petrol tank bolt

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Rob Harknett
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Re: petrol tank bolt

Post by Rob Harknett »

Well tightened does not have the same meaning as screw firmly home and wire on in pairs. I asked an old boy what screw firmly home meant when I was a teenager, he said it meant just nip them up and wire them on. I've stood by and quoted that advice ever since.The rubbers need to be allowed to do the job intended. Later tanks only have a rubber band holding the rear end on. Give a thought to Clive's mini bushes, how are they made to do the job intended ? Two washers with a stud each end with uncompressed rubber in the middle. Why not just a bolt well tightened through a rubber bush?
Is your tank sealed?? If that flakes off today fuel is usually blamed, cant blame the fuel for split tank seams and leaking fuel lines.
56G80S
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Re: petrol tank bolt

Post by 56G80S »

Rob's comment makes sense to me.

If they bolts are wound up tight, there's no point in having rubber bushes there at all. Don't forget the thin ones under the mounting point and above the large washer. The sleeve while just be jammed up against the tank and down against the washer so all and any vibration will go straight through, metal to metal.

I thought the sleeves were only there to prevent immediate disaster from bolts going through into tanks.

Johnny B
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iansoady
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Re: petrol tank bolt

Post by iansoady »

But the sleeve stops the rubber from being compressed too much and if correctly fitted there will be no metal to metal contact between the sleeve / bolt and the mounting lug at all.
Ian
1931 Sunbeam Model 10
1999 Honda SLR650
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Rob Harknett
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Re: petrol tank bolt

Post by Rob Harknett »

Can't see how the sleeve can stop you over tightening the rubber. Work it out. Sleeve length 13/16 " Thin rubber 3/16" + Thick rubber 5/8" = 13/16" same as the sleeve length. This leaves you only the thickness of the metal washer to tighten/compress the rubber, before you have metal to metal contact. So the sleeve does nothing until the bolt is over tightened, then the sleeve will stop further tightening by making metal to metal contact. Just nip the bolt on and wire up in pairs. Prior to using bolts a stud on a washer with a tab for wiring on was used. There was no sleeve. The stud/washer type fitting was tightened by hand, I then use a nail or something through the wire on hole in the tab, just to nip it up a bit after hand tightening. Between the change over from this stud /washer type fitting and hex head bolt, the old type fitting was still used on the back r/h side of the tank, ( by oil tank ) as it was difficult to access with a spanner. If you ever had trouble tightening a hex head bolt there , it was because you were using the wrong fitting.
MikeM.
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Re: petrol tank bolt

Post by MikeM. »

Hey Rob, how about the thickness of the lugs on the frame, have you taken them into account?
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Re: petrol tank bolt

Post by aobp11 »

Can't see how the sleeve can stop you over tightening the rubber.
Hello Rob, you exactly explained how the sleeve stops over tightening the rubber! BTW I think the dia of the hole in the washer is equal to the ID of the sleeve, and the washer thickness plays no role. MikeD's remark is to the point of course.

Albert
56G80S
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Re: petrol tank bolt

Post by 56G80S »

Well, it looks like there's differing views on this but I've had a result on replacing my tank.

I've bodged the job.

For this summer only I've made better use of the portion of sound thread remaining at the top of the threaded strip in the bottom of the tank by reducing the thickness of the top thick rubber by 1/8" and stopping winding the bolts in when the rubber just starts to bulge. While I'll continue to use the approach Rob suggests, and which I've usually done, the fact that I've previously not been using the full depth of thread may be the cause of my problem. With only about 3/8" there it makes sense to use it all!

Will wire up when I get some wire - this sad lad used to strip the earth wire out of household electrical cable and use that but might see if I can get something a bit better.

When winter comes I'll take the tank off and use one of the fixes set out above.

Found this a useful discussion and hope author of the original post did to.

Cheers

Johnny B
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Rob Harknett
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Re: petrol tank bolt

Post by Rob Harknett »

MikeM. wrote:Hey Rob, how about the thickness of the lugs on the frame, have you taken them into account?
YES & no, re consideration of lugs. Take another look at the sizes. the sleeve is 13/16" long, the thick rubber 5/8" Next time you fit rubbers with sleeves you will note the sleeve hangs out the rubber 3/16" . The sleeve drops through the frame lug hole. I usually pull the sleeve through even more when fitting. I then place the tank on the lugs, then lift the tank to put in the rubbers, as the sleeve is poking right through the lug they stay put. I then put in all the bolts screwing them in 2/3 turns. Easiest way I have found of fitting the rubbers and tank to get it all lined up easier, without rubbers falling off the lugs. If anything the sleeve will prevent screwing the bolt too far into the tank. Note the tank bolt length. 1 1/4" take away 13/16" = 7/16", take away 1/16" for steel washer = max 3/8" of bolt thread left to screw into the tank. The dimensions & how parts fit explain why the lug thickness was not to be considered.
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iansoady
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Re: petrol tank bolt

Post by iansoady »

Rob Harknett wrote:If anything the sleeve will prevent screwing the bolt too far into the tank. Note the tank bolt length. 1 1/4" take away 13/16" = 7/16", take away 1/16" for steel washer = max 3/8" of bolt thread left to screw into the tank.
I think that's the very point I (and others) have been making and IMO that's exactly why it's the length it is. Unless you have the strength of a gorilla you can never get the bolt to touch the tank - even if you had, the threads would strip long before the sleeve would compress. Hence doing it up "normally" tight is fine.
Ian
1931 Sunbeam Model 10
1999 Honda SLR650
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Rob Harknett
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Re: petrol tank bolt

Post by Rob Harknett »

Indeed Ian, as the sizes of the parts prove, which should also end the topic as to tightening the bolts, there's only one way, the correct way, which the dimensions also dictate.
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