Why ball bearing mains?

DSM-IV code 295.10 :lol:

Yes Sir Dances an ex-wife MD head-shrinker DX'd me with a hand full of codes and tried various meds on me that I couldn't stand their dulling of my LSD and mushroom plus brain injury induced reality - but she still left her 1st husband for me d/t the fantastic rides out of this world. We agree'd to stay together until honey moon wore off, which lasted 7 yr then I got bored with her glamor focus and we moved on to our next serial monogamous relationship. Ms Peel gave me better longer lasting multiple orgasms - I only wish yo'all eventually experience too once giving up normal scope of power handling on edges of life and death.

No one else talks about cycles entering and raveling in reversed control input phenomena but aircraft test pilots and Peel's pilot. Its an emergency in aircraft and ordinary cycles but its Flabbergastingly Fabulous on a tamed isolastic wonder. Btw the name of my riding school will be "Ricochet Rabbit Riding Ranch and Rifle Range".

Two questions:

Why did she stop at only a handful?
What does this have to do with the thread?

Dances with Shrapnel said:

Seeing how it appears to be a common problem between the Seeley Mk 2 and Featherbed, maybe the rear cross brace failure on the frames are a result of torsional fatigue rather than engine vibration.

As for the selection of BF for the Norton big twin and similar 360 degree twins, this was all nicely outlined in another thread. The hierarchy is:

1.) Does the BF cause unacceptable vibration comfort to the rider for the intended use?
2.) Does the BF break the frame or other components?
3.) Does the BF minimize the internal stresses in the engine?

Items one and two always take precedence over item 3; thus item 3 is usually compromised.
The isolastic system more or less obviated items 1 an 2 above thus leaving the designers to optimize item 3.

Click to expand...

You choose the BF to suit the revs at which you want to use your engine . If the valve gear won't keep up or the piston speeds are too high, there is no point in building a top end motor, but a 53% BF in a commando is probably ideal at 3000rpm. If you want to use the bike mainly to ride to work, keep it standard , otherwise ...... ? If you had to ride my Seeley in traffic, it would drive you insane, but when it's raced you use 3000rpm to 7000rpm, and it is really great with a 72% BF.

The reference to BF in this article might interest you:
http://guskuhn.net/GKMLtd/Racing/1996TrackTest.htm

How can there be 10 thou end float with a ball bearing main bearing? Surly the ball bearing holds the crank in location ,unless the bearing is not a locating type. or slack on the shaft .

Since there is nothing to positively lock the bearing to the shaft, why not ?

When Norton motors ONLY had ball bearings as mainbearings on the crank ie most single cylinders, the manual shows checking for crank endfloat by using a pair of tyre levers to lever the crank in and out, while fitted in the cases.

P.S. the overheadcam motors need a small negative enfloat when assembled (cold) so that in operation once warm the endfloat is about zero. Or trouble with the mesh of the bevel gears will ensue...

Hopethishelps.

john robert bould » Sun Jan 13, 2013 1:44 pm
How can there be 10 thou end float with a ball bearing main bearing? Surly the ball bearing holds the crank in location ,unless the bearing is not a locating type. or slack on the shaft .

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hm: Crank shift space ain't the same as crank actually shifting across that much space. Rod end shells on journals have a big influence on keeping crank essentially centered over the bores, unless the bores screwy. Idealy ball inner race is a thermal interference fix on shaft and the outter races also held well in the cases, at least rather better than the rolling element drag. Video by Mr. Hudson a very famous late authority on rebuilding is shown frowning at the TS ball not slipping on/off the crank stone cold so he whips out sandpaper on crank till bearing slipped on/off easy as pie him looking up grinning to move on, like using the huge blow torch roaring over conversation till cameraman had to put out the oil rags fire... Therefore > if cases and crank and bores constructed well then a press fit TS ball should trap crank centered in its load vectors first time every time.

Please correct or refine this hobot mental animation of the dynamics.
if TS ball traps crank from shifting then its a pinch point in the bowing jump rope distortions of a straining crank. If the TS ball has pinched the shaft in two planes, ie: only allowing shaft rotation, not shifting or orbiting then the bowing flexing action must be minimal at the ball contact ring for a nodal point - hinge of stillness with all the deflection happening on either side of the balls. The end of the crank traces out a distorted squashed cone, pinched in narrower-flatter above rotation center and wider peakier below midline. Replacing with a barrel roller that is free to shift on its roller elements needs something to limit crank shifting if the rods didn't anyway. As the crank bows its contact on the width of the rollers shifts closer to outer roller ends, so superduperblend should develop more and more thrust into center of the crank axis, which may or may not be an issue. Ball would not develop its own side thrust, if matters.
Seems to me the s-blends can transmit more loads into cases than balls, if that matters.


The down side of balls under great shock stress is they moosh down out of round.

Ducati used angular contact bearings for the mains for the 1971 750 GT,that followed though to the last beveldrive twins in the mid 1980's.
I imagine Norton might have considered that option but it would have taken a new crank case to suit the large OD of the bearing.
Those bearings are preloaded around 0.003" (cold) via crankshaft shims in the Ducati.

We seem to have got a bit of confusion here on end play vs. which combination of main bearings are used. Maybe it's time for a little review of the basics.

1. Early Commandos had a roller main bearing (not "superblend") on drive side and ball bearing on timing side. The ball bearing was in fact a tight enough fit that you probably couldn't measure any end float in the crank by prying the crankshaft against the cases. To disassemble the bottom end, you first removed the drive side case half with some judicious taps with a soft hammer, or piece of wood, or whatever. Maybe even a little heat on the case, but the outer race stayed in the case. Unless the cases were pretty worn, you had to heat the timing side crankcase half to get the crankshaft and bearing out, after which you could pull the timing side ball bearing off with a puller. Granted it was not as tight as on the later crankshafts with superblends on both sides, but it was still tight enough most of the time to require a bearing puller to remove it. I've seen it suggested that you could also remove the crankshaft and leave the bearing in the case by hammering on the end of the crankshaft with a brass hammer, but that never seemed like a bright idea to me. The factory specs for the timing side fit allowed a range of .0004" clearance to .0001" interference fit. All the ones I ever worked on were tight enough to require a bearing puller to remove. Maybe John Hudson had a crankshaft at the .0004" clearance end of the spec.

2. If you replaced the main bearings on an early Commando crankshaft with superblends, you had a tighter interference fit on the drive side, because the timing side shaft was slightly smaller in diameter than the drive side, to accommodate the fit required for the ball bearing. We're not talking huge differences here, something like .0003" - .0005" difference between main and timing side shafts. Norton put out a service note recommending the change to superblends for both main bearings on the older engines, and said to shim the crankshaft for .010" - .020" end float. That's the first mention I've seen of a need to set end float on a Commando.

3. When the factory went to superblends on both mains somewhere in '72, they enlarged the timing side shaft to the same size as the drive side to accommodate them. The recommended end float was still .010" - .020".

4. As Jim Comstock pointed out, end float doesn't seem to really be very critical for Commando engines. I've seen stock street Commandos that ran for years with no crankshaft issues, that measured .040"+ end float when torn down. Most Commando race engine builders I know shoot for something like .005"-.010" end float. That's what I use, but I've raced engines with way more crankshaft end float with absolutely no problems. It's nice to set it if you're already building an engine, but it's nothing to lose sleep over. No need for concern over the rods not being centered. There's plenty of clearance at the small end between piston and rod to allow the crank to float back and forth a bit.

5. Yes hobot, and others, we all know by now that "superblend" is an advertising term, not a technical one, but it's still a convenient way to refer to the roller bearing Norton used for all the later Commandos. Easier than saying 6MRJA30 or NJ306E or part number 063114, and at least everyone by now knows what you mean by the term.

OK, that was my crabby bit for the day. I'm better now.

Ken

acotrel said:

Dances with Shrapnel said:

Seeing how it appears to be a common problem between the Seeley Mk 2 and Featherbed, maybe the rear cross brace failure on the frames are a result of torsional fatigue rather than engine vibration.

As for the selection of BF for the Norton big twin and similar 360 degree twins, this was all nicely outlined in another thread. The hierarchy is:

1.) Does the BF cause unacceptable vibration comfort to the rider for the intended use?
2.) Does the BF break the frame or other components?
3.) Does the BF minimize the internal stresses in the engine?

Items one and two always take precedence over item 3; thus item 3 is usually compromised.
The isolastic system more or less obviated items 1 an 2 above thus leaving the designers to optimize item 3.

Click to expand...

You choose the BF to suit the revs at which you want to use your engine . If the valve gear won't keep up or the piston speeds are too high, there is no point in building a top end motor, but a 53% BF in a commando is probably ideal at 3000rpm. If you want to use the bike mainly to ride to work, keep it standard , otherwise ...... ? If you had to ride my Seeley in traffic, it would drive you insane, but when it's raced you use 3000rpm to 7000rpm, and it is really great with a 72% BF.

The reference to BF in this article might interest you:
http://guskuhn.net/GKMLtd/Racing/1996TrackTest.htm

Click to expand...

This is all regurgitation of ancient history. The isolastic system eclipsed all of this.

The Gus Kuhn article you reference is fine but truely apples to orangutangs as they were dealing with a solid mount engine and trans - of course they had to compromise the BF to keep the rider from being frayed and frame from failing. The higher balance factors are a relic of the older solid mounted engines - still valid as a necessary compromise if you run a Seeley or Featherbed today but totally unnecessary and sub optimal when running isolastics.

In the context of racing and street riding an Isolastic Commando, the higher balance factors are no longer a necessary compromise.

I think DWS has the right of it here. Commandos with isolastics and frames with the engine rigidly mounted are two completely different breeds when it comes to picking a balance factor. We do seem to have got them confused with each other in some of these discussions. On the other hand, we haven't discussed BF for hybrids like the "featherlastic" yet. I'd assume it's the same as for a Commando, but I'm sure we could beat the subject to death for a few pages.

Ken

On Ken's beaten to death note, seems to me that a rubber mounted engine experiences less shock loads through its parts than a solid mounted one. When cranks snatches pistons down the motor and jump up to meet the pistons some and on combustion would recoil away from pistons some. I'm imagining this going by hammer and other hits to my skull with and without some amount of cushioning between, other than thin flesh, but for sure thick hippie hair helped dull strike spikes.

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".

Lots of good ideas there, Thomas. It looks like we all have some experience with bottom end failures, but don't all draw the same conclusions from them. The first set of cases that I had break in a race bike were the early '71 cases that Farrell likes, and the crank had the original roller drive side and ball timing side races. The case cracked on the drive side at the back just above the top cradle bolt, where the early cases were very thin. I had the cracks welded, along with some added reinforcing ribs, and used that set of cases with no more problems for several years of road racing. The original crankshaft eventually cracked around the drive side mainshaft, after a few seasons of racing. Over the next couple decades I had several other cases break on the drive side half, on a line from the mainshaft bearing bore back to the case joint behind the cylinder, just above the top cradle bolt. The cases that broke included another early 750 case that I had reinforced with ribs behind the cylinder and above and below the upper cradle mount, a stock 850 case in a short stroke 750 engine, a heavily reinforced MKIII case in a 920 engine, and a heavily reinforced 850 case in another 920 engine. I also managed to break several race-prepped crankshafts, and there may have been a couple more broken cases. The breakage all happened between 1972 and 1993, and I'm only describing the ones I recall in detail. The conclusions I drew from my experience were that the engines with reinforced cases and one-piece crankshafts lasted longer than the others, and I never saw any connection between whether the timing side bearing was ball or a roller. The 920 engine I'm running now has heavily reinforced 850 cases and a one-piece Nourish crankshaft, and really seems to be bulletproof (so far). I also think that the combination of original Commando cases and crankshafts, of any model, in a road race bike that makes high horsepower and is ridden aggressively, will eventually result in broken cases or crankshaft, or both. It's just a matter of time. With modern aftermarket replacement cases, crankshafts, rods, etc., I think it is possible to build much more reliable Commando race engines. It's still possible to break them, but it takes a lot more abuse to do so.

Just my humble opinion, and it could be wrong. I'm not trying to convince anyone, or prove anyone right or wrong, just passing on some experience.

About the only thing I'm really sure of is that, all other things being equal, the more horsepower the engine makes and the harder the pilot rides, the more often things will break.

Ken

This is a great thread with tons of info...another reason I love this site.

comnoz said:

I have good pullers for the bearing race on the crank ..............................

Click to expand...

Jim,

Pictures, brand, and/or catalog number for the puller you use will be appreciated - at your leisure.

lcrken said:

We seem to have got a bit of confusion here on end play vs. which combination of main bearings are used. Maybe it's time for a little review of the basics.

4. As Jim Comstock pointed out, end float doesn't seem to really be very critical for Commando engines. I've seen stock street Commandos that ran for years with no crankshaft issues, that measured .040"+ end float when torn down. Most Commando race engine builders I know shoot for something like .005"-.010" end float. That's what I use, but I've raced engines with way more crankshaft end float with absolutely no problems. It's nice to set it if you're already building an engine, but it's nothing to lose sleep over. No need for concern over the rods not being centered. There's plenty of clearance at the small end between piston and rod to allow the crank to float back and forth a bit.

Ken

Click to expand...

Ken,

When I built my race motors in the mid '70s as a nieve 21 year old I did not own a dial guage, they were expensive luxuries, not cheap and disposable like they are now....setting up the crank involved making sure it rotated freely and there was some sideways movement....who knows how much, just not much.....I di read John Hudson's notes.....but I would have to go find my copy...dutifully typed by my new wife from a set borrowed from the local Norton shop.....to see hwt ahe said about that...I know he didn't say anything to worry me...or I would have worried about it :? Both motors ran 'Superblend' and Les Emery's insistance that I could save a few pounds using a ball did not convince me much as in both cases I already had the rollers....

To me this is still so much a non-issue....I will use Andover Norton supplied 'Superblends', even if they are 'FAG made in India', and considering the cost of the rest of the engine price is simply no issue, and like you I am pretty convinced that there is enough clearance in piston and rod to let it all move if it wants to.......

But like the guys say...its an interesting discussion that brings out some useful views....but it does seem there are some firmly in the 'balls' camp whatever is said.....

My 750 revs to 9000 with no issues, its short stroke and a FOUR bearing crank. sorry to say it.s in my Laverda 750S :lol: I think if Nortons had developed the Commando unit it would be the same as the Modern Laverda, 270 crank with balance shaft ,D.O.H.C eight valve ,fuel injection etc. 92 HP.

On 750 SF Laverda you had 4 ball bearings AND roller cages in the outer primary cover on both crankshaft and gearbox shaft acting as outriggers . quite clever