Lotus Elan

Tricky sheared off bolt

PostPost by: JonB » Mon May 22, 2023 12:32 pm

Eh up

This morning I was continuing tripdown of my S4 body. Came across a bit of a show stopper with one of the light pods - outer bolt has sheared off leving the pod in position. The bolt head came off, leving the threaded shaft passing through both the pod and body bobbins.

IMG_1383.jpg and
Remains of bolt as seen from the inside of the light pod.


You can see the problem. It's very hard to get at and I can't curt the bolt between pod and body because the body bobbin sticks out into a recess in the side of the pod. So I'd be cutting through the body bobbin if sliding a hacksaw blade down there.


IMG_1384.jpg and
For illustrative purposes - it's the body bobbin on the other side. See how it sticks out? Can't get a hacksaw in there..


Any ideas? I thought I might be able to drill it out with a very long drill bit passing through the bobbins on the other side of the pod.

Thanks
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PostPost by: USA64 » Mon May 22, 2023 2:32 pm

Is it actually threaded through the pod bobbin?
We are supposed to be having fun, are we not?
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PostPost by: JonB » Mon May 22, 2023 2:36 pm

Yes. And seized solid.
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PostPost by: Andy8421 » Mon May 22, 2023 2:52 pm

JonB wrote:
You can see the problem. It's very hard to get at and I can't curt the bolt between pod and body because the body bobbin sticks out into a recess in the side of the pod. So I'd be cutting through the body bobbin if sliding a hacksaw blade down there.

JonB

Jon,

While you probably don't want to hear it, your suggestion above may the best bet "So I'd be cutting through the body bobbin if sliding a hacksaw blade down there"

Its not tricky to glass a new bobbin in place after you have cut the old one in two, though getting the alignment right will be a PITA.
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PostPost by: jono » Mon May 22, 2023 3:06 pm

I had this on my current plus 2 resto - but three of them!

One had been mullered by a previous hamfisted owner and was running out of axis so the pod was cock eyed. The others were just broken and seized.

I managed to fixed the knackered one by die grinding the bobbin, filling it it with epoxy metal then drilling and helicoiling - centering took some sorting but it worked fine.

The others, one was cleared by progressively increasing the bit size then tapping out the remains and the other was drilled, tapped and helicoiled.

A 90 degree air drill was needed for working space.

PITA and fiddly but the pods are now perfectly aligned.

No easy jobs on these cars!
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PostPost by: nmauduit » Mon May 22, 2023 3:29 pm

I had that on my S4 as well, drilling + WD40 + waiting + lots of cursing eventually did the job, a bit of damage to the bobbin since the drilling erred some, but the remaing was enough to guide the new (stainless) replacement hex screw. The drilling must have heated up the remaing bit, plus vibrations etc it eventually got loose iirc.
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PostPost by: Craven » Mon May 22, 2023 3:31 pm

I made an alignment jig from a correct length and squared off broom handle tap for a UNC stud each end, screw in one end to good side bobbin and use the other end to hold the new bobbin in place.
FWIW.
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PostPost by: smo17003 » Mon May 22, 2023 4:05 pm

Jon,

It looks like you have access to the pod bobbin, and it's more or less already history, so why not cut the bobbin (with seized bolt) off from inside the pod? The pod bobbin needs repairing anyway so why double the work by cutting a perfectly good body bobbin? I have a couple of knackered pods, but with good bobbins, if you need to replace one.

I have a similar problem with my S3 but on mine the body bobbin has completely sheared off. That should be fun.

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PostPost by: JonB » Mon May 22, 2023 7:09 pm

Ok. I’m going to try to drill it out first. Right angled drill thing on order with a new set of cobalt bits. Fingers crossed!
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PostPost by: nmauduit » Tue May 23, 2023 2:28 pm

maybe try to hand file a flat (or dremel a dip with a stone or something) so that the bit gets centered at first (and start with a small bit, then gradually increase) - if you have some, you may try left thread screw extractors, but the diameter is a bit small and the smaller one break so easily I would not bother.

good luck !
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PostPost by: JonB » Tue May 23, 2023 5:21 pm

Fortunately there’s space for the angle grinder so flatting the end of the bolt should be easy enough.
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PostPost by: Matt Elan » Tue May 23, 2023 5:54 pm

Hi Jon
Can you get some heat on the bobbin and a grip on the remains of the bolt? The bobbins are some sort of light alloy or pot metal so will expand more than the steel bolt even if you use a hot air gun on it. Probably worth a try otherwise it’s drilling out or replacing the bobbin.
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PostPost by: snowyelan » Tue May 23, 2023 6:36 pm

Looking at it there is enough of the bolt sticking out to use as a pilot for locating a drill jig. If you have a scrap of steel bar and a drill press I'd make up a fixture with a shallow 1/4" bore in it and a 1/8" thru hole. You can clamp this over the bobbin and it will keep the drill bit concentric to the bolt. Once the 1/8" is drilled thru simply drill out the jig in the drill press to 3/16" or so, then to a #7. Without the jig there is a good chance the bit will wander. Grey being the bobbin, red the bolt, and green the jig. All in cross section. Use lots of cutting oil and clear the chips frequently.

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Last edited by snowyelan on Tue May 23, 2023 6:46 pm, edited 1 time in total.
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PostPost by: jono » Tue May 23, 2023 6:39 pm

I flatted mine back then used and automatic punch to put a pip as near the centre of the stud as I could, then start with a small drill and work your way up. Sometimes you find the last bit of thread snags and turns itself out of the hole on the drill bit.
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PostPost by: JonB » Wed May 24, 2023 8:38 am

In the end I chose to grind the end of the bolt flat with an angle grinder, very carefully as there wasn't much room in there. Then centre punch (three times as I kept getting it wrong) followed by a small cobalt drill bit. Then carefully working up the sizes as jono said, until finally the pod came free. For the remainder of the bolt (in the body bobbin) I tried an easy-out which turned out to be futile so I drilled it out as before. It took a couple of hours and I was uncharacteristically patient. But in the end I prevailed.

Now I have a pair of bobbins with 5 or 6mm holes drilled in them. The bobbin bolt is 7/16 UNC I believe. I should be able to restore the thread with a tap.. maybe.. or it'll be a Helicoil as I have seen recommended elsewhere on the forum.
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