80° crankshaft

Status
Not open for further replies.
J

Jeandr

Joined
Jan 22, 2008
Messages
2,585
Country flag
I did the electrics on this bike, it is the most complicated electrical I have ever done and even seen on a British bike. There are 5 fuses, 3 relays (not counting the flasher relay). Boyer microdigital electronic ignition, Sparks 3 phase alternator, LED taillight, halogen headlight, FIVE (5) idiot lights indicating flashers (2), pilot light on, high beam and a spare. CNW electric tach and speedo, oil pressure gauge, oil temperature gauge and voltmeter.

What sets it apart more than anything else, is the 80° crankshaft which is supposed to make it as smooth as a Ducati or a 4 cylinder UJM. The guy did a lot of work himself, especially putting it all together. It's a nice bike, but everything is so tightly packed together it's a nightmare to work on. For example to remove the left hand panel, the seat has to be taken off and then the clip can be maneuvered with fingertips, after that you need to have your hands massaged because of the cramps.

I have a 1Mb (well a bit less) sound file of the engine running if anyone is interested in hearing how it sounds. Send me a PM with your e-mail and I will send it off. It sounds a bit like a Ducati, at least that is what I have been told, the sure thing is it doesn't sound like any Norton you have ever heard.

Jean


80° crankshaft

80° crankshaft

80° crankshaft

80° crankshaft

80° crankshaft
 
Wow! The more I look at these pictures, the more neat tricks I see! Where did those barrels come from? The work on the left front fork lower is neat! As is the rear brake master cylinder mount. Very unobtrusive.

Sweet machine.
 
1. how much did that angle in the carb boot reduce intake efficiency?
2. 80°? Where did that figure come from?
 
Great mother of Norton. What an amazingly meticulous machine.

I like it "okay".

I would offer more than my customary $350.00 for it, if it was for sale.
 
I only did the electrical system

I only did the electrical system on this bike, it's not mine, there is a lot of neat stuff though 8)

To answer a few questions:

The 80° angle was determined to be the best for a Norton by the guy who does the crankshaft modifications, for a Triumph, the angle is not the same. There is an article about a 90° cranked Norton in Classic Bike Guide (August 2003). The guy who does the 80° crank is from Toronto, check out his web site at http://www.offsetcrank.com/index.html How he came to 80°, you will have to ask him. On his site there is mention of 74°, 80° and 90° of offset, I think he says the 80° is the smoothest.

The carbs are from CNW, including the spigot, IMOHO, not any worse than the stock Norton way to mount their carbs.

I think the barrels came from British Cycle in Nova Scotia http://www.britishcycle.com/ The owner of the bike told me they were an old set British Cycle had and he got them at a discount but he had to do a lot of fitting to get them on because nothing lined up.

The wheels are Morris mags the owner bought in the seventies.

Jean
 
In general, the discussion on offset crank angles falls into 2 theoretical categories:
1. 90° produces the best balance of motion between the 2 cylinders - this will always be 90° regardless of engine design, etc.
2. the point where 1 piston is stopped, and the other piston is at maximum velocity (its rod is at 90° to the crank) - this will vary based on rod ratio. The original Triumph design used 76° because that's where the 2.01:1 rod ratio places the throw.
The crank offset angle = 90° minus the maximum thrust angle.
Maximum thrust angle: arc tan (1/(2*rod length)/(stroke length))
The Triumph 650 rod = 6.500”, stroke = 3.228”
(2*rod length) ÷ (stroke length) = 4.027
1 ÷ 4.027 = .2483
arc tan .2483 = 13.94
90 - 13.94 = 76.06°, hence 76°

The Norton rod = 5.875”, stroke = 3.504”
(2*rod length) ÷ (stroke length) = 3.353
1 ÷ 3.717 = .2982
arc tan .2982 = 16.60
90 - 16.60 = 73.40°

80° may have been used (and there are numerous comments that the angle isn't critical to vibration reduction; Yamaha 650 uses 83° because it's almost a bolt-in), but Geoff Collins (who made the crank in that Norton) recommends 90°.
 
panic said:
In general, the discussion on offset crank angles falls into 2 theoretical categories:
1. 90° produces the best balance of motion between the 2 cylinders - this will always be 90° regardless of engine design, etc.
2. the point where 1 piston is stopped, and the other piston is at maximum velocity (its rod is at 90° to the crank) - this will vary based on rod ratio. The original Triumph design used 76° because that's where the 2.01:1 rod ratio places the throw.
The crank offset angle = 90° minus the maximum thrust angle.
Maximum thrust angle: arc tan (1/(2*rod length)/(stroke length))
The Triumph 650 rod = 6.500”, stroke = 3.228”
(2*rod length) ÷ (stroke length) = 4.027
1 ÷ 4.027 = .2483
arc tan .2483 = 13.94
90 - 13.94 = 76.06°, hence 76°

The Norton rod = 5.875”, stroke = 3.504”
(2*rod length) ÷ (stroke length) = 3.353
1 ÷ 3.717 = .2982
arc tan .2982 = 16.60
90 - 16.60 = 73.40°

80° may have been used (and there are numerous comments that the angle isn't critical to vibration reduction; Yamaha 650 uses 83° because it's almost a bolt-in), but Geoff Collins (who made the crank in that Norton) recommends 90°.
Click to expand...

Nice math. I always thought the Yamaha was a 180° design, but read this http://www.sense.net/~blaine/270.html they talk about how the cranks are linked together with a 13 spline "coupling", that is where the 83° comes from. The Yamaha is a 360° crank from the factory, mainly for the music it makes I guess ;-)

Jean
 
:oops: I looked at pictures of Yamaha 650 cranks and they are indeed 180°, who would have believed something written on the internet could be wrong, what is this world coming to?

Jean
 
Re: " Yamaha 650 cranks and they are indeed 180°"

Referring to the SOHC XS-1, XS-650 parallel twins, all of which were 360°.
 
I agree with panic, the XS 650 cranks were 360°. (Haynes XS 650 manual mentions it and the manual photos shows it has a 360° crank).
 
L.A.B. said:
I agree with panic, the XS 650 cranks were 360°. (Haynes XS 650 manual mentions it and the manual photos shows it has a 360° crank).
Click to expand...

Mmmmfff pffff (gee it's hard to speak with feet in mouth :oops: )
 
A crank set at 90 degrees will reduce the primary vibration about 50% compared with the traditional setup of the two pistons moving in unison. However, at 90 degrees, the secondary vibration, i.e. that at twice engine speed, will be cancelled out. Thus the buzz that is typical of 4 cylinder engines will not be there, giving rise to a throb rather than a tingle, according to those who have done this on Triumphs and BSAs.

The balance weight will need to lightened to oppose the resultant vector of the two reciprocating masses, placed opposite the half-way point between the two crankpins, in order to maintain an approximately circular vibration track (as opposed to pure up and down) which is what the Isolastic will be best able to absorb.

There will be a small theoretical disadvantage of the offset crank for the Commando in particular, as it will create a small lateral, side to side vibration, akin to, though not as severe as a 180 degree twin (think Suzuki T500). The Isolastic frame is of course not set up to absorb this, unlike a vibration in the plane of the frame.
 
I popped in to see Bob from time to time and watch the progress the owner was making on this bike. The photos don't do it justice, the amount of detail work is insane. The last time I saw it, it was started for me. I put my hands on the cases while it was running and couldn't believe how smooth it was. The sound was glorious. :twisted: I will probably go this route when I rebuild the engine for my 850 P11 project.
 
Great bike Jean! What fork is it and I love the front fender, where does it come from??

Philippe
 
Status
Not open for further replies.
Back
Top