Ode to a job screwed up

[John]

In my experience in fucking threads, the first are always in good shape if I crossthread, hell I had a brain fart and was doing the sump up instead of loosening it, way to strip the bolt doofus...

[pete376403]

A friend with an F650 has had this problem. He's a torque wrench freak - would torque the tyre valve stem caps if he could get a socket to fit - and it stripped just the same. A helicoil was the fix - not too much drama. Now he has a Pegaso and we're waiting for it to happen to that, too.

I never use a torque wrench on the GS1100 sump plug - couldn't even if I wanted to cos the collector for the pipes is in the way - but have never had any misgivings about tightening the plug. The difference between high quality Japanese alloy casting compared to the craploid East German pot metal that Rotax cases are made from - probably too much coal ash in the german stuff.

[stanko]

Why not just drill and tap it to a new size. then you could use a sump plug with finer threads which will not require as much torque to tighten.

You still have to drill and tap for a helicoil, but the new spump plug will only cost $10 instead of $250

[pete376403]

Fine threads and coarse grain soft metal are not a good combination. Plus you;ve still got to fill the original hole with something, so helicoiling that is as good a way as any.
Some drain holes are the same diameter and thread as 13mm spark plugs so they can be used as a temporary plug.

[myvice]

Porsche 911 No 3 (LHS back one, as in closest to the front of the car) sparkplug hole.
Bike sump? No problem!
When you/they are cutting the new thread use grease instead of oil on the tap to capture as much of the scree as possible.
If you can use a solid thread saver, Helicoils are good but (in my opinion) these are better.
Use locktight when installing the Helicoil or whatever you use to prevent it backing out with the sump plug, not common but it can happen.
Every time I drain the oil, about 5 times a day, I squirt a little brake clean into the plug hole just on the off chance there is a little bit of ring, piston, cam, anything harder than the sump metal hiding in there to ruin my day.

[WINJA]

THERES SOME FUCKEN USELESS MECHANICS OUT THERE , I HAD SOME SO CALLED PROFESSIONAL MECHANIC DO THIS TO ONE OF MY BIKES , IF IN DOUBT THEY SHOULD USE A TORQUE WRENCH , IVE NEVER STRIPPED A THREAD , NO MATTER HOW MUCH TRAINING SOME MECHANICS JUST DONT HAVE A FEEL FOR THESE THINGS OR COMMON SENSE . $50 AN HOUR FOR A MONKEY , WHAT A JOKE.
IN MY TRADE THERES SOME MONKEYS TOO , I JUST CANT BELIEVE HOW TIGHT SOME PEOPLE DO FLARE NUTS AND COMPRESSION FITTINGS

[Brian d marge]

Hmmm, interesting, if all the force is taken by the first couple of threads then why were they still intact?
The first thread is still ok, and at first i was able to easily hand screw the plug about 3 turns.
I understand that there is a few mm of thread more than sump plug, but this appears to have been stripped too.

How to tell if a thread has been stripped due to over tightning or cross threading? I would guess if you get semi circle shaped bits of thread then it has been overtightned?

But aye there is an known problem with the sump plug on the F650
http://faq.f650.com/MainIndex/Engine.htm

]]]

When a nut and bolt are in contact ....they are assumed to have 100 percent contact .....but when under load the bolt stretches and the nut compresses ( Compressive strength of alumnuimminiumnunm cast is about 20 ksi and the steeel bolt will be about 90 ish Ksi ,,,these are super rough ,,just to give an Idea)
The Pitch ( distance between the peak of the thread ) changes ..the bolt increases and the nut deacreases ,,the result being that the load is concentrated ,,on the lower most threads ,,the ones nearer the load bearing area of the bolt ,,,,,,the result is a stress concentation.....

The treads that failed in your Engine I assume from what you say are the ones inner most ie inside towards the oil side,,,,

This may be due to installation , or as it was cast the area of the thread was insufficient to sustain the load , so the Local area around the highest stress ( in your case the thread with least thickness ) fail ,,or relieved it self ...transferring the load on to the next thread untill it was all equal again .....

You still are better off intsalling a helicoil ...( and when ever a steel thread is installed into ,,softer female thread make sure ,,the are NO high spots , sharp edges etc or swarf ..as these act as a cutter ,,,,,and cause havoc on the way in AND out ...

Hope that explains why the lower threads take all the load

Kind regards Stephen

[XP@]

Yup, thanks, I get the drift now :-)