Crankshaft end float woes… no movement, just solid with no end play!

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swooshdave said:
I bet that wasn’t the only thing that shrunk that morning.
Click to expand...

I recall this cartoon from the great Shobba...

Crankshaft end float woes… no movement, just solid with no end play!


A couple of extra items for the err...toolkit!
Andy
 
I had previously inquired with RGM, as it wasn’t clear which bearings came with the bottom overhaul kit.

The C3 are not standard, but can be easily swapped in by request. One just needs to put a note in the special comments when ordering.
 
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I just wanted to provide a final update to this saga and after some sound advice from our esteemed group members I swapped the standard main bearings for C3 clearance units. I now have excellent crank end float! Plus the crank spins by hand more freely. Had I left the standard bearings in they may well have overstressed themselves. To conclude… I can strongly recommend C3 clearance main bearings as the default replacement. A big thank you to all those who offered advice.
 
I was wondering if an AGA would be best way of heating your cases... There is no flame or direct heat contact in the oven and the casting would take appreciably longer to come to temperature. But it seems the issue is resolved.. Alls well that ends well.
 
oldmikew said:
I was wondering if an AGA would be best way of heating your cases... There is no flame or direct heat contact in the oven and the casting would take appreciably longer to come to temperature. But it seems the issue is resolved.. Alls well that ends well.
Click to expand...
Mike... yes, I use my wife's AGA for such purposes when she’s out on an extended shopping trip. It’s the perfect tool for heating cases and cylinder heads without overheating them and damaging things like oil seals. Place in the bottom left (lowest temp) oven and you’re good to go!
 
Well, this has certainly been an eye opener. Just checked RGM's website and sure enough they sell both C3 and standard.
It appears the lower end overhaul kit includes the standard bearing, does not mention C3 available on request.
I'm sure one can request the C3 at order, but is an extra step one must make consciously,
My question is if C3 is the preferred bearing, why are standard's being offered?
 
MichaelB said:
Well, this has certainly been an eye opener. Just checked RGM's website and sure enough they sell both C3 and standard.
It appears the lower end overhaul kit includes the standard bearing, does not mention C3 available on request.
I'm sure one can request the C3 at order, but is an extra step one must make consciously,
My question is if C3 is the preferred bearing, why are standard's being offered?
Click to expand...


Yes, that’s exactly how I got caught out. If only I had known all this before ordering it could have saved me a lot of unnecessary cost and hassle. For those who venture into the world of rebuilding Norton engines for the first time, there are a number of banana skins to avoid. Perhaps there are cases of standard bearings replacing old without problems but the fact Andover’s stopped selling non-C3 Norton main bearings years ago speaks volumes!
 
Soundbite said:
Would you have a copy of this by chance?
Click to expand...

On Main Bearing dimension and specifications
On our new Triumph pages you will notice we list two main bearings for the drive side of 650/750 Triumph engines. A somewhat puzzling part number, 68.0625, and another non-standard one, 70.2879C3.


A few years ago I had reports from people I have known and respected as meticulous engine rebuilders for many years. Mick Hemmings and Rudi Kolano complained about the Norton main bearings, and Germany’s best Triumph engine man Joerg Winkelmann about the Triumph ones.
Norton specified standard tolerance bearings for their 06.4118 “Superblends”, Triumph even specified C2 bearings (tighter tolerance) for their drive side main bearings 70.2879.


With modern manufacturing techniques it appears tolerances can now be held at the low side of the norm. The problem became apparent in engines freshly assembled in the workshops of these three protagonists as well in engines that failed and came into their workshops from customers frustrated with the work of previous repairers.


The common problem was that the crankshafts didn’t turn freely, in fact in many cases didn’t turn at all. Which was happily ignored by many “engine specialists”. We therefore changed the Norton main bearings to C3 spec (bigger tolerance) a few years ago and at first the Triumph ones to standard clearance from the C2 “tight” spec. We used the BSA A65 part number for these (68-0625), because BSA A65s had that bearing in STD tolerance and used that number for it. In many cases it was found even the standard clearance was still too tight in Triumph engines, so we introduced the C3 main bearing, now called 70-2879C3.


On the drive side Nortons and Triumphs started out with ball bearings in their twins. These weren’t critical at first but with increasing power figures became a weak point in the engines. Nortons can easily be changed to the Superblend on the timing side. In fact I’d use the Superblends on the timing side in every Norton twin engine.Triumphs stayed with the ball bearing in imperial size till 1972 when they changed the late 650s to a metric bearing dimension.



This was again a ball bearing but later in the T140’s life this was changed to a roller bearing with a split inner ring. Triumphs as a compromise meanwhile intentionally de-tuned the 750 engines with a soft exhaust cam to extend the timing side main bearing life.
 
dynodave said:
To be sure of the reason you must go inside the cases and push the crank cheek with a screwdriver and try to force it back and forth. If the screw driver moves it but a hand hold push pull does not ...
I've had this happen 2 times, Both were the result of not using C3 clearance bearings. Removed and replaced fixed it. Believe it or not it is not long ago some parts dealers still have the incorrect standard clearance bearing and are still selling them. Ihave one standard set I will never use on a norton.
The problen stems from standard bearings are engineered to be used in steel or iron housings not aluminum, which calls for MORE shrink fit so you need more internal bearing clearance.
Click to expand...
Props to DD for solving this and bringing it to light..
 
28 Oct 2011 ?
not exactically new!
www.accessnorton.com

C3 vs CN

If both C3 and CN crankshaft bearings are available, is it still best to go to the C3 bearing? I have never been clear on the reason for this shift in the recommended bearing. Thanks, Russ
www.accessnorton.com www.accessnorton.com

I love this from JS
snip
"A club is but a club, i.e. a gathering of enthusiasts of varying knowledge, so I tend to rather listen to professionals.

If two professionals, who have in the past shown they are competent in what they do, and one of them a master toolmaker to boot, tell me (and show me!) that the standard bearing spec has become too tight and if, after they told me that, they have built a great number of engines of which I have ridden some with the C3 bearings which work fine on road and track, I tend to believe them."

Folks are also, like Joe, hard to convince and slow to catch on.
 
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I wonder ,if the engine is warmed up before being revved and the cases donot actually have negative clearance , whether this is a huge problem for everyday use in warm climates .
 
oldmikew said:
I wonder ,if the engine is warmed up before being revved and the cases donot actually have negative clearance
Click to expand...
Please define negative clearance
Some new physics ?
What is happening is no engineering mystery but the consequences are not entirely desirable.
 
oldmikew said:
I wonder ,if the engine is warmed up before being revved and the cases do not actually have negative clearance , whether this is a huge problem for everyday use in warm climates .
Click to expand...
I know when I put superblends in a 1965 Atlas it had no movement side to side , but if you warmed the cases about 20 degrees above room temp. It had the end play I wanted,

I would think the clearance is also determined by the OD of the shaft the inner race it is put on to. If I did the math right there is approx . .0012 difference in the CN and C3 Radial play and it can be less because I'm using the extremes of the tolerances of the two bearings CN and C3. The tolerance numbers actually overlap so there can be Much less

I did request CN bearings from RGM, I see no ID marks on them , but I had no end play problems in 1973 850 and MK3 cases with end play , I added a 10 thou shim to each Engine to get the end play at about 7 thou and it slide bask and forth in the cases easily.
 
The 2011 thread on this subject also refers to overlapping tolerance of CN and C3.
This post also contains some data on tolerances from 'ten years ago' https://www.accessnorton.com/NortonCommando/c3-vs-cn.10179/post-137420

The '2001' data are as follows:
Clearances before installation
C1 5-15microns (for a 30mm ID bearing)
C2 5-30
C0 25-50
C3 45-70
C4 60-85
C5 85-110

From the 2019 FAG HR-1 Catalogue (Section 1.10, Pg 424)

Crankshaft end float woes… no movement, just solid with no end play!


Tolerances look to have changed over time. I know it's only 2 different years, but I've attempted to show the CN and C3 differences using the ranges (max/min) plus a mid point as the mean and interpolated values using 'Box & Whisker' plots.

Crankshaft end float woes… no movement, just solid with no end play!

This shows how clearances have changed over time. There is now considerable overlap between the range of a 2019 C3 and a 2001 CN. Also increased overlap between a 2019 C3 and CN. It's therefore possible to see how a CN bearing from 2001 would fit leaving sufficient end float but also why a CN bearing to 2019 spec might not.

It's all a bit 'How many angels can dance on the head of a pin?' but at least this might help explain some of the different experiences.

Andy
 
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