Seeley Norton

Hi all, just curious to find out if there are more Seeley Norton's out there?! Please show a picture.
I built this 500cc classic racer 20 years ago and had a lot of joy racing it over the years.

Like this one??

Kenny Cumming's excellent site http://www.shelbynyc.com/nycnorton/Racer2009.htm

Allright!
Seeley920 does this mean your Seeley Norton is 920cc? If so what crankbalance factor did you use to cope with vibrations?

Actually it's a 750...I've got 2 motors, one "normal" 73x89 mm and a shortstroke 77x80.4 mm, I use the same balance factor on both....78%, no problems with vibration. Thats what Gus Kuhn Seeleys were all balance to. One of my mates has a 920, 960 and 1007 and they're all balanced the same!

I started at 80% and came down to 72% (dry) as most comfortable.

Yes that would probably work well, I think sometimes you need to experiment with the balance factor to suit yourself and how your engine is mounted etc. Maybe the 500 needs a lower factor than a 750?

What did you take into account to figure out the balance factor?

This is how I was told to do mine:

I have a 750 motor in a featherbed frame leaning forward like your and it is set up with an 84% bal factor. I think this is what you want. I built this bike and have been racing it since 1986, I started with 74% and it was ok, but I keep breaking exhaust brackets and clamps from the vibrations. I rode it for one season like that and then changed it to 84% and that made all the difference in the world. The motor runs very smooth all the way up to 8500 RPM.
What you want to do is take the total weight of the following.
1. Connecting Rod complete with rod bolts and nuts, and the rod inserts.
2. Pistons complete with the rings, wrist pins, and circlips.
Now find a weight that is 84% of the total, put it on the rod journals, and bal the crank by drilling holes in the flywheel. If you need to make the crank heavier then you drill the holes and weld them up with a heavy metal like Mallory.

I haven't yet ran my café racer on the road, but starting it and revving it it looks pretty good (84%).

In Paul Dunstall's Norton Tuning Manual he mentions factors of 84% for an Atlas 750, 70% for a 650 (in Featherbed frames) and 52% for a Commando with a stock frame and isolastics. There is no mention on how this is done however.

Jean

Him Jean,

I used 84% in my fetaherbed years ago, and it was good...I didn't even have a headsteady, just the top part which braces the frame, never had any problems with vibration.

However the Seeley is a different frame, and 72-78% seems to work best in them, depending on the motor. Don't forget, the motor will still vibrate, justy in a different plane....i.e. backwards and forwards, rather than up and down, it's just that you don't notice it as much.

I always have my cranks dynamically balanced.

Hopefully this photo loads. A local small museum had this on display. The owner's widow decided to sell off the motorcycles, so now the Seeley belongs to one of our club members.

To balance the crank you would use 100% of the rotating weight. That is the big end of the rod with rod bearings and bolts. Then add the balance factor percentage X the reciprocating weight which is the small end of the rod and the piston and pin and rings. This will give you the needed bob weight.
Using this formula means Jeans motor is actually balanced somewhere between 70 and 75%. Jim

Jim: I am with you there about balancing.
Illf8ed: rather small picture but it looks like a beautiful built MK4 Seeley.
Let's have some more Seeley pictures!