Bad news from the stars

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LAB,
I was looking at the Stainless Fastener Cross reference list. I believe they have it wrong in there and you are correct it should be 5/16 x 26 bsc as that is the size they show for the studs. Sorry about the wrong info.
Htown
 
Perhaps someone has been grinding away at the nut on the bench grinder on one side of the workshop (for reasons unknown), it's not been held properly, has been grabbed by the grinder, flung across the shop and ended up in an engine build.
 
davamb said:
Perhaps someone has been grinding away at the nut on the bench grinder on one side of the workshop (for reasons unknown), it's not been held properly, has been grabbed by the grinder, flung across the shop and ended up in an engine build.
Click to expand...

Yer have done that before but usually when not working on the motor I will have things covered up just for that reason, but a lot of strange things can happen when rebuilding motors or doing anything in your workshop, like dropping things ( small nuts and bolts etc) on the workshop floor to never be found again, bench grinders can be so dangerous with things flying out of your grip.

Ashley
 
Given that the history of this motor is really unknown the safest thing to do is to dismantle it and take a look inside. This may well have been a nut used on the con rods, why would we expect an engine builder, who would not notice that he left a nut inside an engine, or failed to correctly tighten the crank nuts, to use the correct nuts and bolts?

I would at the very least remove the head and barrels and see if you can ascertain whether this nut has come off either the crank or the conrods. If no missing nuts are found I think it safe to assume that someone dropped a barrel base nut in there and didn't notice.

If there are amy missing nuts on either crank or con rods don't be tempted to try to fix this without splitting the cases.
 
dave M said:
If no missing nuts are found I think it safe to assume that someone dropped a barrel base nut in there and didn't notice.
Click to expand...

I don't think it would be one from that engine, as the (five) 850 barrel base nuts are UNF and have A/F (4x 7/16 & 1x 9/16) sized hexagons, not 1/4W.
 
I didn't see that the thread had been identified, Les, however my point remains, regardless of where the nut came from, even if it was dropped in by a naughty boy, the prudent thing to do would be to investigate thoroughly, rather than simply forget it and take a chance. As we onow Comando bottom ends are quite robust but when they go it is often in a spectacular and expensive fashion.
 
Since it has been only 16 months since the rebuild, have you contacted the shop that did the work? I would think that a reputable shop would want to soften the negative publicity of a loose nut rattling around in the crankcase of an engine they recently rebuilt. The right thing to do is for the shop to open the engine and inspect and repair any damage found! At their own expense, of course.
 
A base stud thread was stripped accidentally on a rebuild, and an impatient rebuilder decided that he could just thread in a longer stud and add a nut to the underside of that longer stud which is now pertruding into the crankcase rather than helicoil the crankcase. The nut does it's job for a while, then loosens eventually due to vibration and drops into the crankcase and becomes a pinball...
that's my guess...
 
L.A.B. said:
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!
Click to expand...

I agree with LAB.
 
Bottom line is the nut was apparently in the crankcase so the OP should have a look and see; regardless of origin of nut. Step at a time here. No need to spell out a logic tree but lift barrel and see if anything is missing and if the rods or something else was nicked or dinged.
Not sure if I would bother going back to shop that did the deed but would put them on notice and see if they are willing to compensate...good luck.
 
Mark said:
L.A.B. said:
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!
Click to expand...

I agree with LAB.
Click to expand...

Respectfully, I don't agree. A spinning fly wheel would have left dent like damage on the nut. This looks as though it was held and purposely ground on a wheel. Even assuming it was somehow held in place as the crank spun against it this would be in an oil rich environment thus keeping it cool enough so as to not discolor from heat. The large photo clearly shows heat bluing caused by what I think is a poor grinding job.
 
If its heat from grinding against the flywheel, imagine what else might be found inside those cases !!

Open it and have a look, its not safe to just blythely speculate that it might be alright.
 
I'd think that the dent is on the inside of the case.

What are the odds that the engines rebuilder smashed a nut, welded on it, then ground the weld off and then put it into this guys crankcase?
 
One other thing that maybe easy to check NKN. I had in my head that I've seen something like this before on my own bike.

Just came back in from the garage after taking a look at my muffler clamps. They are the original type and mounted with the clamping flanges at the bottom with the bolts running from the outside in. The bolt heads of each one are ground down in a similar manner as your nut and these bolts are what touch the pavement first when carrying a good lean. Were they fastened with the bolts from inside and nuts outboard, the nuts would look the same as yours do.

Don't know how the nut would have gotten in the engine, maybe it did just drop from the frame? By the way, my muffler clamp bolt & nut measure 0.516"
 
Are you positive this nut came out of the drain hole? Is it possible this nut was wedged in between the frame and engine and fell out into the oil pan when it was jostled or bumped by your arm or the center stand spring? I know it's a long shot but I've dropped all sorts of fasteners while working on cars and bikes and have them land in the craziest places.

You can buy an illuminated borescope attachment for Android smart phones for under 20 bucks.
http://www.ebay.com/itm/New-5m-Waterpro ... SwoudW6hjo
 
In the end this motor would not be run in my bike until it was torn down and looked at. That nut has been pounded and scraped really good, my guess is you also have other damage. Not worth the risk, Just my opinion. :shock:
 
Looks to me like when the nut came off the crank the stud hit it, if you look close it looks like you can see threads imprinted in the nut and the chunk that is missing. Or am I just seeing things???????????
 
dave M said:
I didn't see that the thread had been identified, Les,
Click to expand...

It hasn't, but the fact that the nut obviously has a 1/4 Whitworth size hexagon seems to rule out any possibility of it being a "base nut" from that particular (850) engine as you'd suggested.

Biscuit said:
Mark said:
L.A.B. said:
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!
Click to expand...

I agree with LAB.
Click to expand...

Respectfully, I don't agree. A spinning fly wheel would have left dent like damage on the nut.
Click to expand...

The flywheel periphery is reasonably smooth and (almost?) circular so I don't agree it would necessarily dent the nut.

Bad news from the stars


Biscuit said:
This looks as though it was held and purposely ground on a wheel. Even assuming it was somehow held in place as the crank spun against it this would be in an oil rich environment thus keeping it cool enough so as to not discolor from heat. The large photo clearly shows heat bluing caused by what I think is a poor grinding job.
Click to expand...

Again I don't entirely agree, as there appears to have been sufficient force to partially crush the nut and if that was caused by the flywheel it would almost certainly result in metal to metal contact and the nut overheating regardless of how much oil was present.
If/when we get to see the crank I wouldn't be surprised to see some score marks on the flywheel.
 
"I so enjoy rampant speculation!"

Yes, this is fun! A real mystery. Having said that, I'll add more fuel to the inferno.
I don't believe there is sufficient clearance for the crank nuts to back-off without hitting the rod as it spins around.
The nut would have whittled a slot into the rod in short order. It certainly would have made a loud racket that you would have heard.

My money is on 1 of 2 scenarios.
a. the nut fell off the muffler clamp, frame rails, etc into the oil pan
2. the nut fell into the sump during assembly (which is crazy for a pro builder).

I would love to see inside this motor.
 
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