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BSA levels of vibration

My Friend's bike was biased in one axis by about 1.5mm. The clutch came together without problem,worked and felt fine but would only last about 10K. We drilled out the mating holes and made offset bushes to correct the problem. We mounted a solid bar of steel to the crank and used that as a 'Go-No-Go' gauge - the studs should be symmetrical all way around. It was a painI. It is a rare thing caused by a sleepy machinist- I think Pete Roper has seen a few.

I agree having the flywheel separately balanced is a good move- they should always be done like that.

Lovely bike but I don't know if I would have gone with the upswepts - although in canada it might come in handy to keep your thighs warm on winter nights.

In general I have found balancing to the 'n'th degree to be an unnecessary step unless vastly different con rods/pistons or a lightened flywheel is used. It just changes the RPM at which the vibration happens - which if it is at a point that is particularly annoying then it makes sense to do it.

I feel your pain.
 
Agreed, that is one sweet looking ride. I can see why you have persevered with the vibes. Just walking past it in the garage would make me twinge with delight, I would have to stop and caress its beautiful curves, wisper sweet nothings into its open bell mouths, and make promises of carpet burns to my knees on our next outing. :silly: :woohoo: :blink:
 
Again, thank all of you for your suggestions. I will first off try to run the bike without its exhaust system. If that fails to change anything...

I will take the bike apart again, and I will have the flywheel and crank balanced separately.

I'm not sure about how to check if the transmission centerline matches up with the crank centerline. I admit that I have not considered that a misaligned transmission would cause this vibration. If anyone could tell me a clear cut, step by step procedure that would tell me if there is such a misalignment, I will definitely do that test.

Perry Beltrame
 
When crank case was empty I had the deck height checked. Similar process would be slide empty gear box over the same shaft to see if the cases/dowels etc line up.

If they don't line up I would have the holes in the gearbox welded up and re drilled rather than making stepped/offset dowells
 
If you had the crank and flywheel balanced as an assembly originally you will need to re balance the crank again as well if you decide to do them separately. I cant see why you would have had them balance as an assembly to start with...thats an idea that will only give you problems down the track if you want to change a flywheel which is a real possibility.
Reading this post I can almost guarantee this will be your problem. Re balance the flywheel and ring gear together (mark them both after balancing and keep them in the same position when installing)minus the clutch plates and the crank separately.
Ciao
 
Thanks for the responses.

Ghezzi--I'm sorry, I still don't understand how to align the transmission. You mention sliding over the "same shaft. " Does this mean that there is a dummy shaft in the position of the crank? How does the splined imput for the clutch slide over this shaft?
 
Hi Perry,

I've come into this late. I've read your posts and scanned the suggestions.

A few things I may have missed.

Does it vibrate out of gear?
Does it vibrate when rolling in neutral?
Have you ridden another comparable model to see if this vibration is abnormal. Guzzis do vibrate. :lol:

Just some easily checked things first.

If it is only noticable whilst riding then my first guess would be shaft bearing. This is an interference fit and if it is sloppy this is a possibility.

Swing arm should be central between the frame. Make sure the pins have the same amount protruding each side. This shouldn't be the problem as the yoke acts like a drive shaft and corrects for small amounts of lateral error.

Cardan joint should have no play at all. The caps shouldn't turn in the yokes either.

Ensure the splines are greased and the no excess wear.

Make sure all the circlips are in place on the shaft.

Check the gearbox is tight. Fold back the rubber cover and change gears. Look to see if the output shaft moves forwards or backwards at all.

Tyres are balanced.

I find it hard to believe its crank balance. You've had it done and so many put big bore kits in their bikes and don't balance the crank at all with no real issue.

Carby mixture. Too rich and the damn things do chug. Unlikely as you mention ignition off at some point.

Have a friend with a LM II. Similar vintage. His swing arm had been welded out of line so the rear drive wasn't at 90 deg to the shaft.

Cheers
 
Perry, when they check a block for "deck height", they insert a large rod or pipe through the bearing housings.
(I admit this should not be neccessary on a V twin, more an in line multi or V8 blue print)
However, with this rod now protruding from each end of the crank cases, take your empty gearbox housing and mount it. If the holes are different diameters then obviously a stepped rod will need to be machined on a lathe.

While I have never seen it done, an engineering shop will most likely have cleverer, quickerer and cheaperer means of checking alignment, but the principle remains the same. Talk to your favourite engine machine shop.
 
Ghezzi, Morizzi,

Thanks to both of you for helping me with this problem.

I'm not sure if I'm willing to go to the lengths required to check the transmission/engine alignment in the manner you suggest, Ghezzi. If there is an easier way, let me know, please.

Morizzi,

The bike vibrates in neutral just when revving it up. Kill the engine while riding and the bike becomes perfectly smooth. The u-joints and carrier bearing were newly replaced at the same time as the engine rebuild (6,000 miles ago), the dogbone is well greased as are the splines in the rear cush drive. It is unquestionalby the engine that is vibrating.

I hadn't riden any Guzzis for several years before I got my bike up and running, but the vibration I get now is pretty severe and clearly an indication that something is wrong--I just need to figure out what!

I also don't think that it's a tuning issue. I have synchronized the carbs and checked the ignition timing for both cylinders. The plugs come out clean. Also, when compression braking down a hill at 3000rpms I can switch off the ignition so that the engine is still spinning but without any combustion taking place. It still vibrates. While the vibration is at its worse under load, it is always there.

The more I think about it, the more I read others' suggestions, it seems that it must be the weird exhaust system I've installed, or that the flywheel/ring gear and crankshaft must be balanced separately. I will try those fixes.

Perry Beltrame
 
Hi Perry,

No problems. I didn't read all the posts word for word.

Getting worse? That's not a balance issue. Something is coming loose or going out of spec.

What's the compression like?

G5's had iron bores same as my SP. They need different ring material to the nigasil bikes.

Not something silly like the advanced weights and springs getting jammed? I'd check the timing with a timing light. Should reach max advance about 4500-5000rpm. the advance should be smooth in an erratic sort of way. :lol:

It just dawned on me as I typed this that the springs and weights are different for a G5 to a Lemans. If your bike is highly modified then your advance would be greater than the 2 deg specified for the old G5 chugger.

I'd also check valve timing. Make sure the little poppits open and close when they should.

Valve clearances aren't closing up are they?

Timing chain is correct tension with a spring adjusted tensioner?

How long does it take before the oil light comes on if you kill the engine?

Tappets and cams in good condition? Push rods correct and straight?

Just a few more thoughts. Ignore if already addressed.

Good luck.
 
Perry, an easier check of case alignment would be after removal stand the engine face down and chock it securely.
Remove (starter motor plus) bell housing nuts and slowly lift the gearbox vertically.
With gearbox and clutch splines still engaged but gearbox housing just clear of the crankcase studs, rotate the box left/right.
Now see if it re-aligns easily with the studs and slides down nicely under its own weight or;
Do you have to push it off centre a little and wiggle or use force to refit it?

If the gearbox will not clear the crank case studs without clutch and gearbox splines first separating, then you can always remove the studs to repeat the test. It is only time and sweat, and maybe a few skinned knuckles. :silly:
 
Ghezzi,

Thanks. That makes sense to me and seems easy enough to check after I've removed the engine/transmission from the bike.

Perry
 
Drumnagorrach said:
Just to add to the light flywheels don't vibrate opinion, I fitted a "Ram lightweight single plate clutch/alloy flywheel " set to my old t3,just because it was cheaper than a standard flywheel. It didn't vibrate ,just revved a lot quicker ,and actually slowed down when I shut the throttle after overtaking .
BTW. If you thought a Beezer A50 vibrated ,you should try a B50.
Click to expand...

To the uninitiated, "BSA" stands for "Bastard Shook Apart".

ralph
 
Have you checked the most obvious things - are all nuts, bolts, studs etc tight? Have your main stand springs lost tension, allowing the stand to jump up and down? Are your wheels balanced? Are you missing a bolt somewhere? Is something broken? And so on.

It seems to me you have done all the engine stuff if you have had it down 3 times, so start looking elsewhere. It's probably going to be something really simple and, after you find it, blatantly obvious. I have found that, when completely baffled, if I sit down with a coffee and let my eyes wander over the bike, something I have overlooked will leap out at me and provide the answer.
 
My G5 with extensive mods vibrated badly at 3000/3500 rpm. I did much of the above to reduce or eliminate the vibration to no avail...until I removed the dunstal repops I had installed and replaced the OEM exhaust. Seems that my particular combination of mods along with the Dunstal shorties set up an engine resonance that was transferred to the frame and forks. You did briefly mention a "weird exhaust" so pulling that seems worthwhile given the alternatives you are considering.
Harry
 
Harry,

After reading your post on exhaust induced vibes, I replaced the "stock" crossover on my G5 with a "shorty" crossover. What a difference!

Before the swap the bike vibrated throughout the RPM range. Now I get a very narrow band of vibration. Greatly improved.

Thanks for the post.

Alex
 
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