88 crankshaft fixings

Attachments show recently dismantled 1961 650 crankshaft. Nuts, bolts and studs look very similar to previous thread photos. Crank cheek has only minimal recess for bolt and nut shoulders. Note that the bolts have plain shoulders whereas the nuts have a taper.

While making the first Norton Twins Engine Rebuild Video, John Hudson said that he was happy to reuse the original studs, nuts and bolts off a crankshaft if they passed a very thorough examination for stretching or wear. His reasoning, at the time, (1990s) being the doubtful quality of parts being sold in those days.

The last time I tried to purchase crankshaft assembly nuts etc, I was told that only a kit of studs and nuts were available. The nuts all came with plain rounded shoulders and were very similar to model 99 cylinder base nuts.

I am planning on using aerospace bolts (NAS 6305). There is no question about quality since they exceed military spec. They have 160000 psi tensile strength. They are used for ring gears in Formula 1 cars so I think they far exceed the needs of any crankshaft. I still have to find out if I can get studs though. There is the option of using 12 point nuts for more torque but you have to use special washers under nut and bolthead or all bets are off.

I have no religious conviction about using original parts if I can bulletproof the crankshaft.

I am planning on using aerospace bolts (NAS 6305). There is no question about quality since they exceed military spec. They have 160000 psi tensile strength. They are used for ring gears in Formula 1 cars so I think they far exceed the needs of any crankshaft. I still have to find out if I can get studs though. There is the option of using 12 point nuts for more torque but you have to use special washers under nut and bolthead or all bets are off.

I have no religious conviction about using original parts if I can bulletproof the crankshaft.

well I got some aerospace Bolts with a red die inside them as if the bolt fractures the die runs out, then they know the bolt as failed and it then can be changed, yours anna j

I am planning on using aerospace bolts (NAS 6305). There is no question about quality since they exceed military spec. They have 160000 psi tensile strength. They are used for ring gears in Formula 1 cars so I think they far exceed the needs of any crankshaft. I still have to find out if I can get studs though. There is the option of using 12 point nuts for more torque but you have to use special washers under nut and bolthead or all bets are off.

I have no religious conviction about using original parts if I can bulletproof the crankshaft.

well I got some aerospace Bolts with a red die inside them as if the bolt fractures the die runs out, then they know the bolt as failed and it then can be changed, yours anna j

Previously David Cooper wrote:

And another. (Cannot seem to post two at a time this evening). ps Rob - some of my boltt were a VERY tight fit. Afterwards I read that two are supposed to act as dowels but I don't know if the bolts are different, or the holes. Do you have any evidence of this, please? Thanks David Cooper

Neither the Haynes manual nor the factory manual mention this difference in the bolts. If there is a difference (and I haven't noticed it) it would have to be in the holes so that the bolts are all interchangeable. That would be a good thing. Can you imagine trying to fit the right bolt in the right hole when they differ by a few thou? Can you check by fitting another bolt in the tight hole?

Previously Rob Bradley wrote:

Continuing my crankshaft saga, I've now had another surprise concerning the bolts holding the assembly together.

Having re-used the original bolts and nuts more than once, I decided it might be time for some new ones, which I got from Andover Norton. I noticed straight away that they looked different from the originals in just being chamfered whereas my old ones have a shoulder. The significance of this dawned on me when I tried to fit them and found that in the two outermost holes they wouldn't sit flat on the crank web. This is because these two holes have been drilled where the casting starts to curve upwards to the big ends, and thus there is a recess on the inboard side which the hexagons are too big to fit into.

Not easy to describe but the attached pictures should make it clear.

I contacted Andover Norton and they say the bolts and nuts they supply are correct according to the 1947 drawings. My crank is a 1963 item, so maybe some changes were made after 1947? Or is it just an example of Norton's manufacturing variability?

Possibly this may only be an issue on the 88 crank, as my 99 crank only has a very small recess at these positions, and so I suspect on the larger cranks the bolt holes may be on a flat surface. But I'm not going to pull my Commando to bits to look!

It's easy enough to file two of the new nuts and bolts to fit, or I could just re-use the originals again.

Can anyone solve this mystery for the benefit of Andover Norton and other unsuspecting 88 owners?

P.S. Sorry for the two identical images of bolts, the editing option won't let me delete one.

Hi. just looking at a commando crank on the net . looking at it with the crank pins at 12 0 clock the top two nuts are small ones the second pair are large nuts the bottom pair are studs with nuts and lock tabs both sides. i can only assume the ones causeing the problem are the ones that suppose to be smaller nuts same bolt size just physically smaller nut. on about the bolts being tight fit thats what they say they should be. just wondering if you marked the crank and kept it same way around .it might be alignment issue. i have never done one myself just thought it might help

Baz

Just to add a few more details.

Some of the Commando cranks had 3/8" bolts/studs.

Plus ......it is possible to use a torque wrench to tighten the nuts and bolts. I have put together lots of cranks using a torque wrench with a ring spanner adapted to fit the wrench drive. I set the torque load by testing it out on a nut & bolt held in a vice. Explaining the mechanics would take too long in this thread but it works for me and I have never had a failure in 40 years.

Now you have got me a bit worried.................so I have just gone back inside my garage to check on the chunks on my crankshaft.

I have a similar issue as Rob and in the same position. One crank cheek hole that is significantly smaller than the others. measuring up with a metric caliper gave all the holes bar one at roughly 8.2mm. The odd one being just 8.0mm in both corresponding cheeks. The flywheel holes were all about 8.2mm and allowed all the bolts and studs to wobble by about 0.008". (8 thou). But only on their shafts. The threaded sections are a very tight squeeze to get through the holes.

Adding to the mystery of my crankshaft.............When I sent it off for a grind it was all complete but came back in disassembled sections and stamp marked with 'T' & 'S' on the flywheel. I was impressed. However, when I tried to match up the whole shaft I discovered an extra locating pin in the Timing side cheek. The flywheel locating pin still being in position. Somebody else is short of a very important piece of their flywheel.

Previously phil_hannam wrote:

Now you have got me a bit worried.................so I have just gone back inside my garage to check on the chunks on my crankshaft.

I have a similar issue as Rob and in the same position. One crank cheek hole that is significantly smaller than the others. measuring up with a metric caliper gave all the holes bar one at roughly 8.2mm. The odd one being just 8.0mm in both corresponding cheeks. The flywheel holes were all about 8.2mm and allowed all the bolts and studs to wobble by about 0.008". (8 thou). But only on their shafts. The threaded sections are a very tight squeeze to get through the holes.

Adding to the mystery of my crankshaft.............When I sent it off for a grind it was all complete but came back in disassembled sections and stamp marked with 'T' & 'S' on the flywheel. I was impressed. However, when I tried to match up the whole shaft I discovered an extra locating pin in the Timing side cheek. The flywheel locating pin still being in position. Somebody else is short of a very important piece of their flywheel.

More likely is that you have someone else's timing side cheek. The machinist probably didn't take anyone's dowel out, just left them in place.

As you say, the other fellow is unfortunate and will be complaining.