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BSA levels of vibration

PerryB

Just got it firing!
Joined
Nov 5, 2010
Messages
21
I finished rebuilding my G5 four years ago and ever since the bike has vibrated terribly, with the worst vibration at about 3,000rpms. I have taken the motor apart three times, had it professionally balanced, had the balance checked by a different shop, all to no effect. The motor has some high performance modifications, including a lightened flywheel. No changes to carb sync or ignition timing will reduce the vibration. The vibration is worse under load, but is present even when compression braking down a hill with the ignition off.

I will appreciate any suggestions.

Perry Beltrame
 
Having a heavy flywheel reduces the effects of the individual firing strokes. I don't recognize the G5 model, but I'm guessing it might be a 500 twin with 360° firing cycle. As far as balance is concerned, it is similar to a single banger, and only a balance percentage is performed.

Since you have lightened your flywheel, I would expect that the vibrations would increase, but you will get a motor more willing to rev quickly. It's the price you pay.
 
Have you checked the flywheel timing marks by dial guage and degree wheel?

What high performance mods, piston/conrod changes including difference in weight of individual components from stock. Compression ratio? Rod/stroke ratio change?

How much was the flywheel lightened? Flywheel weight is more to do with strength of individual power pulses rather than weight of reciprocal components. The idea is to smooth the rotation of everything as the crank will actually try to accelerate and decelaerate violently several times per 720 degrees of rotation.
 
kiwi dave said:
I don't recognize the G5 model, but I'm guessing it might be a 500 twin with 360° firing cycle. As far as balance is concerned, it is similar to a single banger, and only a balance percentage is performed.

Moto Guzzi V1000 G5 - like a Convert but with a five-speed or an SP in Convert bodywork. Not a BSA.
 
That is a head scratcher.

I have modified a few engines and I can tell you that it is possible to put as much compression as possible and lighten the hell out of the flywheel - in fact you can't make it light enough - without causing much vibration. The factory has changed the balance factor over the years by I think 2% but this doesn't really change things - it just moves the RPM at which you can feel the secondary harmonics. Noisy yes - Pete Roper's Skeletons fornicating on a tin roof springs to mindv- vibratory no.

I also assume you are using the proper schnoor washers to attach the flywheel and not the crap metal tabs? Was the crank magnafluxed/crack tested?

The only other thing that can affect the balance is the oil level - the crank picks up the oil like a big dough hook. This is why a good windage tray with scrapers that actually shear oil of the crank are a boon in racing. If you think about it the oil that sticks to the rotating assembly weighs a great deal more than the grams that the engine is balanced to AND it perpetually shifts it CofG as the bike accelerates, brakes and corners.

Is it possible you have two duff balance shops in the same area? If you take it apart for the third time I'd insist on seeing it on the machine while the guy checks it.

This sounds painful
 
This is very interesting!

I too have a G5 with the mystery vibration! I think it is an engine whilst under power situation as no vibe with a dead engine (coasting downhill with clutch in and throttle closed).

see: https://www.guzzitech.com/forum/197/8329.html

Latest efforts include replacing Dyna III ignition module.

Next step: Remove pistons- clean and balance
Check cam chain (no junk in oil)

Alex

BTW this is what a G5 looks like (well this one anayway):

Donesm.jpg
 
Series4 said:
if it's there with dead engine it could be swing arm alignment or cardan issues

I would just check your u-joint....if it vibrate going down hill with the ignition off its not the engine....

also, you didnt mention if it was vibrating while at complete stop if you rev it?

if it vibrates more in the right foot peg its the u-joint for sure....

good luck to you
 
Thanks for all the replies.

A few clarifications and some more information:
The modifications are...

A modest cam from Raceco in the UK. It is correctly timed for both cylinders and the lift is also correct. I have checked this with a degree wheel and a dial indicator.

The pistons are stock Guzzi, second oversized. They have been matched weighted to a tenth of a gram.

It has 40mm Dellortos with matched intake manifolds.

It has a Dyna III ignition that has been timed correctly with correct air gaps.

I have checked the cc's of both combustion chambers and matched them to about two tenths of a cc. I have set the squish on both cylinders down to .040".

The flywheel and ring gear were lightened by a shop in Texas. During balancing the flywheel/ring gear were mounted on the crank and the bob-weight was set at 52% of the reciprocating mass.

The bike vibrates even when stopped when you rev the engine in neutral. It is at its worst at 3,000rpm but is bad from 2,500 up to redline.

One of the balance shops was here in Colorado, the other in California.

The flywheel bolts use "serrated" shnoor (spelling) washers.

I use a sump extention that has a windage tray and an external filter, sold by MG Cycle in Wisconsin.

While the entire bike vibrates, I feel the vibrations most accutely in the right hand grip.

I have run out of things to check or change to eliminate the vibration and really hope that the gurus on this forum can help. Any suggestions will be greatly appreciated.

Sorry about any confusion with the BSA reference. A friend of mine owned a '64 650 Lightening twin that I rode around quite a bit and I was always shoked at how badly it vibrated!

Thanks!

Perry
 
Perry, I just spoke to my local engine balance guy. He favours balancing the flywheel and ring gear seperately from the crank, in case there is need to change these components at a later date.

Possibility also of flywheel being bolted in wrong position during balancing?

Even though pistons are match weighted, what is their actual weight compared to original stock bore/pistons.
(eg. Ducati hi comp pistons can be heavier than stock, combined with lightened flywheel = disastrous results)

Was crank reground? Rods resized? Cases line bored? Although any misalignment here should have caused seizure.
Crank crack tested/magnafluxed? Thought it would have exploded by now.

Bent frame, broken engine mounts (thinking aloud here :? ) damage should be visible yet shouldn't cause this much drama. The problem has to be simple and should be obvious, not elusive. :( :angry: :silly:
 
Thanks Ghezzi.

The bike was not running when I bought it, so I never knew if it vibrated originally. I have ridden other Guzzi and Ducatis and the vibration I have now is way beyond anything I've felt with other Guzzis or Ducatis.

The original flywheel had significant grooving in the internal teeth that mesh with the spring plate and the intermediate plate so I bought a good used one with its ring gear. It was this "new" flywheel/ring gear that I had lightened and is currently on the bike.

I have checked the frame for bends and cracks; there are none that I can see, tightened and retightened the mounting points; no difference.

The new pistons were weight matched and then their overall weights as well as the weight of the upper portion of the connecting rods were weighed for the balance calculation, so the oversized, heavier pistons should be compensated for during balancing.

The flywheel, ring gear, and crank all had big black "X" marks on each of them for alignment.

I never had the case bored because or the crank magnafluxed because there was no indication that there was any problem with the engine when I disassembled it. I've put over 6000 miles on the bike since the rebuild and it hasn't thrown a rod or cracked the cases. The bike runs excellently, except for this vibration.

I agree that a problem this bad should have an obvious cause, but I'm out of ideas.

Thanks again, and any ideas welcomed!

Perry
 
I'll make another suggestion, after my faux pas beforehand. :oops: I should've known better.

Check that the header pipes aren't touching the frame anywhere else other than their designated points. I chased bad vibration on my Anniversary Cali once before realizing this cause.
 
Hey Perry,

Are your plugs showing any signs of distress?

On my G5 I think I am now getting detonation... about 300 miles on this NGK BP7ES:

Plug2sm.jpg


I am going to go down this path.

Good luck!

Alex
 
Thanks for all the suggestions.

I am considering running the bike without the exhaust system to see if the bike still vibrates.

I would like to post a picture of the exhaust system, but can't figure out how to do it on this site.

There are no running problems with the bike, the plugs look very good, the bike get great gas milage.

Perry Beltrame
 
Perry, just re-read this thread and had another thought (I know, thats dangerous).

When you replaced the flywheel/ringear with second hand components you said they had a black "X" marked on them to align with the "X" marked on your original crank. Those components came off a different crank.

1. Are all components marked exactly the same at the factory?
2. Is there an official way of aligning these and all new replacement components?
3. Were the replacement bits off the same model engine as yours?

My Guzziology book & manuals are on permanent loan.
My hi-comp Mk3 with lightened flywheel was as smooth as a babies bum.

The flywheel is the only part you replaced from your box of bits so I'm thinking it has got to be the culprit.

Oh, and just to clarify a point every Guzzi I have had has timing marks on the ring gear which are always out by a few degrees. On the off chance they are out by a large amount, check them again with degree wheel and dial guage.
Normally you are rewarded with a smoother idling and running engine, but in your case they would have to be way out to cause excessive vibes, and that still doesn't account for bad vibes while decelerating.

Only other option is the nose of the crank bent or the alternator rotor not centralized or balanced?
You could remove the rotor and run 'total loss' for a time to test it, disconnect headlight if its hard wired.
 
Hmmmm,

I doubt that the alternator balance could cause something that nasty however it is possible that this is one of those very rare Guzzi's where Guiseppe typed in the wrong G code when machining the bell housing so the end of the crank is out of line with the centre of the clutch. My buddy had one and it vibrated and ate clutches like mad. It is a very rare thing and tricky to diagnose.
 
... and thinking about it that might explain the grooving on the ring gear.
 
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.
 
This is a picture of my bike. It started as a G5 with floorboards and buck-horn handle bars!

Thank you for all the ideas.

The clutch works flawlessly--very smooth with no stickiness or disengagement problems. I also had no problems mating the tranmission up to the engine when re-assemblying the bike. The wear marks on the old flywhell looked to me just like normal age and high milage wear. I don't think that there could be any problems with the center of the crank not being aligned with the clutch hub, but it is a possibility. I will have to think about how to measure that to see if there is any problem

I will run the bike with out the exhaust system to see if my high mounting is causing the vibration.

As for the alternator causing the problem--this seems to me very unlikely. I had to replace the stator about two years ago and the new one cam with a balance hole already drilled in it. The bike ran exactly the same (except that the batery would charge!) with the new one. I can not run the bike without the stator as it forms the front crank seal surface.

As for the "new" flywheel being somehow incompatible with my bike--this also seems unlikely as I had the entire engine balanced with this flywheel in place. Should the exhaust removal not solve my problem I will next have the lightend flywheel/ring gear balanced separately from the crank, then have the crank balanced without this flywheel. Since this will be the forth time that I have torn down this engine in that last four years I may just have to live with this problem.

Perry Beltrame
 

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