Bad news from the stars

If it hasn't blown by now - then I wouldn't worry about it (if that's possible - but tearing it down would solve the mystery). Its probably an odd nut that someone "oops" dropped in. The first Norton I got had a chunk of wood in the sump - that's right - a chunk of wood - proof that Neanderthals are still with us.

If it was me, I would be hoping that it was the last one in there rattling around...

It's about the right length for a crankshaft nut. The 5/16" nuts on pre-MKIII crankshafts were about 1/2" long for the long ones, and about 3/8" long for the short ones. This looks a lot like one of the short ones. Is it 5/16" or 3/8" thread size?

Is it cad plated, or plain? As Dances pointed out, the stock crankshaft nuts were not plated. but the cylinder and head fasteners were.

Ken

jseng1 said:

If it hasn't blown by now - then I wouldn't worry about it (if that's possible - but tearing it down would solve the mystery). Its probably an odd nut that someone "oops" dropped in. The first Norton I got had a chunk of wood in the sump - that's right - a chunk of wood - proof that Neanderthals are still with us.

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I'm sure you heard the story of the old fart that ran the case boring operation for Norton-he retired when they moved to the later location. His replacement couldn't bore a set of cases correctly to save The Queen, so they called the old guy back in to see what the problem was. He looked at the boring bar and said, "Aye, where's me stick?" A volunteer was dispatched to the old location and returned with a grimy chunk of 2x4 with a half-round worn into one end. The old-timer jammed the stick between the upright and the slopped-out arbor and bored a perfect set of cases. Maybe your wood chunk was a piece of that very stick.

It could be a crank flywheel nut. If fit was, I am surprised the bolt hasn't come out and mangled the engine. Don't take a chance because the first you hear the bolt hitting the con rod, will be nano-seconds before it blows apart, and you wont be able to stop it. The worst scenario if there is nothing wrong is that you have to put it back together again, but at least then, by using the right sealers, the engine wont leak. [ if it does now ]

Dereck


You poor bugger.

Well,thanks a lot for all of your replies.

Draining the oil, it looked new. So 3 cases:
- Since the rebuild in 2014, it never run, or only a very few and short time. That's possible because the gas in the tank was smelling old. And the theory of a "oups" dropped nut could be good.
- After the last oil change, it run a very little and the nut unscrewed there.
- Or the seller, who is a retired engineer as he told me, sold the bike because of a strange noise :?

The seller told me that the engine was rebored and bearings were changed. Like the barrel have a brand new paint, it certainly was taken off, but after to know what was really done, there is only confidence. Or not :mrgreen: The seller also gave me a 2014 bill from Richmond Motorcycles Inc. Amount is $ 1,620.00, but it's not that interesting because there is no information about what was really done.



I also asked for a video before buying the bike. There are some strange noises, at 20sec., 29sec., 36sec., 38sec., but who could tell it was coming from the engine?
https://drive.google.com/file/d/0B0Mxex ... s=560e9eef


I put a finger into the drain hole trying to catch something else, but there is not that much space down there. So I'll might begin with an endoscope like suggested by smoothdave, because yes it's a good excuse to have one of those. :roll: But I'll might begin with a cheaper one http://www.ebay.com/sch/i.html?_from=R4 ... e&_sacat=0

lcrken said:

It's about the right length for a crankshaft nut. The 5/16" nuts on pre-MKIII crankshafts were about 1/2" long for the long ones, and about 3/8" long for the short ones. This looks a lot like one of the short ones. Is it 5/16" or 3/8" thread size?

Ken

Click to expand...

At the moment, beginning with your funny threads, I'm not able to say what it really is. All I can do is put those 2 pictures, hope it helps.

lcrken said:

Is it cad plated, or plain? As Dances pointed out, the stock crankshaft nuts were not plated. but the cylinder and head fasteners were.

Ken

Click to expand...

It's not cad plated, just plain.

Seriously mate don't run that engine again either strip it down yourself or pay someone to do it for you who knows what they are doing with Norton's it will put your mind at rest and you will know exactly what's inside that engine it will be money well spent cheers baz

If this came out of an engine of mine under the same circumstances, I'd be spending a lot of time looking at the nut,,, looking at the motor,,, looking at the nut,,, looking at the motor,,, looking at the nut,,, looking at the manual,,, looking at the nut,,, etc., etc.

I'd never tell anyone what to do in regards to tearing down their engine or not, but my take on the mystery nut is "dropped in". I believe the grind marks on one flat are just that, grind marks. Done by someone by hand on a wheel. That's why it's blued in that area, a little too heavy on the grinding with no in between cooling. I think it was done to either clean up a damaged flat or more likely something was once welded to it that purposely was snapped off (the broken corner) and then cleaned up on the grinder. I doubt it came from the internals of a spinning engine because there's absolutely no damage on it that I can see. The magic disappearing black line is intriguing though. It may also have something to do with whatever I think was once welded to it.

It's not a rod nut. The only other nut that could originate in the crankcase is a crank nut. I've got a reference on all Norton bolts and nuts. I'll check it sometime today to see what thread size the crank nuts are. You could then get a bolt that size and either the nut fits or it doesn't.
Later

Did it actually "fall out" of the drain hole, or was it stuck on the strainer, or did you have to reach in to feel it?
I'm thinking it was lodged somewhere else and fell into the drain pan as Holmeslice suggested, if it didn't fall out on it's own.
This is a fun mystery.
Jaydee

As it's an 850, the original crank nuts (and studs) would be 5/16" x 24 UNF with A/F hexagons. However, the hexagon appears to be 1/4W (0.525") and the 0.274" internal measurement suggests it's 5/16".
Unless the crank has been rebuilt using the 750 'bolt' kit which I believe has 5/16" x 26 BSC (Cycle thread) nuts with 1/4W hexagons, that nut doesn't seem to belong there.

Biscuit said:

If this came out of an engine of mine under the same circumstances, I'd be spending a lot of time looking at the nut,,, looking at the motor,,, looking at the nut,,, looking at the motor,,, looking at the nut,,, looking at the manual,,, looking at the nut,,, etc., etc.

Click to expand...

Or how a very simple binary game may rise quite a smart idea. Biscuit, I'll ask my daughter to send you a kiss :wink: She is doing 20 this year :roll:

Biscuit said:

[...] I believe the grind marks on one flat are just that, grind marks. Done by someone by hand on a wheel. That's why it's blued in that area, a little too heavy on the grinding with no in between cooling. I think it was done to either clean up a damaged flat or more likely something was once welded to it that purposely was snapped off (the broken corner) and then cleaned up on the grinder. I doubt it came from the internals of a spinning engine because there's absolutely no damage on it that I can see. The magic disappearing black line is intriguing though. It may also have something to do with whatever I think was once welded to it.

Click to expand...

Really looks that Biscuit is right, just grind marks. Plus a little bite off on the left edge. Plus it was squeezed, perhaps by the crank, before falling on the drain plug. Because yes, I had the feeling that it felt in the same time I was taking the drain plug down. So it might have been stuck on the strainer, and felt when I took the drain plug off. Plus, it was full of oil, so I believe it has to be on the strainer. After it felt, I put a finger inside to check if something else was there. Not that much place for another nut or stud or screw.




Today, watching it in the sun, it looks a little oval...

And it was:








Still a few questions:
- Was it crushed before and somebody grinded it? I don't think so because the grind face has already the smallest size.
- Was it a crank or conrod nut? With htown16 and L.A.B. answers, it might not be a conrod nut neither a crank one (am I right there?)
- If a nut is missing on a crank screw, and like there is no more oil in the crankcase, if I lay the bike on the floor on each side, is there enough place to let the unnuted screw come out of his place? Completely? Perhaps I could hear something falling out?

What do you think?

Most likely a crank nut, and the studs/bolts are usually a tight fit in the crank flages & flywheel, so they won't just slide out.

The inexpensive scope will tell the tale.

Hopefully it was an "oops" nut and all is well.

NKN said:

Still a few questions:
- Was it crushed before and somebody grinded it? I don't think so because the grind face has already the smallest size.

Click to expand...

I think the damage could just as easily have been caused by the flywheel and that you are lucky the nut didn't punch a hole in the crankcase!

NKN said:

- Was it a crank or conrod nut?

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Conrod nuts look different, also, they are 3/8".

NKN said:

If a nut is missing on a crank screw, and like there is no more oil in the crankcase, if I lay the bike on the floor on each side, is there enough place to let the unnuted screw come out of his place? Completely? Perhaps I could hear something falling out?

Click to expand...

Unlikely, and two can't be removed without splitting the crank.

The crank halves are held together with a stud with nuts on each side.
Here is an oem crank nut out of my 74 850 that I am rebuilding. The threads are 5/16 nsf 24 and the hexagons are 1/2"

They also have a stamping on the side

Here is an 850 rod nut, you can see the lock ring

So based on your measurements, it doesn't resemble either an oem 850 crank nut or a rod nut. LAB mentioned the 750 used a 1/4 Whitworth, 5/16 22 bsf and that nut would very close to what you measured across the flats. Since the engine has been rebuilt it is possible that some one used the 750 stud/nut kit.

htown16 said:

LAB mentioned the 750 used a 1/4 Whitworth, 5/16 22 bsf

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I didn't say they were BSF.

Lists say 5/16 x 26 BSC Cycle thread.

https://www.oldbritts.com/11_067120.html

htown16 said:

Since the engine has been rebuilt it is possible that some one ordered the wrong parts.

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It can just be a matter of preference as Mick Hemmings remarks in his heavyweight twins rebuild DVD that ".....it really makes no difference which set you use as long as they are the genuine nuts and bolts....."

You don't have to split the cases to inspect the crank nuts. The head and cylinders need to come off and that can be done with engine in the frame without disturbing the primary. It looks like you could even leave the pistons on the rods.
You could order a 750 5/16 x 22 bsf crankshaft stud and see if the nut fits it. If it did I would have have the topend off for sure for a look. But you could just go ahead and do that anyway for complete peace of mind and to look for other bodgery.

htown16 said:

You could order a 750 5/16 x 22 bsf crankshaft stud and see if the nut fits it.

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LAB has already repeated that there is no BSF involved anywhere here,
so that won't get anyone very far !!!

Rohan said:

htown16 said:

You could order a 750 5/16 x 22 bsf crankshaft stud and see if the nut fits it.

Click to expand...

LAB has already repeated that there is no BSF involved anywhere here,
so that won't get anyone very far !!!

Click to expand...

As the nut has been partially crushed and the hole appears oval I don't think any 5/16" thread is going to fit! :wink:

NKN said:

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The question is what other damage may it have done inside also then.

Without opening it and having a look, it could be a grenade waiting to happen.
Not worth the risk of not having a good look, the results could be catastrophic.
To engine and potentially rider as well...