Recommended Shop for Dynamic Balancing

650SS

Joined
Oct 18, 2011
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9
Can anyone recommend a shop, preferably on the east coast (USA), that has experience dynamically balancing Norton crankshaft? My 1966 650SS turned out disappointingly rough after my last rebuild using unexpectedly heavy .060 over JP pistons and a 82% static balance factor. I could have other problems (JP piston pins too tight in rods so std pins used...now may be too loose in pistons!) but I think I have located some lighter Hepolite pistons so I would like to give it another shot. I also would liked to try the recommended 70% balance factor cited for the 650 as well as dynamic balancing.

Paul Raley
Leonardtown MD
 
A friend has dynamically balanced a Triumph 650 crank, by bolting weights to the big ends. It seemed to work OK, however too much weight on the little ends is not a good thing. Loose gudgeon pins never blew up a motor, however for peace of mind every clearance in a motor should be correct.
 
The old Hepolite and Norton 500-650cc pstons had nice light taper-wall piston pins, did they skip this feature on current offerings from JP? Would not be a surprise.

It is an unfortunate fact that the larger the overbore the pistons are made for they have that much thicker and heavier sides.

I rode an all standard 1961 650 Norton for years and it started to vibrate once it got to 4000 rpm, an engine speed you don't really need to spend a lot of time at anyway on a street bike. I simply geared it up so I could cruise at highway speeds below that rpm, made it a great bike and really saved on the oil consumption and engine wear.

My current 650ss is also lucky enough to be running a set of standard-bore pistons in a nicely re-sleeved cylinder. I balanced it on the kitchen table on a set of knife-edge levels at a bit higher balance factor than standard, around 75%, just for shits and giggles, it seems to be nice and smooth, but I don't have a tach on it yet to accurately pinpoint it's characteristics very well. Lots of fun to ride is all I can say presently.

When I was doing up the crank I did a poor-mans dynamic, putting the crank throws on the knife edges 180 degrees apart without having the central flywheel attached. This way you can match the weight of the two outside porkchops, about all dynamic balancing does anyway, something you can not do at home with a one-piece Triumph or BSA crank. AFter those are matched then put the flywheel back on with your bob weights and drill your holes to balance them. Use a weight on each journal that each shares half the weight you need. My last step is to take off one of the bob weights and leave one on one journal, this lets you see that the counter-weight of the crank is 180 degrees to the center of your rod throws, which you will fine-tune with a little final drilling on the centerline of your central flywheel. It will not change your result enough to worry about at all. Now your crank is balance about as good as it can be.

My bob weights are made from long strips of lead sheet trimmed to the width of the rod journal and weight I need and wound around each rod journal. I hold them on with a bit of electrical tape if I have to. This keeps the bob weight centered around the center of the rod journal as close as it can be. Get the lead strips from those who supply the special drywall materials for use in x-ray rooms of hospitals and other institutions.

I don't support much experimenting trying odd or exotic balance factors unless you are half nuts like me or have a lot of money or time on your hands. Your idea of going with 70% and light pistons will turn out well for you. You can drill a few holes in the piston skirt and put some dimples under the dome if you want, but be conservative and stay away from the piston thrust faces or you will simply decrease their service life.

The lighter the pistons you can find and the lower the balance factor you can use the less the engine will vibrate overall. For high rpm racing there are specific balance factors that can be found that will work in narrow rpm bands with heavy pistons, but they are hard to find for each odd combination. For street use forget them.

Did you balance your wheels and tires well??
 
If you are looking for a shop to do the work, I highly recommend Francis Engineering. They are world renowned for their engine work on everything from motorcycles, to world class truck pulling trucks, speed boats, etc. They have done some amazing work for me & many of the motorcycle race bikes & vintage bike guys I know. Pricing is also very reasonable.

shop tour: http://www.youtube.com/watch?v=DXjx6h3aZco

I haven balanced a tire in years, since using Dynabeads
 
Thanks for the advice and recommendations. That is just what I was looking for.
Paul R.
 
Hepolite pistons are heavy. I have seen a lot of old BHB brand Norton pistons that were much lighter than the Hepolites.

I weighed a set of .060 over Hepolite 650 pistons with pins and rings and they came in at 329 grams. A standard 650 Hepolite came in at 299 grams, but a BHB 650 stc. with rings and pin came in at 280g.

A real shocker is that I weighed a std. size BHB dished Atlas piston which was original to an early Atlas engine I have in the basement, and it came it at 317g, lighter than the .060 650 Hepolite, this would from a balance point of view convert the 650 in which it was installed into an early Atlas!
It is noteworthy to mention that all the early Atlas BHB pistons I have on hand, four, have the nice taper-wall wrist pins, while the Hepolite Commando pistons have heavy straight-wall pins.

The Commando flat top Hepolites that so many have plugged into old Atlas bikes are heavy at 353g in .040 os. A set of domed Commando Powermax racing pistons with taper wall pins came in at 356g.

IF you look at the old road test of the 1962 650ss in the english Motorcycle publication the tester complained about how the bike vibrated between 3500 and 4500 rpm, right where he liked to cruise at. My old 650 Manxman which was all original with 5000 miles on it when I got it started to vibrate towards 4000 rpm and never seemed to get any better as the speed went higher, which is why I geared it up so it would do 70mph at 3500 rpm.

With this accumulated data it looks like there may be nothing you are going to be able to do with modern replacement pistons to get the bike much smoother than it was when it was new, which may have been more smooth than a period Atlas, but not as smooth as the old smaller displacement 88 and 99.

I tried to save the old BHB pistons to re-use on my 650ss but they were well worn and had old rings stuck solidly in some parts of them, I threw in a set of used stc. Hepolites that were in pretty good shape with some new Hastings compression rings and it is running very well.

BHB pistons are just about non-existent. Aside from the std. ones I have taken out of old original engines, I have only seen a small handful of new ones over the years come up for sale. It seems Hepolite was much more popular in later years as a replacement piston and eventually as an oem piston.

If I had a bored oversize 650 Norton I would make sure that I have the taper-wall piston pins to use in it and I would drill a few holes and dimples in the piston off the thrust faces to get it as light as I could. A really sharp racing machinist could probably put a taper in the wall of straight wall wrist pins, but unless you found someone who had previous experience doing exactly that I would not trust them.

Jim Schmidt engineering has offered very light Carrillo/JC rod and piston packages for the Dominator in the past, but I think they are special order which would probably eliminate most of the vibration a 650 Norton has, but you will be looking at quite a bit over $1000 for the package if it is available at all. He would probably also balance your crank for you no matter what parts you decide on. There is no one that will not agree he is one of the top Norton engineers in the country.

In the early 1960s John Gregory was one of the earliest and foremost tuners of the Norton 650 in the country. He raced Model 88, 650 and 750 Nortons at drag strips, on the street and on road race tracks. He told me he balanced all his engines to 78% dry, which would be very close to 70% wet. This is what I shot for when balancing my 650 with it's std. Hepolites and it seems good enough. I have no tach on it right now but when I get some data on how it behaves at different rpm and speeds I will certainly share it.

1962 650ss road test here: https://www.facebook.com/photo.php?fbid ... =3&theater

John Gregory's secret Norton 650 tuning notes here: https://www.facebook.com/photo.php?fbid ... =3&theater

P.S. Heinz Kegler, the head technician for the U.S. Norton distributor Berliner and a rabid Dominator fan, recommended 65.5% balance factor for the 650 Norton. Unfortunately he is dead and I can not ask him if that was wet or dry, my guess is dry, but it is only a guess today.
 
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