancer in the RXS. Never broken a clutch pushrod either. In fact it's possible I'm still using the original after 417,000 miles - I certainly have never bought a new one.

I guess my old relic does have a relatively easy life. I try not to abuse the motor (not always easy on a bike that slow ). I ride with the long life of the engine components in mind.

I've had assorted LCs over the years - the opposite of the RXS really. But immensely good fun. Especially the 350.

The more I think about it, the more I think it's right side mains gone. Trouble is, these motors are so tough and reliable that you sometimes forget that bits do eventually wear out. Having said that, the original mains went to over 300,000 miles and were still fine when I replaced them while doing a rebuild to put a new crank in.
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The RXS100: vehicle of choice for Chuck Norris

[bladerunner]

Only way to tell I guess is strip it down first! I'd have thought if its gone bad enough to give clutch adjustment issues it must be BAD! Hence my question about the pushrod ....I've also had the ball bearing split on the pushrod giving similar adjustment problems with nasty sounds!
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[UnspeedySam]

Get well soon 27cows' RXS! Does definitely sound like the symptoms of a dying bearing. They do seem to go in odd ways sometimes...
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Riding: BMW R1150RT `02 bought mildly crashed
Fixing: Also the BMW as I get less broken bits
Gone: ZZR600 '00, TRX850 '97, RXS100 '93, JS125-6B '07, BMW R1100RS '93, Kawasaki ZX-6R-J2 '01, Honda Bros NT400 NC25 '88

[27cows]

It's not one of the mains but the one behind the clutch. Hence the symptoms not being in line with those of failing main bearings. That bearing is part of the original motor and has done approximately 385,000 miles. Which I have to say is a pretty reasonable life The clutch had been able to move up and down about 2mm, which I guess caused both the rhythmic thump and horrible rumble.

Have replaced all the bearings except the mains with ones out of an old pair of crankcases that have been sitting on the shelf for years. Got this paranoid feeling I've put the gearbox together wrong But I think it's impossible to close the cases if that's actually the case. At least, I hope so

Will hopefully get the motor back in over Easter. Having to use the fat Bandit as commuter/runabout. It's bloody useless through heavy traffic. Hoping to have the DT125R sorted soon too and that can be commuter back up to the RXS, assuming the latter runs well enough to go back into service.
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The RXS100: vehicle of choice for Chuck Norris

[UnspeedySam]

[27cows]

[Ariel Badger]

Gearbox main-shaft bearings or clutch bearing.
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