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NJ306E-M1-C3 Vs 6203 - C3

Norton Models (not Commando or P11)

NJ306E-M1-C3 Vs 6203 - C3

Postby Possum » Wed Jan 18, 2017 12:39 am

I am about to build a 650cc engine for club rally bike with a few country trips; no circuit or street racing.

Is the doubling the cost of main bearings by fitting a NJ306E-M1-C3 to the drive side justified?

One NJ306E-M1-C3 and one 6203 - C3, - the cost is about $115AUD, $87USD, 70GBP

As originally fitted with two 6203 - C3, - the cost is about $65AUD, $50USD, 73GBP

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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby robs ss » Wed Jan 18, 2017 4:26 am

Are you sure the original fitment was two deep groove ball bearings? My understanding (and consistent with my '64 650SS) is a deep groove ball on the timing side and a parallel roller on the drive side.
for my latest rebuild I have gone to "superblends" both sides, wearing the additional work of ensuring end-float is correct, purely as insurance - this based on the superblends history.
Double or not, a $50AUD insurance policy seems cheap in terms of the total build price.
Cheers
Rob
BTW Possum I sent you a PM in late November requesting info on the 650 inlet tract inserts - I want to make a set
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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby grandpaul » Wed Jan 18, 2017 8:33 am

robs ss wrote:Double or not, a $50AUD insurance policy seems cheap in terms of the total build price.

Better insurance costs a lot more and deals with the crank and cases...
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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby Rohan » Wed Jan 18, 2017 5:41 pm

robs ss wrote:Are you sure the original fitment was two deep groove ball bearings?


This I think is the nub of this.
Even the earliest Model 7 dommies had a roller bearing on the drive side.
Same dimensions (externally) as a later 'superblend'*, it must be noted.
*which is just a heavier duty roller bearing

I think some previous owner/bodger has done an el cheapo, and used a ball bearing.
Probably last a while, especially if you were gentle on the throttle hand.
Lotsa old singles used ball bearings all round...

BTW, shop around for those bearings, one of the most heavily discounted items on the planet.
Even yer grandmother should get a 60% discount, and more if she jumps up and down enough.
A heck of a lot more if she buys 1000 or more !

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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby Possum » Wed Jan 18, 2017 8:51 pm

The 650cc engine in question had two x 6203 ball bearings...

As my old tradesman often said, never assume the person before you did the job correctly.

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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby Possum » Wed Jan 18, 2017 9:05 pm

Rob

I did not respond to your your questions as I assumed they were rhetorical, suggesting issues I should investigate further...

I have a collection of 600 / 650 bits that would like to be an engine, before I die.

600cc large inlet head with bronze valves & seats (it is already 28mm, so I do not require inlet tract inserts),
650 barrels,
650 - 10.5:1 Hepolite pistons,
270 / 450 cam & ignition, &
I am well down the road of a 90 degree offset crankshaft.

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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby robs ss » Wed Jan 18, 2017 10:53 pm

Possum
What I was after was the drawings you mentioned you got from Ben Gradler of the inlet tract sleeves.
I would love a copy if you have them
Cheers
Rob
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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby Rohan » Thu Jan 19, 2017 7:33 pm

The later 650 models didn't have the sleeves in the ports, so would you really want to go down that path ?
We diverge here from bearings, a bit....

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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby bad_friday » Fri Jan 20, 2017 1:43 am

Rohan wrote:The later 650 models didn't have the sleeves in the ports, so would you really want to go down that path ?
We diverge here from bearings, a bit....

Mine is a 650SS/1966 and has the sleeves installed.

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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby Possum » Sat Jan 21, 2017 12:56 am

Rob

I don't recall getting any drawings from Ben Gradler. Are you sure you have not got me confused with someone else?

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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby Bernhard » Sat Jan 21, 2017 4:09 am

Rohan wrote:The later 650 models didn't have the sleeves in the ports, so would you really want to go down that path ?
We diverge here from bearings, a bit....


There appears to be some confusion over why Norton fitted split sleeves in the inlet ports on some twins. My Atlas had these fitted because when I originally brought the bike it came with a single Monoblock carb setup-these where probably fitted to the single carb 650s they are simply removed if you convert to a twin carb setup.

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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby dynodave » Sat Jan 21, 2017 5:24 pm

Don't recognize the # 6203 17x40x12mm as any bearing I would use on a NHT crank
I'd be looking for 6306 or some variant of 30x72x19mm

NJ306 brass cage C3 anywhere in the USA from a norton dealer is about $108 for 1 ea
I just bought some NTN brass cage C3 from the NY distributor for $59+ea delivered.
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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby norton bob » Sun Jan 22, 2017 11:38 am

Fitting two ball bearings on a Norton engine was a dodge done to reduce friction losses, used on race motors it was effective. Sleeving the inlet ports was done to match up to the size of carbs found by testing to give the best spread of power for the anticipated usage of the motor. They really had no idea what sort of loons lived the other side of the pond.

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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby dynodave » Sun Jan 22, 2017 2:30 pm

How do the people on the smart side of the pond put a 6203 17x40x12mm on a 30mm crankshaft? Grind it down to 17mm? Even the cam drive gear shaft is over 20mm? :lol:
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Re: NJ306E-M1-C3 Vs 6203 - C3

Postby L.A.B. » Sun Jan 22, 2017 3:11 pm

dynodave wrote:How do the people on the smart side of the pond put a 6203 17x40x12mm on a 30mm crankshaft? Grind it down to 17mm? Even the cam drive gear shaft is over 20mm? :lol:



Nobody either side of the pond mentions fitting a 6203 here, it's a simple case of Possum quoting the wrong bearing number (6203 instead of 6306)

(6203 being the original gearbox layshaft bearing).
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