.motor out of balance.

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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.motor out of balance.

Postby rump » Thu Oct 19, 2017 4:50 am

What is the balance figure for a G9. does anyone know the weight of wire wound pistons that were originally fitted i believe. I have damaging vibrations at 50 miles an hour. rump australia.

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Re: .motor out of balance.

Postby Rob Harknett » Thu Oct 19, 2017 10:40 am

Perhaps some else is causing the vibrations felt. Its been discussed many times here on the forum. Tank bolts perhaps. They should not be tightened so they start to compress the rubbers. Just nipped up then wired on. If tightened correctly they must be wired on or you will soon loose the blots etc. Incorrectly adjusted steering head bearings will also result in a lot of vibration being felt.

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Re: .motor out of balance.

Postby clive » Thu Oct 19, 2017 1:45 pm

so will a front wheel that is out of balance.
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Re: .motor out of balance.

Postby Rob Harknett » Thu Oct 19, 2017 5:25 pm

Interesting point Clive. I have experienced a bumpy ride due to the tyre not being fitted correctly. The last time I fitted a new front tube, I do believe a PO had fitted a wheel balancer. That being like a dummy valve, bolted in via a hole in the rim. This device had come loose and gone inside the wheel, when I fitted the new tube. I could not find quickly, the nut that fixed this device in the rim. So left it out. Try as I may fitting the tyre correct, I still cannot get the smooth ride I had with this device fitted. I have not noticed vibration has increased. Which is more than you may get on a standard machine, as I have a handlebar fairing fitted. Any thoughts ? Does my wheel need that device put back in ? Or have I got a rouge tyre ? I have not checked balancing, by the only way I know how, e.g by spinning the wheel and noting where it rests each spin. To suggest where it may be heaviest.

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Re: .motor out of balance.

Postby clive » Fri Oct 20, 2017 6:38 am

I bought my first G12 in about 1982 with the aim of faster motorway travel. It vibrated badly above 50 to the point where at 70 my hands gradually opened up outside my control preventing me holding on. The PO knew I was not using it and bought it back. He simply balanced the front wheel. I stuck with singles.
Fast forward about 30 years and I risked a twin again when I bought my G11CS. First proper road test following a rebuild and terrible vibration from the handlebars above 50. This time I balanced the front wheel which required a very large lump of lead strapped between two spokes. Vibration massively reduced, although with knobblies it is always going to be a little difficult.
Was it coincidence that it was both twins that needed the wheel balanced, as I have never had to do so for my singles? Or might the different engine vibration accentuate vibration from the front wheel on a twin?
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Re: .motor out of balance.

Postby Rob Harknett » Fri Oct 20, 2017 9:35 am

That's odd Clive, my first G12 seemed to vibrate quite a bit more than singles. Which I had always had, except for a BSA A10 combo. I was taking it steady at first on the G12, just havening done work on the engine. As increased speed, the vibration through the handle bars got worse. So I never used it much, preferring one of my other bikes from the choice of prewar, heavy weight and light weight singles. MOT time came round for the G12. The MOT man said your steering needs adjusting. I said I'd hardy used it since I had checked the bike over. How did it come loose?? bearings bedding in?? Anyway first thing I noticed on the way home from the MOT was vibration had gone.

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Re: .motor out of balance.

Postby rump » Sun Oct 22, 2017 2:22 am

I am a bit laze thats why i need the weight of an original piston as a+40 has thrown the balance factor out if i can get the right weight i will cut some of the weight of the +40 this saves pulling the motor to pieces this motor was rebuilt years a go and not used because of many other faults before my time.I have changed sprockets to gear it up to cut down on reves now it will do 60 before it shakes your back teeth out rump australia.

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