Here's some info about bearings from 1996.
Bottom ends: Something's gotta give
By NCNOC Member: Stevan Thomas Norton Notice#219 10/96
If anyone knows how to blow up bottom ends, it's Oregon racer and engine builder Mike Farrell. Farrell, who has raced Nortons for over twenty years and rebuilt dozens of motors for himself, and customers, was kind enough to share that experience with me over several phone conversations, in which he offered invaluable insight into building a better bottom end.
Although his advice seems most applicable to racers (and flies in the face of conventional wisdom), it's actually relevant to any street rider who uses his or her Norton up to 7,000 RPM, even if only occasionally.
The basic concept, according to Farrell, is this: at top RPM, Norton crankshafts flex more than what dual Super-Blends and what reinforced crankcases will allow. It is better to allow the crank to flex than to try to control it. The best way to accomplish this is to use a Super-Blend bearing on the drive-side and an extra-capacity ball bearing on the timing side.
Farrell had a shop for twenty years and used to rebuild motors for customers. Of about sixty motors he saw with dual Super-Blends, as many as eight showed signs of bearing failure to one degree or another.
"In the worst one I've ever seen, just about everything in the timing case was wrecked," he says. "I know all sorts of things can contribute to bearing failure, including one good over-rev. If you skid a bearing just once, it's on it's way out. "
"If you've ever seen a broken set of broken 850 cases with dual Super-Blends in them," Farrell continues, "you have to ask your self, if these are the best bearings and the strongest cases, why did they break?"
If it's a motor that got rewed up pretty regularly, the most likely reason is simply that the Super-Blend allowed only a limited amount of crank flex. Does this limiting stop the crank from flexing? No, it can't: the crank is flexible and it is going to flex as much as it wants to. Period.
So, with the Super-Blends in place, the crank flexes, and the bearings allow some flex, but when the crank flexes more than the bearings can absorb, the additional flex is transmitted to the aluminum crankcase.
The crankcase must flex because it is not strong enough not to flex. If the cases are rigid enough that they don't want to flex, they crack sooner or later. If the cases were made out of some miracle material that was absolutely rigid and would never break, the bearing would fail so fast you wouldn't believe it.
Farrell's point? Given all this, it seems logical that the stronger your cases are, the more sense it makes to put a ball bearing on the timing side for high RPM work.
Racers in the know prefer to use early 750 cases, as their thinner walls tolerate a certain amount of flex.
Farrell concurs, "I know one well-known drag racer with a multi-engine machine who will only use 1969 cases".
He says that the typical pre-1972 factory set up was a standard (non-Super-Blend) roller on the drive side, and a standard ball on the timing side. The timing side ball did not last as long as the roller. In fact, even if the rollers had worn evenly, it is not uncommon to see the shaft under the bearing has been damaged due to flex, especially if the ball is worn.
The best way to repair this is to have the shaft hard-chrome Plated and ground. Just don't forget to bake the plated piece in the oven at 250 degrees for an hour to prevent hydrogen embrittlement (even if your plater said he did, it's easy enough to do it again to make sure).
In 1972, Norton switched to two roller bearings on the crank, perhaps because the factory engineers were thinking, "well the rollers are lasting pretty well, but the balls are wearing out, so lets put in two of the rollers".
Farrell was there first. "Long before they did this, I thought it was a good idea, even though an old racer who ran Nortons at Daytona I'd be sorry if I did. It didn't last too long before I had it apart again and realized he was right! I haven't seen a single 1972 Norton that got more than about 5,000 miles before it had a main bearing failure.
"They fixed an awful lot of those under warranty and it cost them quite a bit of money. "
That's why, Farrell says, Norton commissioned a bearing house to develop the Super-Blend. It's "exotic for a bearing," he says, but" a definite step in the right direction". It's really good for most motors, though it's not always a cure-all for every situation. Other crank parts can contribute to flex as well. Farrell offered his observations about crankshaft. bolts. He frequently describes the cranks to the flywheel as being "like little rubber bands".
"I've used grade-eight bolts, but ended up preferring the factory parts. If you torque the stock bolts properly, you don't get any thread stretch, but they still pretty obviously stretch. You can see it from the way the oil seeps out between the crank and the flywheel. I've gone so far as to experiment with using a Locktite product to 'glue' the cranks to the flywheel, and oil still seeps out!"
It's a great setup: the drive-side roller allows some flex, the timing-side ball allows some flex (the two extra balls help the bearing to last longer) and Farrell's early cases allow some flex.
"We are getting almost unlimited mileage on the Super-Blends", he says. "I haven't changed them in four seasons."
As a precaution, he does change the timing side balls every year, which you don't need to do on a street motor.
Bear in mind that the crank flexes the most at high RPMs. If you baby your motor and never rev it over 5,500 or 6,000 RPM, chances are you won't have a problem with two Super-Blends. But, as Farrell jokes, "I don't know too many Norton riders who don't run their bike sort of hard, at least occasionally! "
When you go to inspect your own bearings, clean all the oil off them, and use a good light and magnifying glass. Worn-out bearings look pretty good with at light coating of used oil on them.
Farrell concludes, "When you think about putting out about 60 h.p. at the crank, with all that weight that is out of balance most of the time, you realize what tremendous stresses are being generated in that bottom end of yours. It's amazing that the bottom ends hold together as well as they do!
There are plenty of opinions out there, and this is part of how I formed mine. Even though I've talked to countless racers, bearing specialists, engineers and other experts, I find that owning, riding and racing Nortons is a life-long experience".
Mike Farrell and Dick Slusher brought a brace of Redline framed Nortons to the Dirt Track racing event at the National Rally in Quincy last August. If you want to take Mike about bottom ends, or are interested in his steel flywheels, give him a call at (503) 637-3410. He hasn't priced the flywheels yet, but he says they'll be "affordable".