SQ4 Vibration

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adrian.hannam
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SQ4 Vibration

Postby adrian.hannam » Sat Oct 10, 2020 8:56 am

MK1. Well, not really vibration, it doesn't shake. It has been reassembled after inspection, with new rods, and travelled 50 miles. I have only had it briefly up to 60mph, but at speeds over 50 my MK1 has a slight buzz, which is tolerable. I will expect to get pins and needles sensation in my hands. It is off the road now to re-torque the head and attend to the brakes. I have a few theories, but not having ridden a 4 before, what should I expect for the smoothest classic motorcycle ever?
'48 KG outfit, '51 VH, '51 4G (in bits)
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simon.holyfield
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Re: SQ4 Vibration

Postby simon.holyfield » Sat Oct 10, 2020 11:55 am

Hmm, mine went through a stage of tingling in the bars. This was followed by the realisation that the clutch basket screws were not as tight as they could be, and nor was the clutch centre nut.

Normally its very smooth.
cheers

Simes

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Gui.dorey
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Re: SQ4 Vibration

Postby Gui.dorey » Sat Oct 10, 2020 1:41 pm

Could be anything really. I also had some vibrations on mine after the rebuild, as well on another bike I restored early this year. One source of vibration was the head lamp, and I was convinced it was the engine. On another it was the speedo cable touching somewhere. Now when I have a vibration, I usually check all nuts and bolts for anything loose, cables,etc and ususally do find something that needs nipping up. Prime suspects are all engine and gearbox mounts, both to the engine and to the frame, petrol tank, head light, mudguards, handlebars and all the cables fur rubbing against something.

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john.bebb
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Re: SQ4 Vibration

Postby john.bebb » Sun Oct 11, 2020 11:07 pm

Hi Adrian, "what should (you)/I expect for the smoothest classic motorcycle ever"? Basically there are but two probable outcomes where I believe the odds to be ~ 50/50: -
It will EITHER
a/ Blow head gaskets - usually but not infallibly ; - the rear pots.
OR
b/ It will seize - usually pot #3 but pot #4 is also common, there are different causal roots to each pot #.
Cheers & good luck, John

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Re: SQ4 Vibration

Postby nevhunter » Mon Oct 12, 2020 3:19 am

It IS mounted DIRECTLY to the frame, and parts of the frame have natural hormonic frequencies. Pistons at around TDC don't behave as those near BDC do so the two don't exactly balance each other out when they stop and start unless the con rods are infinitely LONG. (impossible) Most four cylinder motors BUZZ at at least one rpm for the same reason. A FLAT four doesn't as the opposing pistons are at TDC together (same time) and DO cancel each other out, but they have an offset issue. A smallish rocking couple, but less than a twin, easily handled by the frame.
Summary... The Sq 4 is exceptionally good in this regard but still not perfect. As Phil Irving suggest some lead weights in the handlebar ends may help IF you wish to go down that road. An unfortunate analogy, but I'll leave it there. You could go out and buy a Honda four Goldwing . Think they even made a "six". Nev


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