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1973 Norton Main bearings

Classic Norton Commando Motorcycles.

1973 Norton Main bearings

Postby norton73 » Thu Aug 10, 2017 5:06 am

I spent the couple weeks before the INOA National working on my wife's '75 preparing it. I thought all my '73 needed was a primary oil leak fixed and a couple things looked at. One issue was a faint knocking noise that at first appeared to come from the timing side, so I had thought it was the cam chain needing adjusting.
I was checking the timing with a strobe light, and with the cap on the primary off, the noise was louder. I thought maybe the noise was my alt. rotor loose on the shaft, so I pulled the cover to check it.
I grabbed the rotor to see if it was loose, and found my noise, the rotor would pull side to side.
I took the Ducati Monster to the rally and parked the Norton.
Last night i found time to look closer;

Image

Image

Looks like 12 thousands side to side, with the motor still assembled, I assume when I disassemble the timing side, there will be more.
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Re: 1973 Norton Main bearings

Postby Fast Eddie » Thu Aug 10, 2017 5:13 am

12 thou end float is fine.

I don't believe failed main bearings would show up as increased end float anyway.

Main nearing failure usually sounds like a low frequency rumble.

A Knocking noise is a classic symptom of big end failure (potentially more damaging than main bearing failure).

But it can also be an awful lot of other things. I'd carefully check the more obvious stuff first, like loose alternator or clutch or etc before tearing the whole plot down.

Then again, a tear down is a great opportunity/ excuse for some upgrade goodies....!

Do keep us all posted woncha?
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Re: 1973 Norton Main bearings

Postby norton73 » Thu Aug 10, 2017 5:21 am

Loose Alt. nut or rotor loose on it's center was what i was expecting to find. When I grab the end of the rotor and pull, it clunks in a very similar manner as the sound I hear when it''s running.

Tear down will continue tonight, I removed all the stuff like carbs and exhaust last night, one exhaust nut was seriously tight and required some heat and leverage to remove. I was trying to be careful not to add thread repair to the list.
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Re: 1973 Norton Main bearings

Postby MexicoMike » Thu Aug 10, 2017 5:57 am

End play in the crank is normal. If I recall correctly, the service manual calls for .005- . 015. I seem to recall something from the norton owners club that said something like up to .20 was OK but I can't swear to these numbers. In any case, some float is normal and may be what you are seeing; it is well within the expected range.
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Re: 1973 Norton Main bearings

Postby olympus » Thu Aug 10, 2017 7:39 am

That's correct 0.005 - 0.015 in is what the manual says or .1270 - .3810

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Re: 1973 Norton Main bearings

Postby lcrken » Thu Aug 10, 2017 10:40 am

Another possible cause of a knocking sound on the timing side is a loose camshaft nut. I had that happen once, and it took forever to finally pin it down.

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Re: 1973 Norton Main bearings

Postby norton73 » Fri Aug 11, 2017 7:06 am

Pulled the top end off and the timing chest contents last night. All nuts tight, as was the timing chain. No signs of anything wrong until I removed the cam sprocket.
I didn't check end play before I removed the sprocket, but once it was off, it moves side to side at least a 1/4 inch in the case.
Cam and followers look fine, just seems like the cam should be tighter. Or is the sprocket the only thing that locate it? Bushings worn? Should there be shims or thrust washers?
I will split the cases tonight or tomorrow.
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Re: 1973 Norton Main bearings

Postby bill » Fri Aug 11, 2017 3:31 pm

the sprocket does help locate the can end play. what you have is normal.
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Re: 1973 Norton Main bearings

Postby concours » Fri Aug 11, 2017 5:18 pm

norton73 wrote:I spent the couple weeks before the INOA National working on my wife's '75 preparing it. I thought all my '73 needed was a primary oil leak fixed and a couple things looked at. One issue was a faint knocking noise that at first appeared to come from the timing side, so I had thought it was the cam chain needing adjusting.
I was checking the timing with a strobe light, and with the cap on the primary off, the noise was louder. I thought maybe the noise was my alt. rotor loose on the shaft, so I pulled the cover to check it.
I grabbed the rotor to see if it was loose, and found my noise, the rotor would pull side to side.
I took the Ducati Monster to the rally and parked the Norton.
Last night i found time to look closer;

Image

Image

Looks like 12 thousands side to side, with the motor still assembled, I assume when I disassemble the timing side, there will be more.

Oil pressure reading?
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Re: 1973 Norton Main bearings

Postby o0norton0o » Fri Aug 11, 2017 6:13 pm

Lot's of things can knock. A while back, I came back from a ride and my bike started knocking all of a sudden while idling in the driveway. It sounded like it came from the bottom so I pulled the head and barrels. One of my cam followers had lost it's stellite pad and when I looked into the crankcase I saw the pad was sitting on top of the cam lobe. I thought, "What the hell is that?", then I looked at the underside of the barrels and saw the follower that was missing it's pad. It sounded more like a "clack" than a "knock" to me, but that's subjective. When I heard the sound I feared that it was a connecting rod knock, but it wasn't that thankfully.

IMO, a knock or a clack is a sound make by a reciprocating motion, rather than a rotating part. So a knock is a part going up and down, not round and round.... in general..
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Re: 1973 Norton Main bearings

Postby olympus » Sat Aug 12, 2017 2:47 am

o0norton0o wrote:Lot's of things can knock.....

A noisey tappet, is a happy tappet....:lol:
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Re: 1973 Norton Main bearings

Postby norton73 » Sat Aug 12, 2017 3:56 pm

Pulled the rest of the motor down today. Everything looks good, crank journals fine, measure at 1.751, still round. Rod bearing look good. Only issue I can see is the inner main race on the primary side turns by hand on the crank. Can't pull it off by hand, but will spin.

Debating whether to replace the mains while I am there. no wear or blueing on the mains, look just fine. Maybe reuse and red locktite the race to the crank and reassemble with new rod insets and go from there
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Re: 1973 Norton Main bearings

Postby norton73 » Sat Aug 12, 2017 3:58 pm

o0norton0o wrote:Lot's of things can knock. A while back, I came back from a ride and my bike started knocking all of a sudden while idling in the driveway. It sounded like it came from the bottom so I pulled the head and barrels. One of my cam followers had lost it's stellite pad and when I looked into the crankcase I saw the pad was sitting on top of the cam lobe. I thought, "What the hell is that?", then I looked at the underside of the barrels and saw the follower that was missing it's pad. It sounded more like a "clack" than a "knock" to me, but that's subjective. When I heard the sound I feared that it was a connecting rod knock, but it wasn't that thankfully.

IMO, a knock or a clack is a sound make by a reciprocating motion, rather than a rotating part. So a knock is a part going up and down, not round and round.... in general..



Cam and followers look great.

While I am in there, I am tempted to replace the cam with a "hotter" one and reface the tappets, not sure I want to change the power characteristics that much though. Pretty happy with the torque between 4-6K.
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Re: 1973 Norton Main bearings

Postby acadian » Sat Aug 12, 2017 4:22 pm

norton73 wrote: the inner main race on the primary side turns by hand on the crank. Can't pull it off by hand, but will spin.


if the inner race spins on the journal, bearing not doing its job... no?
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Re: 1973 Norton Main bearings

Postby pommie john » Sat Aug 12, 2017 4:43 pm

norton73 wrote:......... Maybe reuse and red locktite the race to the crank and reassemble with new rod insets and go from there



Loctite make specific products to secure bearings onto shafts.

http://www.loctite.com.au/3320_AUE_HTML ... 2648195073
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