This subject has probably been discussed in the past but my 1968 D14/4 starts to vibrate at 45 mph and only gets worse the faster I go. Is there a cure? or are all D14/4's like this. In 1967 I owned a 4 speed D10 and I don't remember it vibrating as bad as the D14. I've had the flywheels, crank & piston balanced but no improvement. Any advice appreciated.
Well, you've had the obvious things done already , was there any improvement ?
All engine bolts tight and I know the D14 can be fussy on ignition timing.
Is it road speed induced or engine rpm induced, if latter then the vibes should kick in at 35 or 40 in 3rd gear.
If former , then balancing wheels or spin them and check their truth.
Front wheel balancing is only necessary on ANY vehicle over 60 mph. However I have balanced the front wheel. As I said having the flywheels etc balanced made no difference at all. There are no loose nuts or bolts. I'll check the ignition timing again when the weather is a bit cooler, I can't work in 26 degree heat.However, I'm pretty sure the ignition timing is spot on as per workshop manual.
The nuts and studs holding the engine in place may be tight, but are they the correct type? They should be Imperial studs of the correct plain shank length rather than some bodger's idea of using B&Q metric studding.
This is an insult. I have been restoring pre-war and pre 1930 BSA motorcycles, and a 1938 BSA car for over 55 years as well as owning & racing a BSA Rocket 3, tuned & fettled by me, 135 mph at Snetterton in the mid 1970's. Please be less derisory without adequate info.
Bantam engine studs are different diameter for sure.
Certainly on D7s there are 2 different diameters where they pass through the crankcase dowel tubes front and back.
If you've dismantled the engine yourself for the balancing work , then you will know what you have.
Worth a look , nothing to lose.
Did you discover whether it was rpm induced or road speed induced ? As in my original post , might narrow things down in the diagnosis of vibration source
Just a thought, do you have any bar end mirror , I had vibration on a bike due to the mirror vibrating as its internal cam was loose and it shook/resonated along the handlebars
Quote from: rhyatt on 29 Aug, 2024, 19:49
Bantam engine studs are different diameter for sure.
Certainly on D7s there are 2 different diameters where they pass through the crankcase dowel tubes front and back.
If you've dismantled the engine yourself for the balancing work , then you will know what you have.
Worth a look , nothing to lose.
Did you discover whether it was rpm induced or road speed induced ? As in my original post , might narrow things down in the diagnosis of vibration source
Just a thought, do you have any bar end mirror , I had vibration on a bike due to the mirror vibrating as its internal cam was loose and it shook/resonated along the handlebars
Another question, did this JUST HAPPEN on this particular ride or has it been developing. Have you done anything to the bike that could have caused it? , worth reflecting chronologically.
Y13 People are just trying to help you . They have no idea of the history of your bike.
The vibration occurs over 45 mph in top gear and at lower speeds in lower gears and has always been there since I bought the bike 5 years ago. I have rebuilt the engine twice, all new bearings, seals etc the second rebuild after I had the flywheels, crank & piston professionally balanced. It is definitely engine vibration, impossible to see out of the rear view handlebar mirror over 45 mph. Although it was over 40 years ago I don't remember my D10 vibrating at all! Do any of you own a D14 and if so do you have the same problem? Of course I am now pretty old and perhaps in a year or two if I am still riding I'll be happy at under 45 mph!
ok - so it has been vibrating all the time you've ridden it and the engine is all balanced - so we can probably rule that area out.
I have a D14 and I can't remember it being that bad - the D7 s tend to be a bit smoother due to the different crank.
you hopefully know or have checked what engine bolts you have and can rule them out
wheels you've ruled out.
my personal next step would be to remove the mirror that you have and ride it again at 45 to see if the length of the mirror is upsetting the natural resonance of the handlebars - if no change , I would then fill the bars with sand to change the resonance level and try again.
there i clearly a resonance being set up somewhere that is manifesting itself on the bars
the fuel tank front and back fixing bolts - they can sometimes be bad - ie the front tank lugs can be deformed by the front 2 bolts , thereby ensuring the front of the tank is not secured (2) the rear fixing through bolt is often a bit loose by nature of it holding earths on etc and can equally deform the rear lugs
if you're checking the other things , and had the crank etc balanced - the fact that it has vibrated since day 1 means that there is a fundamental issuethat has remained despite the work you've done
have you explored the flywheel itself(inside the alternator) as this is the biggest rotating lump left
i dont think a slack primary would cause vibes as you describe
clutch basket on its bush waggling??
re my earlier post and handlebars - can you shorten them? change their length I wonder
Thank you for helpful suggestions. I have several other handlebars so not too difficult to swap for another. Other suggestions I'll try in due course. If I get to the bottom of this problem I'll post the solution.
My final thought was to use a 1.5mm thick head gasket instead of the original 0.5mm.
I softened the comp ratio a shade using this method when I used my D14 on the Italian moto Giro. 1000 miles of hard riding in the Italian mountains I figured might give it a slightly easier time .
It was fine
Hi, my D14 already has a thicker head gasket which gives it more power at lower revs.
The the welding on the front engine mounting bracket on the frame sometimes fractures. You often see crude repairs to Bantam frames in this area.