I hope this isn't one time too many - crankshaft end float

I know this has been discussed many times and I know the general consensus is that it's not that important, but being more of a Triumph guy, the issue of crankshaft end float is odd to me.

So, I investigated the various Norton sources I have for crankshaft main bearings and end float (all in inches):

Workshop Manual 065146: .005 to .015
Service Note 68: .010 to .024
Service Note N2/6: Not specified
Service Note N2/9: .010 to .020
Service Note N2/10: .010 to .024
Old Britts: .005 to .010

Each of the service bulletins introduced new thinking on the actual bearings with SuperBlend first being specified in N2/9 and being updated at N2/10.

So, the 1972 Combat I'm building is at .018 with no shims and I'm going to shim it to .012 since that agrees with every source I have directly from Norton and I have two .003 shims.

One interesting thing is that N2/10 says to shim between the outer race and crankcase, but gives the part number for the shim that goes between the crank web and inner race.

Do not shim between the drive side main bearing and crankshaft. It will eventually come out and reek havoc.
No engines with superblends were shimmed from the factory.
Personally I would not shim it unless the play were over about .025. Then maybe reduce it to about .015. Too tight causes problem.
The only problem being too lose might cause is the sprocket on the PTO shaft could rub on the seal. Jim

comnoz said:

Do not shim between the drive side main bearing and crankshaft. It will eventually come out and reek havoc.
No engines with superblends were shimmed from the factory.
Personally I would not shim it unless the play were over about .025. Then maybe reduce it to about .015. Too tight causes problem.
The only problem being too lose might cause is the sprocket on the PTO shaft could rub on the seal. Jim

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Im glad you posted this,
i rebuilt my engine last year and didn't use any shims, then read on the forum about shimming and have had it in the back of my mind since.

When I did my bottom end in '09 end float was at .016 as assembled with no shims. I was told not to sweat the float too much so I didn't.
34,xxx miles later and it still sounds A-OK to me. Now that's not saying that the whole thing won't blow the Hell up tomorrow, but I've had almost 9 years of lower end peace and quiet which is WAY more then I can say about other relationships that I've had.

My mk2a commando came from the factory with 24 thou of end float it was never a problem and covered many many miles

comnoz said:

No engines with superblends were shimmed from the factory.

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Interesting. This engine (209458) was not shimmed. It had roller bearings like specified in the N68 service bulletin (not SuperBlend). I didn't measure the end play before disassembling but it did seem to have quite a bit.

When I assembled the bottom end on my 850, the float was around .025 which was how it came from the factory. I went ahead and put .004 on each side between the case and the bearing. Mostly as an exercise. There were a few things about the process that were a pain.

I assembled the cases with bearings and crank to measure it. Then had to put the cases in the oven again to drop the bearings and put the shims in. Then I discovered how easy it is to slice the end of your finger by checking the inside radius of the shim for burrs! I figured the blood would cause corrosion so I had to clean all that up. Lastly when you drop the bearing in you have to get it to push the shim flat as those thin shims tend to spring. I figured it was all part of being happy with the job I did, which is kind of the point of working on this stuff myself!

Russ

the float on mine is zero and it came like that from the factory in 1971..but its ball and roller never been disturbed

How do you know it’s zero if it’s never been disturbed? You can’t ‘feel’ it from the primary or timing side as the ball race will hold it tight!

The roller bearing however, will / should have some space to allow flex / float / expansion / etc.

When the block was off for a re ring I tried to move the flywheels against the case and still nothing , so I assume it is zero . I doubt the ball race inner on the shaft is still that tight. Its something I monitor because I was told that the roller/ball combination failed at low mileages.. Mine has now done 47,000. Not huge but it has had hard usage .But it has always puzzled me

oldmikew said:

When the block was off for a re ring I tried to move the flywheels against the case and still nothing , so I assume it is zero . I doubt the ball race inner on the shaft is still that tight. Its something I monitor because I was told that the roller/ball combination failed at low mileages.. Mine has now done 47,000. Not huge but it has had hard usage .But it has always puzzled me

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The ball bearing would be tight on the shaft -or the shaft would be destroyed.
Your end play would be zero when the engine is cold. But after a run down the highway it will not be zero. The outer race will float in the case once the engine is hot. Jim

Thanks Jim

oldmikew said:

When the block was off for a re ring I tried to move the flywheels against the case and still nothing , so I assume it is zero . I doubt the ball race inner on the shaft is still that tight. Its something I monitor because I was told that the roller/ball combination failed at low mileages.. Mine has now done 47,000. Not huge but it has had hard usage .But it has always puzzled me

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Making the assumption that Norton is like Triumph when the timing side has a ball bearing, there no "end float" as it's referred to here. The crank is located (locked to) the timing side. However, the drive side with a roller bearing does allow the crankshaft/cases to expand/contract since the rollers can slide horizontally in the race.

marshg246 said:

Making the assumption that Norton is like Triumph when the timing side has a ball bearing, there no "end float" as it's referred to here. The crank is located (locked to) the timing side. However, the drive side with a roller bearing does allow the crankshaft/cases to expand/contract since the rollers can slide horizontally in the race.

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Yes that must be it, but thinking about this more ,since Jims post ,I suppose that as the crankcases heat up and expand that would give clearance when hot. Maybe having had a fairing helps in this regard and I have always been mindful of how long it takes to warm up the engine, but that apart it has been seriously used and it seems to be quite a high mileage for what was still basically an Atlas bottom end.

After a few decades global observations plus my Combat with a reputation long before me, I found ordinary DS roller bearing and TS roller bearing still about pristine and holding crank fast, even though, but likely because this Combat was a sale demo bike in freaking redneck 'hold my drink watch this' wild Ozarks then owned by 2 guys that hated to lose to anything, so hardly ever lolly gagged about, mainly on 2S cam red zone zooming around, then I drag raced to get leap ahead against wheelie bar 1200 over cammed for road use Sportster to upper 70s/2nd - to find bearings still fine & double checked by other competent Nortoneers. Glad to see some rational thinking on factual data points finally getting discussion after decades of slicing ham ends off because mommy did that to find out its only because she couldn't afford a bigger pan at the time.

Now defunct Captain Norton site archived 4 decades old drag racer discussions to see they liked the TS ball for wining reasons as it let the crank flex more before cracking cases, in which case they perfered the thinner 750's as tolerated more flex before fracture than 'beefier' 850's. As crank flexes it levers through bearing races width as pivot vs rest of crank length. As for life time of crank centering nail down TS ball, archives said was about 35K of racing vs maybe 45K of public sluggish use on roller bearing.

I came to my 2000 rpm or shut down habit 1st by old late Nortoneers tutoring me on bearing life best practice, only later I recognized the cam extending affect as well.

Alas none ya newbies ever consider its the rod's firmness squareness tightness on journals in line with piston bore combustion thrusts and intake resistances that determine crankshaft centering so only need cold clearance provision not hot and bothered. DS loads mainly put a bow in the crank and tranny shafts but not much sucking to DS or the friction loads on bearing races would melt through the cases or at least fog-combust engine oil.

Well whilst mine hasnt had such an adventurous life ,ithas been revved well over 7000 a couple of times when caught short whilst overtaking, and has had longish spells at over 100mph and frequently taken upto 6000 . Must admit a lot of bikes in the UK rarely see hard use or revs but they are getting heavy torque loadings as a consequence

Its a dilemma for all us obsolete Norton owners, how much pay back of thrilling road joys vs how much it costs breaking them to hold back ego not winning every game ya might could if was worth it. After a few decades reading various failure and wear modes, seems idle and below 2000ish cruise is worse for cam and bearings so 6000-7000 on factory parts is actually protective of engine, though rough on rest of power train.

Main thing I found limiting factory engine is valve or points float, horrific misfires till rpm back in control. Found this out early on enjoying Combat sprinting past semi truck with oncoming to hit valve float about even with cab, so close call up shift to 3rd to get ahead to pull back into lane in time. Not long ago a sportbiker did this after a cop started chasing him but oncoming in blind turn made him veer back & caught under truck tires dead.