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Bulkhead Bolt Fix: not what I was expecting.


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I am doing the well-known bulkhead bolt fix for the 4 bolts behind the seats. 

When I removed the bolts I am not seeing what I expected to see. There are no spacers on the bolts, which I expected as early cars dont have them, but there is a large gap between the wood panel and something behind it which presumably is fibreglass.

The original bolts were bottomed-out on the threads and in fact were doing naff all, on examination.

The arrangement appears to be:

Plywood
10mm gap
fibreglass (I think)
Chassis bracket

Now I am not sure what to do. If I put shorter bolts in and tighten them, something is going to break because there is 10mm of space in there. 

Is there maybe a possibility that the 10mm was filled with foam which has crumbled and disappeared (as it does)? I suppose I could squirt some expanding foam into the gap.

I thought I knew what is going on here as so many people have done this but not sure now! 

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Not sure about this as I have never seen this bulkhead out or this job done but be careful of expanding foam.  I believe that it is not keen on too much heat.  Maybe it would not be a problem but just a thought from my side

 

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Yes the fireproof pink stuff. It sets like concrete. This is perfectly OK for this area.

I poked something around in the gap and there doesnt seem to be anything in there. It runs up to 20mm above the bolt hole locations and down 100mm or so and its the full width of the bulkhead.

I dont know if all early cars are like this but it means the instructions on LEW are completely wrong for early cars. If the bolts are replaced with shorter and tightened, the wood would bend and eventually break. Also there would not be anything preventing the kind of movement we are trying to stop. Putting spacers in wont help on its own.

I will try to fill the gap with foam then fit bolts and spacers before it sets so that it forms a solid structure. This isnt going to be fun and I am going to need to be careful not to get it expanding out of some gap into the car as it definitely wont come off carpet or leather! 

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This all went well. I half expected going into the garage this morning and seeing the car full of foam, but none leaked out, except through the small holes I drilled to inject the foam.

I ended up enlarging the holes in the plywood and using 25mm long x 16mm dia spacers which were just long enough to allow for some compression.

Then drilled a small hole between the 2 bolts and injected foam. A lot went in but no unexpected orifices for it to leak out of. The gap in the bulkhead seems to be completely enclosed. I did remove the 2 speakers mounted in the bulkhead and had a look there and none there either.

Incidentally there is nothing behind the speakers except for open air, the fuel tank and the road, via the large holes under the tanks. This cant do much for interior noise levels so I put some sound insulating foam in there behind the speakers while they were out.

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Hi Andy,

You mean the speaker hole under your elbows in the fire wall. Thats kinda strange my S1 has a cavity cast in fiberglass to hold the rear of the speakers. Looks original on my car. Maybe someone cut out the back part of the speaker recesses on your car to install larger speakers?

Brian

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34 minutes ago, marcbria said:

Hi Andy,

You mean the speaker hole under your elbows in the fire wall. Thats kinda strange my S1 has a cavity cast in fiberglass to hold the rear of the speakers. Looks original on my car. Maybe someone cut out the back part of the speaker recesses on your car to install larger speakers?

Brian

Thinking about it I am sure you are right. I now remember the car I used to own had box shaped enclosures behind the speakers.

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