What are the warning signs that the main bearings may be on their way out?

SteveA

SteveA

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I have never had main bearing failure. I don't ever want to have it happen.

Most decisions to replace are based on inspection, but what warning signs have people had that suggest you should strip and inspect?
 
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Why we call it "inspection"...(2018)

'74 Roadster, 43,000 miles (of which, the last 31,000 were well cared, not abused, and there is no reason to think the first 12,000 were different). No unusual noise whatsoever, and I listened. Timing side main has failed.
www.accessnorton.com www.accessnorton.com
 
Mine was on the driveside. Made a zzzzzzz noise which changed pitch with revs. Inner race looked like a moonscape.
Russ
 
I have rebuilt a few Norton motors over the last 30 years some with little use and a few with major miles on them, I always replace the main bearing but some bearings I have pull have had no signs of wear at all, the super blend bearings seem to get long life, but there are bearing manufactures all over the world and each country has its standards, I think original main bearing, well in my 850 were made in Germany and when I built my motor for the Featherbed frame back in the early 80s the main bearings were still good, but they were replaced anyway, I still have those old bearing and thinking about reusing them in my project bike, it all depends on how the bike was treated, did it get serviced regularly or was it used as a trasher bike or missed used and if rebuilt at some stage did it get good quality bearings fitted.
As others have said they normally give sign there is something not right and if any major metal in your oil change is a good sign a bearing is failing or a clunking sound if they are really bad.

Ashley
 
concours said:
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Why we call it "inspection"...(2018)

'74 Roadster, 43,000 miles (of which, the last 31,000 were well cared, not abused, and there is no reason to think the first 12,000 were different). No unusual noise whatsoever, and I listened. Timing side main has failed.
www.accessnorton.com www.accessnorton.com
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Yes, I figured that was one.

There was a new whine I heard over the weekend that seemed to come from aaround the clutch area, and a bit of vibration that came on at around 6000 that went away over 7000.

These bearings have been in since I first built it in 2014, so I am going to change them anyway. They did look fine last year, but I have from now until next season and a set of bearing is a lot less than a catastrophic failure.

I am a deaf as a post, 70% hearing loss, so it's amazing if I hear anything, the whine might be quite loud!
 
A mechanic's stethoscope might indicate a warning, I've never used one but know they exist.
 
Fast Eddie said:
Quite! It takes a few goes to learn the normal from the abnormal doesn’t it?

A loong screwdriver is also good for this.
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Loudest on the cylinder, I suspect a failed rod bearing. I'll let you know how it inspects. Sounds telegraph & amplify in many different ways based on the mass/design/materials of the structure transmitting it.
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What are the warning signs that the main bearings may be on their way out?
 
I would not use a stethoscope on my Norton. It would rupture my eardrums.

This thread has been educational and scary enough without using a stethoscope.

My motor has been whining off and on for a while at idle when hot. And like SteveA it sounds like it is coming from the clutch. However pulling in the clutch lever does not change the whine, so I doubt it is the clutch. Has also developed a vibration at around 70mph in 4th. Smooth above and below that speed. I did push it a few times like a teenager. And like people say it was running great when it blew up. It hasn't yet, but I can hear myself using that very phrase in the future. Winter project looms??
 
SteveA said:
a set of bearing is a lot less than a catastrophic failure
Click to expand...
Mains do not fail catastrophically, its a gradual decline to a noisy low down rumble, unlike a shell bearing where a seizure will take out a rod and the cases. Worn shell bearing will also be noisy, at low revs its a pinking sound that goes away as the revs rise and the oil pressure gives some relief and cushioning.

If you have a new noise that does not have an obvious cause then mk1 eyeball during a strip down is the best route but I would get someone with a keen ear and knowledge of engine failure modes to listen first.

I got the ominous sounds of main bearing failure once but it was not the main but the gearbox sleeve gear bearing was CN not C3 internal clearance, that was self inflicted and as it was the last thing changed the first item to look at.
 
OK, I said it already, but, AN main bearings ordered, order includes a set of shell bearings for the rods.

The crank will be fully stripped and rebuilt over 'winter', which feels like it has started already, but isn't official until we start burning wood......

I haven't laid a spanner on the bike yet, I don't know what the magnetic plug looks like yet, I certainly won't be surprised if it and the oil that comes out presents evidence.

But as I have said before, it's a race bike, if in any doubt just pull the motor and do it, preferably leisurely and thoroughly. Decision made.

But to be honest, the decision was made Sunday when still at the race track.
 
About my whining motor sound coming out of the primary. Took two test rides and the whine at idle went away when I slackened up the rear chain, so probably the sleeve gear bush crying due to too many years of running the chain a little tight on occasion. For example, every time I installed a new chain, I probably ran it too tight initially. Static without my weight on the bike, 2 inches of chain movement gets rid of the whine. The minor noticeable vibration I get around 70mph is probably relatively normal for a solid mounted motor. I might not feel it at all on a Commando.
 
Kommando said:
Worn shell bearing will also be noisy, at low revs its a "pinking sound" that goes away as the revs rise and the oil pressure gives some relief and cushioning.

You nailed it...."pinking sound"
Experienced that sound though very slight on a 750 years ago ...pulled it down straight away ...luckily
 
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