petrol tank bolt

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
Mick D
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Location: Aberdeenshire

Re: petrol tank bolt

Post by Mick D »

Hi

A2 stainless is horrible stuff to work without decent tooling - it work hardens as you 'look at it'. You will need sharp cobalt or carbide drills running much slower than your B&D can achieve and with more pressure than I expect, you can exert. Tapping with HSS taps and cutting fluid may just be possible but it will be hard work and may cost you a tap or two.

Have a go by all means, but I think it will end in tears.

Regards Mick
56G80S
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Re: petrol tank bolt

Post by 56G80S »

Cheers, Mick. It won't end in tears, I won't bother thanks to your advice. Time saved. Wish I had a "proper" workshop though.

They'll be going straight back on Ebay.

As I've often said, IKBA! Stainless is a foreign country to me.

I wonder if I can get brass grub screws?

Johnny B
Mick D
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Location: Aberdeenshire

Re: petrol tank bolt

Post by Mick D »

Hi Johnny

The simplest solution for one with limited tooling would be a thread insert, (Helicoil), the boring required is minimal and can be carried out using a power drill carefully. An insert repair kit, (10 inserts), will cost you about £30 or maybe someone local to you already has one.

https://uni-thread.com/tr_bsc_kits.php

Regards Mick
56G80S
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Re: petrol tank bolt

Post by 56G80S »

Hi Mick

Yes, I helicoiled (V-coiled) the head for the rocker bolts and all good.

I researched the topic and generally success results were mediocre with helicoils, I think Rob Swift found only 50% success. For some reason (although I bought some) I didn't in the end fancy Clive's solution with the Mini cotton reels. From memory (not measured) the mounting points are only about 1/4" thick.

Now going to use brass M12 bolt and make up a solution, test on a bit of scrap before going ahead. Bought some Loctite 638 as advised by Group Leader.

Thanks a lot for the advice though, you know what you're doing, I'm no engineer.

Johnny B
56G80S
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Re: petrol tank bolt

Post by 56G80S »

Here's the M12 bolt solution that I tested today, it's just a few turns in
M12 brass hollow internal thread (2) small.jpg
Then more fully wound in:
M12 brass hollow internal thread (1) small.jpg
This was just a test to be sure there would be enough meat. I should've cut the bolt head off but was in a rush and although, in fact. it would be viable to cut lengths off this, cut a slot and screw into the tank mounting points (once drilled and tapped M12) the thread isn't brilliant as there was a bit of movement in the drill vice.

What I will actually do is use some M12 allen key head grub screws in brass. Drilling through the allen key entry point will make sure I have fully centralised. I have the grub screws ready.

The tank bolts themselves have not held up well, they've been fretting and I had to clean the thread up so new bolts going on the list for AMOC Spares. I think that I will enlist assistance in holding the tank steady and make sure I have something between the tank and the mounting bracket!

Johnny B
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Jdraper
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Joined: Mon Mar 07, 2011 9:41 am
Location: BUCKS UK

Re: petrol tank bolt

Post by Jdraper »

Two of my tank threads would no longer hold and I would often find them pulled out dangling on the lockwire.. time for a solution, and most of the ones offered up so far have not really been within my capability. I looked at alternatives including drilling out & re-tapping out larger, but idly looking at thread sizes one day I noticed that M8, fine pitch is a pretty good match for the original tank bolts, but slightly wider.. Hmm. This may count as a bodge, but I found a supplier of M8 bolts, fine pitch, with cross drillings for lock wiring from a racing supplier. Unfortunately, only available as 35mm long, which is around 1/4" longer than original. However I bought a pair of said bolts (horribly expensive, at £5.50 each as they are titanium) and they work a treat. I use all the rubber part & collar as supplied by the spares scheme and note that he rubber washers are slightly thicker than original, which made them a pig to fit. In the end, I didn't use the extra thick washer, as the thicker rubber took up the extra length of the bolt. Downside is that I have to carry a 10mm spanner as well now.

May be a help to someone for a low impact, quick fix before going full-workshop on the tank.

Jeremy
PS must be 1mm fine pitch
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56G80S
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Re: petrol tank bolt

Post by 56G80S »

Reviving this thread (!) as although I am confident my other solution will work, this would be a heck of a lot quicker and easier.

I note that Boltworld have high tensile M8 Fine pitch 35mm bolts for a fraction of what Jeremy paid, although not with the drilling for wiring on. Having said that, I did lots of miles without wiring on.

Perhaps I was just lucky.

Johnny B
Jdraper
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Re: petrol tank bolt

Post by Jdraper »

The M8 fines pitch bolts are still holding up well after 500 miles or so. A pleasing, simple solution as long as your existing threads are not really knackered, but are tired enough to not hold. You can see the state of the thread of the old bolt in my last photo. I did try new AMOC bolts, but they still pulled out after a few miles. I repeat 'fine thread' as there are plenty of coarse thread M8 bolts around, and they are not suitable.. You have to look a bit harder for the fine pitch ones...

Jeremy
56G80S
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Re: petrol tank bolt

Post by 56G80S »

Back on this again!

Just realised that I could use a half nut between the tank mounting plate and the tank (doubt a full nut would slide in the gap).

Probably get brass nuts (it is cold). This would support a greater length of the homemade M12 hollow drilled and tapped for "original" tank bolts approach. It would prevent any "rocking" brought on by the narrowness of the mounting plate and provide for more tank bolt thread engagement hopefully eliminating fretting using some Loctite threadlocker.

Club ones nicely the right length, pre-drilled for lockwire. With the steel sleeve in the rubbers, no fear of hitting the tank.

Just need to get strong enough to move the gennie around at the lock-up so I can use the drill in the old, not so steady, Black & Decker drill stand. I didn't think it would be accurate enough but taking time, using cutting oil it seemed to work OK looking at my earlier rushed attempt; be even better if I lock the drill vice down properly.

Johnny B
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Pharisee
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Re: petrol tank bolt

Post by Pharisee »

I finished a repair on my G80 tank today. Three of the mounting points had been stripped and the forth wasn't much better. I bit the bullet and drilled out the stripped threads to 7/16". I turned up 4 new inserts from some 1/2" diameter mild steel bar. They are tapped 5/6" x 26 tpi and have a full 1/2" of thread. I've silver soldered them into the mounting plates. Ok... not the prettiest bit of soldering but I can say for certain that they won't be falling out any day soon.
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