Norton crankshaft flange squaring

I'm fairly new to the forum so I don't know if this subject has been covered. I did some searches and did not find previous discussion of the topic.

I build a lot of Norton engines and have for years relied upon a crankshaft specialist who has chosen to live in this small town after being a Porsche race team engine machinist.

Several years ago, he pointed out to me that Norton crankshafts are improperly machined, from the factory. The crankshaft mating flanges are not properly squared to the flywheel. The cranks were apparently assembled without being properly squared, and were then given final polish. So, basically, the cranks are crooked...improperly aligned, due to manufacturing inaccuracies.

Since then, my machinist now squares the crank flanges to their pin centers, then squares the flywheel mating surfaces, then assembles the crank and grinds/polishes the journals. (Downside: This means that even a perfectly good crank, journal-wise, has to be ground .010 under following this procedure, unless the flanges were near-perfect prior to the squaring. So far, no crank has met this standard, all are pretty far out.) This procedure also requires adjustment of the endfloat of the crank in the cases.

I'm mentioning this (knowing the post will be greeted with multiple calls of "hogwash" or worse) because while costly ($250 for the complete crank preparation) I feel this process results in a smoother running engine, with less stress on the flywheel fixing hardware, and better alignment of the rod bearings on their journals.

Let me emphasize that we never begin work on a crank without thorough crack-checking.

Submitted for consideration and discussion.

Skip Schloss

$250 sounds very reasonable. What do we get for that ? - What happens if the main-shafts are not central and square to the flywheel ? I have never thought to check that because my last bike had a billet crank. Is there a superblend bearing with a slightly smaller ID, so I could slightly reduce the main-shaft size ?

What we get for $250 is the crack checking, the squaring of all crank components, the grinding and final polish of the journals.

Now, most of the recent engines I've built use a lightweight flywheel from a prominent Norton parts builder I shall not name because he doesn't want to sell flywheels separately.

My machinist is happy to adapt these flywheels, and accompanying hardware, for no addition to the $250 fee...because the flywheels are perfect as delivered and require no additional machining.

Skip Schloss

I now realize that the tradition on the forum is to list one's bikes below the sig line.

1974 Norton Production Racer Replica, 850
1973 Norton Production Racer Replica, factory Short Stroke 750
1975 BMW R90S
2000 Ducati ST2
1959 Bonneville 650
1962 Ducati 350
1975 Norton Mk. III (under construction)

I wonder how Norton achieved this?
I dont have any unassembled cranks otherwise I would do some checking,
sounds like a mission for Comnoz or at least his opinion.
I'm sure you are gonna get plenty of discussion on this.

How do they grind the crank after assembly? on a standard crank the flywheel sides intrude into tne line of the inner surface of the crank journal. This sounds like a worthwhile exercise but I doubt many machine shops have the ability to do this.

OP, Please define "squaring" as used in your description. Making both rod journals concentric after the crank is assembled? Making the main journals concentric? Making the journals all parallel? :?: :idea:
Or making the flywheel bolt flange perpendicular to the rod journal?

what he means is the journals are not at 90 degrees to the flywheel mounting face.

When the crankshaft was built in the factory, if the crank was bolted together then the journals were ground, it shouldn't matter if the flanges were square to the flywheels or journals.

Makes me wonder what problem is being solved by squaring the flanges and mating flywheel surfaces? Especially if you have to grind the journals undersize.

Stephen Hill

Could the factory grind the journals with the crank all bolted up ?

I always understood (for no particular reason) that the journals were ground separately, and then the crank all bolted up.
That eliminates the possibility of swarf getting inside the crank too, a real risk while grinding journals....

If the crank bolted up very far out of square, you'd spot it a mile away when you tried to swing it in the lathe when checking it was true.
The ends of the crank doing gyroscopics is a bit of a giveaway...

I don't think you can easily grind the journals if the crank is assembled. The flywheel weight is wider than the inner part of the journal making it difficult to access the journal with a grinding stone. I always have to dissasemble the crank and give the two cheeks to the machine shop who gring the journals concentric with the shafts.

As above...

All my cranks are delivered to the grinder with the flywheel removed and the flanges bolted together.

Skip, maybe your crankshaft man can enlighten us on how much Norton cranks run untrue , I'm not asking how he solves the problem
but I'm keen to know how much the discrepancy is between a standard crank to his modified crank,
surely someone paying money to have their crank rectified is entitled to know this info.

I believe that the original assembly workman at the factory pulled the Flywheel from one bin, the drive side journal from another bin and the timing journal from yet another. With this he assembled the Norton crank and that's as far as the QA that went into the total alignment of the assembly other than a general visual inspection of the matting surfaces. It was hit or miss if you got one Commando that put out more power than the next on the showroom floor. I have never heard of the mating surfaces being misaligned as a problem and I do not doubt that this has occurred. I think the biggest misalignment occurs between the 7 holes in the two journals as a matched pair. When the crank assembly reaches TDC one journal could be 0.010" lower than it's mate. Hence why ARP bolts used when careful assembly to the crank once the holes are properly aligned and line bored so the journal center line are axial with each as a pair. This is the easiest way of getting free horsepower when both cylinders are working as an even pair together. Comnoz has shown a Thread with pics of machining a Norton head so both chambers are more evenly matched for volume. This may not have anything to do with this thread but more so in how to match both cylinders of a Norton vertical twin engine to work together as a single unit. Careful assembly to key components. Just think of two carbs out of sync and you have been riding that way for a long time. Once you get them both to sync, you wonder where all that power came from.
Cheers,
Tom
CNN

After repeatedly hearing what clapped out machine tools Norton was using in the factory, I find it difficult to believe that they could machine the three crankshaft components independently, bolt them up, and have the journals run true with no further machining.

We heard that two people dismantled their cranks for grinding.
Anyone had their crankshaft journals ground when assembled as a single unit?

Stephen Hill

Stephen Hill said:

We heard that two people dismantled their cranks for grinding.
Anyone had their crankshaft journals ground when assembled as a single unit?

Stephen Hill

Click to expand...

Stephen,
I have also dismantled the crank and bolted the cheeks together for the machine shop. I don't think there is enough room for the stone to reach the 0.090" thou inboard radius on the journal which "you must specify" to the grinder to not remove as it becomes a stress riser and will crack at this location. It will grenade the whole works if it is not maintained during the process. The flywheel is too wide in stock configuration. Jim Schmidt's Norton Race Manual shows a crank mod for racing and you may be able to grind the journals in situ.
Cheers,
Tom
CNN

I think the biggest problem is not the height of the pistons at TDC. However if the main -shafts are skewed or off centre..... ?

Nobody has had their crank ground as an assembled unit?

Stephen Hill

Stephen Hill said:

Nobody has had their crank ground as an assembled unit?

Stephen Hill

Click to expand...

As CNN pointed out, you can't grind the journals on a stock crank with it assembled. The flywheel is too wide to clear the grinding wheel. Plenty of people, including me, have had non-stock Commando cranks ground while assembled, but I'm assuming you are asking about stock crankshafts.

Ken

lcrken said:

Stephen Hill said:

Nobody has had their crank ground as an assembled unit?

Stephen Hill

Click to expand...

As CNN pointed out, you can't grind the journals on a stock crank with it assembled. The flywheel is too wide to clear the grinding wheel. Plenty of people, including me, have had non-stock Commando cranks ground while assembled, but I'm assuming you are asking about stock crankshafts.

Ken

Click to expand...

Is it that the stock factory 850 flywheel overhangs the journals. I have read here and elsewhere the 750 and other smaller Norton twins don't have this issue as they have less mass and so are narrow enough to be left in place and not overhang the journals.

toppy said:

Is it that the stock factory 850 flywheel overhangs the journals. I have read here and elsewhere the 750 and other smaller Norton twins don't have this issue as they have less mass and so are narrow enough to be left in place and not overhang the journals.

Click to expand...

You could be right. I know that when I had my first Commando crankshaft (for a 750) at the grinder, I had to bolt it up without the flywheel to get him to grind it. And I've done it that way ever since. That was 40 years ago, and my memory of it isn't all that great. There may have been a different reason. My memory says it was the width of the flywheel that caused the issue, but I'll take a look at a couple of cranks today to see if that's really the problem.

Ken