Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board A whole new "issue" for my A-65....

This is a new one on me , anyone ever experience serious engine vibration that mysterious went away ? I was riding home today on my admittedly wore out but very reliable A-65 , riding with light traffic , probably a steady 80 MPH , when the engine started vibrating, getting steadily worse till I was looking at the shoulder of the road with hand over the clutch lever , I slowed a bit , the vies went away , and I rode another 15 miles or so without incident. Of course I was imagining all sorts of sounds and vibes, but probably nothing more than "normal" for this bike ....... in a bright and cheerful world I would chalk this up to contaminated fuel, since I did just fill the tank , but this was pretty bad , any ideas ? Also , the bike wasnt misfiring at all while this was occuring , it felt more like a cracked frame or engine mounts?? that all seems to be in order but will give it a closer look .

as I say , this engine has seen more miles on the bottom end than an A-65 probably should , and still gets ridden hard , so a complete overhaul is in the future , now I am considering making it a priority . this is the first time I have had cause to doubt the bikes reliability so any tips on odd bits to double check while i am in there would be appreciated .

As always , any info or tips are appreciated -BONZO

I find the head steady bolt at the engine coming loose all the time. But that would not go away or come on suddenly. Gas with a jigger of water as you say but that would hurt the plugs enough to keep running bad. A wire that has morphed into an on off switch triggered because 80 is just a little too much fun? It does sound like the symptom we get on Norton's when the Boyer wires start to break. Only other thing is cylinder pressure related you didn't say if you went right back to 80 when she recovered. Coughing spell too many Marlboro's ?

If the engine mounts are all tight, I would be pessimistic and suspect a drive side main bearing. Wouldn't hurt to put the bike on the center stand and check for play in swingarm bushings, rear wheel bearings, etc.

-norbsa , Head steady was still tight , my first thought , but this was worse than no head steady . I havent had a cjance to really look at it , plugs may be a victim ,it did "seem" to suffer after the incident , but i chalked that up to the goosants , figured I may have been imagining things?? I did wick it back up when it straightened up , possibly a foolish move , but I figure if something frags it will save me some troubleshooting time ?? As far as 80 being too much fun ?? I aint kiddin when I say this bike is pretty much normally ridden at 75 MPH , and with some of the mods I've been playing with since the weather broke , 80-90+ arent at all unpleasant on this thing with a single 928 Concentric, a year ago I would have laughed at a statement like this . I hadnt really considered a wiring issue , worth looking into , I know the SOD who wired the bike , but as I mention , I lent an ear while all this was happenong and the engine didnt seem to miss a beat ?? sorta had a surgeing feel , but that may have been my nervous hand at the throttle ?
Nick , I'll give this a looking over . engine mounts are tight , havent checked much else as yet . Nothing visibly broken . I have had loose swingarm/wheels etc... and that usually seems to manifest itself as squirrely handling and near tank slappers that go away with decreased speed , have you had bizarre vibration issues stem from this , I hadnt considered it ? That dark cloud overhead , gut feeling has me thinking more along the line of the main bearings as you suggest , possibly primary drive ?? I'd be way happy to find a loose axel and cure this !! I do know the shift lever/final drive chain and chain guard have all been yelling at me to adjust or replace the chain/chain-sprockets , butthe rear sprocket doesnt show a lotta wear ?I di have episodes sorta similar to this , on retrospect , hauling a sidecar when the rear sprocket was so worn the chain skipped teeth and actually jumped the sprocket . Went through a stash of sprockets in short order in those days .


Thanks for the suggestions , something to look at/food for thought -BONZO

As dumb as it sounds, did you pick up something in a tire? And if eventually shed itself?

Bonzo -

Sometimes when I'm riding the Firebird, it feels smooth as silk; sometimes it feels like it's hammering like a gravel crusher. Most all of that is "subjective", it depends on my mood and my state of health at the moment.

Yours is probably something different since it all happened at once; vibration starts, gets worse, it's bad enough so you're looking for a bail-out spot, you slow down, it goes away .... you speed back up slowly, waiting for it to happen again but it doesn't.

I'm trying to imagine what might have "gotten out of whack" that settled back in once you slowed down. Can't be a loose bolt or a cracked something, it's bound to be something with running clearance (like a main bearing or tranny bearing) that has enough play to resonate under exactly the right conditions, but then doesn't do it under slightly different conditions.

Maybe it's trying to warn you in a gentle way that you're due for some engine work. If 'twas mine, I'd have it on the lift and pull the primary cover and inner timing cover, get the dial indicator out, and check the radial and axial play in the crank at the timing side. If it's not WAY out, I'd button it back up and wait for the next signal; if is IS out, well, you know the rest.

Lannis

Rich , something in a tire would be extremely doubtful , but I will add that to the list of things to look at , more possible might be something in the spokes , since the bike started talking to me through the seat/handlebars/rider pegs and gas tank all at once ,but the only time I had something in the spokes it took out14 or 15 spokes from one side before I gott he bike stopped , the only shaking I remember on that stunt was me .

Lannis ,This is in the same line as Nick mentions , and what I sorta suspect . When I get a chance , maybe late this evening , I will give this thing a thorough looking over , if nothing I will open the primary side , if nothing immediately jumps out at me, the engine will be and on the bench . I know this engine is worn and abused , definitely desrved an overhaul over the past winter , but I was too busy starting other projects that I will never finish . There is no way I will ride this bike again until I know for sure what happened and it is repaired to my satisfaction . I've been having so many of those "close ones" lately that I went out and bought some actual protective gear , I dont wanna test it the wrong way .

Oh well , I have quite a few things to get outta the way before I can look at the bike so I better git to gittin-BONZO

Possibly a full score symphony!!
You know how you can rotate your finger around the top of a quality glass and it results in a ringing sound? Sound is vibration.
You and the BSA, just tooling along a steady pace, everything (engine, trans, gears, chains, tires, wind, etc) was just set up to an un-choreographed harmonic disturbance. You broke the spell when you slowed down. Difficult to reproduce.
Am I too far out on a limb here?

Bonzo,
It's a long shot I know, but check your header pipe mounts. Happened to me one time coming back home from a weekend todo. Bad vibration for little bit than went away. The pipe bracket must have come loose,vibrated againstthe frame and than broke off. Cause when I stopped it was gone. Used a hose clamp to get the rest of the way home, no more vibration. Never did find anything else wrong.

Nert , out on a limb??? Nahhh , that actually happened to me once , when I slowed it down I had actually gone back in time .... or maybe I saw that on Star Trek???

Anyway , Igot around to it late last night , decided to take it for short ride through the neighborhood with a clear head and the thing does have some new vibration , not "BAD" but different , feels sorta like a Triumph with that rumblng feel . I parked it , gaveit a throrough looking over came up with a huge list of cosmetic and secondary issues that should get some attention but prolly wont then I noticed the final drive sprocket at the trans was loose .Crash bang boom , stripped it down looking at everything along the way, drive side bearing isnt wasted bad enough to notice , crank end float is way out of spec , but I have known aboutt his for a while , evrything else clean and tight , button it up , go for ride , no change ..... curses , foiled again !!! I didnt change plugs and check Boyer wiring , that is next , it was way late and I hate having to get up early so I called it a night . If the plugs/wiring show nothing the engine will come out as soon as I get a free evening .
Stay tuned if you are at all interested -BONZO

How many miles is "a lot" on a an A65 bottom end?

TTFN,

With Bonzo driving 40,000 max.

Semper , I have no instruments to verify , but my best guess would be in the low 40,000 miles . A good bit of that was hauling a sidecar also .I know there are other air cooled twins outthere that can do far better miles on a bottom end , but for an A-65 I am more than happy with this .
Anyway , just as an update , i think I have found the culprit and the bike runs/rides just like it has been . It turns out I may indeed have had a fuel problem . I would have bet $$ this wasntthe case but after checking everything I could think of , and following up on your input (I wasnt able to recreate that reonance time travel thing though ) when I pulled the plugs the porcelin had a rich chocolate brown colored coating and pretty much clean way down at the base , I didnt figure this was too bad , but I really dont know what I am looking t , but what caught my attention was the electrodes . They look sorta like a set of burnt contact breaker points . I've never seen this before , and these plugs have lessthan 1.000 miles on them . I suspect some sorta detonation problem , drained the tank , cleaned fuel filters , checked wiring , especially at the Boyer plate , reset timing (I checked and was on the mark) and it runs just fine by my standards . Had a rare opportunity to take off and get lost for a few hours , my day off , weather was nearly perfect, and I didnt have to be anywhere for 4 hours ......how often does that happen ?? Ran the thing on freeways and backroads ,didnt give me a bit of trouble .

I suppose I am disapointed , I was hoping to have a genuine scooby doo mystery on my hands but at least I found a loose sprocket and a loosening front wheel before they became a problem .

Thanks again for the tips -BONZO

I was going to say check the rotor nut is still tight but you have, well then carbs and electrics I guess. I had my beemer running rough now and then due to a poor plug cap, that simple but it took me ages to find...

Your obviously experienced enough not to notice the usual illusive rattles and shakes that come and go from time to time. Lets face it though, if we didn't lose a bit of mechanical sympathy we'd never ride them past the end of the street. The (much-maligned) oil warning light can be handy. Remove the plug caps and turn on the ignition. If the red light goes out when you kick it over its a fair indication things aren’t to bad downstairs. (Turn ignition off strait away!) Also, if the left-hand big end is shot, it's usually fairly obvious from the Knocking. Another obvious thing to try is a compression test. Probably you’ve tried all this but good luck anyway.

Rotor nut is tight , no idiot lihgt intstalled , just an oil pressure gauge , and it appears normal , at this point I'm thinking bad fuel , combined with worn out engine. Bike runs well at this point , but the engine is gonna come out and be replaced with a fresh unit while it is in autopsy ....

FWIW-BONZO

What I noticed last Sunday is that my fuel tank starts making noise when it's near empty. It contains less than 3 liters now (abt. 1 gallon?) and picks up vibrations which it does not when its more full.

Bonzo. Sounds like your determined to give this engine a fair trial and then hang it. Your perogative of course.If theirs no knocking, the oil pressure is fine and the compresion tests show similar results for both barrels, it's hard to see why you'd switch it. Maybe you just want to give the spare engine a wiz, Fair enough too. Enjoy.