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Crankshaft for 650SS 1968 Mercury

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Hi all .. I'm a new member from NSW Australia and have just joined the Norton Owners Club.  I have a 1968 Mercury 650SS.  I have just bought a "basket case" and I have 2 crankshaft cheeks but no flywheel.  Can anyone please advise me if any other flywheel, ie, Commando, etc will suit the 2 cheeks that I have, as I am having trouble finding a 650SS flywheel in Australia.  The engine number is 18-SS/129465/P.  Crankcase, gearbox and frame are all matching numbers.  The flywheel part number is different to other models.  Thanks in advance - Denis

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The 650 flywheel is peculiar to that engine size, the Atlas and 750 Commando one is different, heavier, I think, and balanced differently,  it would 'fit' to your 650 cheeks easily enough, but you would only find out what that engine would run like by trying it, very roughly, I wouId imagine. I suppose one could be modified if you had a drawing of the original but it would be an awful lot of trouble to go to to make a standard bike, and would probably cost more than getting one sent from over here.

Good luck.

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Hi Dennis.....your Mercury 650 does indeed have an Australian heritage having been imported by Burling & Simmons into  New South Wales. However my records show that this happened in March 1969.

The crankshaft will accept an Atlas (and even a Commando) flywheel but will need to be rebalanced to suit your conrods and pistons. If used, a Commando flywheel will need some serious machining due to its balance factor being considerably different to that of a 650.

The other point to check is that after mounting the pistons on their conrods they clear the shoulder of flywheel at BDC.

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Hi Denis,

               I have an Atlas crank. I reside in Melbourne. If you are interested I will check the journal size.

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I have looked at my Norton Publications 2001.  It says the 650SS timing side crank cheek P/N 23262 covers 650SS and 750 and also that the driveside crank cheek P/N 23261 covers 650SS and 750.  The Flywheel only P/N 23315 says 650SS and (99) and the Flywheel only P/N 24248 says all 750s.

Strangely enough, I also have an original Norton Commando spare parts book which says, timing side cheek P/N NM.23262, which is the same as the 650SS but the driveside cheek P/N 06052 doesn't match.  Can you throw any light on this for me. 

I have just taken the P/Ns off my 650SS which says, timing side cheek P/N NM.23260 and the drive side cheek says 8008.  Does that make any sense.  Thanks again for any assistance.

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When the Atlas motor went into the isolastic frame to make the Commando, a completely new primary drive with triplex chain was introduced, the drive side shaft being redesigned to suit, hence the change to the part number.

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Denis I have a complete Atlas crankshaft assembly. It appears to be 20 thou under.

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Hi Dennis......The attached photos should help to ID any crankshaft chunks you are offered.

The Timing Side cheek, as you have discovered is almost the same for all the bigger engines. The 650 & Atlas flywheels were slightly different in terms of mass and machining but with some engineering can be used in either engine.  The photos show the difference.

The Commando Drive-Side cheek has a different shaft to enable the Triplex sprocket to fit. A quick 'spot the difference' check is to look for the alternator key-way. On the Atlas & other smaller Dominator cranks this is placed next to the sprocket taper. On Commando shafts it is further outboard next to the crank nut thread.

In reply to by andrew_westmore

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Andrew, thank you for your reply.  Have to way up what to do.  The Atlas crank, maybe I could fit my 650SS crank cheeks to it , and rebalance it.  Denis.

Hi  Phillip  thank  you  for the photos, you can see the difference in the thickness of  the 650ss flywheel compared to the others.

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Hi Denis, why not install my crank complete in your cases. The crank would need to be re-balanced. If you go to the forum archives the correct balance factor is available. Philip Hannam probably knows the figure without looking it up !

Cheers Andrew

Andrew thank for your input, if i could  ask Phillip Hannam, if i fitted Andrews crank, what would i have to do re balancing etc. Regards Denis?

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Denis.....get all the crankshaft parts in a bundle and take to a recommended company that knows how to balance a crankshaft. So that is the refurbished crank, the rods, big-end bearings and pistons. Some of the better companies can regrind the crankshaft and then balance it as well.

The balance factor should be around 70% for a 650 engine.  That is for a static balance with a dry crankshaft. Some engineers like to fill the shaft with oil to replicate running conditions. Dynamic balancing, where the crank is spun at speed, is also another option. Everybody has their favourite.

The attachments are words of wisdom  from John Hudson, plus a DIY version offered years ago in Motorcycle mechanics.  Plus more....the Steve Robinson Notes on crankshaft balancing.

Phillip, thanks for all the information re crankshaft.  So, the two crank cheeks I have off my 650ss with a missing flywheel have been machined with new bearings. The question is could I use the 650ss crank cheeks for instance on Andrew's Atlas flywheel and rebalance it or use the Atlas crankshaft complete. Is the drive side the same on the Atlas re bearing, sprocket, seals, etc. the same as the 650ss?  Just trying to work out which way to go. What are your thoughts? 

Do appreciate all of your input. Regards Denis Curry.

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I had a crank ground and balanced at SRM recently, £460. Including return postage.  Regards, Al.

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Denis......The Atlas and 650 crankshafts are identical apart from the respective flywheels being machined and balanced a little differently.

SRM are a good company but very pricey.  I think the postage costs from Australia would also be off the planet.  Go local.

In reply to by andrew_westmore

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Hi Andrew .. thanks for your reply.  I'll be in touch.  Denis Curry

Phillip, thanks for your reply.  It gives me something to work with.  You have been most helpful.

In reply to by andrew_westmore

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Andrew - Can we talk further about the Atlas crankshaft assembly by email or phone.

Rgds - Denis

 


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